ACI 318-19 Building Code Requirements for Structural Concrete.pdf
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This document summarizes the contents and purpose of ACI 318-19, which provides minimum requirements for structural concrete design and construction. It was developed by an ANSI-approved consensus process and covers topics like structural analysis, load combinations, reinforcement, inspection, and evaluation of existing structures. The document lists the members of the committee that developed ACI 318-19 and notes some key enhancements in this edition, including reorganization of content and the first use of color illustrations. It also discusses the role of the accompanying commentary document.
![eanc = eccentricity of the anchorage device or group of
devices with respect to the centroid of the cross
section, in.
dpile = diameter of pile at footing base, in.
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structural system
eh = distance from the inner surface of the shaft of a J-
or L-bolt to the outer tip of the J- or L-bolt, in.
eƍ
N = distance between resultant tension load on a group
of anchors loaded in tension and the centroid of the
group of anchors loaded in tension, in.; eƍ
N is always
positive
eƍV = distance between resultant shear load on a group of
anchors loaded in shear in the same direction, and
the centroid of the group of anchors loaded in shear
in the same direction, in.; eƍV is always positive
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forces
Ec = modulus of elasticity of concrete, psi
Ecb = modulus of elasticity of beam concrete, psi
Ecs = modulus of elasticity of slab concrete, psi
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Ep = modulus of elasticity of prestressing reinforcement,
psi
Es = modulus of elasticity of reinforcement and struc-
tural steel, excluding prestressing reinforcement,
psi
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concrete, psi
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of initial prestress, psi
ci
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concrete at time of initial prestress, psi
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strut or a nodal zone, psi
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of section where tensile stress is caused by exter-
nally applied loads, psi
fdc = decompression stress; stress in the prestressed rein-
forcement if stress is zero in the concrete at the
same level as the centroid of the prestressed rein-
forcement, psi
fpc = compressive stress in concrete, after allowance
for all prestress losses, at centroid of cross section
resisting externally applied loads or at junction of
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ÀDQJHSVL,QDFRPSRVLWHPHPEHUfpc is the resul-
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PART 1: GENERAL 19
CODE COMMENTARY
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![İt = net tensile strain in extreme layer of longitu-
dinal tension reinforcement at nominal strength,
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shrinkage, and temperature
İty = value of net tensile strain in the extreme layer of
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compression-controlled section
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members
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ical properties of lightweight concrete relative to
normalweight concrete of the same compressive
strength
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ical properties of lightweight concrete in certain
concrete anchorage applications
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ȡƐ = ratio of area of distributed longitudinal reinforce-
ment to gross concrete area perpendicular to that
reinforcement
ȡp = ratio of Aps to bdp
ȡs = ratio of volume of spiral reinforcement to total
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out-to-out of spirals
ȡt = ratio of area of distributed transverse reinforce-
ment to gross concrete area perpendicular to that
reinforcement
ȡv = ratio of tie reinforcement area to area of contact
surface
ȡw = ratio of As to bwd
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ࢥp = strength reduction factor for moment in preten-
sioned member at cross section closest to the end of
the member where all strands are fully developed
IJcr = characteristic bond stress of adhesive anchor in
cracked concrete, psi
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erties is caused by the reduced ratio of tensile-
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concrete where the reduction is not related directly
to tensile strength.
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compressive stress, psi
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PART 1: GENERAL 29
CODE COMMENTARY
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![anchor, adhesive—a post-installed anchor, inserted into
hardened concrete with an anchor hole diameter not greater
than 1.5 times the anchor diameter, that transfers loads to the
concrete by bond between the anchor and the adhesive, and
bond between the adhesive and the concrete.
anchor, cast-in—headed bolt, headed stud, or hooked
bolt installed before placing concrete.
anchor, expansion—post-installed anchor, inserted into
hardened concrete that transfers loads to or from the concrete
by direct bearing or friction, or both.
anchor, adhesive—The design model included in Chapter
17 for adhesive anchors is based on the behavior of anchors
with hole diameters not exceeding 1.5 times the anchor
diameter. Anchors with hole diameters exceeding 1.5 times
WKH DQFKRU GLDPHWHU EHKDYH GL൵HUHQWO DQG DUH WKHUHIRUH
excluded from the scope of Chapter 17 and ACI 355.4. To
limit shrinkage and reduce displacement under load, most
adhesive anchor systems require the annular gap to be as
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hole and ensuring complete coverage of the bonded area over
the embedded length. The annular gap for reinforcing bars is
generally greater than that for threaded rods. The required
hole size is provided in the Manufacturer’s Printed Installa-
tion Instructions (MPII).
anchor, expansion—Expansion anchors may be torque-
controlled, where the expansion is achieved by a torque
acting on the screw or bolt; or displacement controlled,
where the expansion is achieved by impact forces acting on
a sleeve or plug and the expansion is controlled by the length
of travel of the sleeve or plug.
hef
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(A) Cast-in anchors: (a) hex head bolt with washer;
(b) L-bolt; (c) J-bolt; and (d) welded headed stud.
(B) Post-installed anchors: (a) adhesive anchor; (b) undercut anchor;
(c) torque-controlled expansion anchors [(c1) sleeve-type and (c2) stud-type];
(d) drop-in type displacement-controlled expansion anchor; and (e) screw anchor.
(a) (c)
(b) (d)
(a) (c1) (c2)
(b) (d) (e)
Fig. R2.1––Types of anchors.
American Concrete Institute – Copyrighted © Material – www.concrete.org
32 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![the relevant PTI or AASHTO LFRDUS bearing stress and,
ZKHUH DSSOLFDEOH VWL൵QHVV UHTXLUHPHQWV 0RVW FRPPHU-
cially marketed multi-bearing surface anchorage devices
are special anchorage devices. As provided in 25.9.3, such
devices can be used only if they have been shown experi-
mentally to be in compliance with the AASHTO require-
ments. This demonstration of compliance will ordinarily be
furnished by the device manufacturer.
anchorage zone—In post-tensioned members, the portion
of the member through which the concentrated prestressing
force is transferred to the concrete and distributed more
uniformly across the section. Its extent is equal to the largest
dimension of the cross section. For anchorage devices
located away from the end of a member, the anchorage
zone includes the disturbed regions ahead of and behind the
anchorage devices. Refer to Fig. R25.9.1.1b.
cementitious materials—Cementitious materials permitted
for use in this Code are addressed in 26.4.1.1. Fly ash, raw or
calcined natural pozzolan, slag cement, and silica fume are
considered supplementary cementitious materials.
anchorage zone—in post-tensioned members, portion
of the member through which the concentrated prestressing
forceistransferredtoconcreteanddistributedmoreuniformly
across the section; its extent is equal to the largest dimen-
sion of the cross section; for anchorage devices located away
from the end of a member, the anchorage zone includes the
disturbed regions ahead of and behind the anchorage device.
attachment—structural assembly, external to the surface
of the concrete, that transmits loads to or receives loads from
the anchor.
B-region—portion of a member in which it is reasonable
WRDVVXPHWKDWVWUDLQVGXHWRÀH[XUHYDUOLQHDUOWKURXJK
section.
base of structure—level at which horizontal earthquake
ground motions are assumed to be imparted to a building.
This level does not necessarily coincide with the ground
level.
beam²PHPEHUVXEMHFWHGSULPDULOWRÀH[XUHDQGVKHDU
with or without axial force or torsion; beams in a moment
frame that forms part of the lateral-force-resisting system are
predominantly horizontal members; a girder is a beam.
boundary element—portion along wall and diaphragm
edge, including edges of openings, strengthened by longitu-
dinal and transverse reinforcement.
breakout strength, concrete—strength corresponding to
a volume of concrete surrounding the anchor or group of
anchors separating from the member.
EXLOGLQJ R൶FLDO—term used to identify the Authority
having jurisdiction or individual charged with administra-
tion and enforcement of provisions of the building code.
Such terms as building commissioner or building inspector
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used in this Code, is intended to include those variations, as
well as others that are used in the same sense.
caisson—see drilled pier.
cementitious materials—materials that have cementing
value if used in grout, mortar, or concrete, including port-
land cement, blended hydraulic cements, expansive cement,
ÀDVKUDZRUFDOFLQHGQDWXUDOSR]]RODQVODJFHPHQWDQG
silica fume, but excluding alternative cements.
collector—element that acts in axial tension or compres-
sion to transmit forces between a diaphragm and a vertical
element of the lateral-force-resisting system.
column—member, usually vertical or predominantly
vertical, used primarily to support axial compressive load,
but that can also resist moment, shear, or torsion. Columns
American Concrete Institute – Copyrighted © Material – www.concrete.org
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34 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![the requirements of ASTM A615, A706, or A955 shall be
considered as ductile steel elements.
stirrup—reinforcement used to resist shear and torsion
forces in a member; typically deformed bars, deformed
wires, or welded wire reinforcement either single leg or bent
into L, U, or rectangular shapes and located perpendicular
to, or at an angle to, longitudinal reinforcement. See also tie.
strength, design—nominal strength multiplied by a
VWUHQJWKUHGXFWLRQIDFWRUࢥ
strength, nominal—strength of a member or cross section
calculated in accordance with provisions and assumptions of
the strength design method of this Code before application
of any strength reduction factors.
strength, required—strength of a member or cross
section required to resist factored loads or related internal
moments and forces in such combinations as stipulated in
this Code.
stretch length—length of anchor, extending beyond
concrete in which it is anchored, subject to full tensile load
applied to anchor, and for which cross-sectional area is
minimum and constant.
structural concrete—concrete used for structural
purposes, including plain and reinforced concrete.
structural diaphragm²PHPEHUVXFKDVDÀRRURUURRI
slab, that transmits forces acting in the plane of the member
to vertical elements of the lateral-force-resisting system. A
structural diaphragm may include chords and collectors as
part of the diaphragm.
structural integrity—ability of a structure through
strength, redundancy, ductility, and detailing of reinforce-
ment to redistribute stresses and maintain overall stability if
ORFDOL]HGGDPDJHRUVLJQL¿FDQWRYHUVWUHVVRFFXUV
structural system—interconnected members designed to
meet performance requirements.
structural truss—assemblage of reinforced concrete
members subjected primarily to axial forces.
structural wall—wall proportioned to resist combina-
tions of moments, shears, and axial forces in the plane of the
wall; a shear wall is a structural wall.
structural wall, ductile coupled—a seismic-force-
resisting-system complying with 18.10.9.
structural wall, ordinary reinforced concrete—a wall
complying with Chapter 11.
structural wall, ordinary plain concrete—a wall
complying with Chapter 14.
stirrup—The term “stirrup” is usually applied to trans-
verse reinforcement in beams or slabs and the term “ties”
or “hoops” to transverse reinforcement in compression
members.
strength, nominal²1RPLQDORUVSHFL¿HGYDOXHVRIPDWH-
rial strengths and dimensions are used in the calculation
of nominal strength. The subscript n is used to denote the
nominal strengths; for example, nominal axial load strength
Pn, nominal moment strength Mn, and nominal shear
strength Vn. For additional discussion on the concepts and
nomenclature for strength design, refer to the Commentary
of Chapter 22.
strength, required—The subscript u is used only to
denote the required strengths; for example, required axial
load strength Pu, required moment strength Mu, and required
shear strength Vu, calculated from the applied factored loads
and forces. The basic requirement for strength design may
EHH[SUHVVHGDVIROORZVGHVLJQVWUHQJWK•UHTXLUHGVWUHQJWK
IRUH[DPSOHࢥPn•PuࢥMn•MuࢥVn•Vu. For additional
discussion on the concepts and nomenclature for strength
design, refer to the Commentary of Chapter 22.
stretch length—Length of an anchor over which inelastic
elongations are designed to occur under earthquake load-
ings. Examples illustrating stretch length are shown in Fig.
R17.10.5.3.
American Concrete Institute – Copyrighted © Material – www.concrete.org
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CODE COMMENTARY](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-46-320.jpg)
![structural wall, intermediate precast—a wall complying
with 18.5.
structural wall, special—a cast-in-place structural wall
in accordance with 18.2.3 through 18.2.8 and 18.10; or a
precast structural wall in accordance with 18.2.3 through
18.2.8 and 18.11.
strut—compression member in a strut-and-tie model
representing the resultant of a parallel or a fan-shaped
FRPSUHVVLRQ¿HOG
strut, boundary—strut located along the boundary of a
member or discontinuity region.
strut, interior—strut not located along the boundary of a
member or discontinuity region.
strut-and-tie model—truss model of a member or of
a D-region in such a member, made up of struts and ties
connected at nodes and capable of transferring the factored
loads to the supports or to adjacent B-regions.
tendon—in post-tensioned members, a tendon is a
complete assembly consisting of anchorages, prestressing
reinforcement, and sheathing with coating for unbonded
DSSOLFDWLRQVRUGXFWV¿OOHGZLWKJURXWIRUERQGHGDSSOLFDWLRQV
tendon, bonded—tendon in which prestressed reinforce-
ment is continuously bonded to the concrete through grouting
of ducts embedded within the concrete cross section.
tendon, external—a tendon external to the member
concrete cross section in post-tensioned applications.
tendon, unbonded—tendon in which prestressed rein-
forcement is prevented from bonding to the concrete. The
prestressing force is permanently transferred to the concrete
at the tendon ends by the anchorages only.
tension-controlled section—a cross section in which
the net tensile strain in the extreme tension steel at nominal
strength is greater than or equal to İty + 0.003.
tie—(a) reinforcing bar or wire enclosing longitudinal
reinforcement; a continuously wound transverse bar or wire
in the form of a circle, rectangle, or other polygonal shape
without reentrant corners enclosing longitudinal reinforce-
ment; see also stirrup, hoop; (b) tension element in a strut-
and-tie model.
transfer—act of transferring stress in prestressed rein-
forcement from jacks or pretensioning bed to concrete
member.
structural wall, intermediate precast—Requirements of
18.5 are intended to result in an intermediate precast struc-
tural wall having minimum strength and toughness equiv-
alent to that for an ordinary reinforced concrete structural
wall of cast-in-place concrete. A precast concrete wall not
satisfying the requirements of 18.5 is considered to have
ductility and structural integrity less than that for an inter-
mediate precast structural wall.
structural wall, special—Requirements of 18.2.3 through
18.2.8 and 18.11 are intended to result in a special precast
structural wall having minimum strength and toughness
equivalent to that for a special reinforced concrete structural
wall of cast-in-place concrete.
strut, boundary—A boundary strut is intended to apply
WRWKHÀH[XUDOFRPSUHVVLRQ]RQHRIDEHDPZDOORURWKHU
member. Boundary struts are not subject to transverse tension
and are therefore stronger than interior struts (Fig. R23.2.1).
strut, interior—Interior struts are subject to tension,
acting perpendicular to the strut in the plane of the model,
from shear (Fig. R23.2.1).
tendon, external—In new or existing post-tensioned
applications, a tendon totally or partially external to the
member concrete cross section, or inside a box section, and
attached at the anchor device and deviation points.
American Concrete Institute – Copyrighted © Material – www.concrete.org
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PART 1: GENERAL 45
CODE COMMENTARY
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![5.1—Scope
5.1.1 This chapter shall apply to selection of load factors
and combinations used in design, except as permitted in
Chapter 27.
5.2—General
5.2.1 Loads shall include self-weight; applied loads; and
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5.2.2 Loads and Seismic Design Categories (SDCs) shall
be in accordance with the general building code, or deter-
PLQHGEWKHEXLOGLQJR൶FLDO
R5.2—General
R5.2.1 Provisions in the Code are associated with dead,
live, wind, and earthquake loads such as those recommended
in $6(6(,7KHFRPPHQWDUWR$SSHQGL[RI$6(
SEI 7 provides service-level wind loads Wa for serviceability
checks; however, these loads are not appropriate for strength
design.
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governs. However, if the nature of the loads contained in a
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R5.2.2 Seismic Design Categories (SDCs) in this Code
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are used by the International Building Code (2018 IBC) and
the National Fire Protection Association (NFPA 5000 2012).
The BOCA National Building Code (BOCA 1999) and “The
Standard Building Code” (SBC 1999) used seismic perfor-
mance categories. The “Uniform Building Code” (IBCO
1997) relates seismic design requirements to seismic zones,
whereas editions of ACI 318 prior to 2008 related seismic
design requirements to seismic risk levels. Table R5.2.2
correlates SDC to seismic risk terminology used in ACI
318 for several editions before the 2008 edition, and to the
various methods of assigning design requirements used in
the United States under the various model building codes,
WKH $6(6(, VWDQGDUG DQG WKH 1DWLRQDO (DUWKTXDNH
Hazard Reduction Program (NEHRP 1994).
Design requirements for earthquake-resistant structures in
this Code are determined by the SDC to which the structure
is assigned. In general, the SDC relates to seismic hazard
level, soil type, occupancy, and building use. Assignment of
a building to an SDC is under the jurisdiction of the general
building code rather than this Code.
In the absence of a general building code that prescribes
HDUWKTXDNH H൵HFWV DQG VHLVPLF ]RQLQJ LW LV WKH LQWHQW RI
Committee 318 that application of provisions for earth-
quake-resistant design be consistent with national standards
RUPRGHOEXLOGLQJFRGHVVXFKDV$6(6(,,%
and NFPA 5000. The model building codes also specify
overstrength factors Ÿo that are related to the seismic-force-
resisting system used for the structure and design of certain
elements.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 2: LOADS ANALYSIS 61
CODE COMMENTARY
5
Loads
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R5.2.2 Seism
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CHAPTER 5—LOADS
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![5.2.3 Live load reductions shall be permitted in accor-
dance with the general building code or, in the absence of a
general building code, in accordance with $6(6(,.
5.3—Load factors and combinations
5.3.1 Required strength U shall be at least equal to the
H൵HFWVRIIDFWRUHGORDGVLQ7DEOHZLWKH[FHSWLRQVDQG
additions in 5.3.3 through 5.3.13.
Table 5.3.1—Load combinations
Load combination Equation
Primary
load
U = 1.4D (5.3.1a) D
U = 1.2D + 1.6L + 0.5(Lr or S or R) (5.3.1b) L
U = 1.2D + 1.6(Lr or S or R) + (1.0L or 0.5W) (5.3.1c) Lr or S or R
U = 1.2D + 1.0W + 1.0L + 0.5(Lr or S or R) (5.3.1d) W
U = 1.2D + 1.0E + 1.0L + 0.2S (5.3.1e) E
U = 0.9D + 1.0W (5.3.1f) W
U = 0.9D + 1.0E (5.3.1g) E
R5.3—Load factors and combinations
R5.3.1 The required strength U is expressed in terms of
IDFWRUHGORDGV)DFWRUHGORDGVDUHWKHORDGVVSHFL¿HGLQWKH
general building code multiplied by appropriate load factors.
,IWKHORDGH൵HFWVVXFKDVLQWHUQDOIRUFHVDQGPRPHQWVDUH
linearly related to the loads, the required strength U may be
H[SUHVVHGLQWHUPVRIORDGH൵HFWVPXOWLSOLHGEWKHDSSURSULDWH
ORDGIDFWRUVZLWKWKHLGHQWLFDOUHVXOW,IWKHORDGH൵HFWVDUH
QRQOLQHDUOUHODWHGWRWKHORDGVVXFKDVIUDPH3GHOWDH൵HFWV
(Rogowsky and Wight 2010), the loads are factored before
GHWHUPLQLQJWKHORDGH൵HFWV7SLFDOSUDFWLFHIRUIRXQGDWLRQ
design is discussed in R13.2.6.1 1RQOLQHDU ¿QLWH HOHPHQW
analysis using factored load cases is discussed in R6.9.3.
7KH IDFWRU DVVLJQHG WR HDFK ORDG LV LQÀXHQFHG E WKH
GHJUHHRIDFFXUDFWRZKLFKWKHORDGH൵HFWXVXDOOFDQEH
calculated and the variation that might be expected in the
load during the lifetime of the structure. Dead loads, because
they are more accurately determined and less variable, are
assigned a lower load factor than live loads. Load factors
also account for variability in the structural analysis used to
calculate moments and shears.
7KHRGHJLYHVORDGIDFWRUVIRUVSHFL¿FFRPELQDWLRQVRI
loads. In assigning factors to combinations of loading, some
consideration is given to the probability of simultaneous
occurrence. While most of the usual combinations of load-
ings are included, it should not be assumed that all cases are
covered.
Due regard is to be given to the sign (positive or nega-
tive) in determining U for combinations of loadings, as one
WSHRIORDGLQJPDSURGXFHH൵HFWVRIRSSRVLWHVHQVHWRWKDW
produced by another type. The load combinations with 0.9D
are included for the case where a higher dead load reduces
WKHH൵HFWVRIRWKHUORDGV7KHORDGLQJFDVHPDDOVREHFULW-
ical for tension-controlled column sections. In such a case,
a reduction in compressive axial load or development of
tension with or without an increase in moment may result in
a critical load combination.
Table R5.2.2—Correlation between seismic-related terminology in model codes
Code, standard, or resource document and edition
Level of seismic risk or assigned seismic performance or design categories as
GH¿QHGLQWKHRGH
ACI 318-08, ACI 318-11, ACI 318-14, ACI 318-19; IBC of 2000, 2003,
2006, 2009, 2012, 2015, 2018; NFPA 5000 of 2003, 2006, 2009, 2012,
2015, 2018; ASCE 7-98, 7-02, 7-05, 7-10, 7-16; NEHRP 1997, 2000,
2003, 2009, 2015
SDC[1]
A, B SDC C SDC D, E, F
ACI 318-05 and previous editions Low seismic risk 0RGHUDWHLQWHUPHGLDWHVHLVPLFULVN High seismic risk
BOCA National Building Code 1993, 1996, 1999; Standard Building
Code 1994, 1997, 1999; ASCE 7-93, 7-95; NEHRP 1991, 1994
SPC[2]
A, B SPC C SPC D, E
Uniform Building Code 1991, 1994, 1997 Seismic Zone 0, 1 Seismic Zone 2 Seismic Zone 3, 4
[1]
6' VHLVPLFGHVLJQFDWHJRUDVGH¿QHGLQFRGHVWDQGDUGRUUHVRXUFHGRFXPHQW
[2]
63 VHLVPLFSHUIRUPDQFHFDWHJRUDVGH¿QHGLQFRGHVWDQGDUGRUUHVRXUFHGRFXPHQW
American Concrete Institute – Copyrighted © Material – www.concrete.org
62 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
WVVXFKDV
the loads,
IORDGH൵H
HLGHQWLF
WRWKHORD
Wight 201
HORDGH൵
discussed in
ysis using fac
7KH I
ast equal to the
ZLWKH[F
tio
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R5.3.1 The re
UHGORDGV)DFWR
ding code m
Equ
Prim
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(5.3.1a) D
.3.1b) L
y
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(Rog
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WRUV
DUO
sky
buil
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ultip
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![Consideration should be given to various combinations of
loading to determine the most critical design condition. This
is particularly true when strength is dependent on more than
RQHORDGH൵HFWVXFKDVVWUHQJWKIRUFRPELQHGÀH[XUHDQG
axial load or shear strength in members with axial load.
If unusual circumstances require greater reliance on the
strength of particular members than circumstances encoun-
tered in usual practice, some reduction in the stipulated
strength reduction factors ࢥ or increase in the stipulated load
factors may be appropriate for such members.
Rain load R in Eq. (5.3.1b), (5.3.1c), and (5.3.1d) should
account for all likely accumulations of water. Roofs should be
GHVLJQHGZLWKVX൶FLHQWVORSHRUFDPEHUWRHQVXUHDGHTXDWH
GUDLQDJHDFFRXQWLQJIRUDQORQJWHUPGHÀHFWLRQRIWKHURRI
GXHWRWKHGHDGORDGV,IGHÀHFWLRQRIURRIPHPEHUVPD
UHVXOWLQSRQGLQJRIZDWHUDFFRPSDQLHGELQFUHDVHGGHÀHF-
tion and additional ponding, the design should ensure that
this process is self-limiting.
Model building codes and design load references refer
to earthquake forces at the strength level, and the corre-
sponding load factor is 1.0 ($6(6(,; BOCA 1999; SBC
1999; UBC (ICBO 1997); 2018 IBC). In the absence of a
general building code that prescribes strength level earth-
TXDNHH൵HFWVDKLJKHUORDGIDFWRURQE would be required.
7KHORDGH൵HFWE in model building codes and design load
UHIHUHQFHVWDQGDUGVLQFOXGHVWKHH൵HFWRIERWKKRUL]RQWDODQG
vertical ground motions (as Eh and Ev, respectively). The
H൵HFWIRUYHUWLFDOJURXQGPRWLRQVLVDSSOLHGDVDQDGGLWLRQ
WRRUVXEWUDFWLRQIURPWKHGHDGORDGH൵HFW D), and it applies
to all structural elements, whether part of the seismic force-
UHVLVWLQJVVWHPRUQRWXQOHVVVSHFL¿FDOOH[FOXGHGEWKH
general building code.
R5.3.3 7KH ORDG PRGL¿FDWLRQ IDFWRU LQ WKLV SURYLVLRQ LV
GL൵HUHQW WKDQ WKH OLYH ORDG UHGXFWLRQV EDVHG RQ WKH ORDGHG
area that may be allowed in the general building code. The
live load reduction, based on loaded area, adjusts the nominal
live load (L0LQ$6(6(, WRL. The live load reduction, as
VSHFL¿HGLQWKHJHQHUDOEXLOGLQJFRGHFDQEHXVHGLQFRPEL-
QDWLRQZLWKWKHORDGIDFWRUVSHFL¿HGLQWKLVSURYLVLRQ
5.3.27KHH൵HFWRIRQHRUPRUHORDGVQRWDFWLQJVLPXOWDQH-
ously shall be investigated.
5.3.3 The load factor on live load L in Eq. (5.3.1c),
(5.3.1d), and (5.3.1e) shall be permitted to be reduced to 0.5
except for (a), (b), or (c):
(a) Garages
(b) Areas occupied as places of public assembly
(c) Areas where LLVJUHDWHUWKDQOEIW2
5.3.4 If applicable, L shall include (a) through (f):
(a) Concentrated live loads
(b) Vehicular loads
(c) Crane loads
(d) Loads on hand rails, guardrails, and vehicular barrier
systems
H ,PSDFWH൵HFWV
I 9LEUDWLRQH൵HFWV
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 2: LOADS ANALYSIS 63
CODE COMMENTARY
5
Loads
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WLQJVVWHP
general b
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ding load factor
(ICBO 199
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vertic
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gro
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buil
(
7);
);
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![G ,IWKHH൵HFWRIF is not permanent but, when present,
counteracts the primary load, F shall not be included in
Eq. (5.3.1a) through (5.3.1g).
5.3.8 If lateral earth pressure H is present, it shall be
included in the load combination equations of 5.3.1 in accor-
dance with (a), (b), or (c):
(a) If HDFWVDORQHRUDGGVWRWKHSULPDUORDGH൵HFWLW
shall be included with a load factor of 1.6.
E ,I WKH H൵HFW RI H is permanent and counteracts the
SULPDUORDGH൵HFWLWVKDOOEHLQFOXGHGZLWKDORDGIDFWRU
of 0.9.
F ,IWKHH൵HFWRIH is not permanent but, when present,
FRXQWHUDFWV WKH SULPDU ORDG H൵HFW H shall not be
included.
5.3.9,IDVWUXFWXUHLVLQDÀRRG]RQHWKHÀRRGORDGVDQG
the appropriate load factors and combinations of $6(6(,
7 shall be used.
5.3.10 If a structure is subjected to forces from atmo-
spheric ice loads, the ice loads and the appropriate load
IDFWRUVDQGFRPELQDWLRQVRI$6(6(,VKDOOEHXVHG
5.3.11 Required strength U shall include internal load
H൵HFWVGXHWRUHDFWLRQVLQGXFHGESUHVWUHVVLQJZLWKDORDG
factor of 1.0.
5.3.12 For post-tensioned anchorage zone design, a load
factor of 1.2 shall be applied to the maximum prestressing
reinforcement jacking force.
5.3.13 /RDG IDFWRUV IRU WKH H൵HFWV RI SUHVWUHVVLQJ XVHG
with the strut-and-tie method shall be included in the load
combination equations of 5.3.1 in accordance with (a) or (b):
(a) A load factor of 1.2 shall be applied to the prestressing
H൵HFWVZKHUHWKHSUHVWUHVVLQJH൵HFWVLQFUHDVHWKHQHWIRUFH
in struts or ties.
(b) A load factor of 0.9 shall be applied to the prestressing
H൵HFWVZKHUHWKHSUHVWUHVVLQJH൵HFWVUHGXFHWKHQHWIRUFH
in struts or ties.
R5.3.8 The required load factors for lateral pressures from
VRLO ZDWHU LQ VRLO DQG RWKHU PDWHULDOV UHÀHFW WKHLU YDUL-
ability and the possibility that the materials may be removed.
The commentary of $6(6(, includes additional useful
discussion pertaining to load factors for H.
R5.3.9 $UHDV VXEMHFW WR ÀRRGLQJ DUH GH¿QHG E ÀRRG
hazard maps, usually maintained by local governmental
jurisdictions.
R5.3.10 Ice buildup on a structural member increases the
DSSOLHGORDGDQGWKHSURMHFWHGDUHDH[SRVHGWRZLQG$6(
SEI 7 provides maps of probable ice thicknesses due to
freezing rain, with concurrent 3-second gust speeds, for a
50-year return period.
R5.3.11 For statically indeterminate structures, the
LQWHUQDOORDGH൵HFWVGXHWRUHDFWLRQVLQGXFHGESUHVWUHVVLQJ
forces, sometimes referred to as secondary moments, can be
VLJQL¿FDQW Bondy 2003; Lin and Thornton 1972; Collins
and Mitchell 1997).
R5.3.12 The load factor of 1.2 applied to the maximum
tendon jacking force results in a design load of about 113
SHUFHQW RI WKH VSHFL¿HG SUHVWUHVVLQJ UHLQIRUFHPHQW LHOG
strength, but not more than 96 percent of the nominal tensile
strength of the prestressing reinforcement. This compares
well with the maximum anchorage capacity, which is at least
95 percent of the nominal tensile strength of the prestressing
reinforcement.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 2: LOADS ANALYSIS 65
CODE COMMENTARY
5
Loads
GWKHSURMHF
maps of p
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L
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10 I
ORDG
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![6.1—Scope
6.1.1 This chapter shall apply to methods of analysis,
modeling of members and structural systems, and calcula-
WLRQRIORDGH൵HFWV
6.2—General
6.2.1 Members and structural systems shall be permitted
to be modeled in accordance with 6.3.
6.2.2 All members and structural systems shall be
DQDO]HGWRGHWHUPLQHWKHPD[LPXPORDGH൵HFWVLQFOXGLQJ
the arrangements of live load in accordance with 6.4.
6.2.3 Methods of analysis permitted by this chapter shall
be (a) through (e):
D 7KH VLPSOL¿HG PHWKRG IRU DQDOVLV RI FRQWLQXRXV
beams and one-way slabs for gravity loads in 6.5
E /LQHDUHODVWLF¿UVWRUGHUDQDOVLVLQ
(c) Linear elastic second-order analysis in 6.7
(d) Inelastic analysis in 6.8
(e) Finite element analysis in 6.9
R6.1—Scope
The provisions of this chapter apply to analyses used to
GHWHUPLQHORDGH൵HFWVIRUGHVLJQ
Section 6.2 provides general requirements that are
applicable for all analysis procedures.
Section 6.2.4 directs the licensed design professional
WR VSHFL¿F DQDOVLV SURYLVLRQV WKDW DUH QRW FRQWDLQHG LQ
this chapter. Sections 6.2.4.1 and 6.2.4.2 identify analysis
SURYLVLRQVWKDWDUHVSHFL¿FWRWZRZDVODEVDQGZDOOV
Section 6.3 addresses modeling assumptions used in
establishing the analysis model.
Section 6.4 prescribes the arrangements of live loads that
are to be considered in the analysis.
6HFWLRQSURYLGHVDVLPSOL¿HGPHWKRGRIDQDOVLVIRU
nonprestressed continuous beams and one-way slabs that
can be used in place of a more rigorous analysis when the
VWLSXODWHGFRQGLWLRQVDUHVDWLV¿HG
Section 6.6 includes provisions for a comprehensive linear
HODVWLF¿UVWRUGHUDQDOVLV7KHH൵HFWVRIFUDFNHGVHFWLRQV
and creep are included in the analysis through the use of
H൵HFWLYHVWL൵QHVVHV
Section 6.7 includes provisions for linear elastic second-
RUGHUDQDOVLV,QFOXVLRQRIWKHH൵HFWVRIFUDFNLQJDQGFUHHS
is required.
Section 6.8 includes provisions for inelastic analysis.
6HFWLRQLQFOXGHVSURYLVLRQVIRUWKHXVHRIWKH¿QLWH
element method.
R6.2—General
R6.2.3 $ ¿UVWRUGHU DQDOVLV VDWLV¿HV WKH HTXDWLRQV RI
equilibrium using the original undeformed geometry of
WKHVWUXFWXUH:KHQRQO¿UVWRUGHUUHVXOWVDUHFRQVLGHUHG
VOHQGHUQHVV H൵HFWV DUH QRW DFFRXQWHG IRU %HFDXVH WKHVH
H൵HFWV FDQ EH LPSRUWDQW SURYLGHV SURFHGXUHV WR
calculate both individual member slenderness (Pį H൵HFWV
and sidesway (P¨ H൵HFWVIRUWKHRYHUDOOVWUXFWXUHXVLQJWKH
¿UVWRUGHUUHVXOWV
$ VHFRQGRUGHU DQDOVLV VDWLV¿HV WKH HTXDWLRQV RI
equilibrium using the deformed geometry of the structure.
If the second-order analysis uses nodes along compression
PHPEHUVWKHDQDOVLVDFFRXQWVIRUVOHQGHUQHVVH൵HFWVGXH
to lateral deformations along individual members, as well as
sidesway of the overall structure. If the second-order analysis
uses nodes at the member intersections only, the analysis
FDSWXUHV WKH VLGHVZD H൵HFWV IRU WKH RYHUDOO VWUXFWXUH EXW
QHJOHFWVLQGLYLGXDOPHPEHUVOHQGHUQHVVH൵HFWV,QWKLVFDVH
WKHPRPHQWPDJQL¿HUPHWKRG LVXVHGWRGHWHUPLQH
LQGLYLGXDOPHPEHUVOHQGHUQHVVH൵HFWV
American Concrete Institute – Copyrighted © Material – www.concrete.org
QFOXVLRQRI
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PART 2: LOADS ANALYSIS 67
CODE COMMENTARY
6
Analysis
CHAPTER 6—STRUCTURAL ANALYSIS
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![all sections occurs with factored L applied simultaneously
to all panels.
6.4.3.3)RUORDGLQJFRQGLWLRQVRWKHUWKDQWKRVHGH¿QHGLQ
6.4.3.1 or 6.4.3.2, it shall be permitted to assume (a) and (b):
(a) Maximum positive Mu near midspan of panel occurs
with 75 percent of factored L on the panel and alternate
panels
(b) Maximum negative Mu at a support occurs with 75
percent of factored L on adjacent panels only
6.5—Simplified method of analysis for
nonprestressed continuous beams and one-way
slabs
6.5.1 It shall be permitted to calculate Mu and Vu due to
gravity loads in accordance with this section for continuous
beams and one-way slabs satisfying (a) through (e):
(a) Members are prismatic
(b) Loads are uniformly distributed
(c) L”D
(d) There are at least two spans
(e) The longer of two adjacent spans does not exceed the
shorter by more than 20 percent
6.5.2 Mu due to gravity loads shall be calculated in accor-
dance with Table 6.5.2.
R6.4.3.3 The use of only 75 percent of the full factored
live load for maximum moment loading patterns is based
on the fact that maximum negative and maximum positive
live load moments cannot occur simultaneously and that
redistribution of maximum moments is thus possible before
IDLOXUHRFFXUV7KLVSURFHGXUHLQH൵HFWSHUPLWVVRPHORFDO
overstress under the full factored live load if it is distributed
in the prescribed manner, but still ensures that the design
strength of the slab system after redistribution of moment is
not less than that required to resist the full factored dead and
live loads on all panels.
R6.5—Simplified method of analysis for
nonprestressed continuous beams and one-way
slabs
R6.5.2 The approximate moments and shears give
reasonable values for the stated conditions if the continuous
beams and one-way slabs are part of a frame or continuous
construction. Because the load patterns that produce critical
YDOXHVIRUPRPHQWVLQFROXPQVRIIUDPHVGL൵HUIURPWKRVH
for maximum negative moments in beams, column moments
should be evaluated separately.
American Concrete Institute – Copyrighted © Material – www.concrete.org
The appro
nable value
beams a
e to
n for continuous
) through
but
ns
nt
nt
does not excee the
74 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Table 6.5.2—Approximate moments for nonprestressed continuous beams and one-way slabs
Moment Location Condition Mu
Positive
End span
Discontinuous end integral with support wuƐn
2
Discontinuous end unrestrained wuƐn
2
Interior spans All wuƐn
2
Negative[1]
Interior face of exterior support
Member built integrally with supporting spandrel beam wuƐn
2
Member built integrally with supporting column wuƐn
2
([WHULRUIDFHRI¿UVWLQWHULRUVXSSRUW
Two spans wuƐn
2
More than two spans wuƐn
2
Face of other supports All wuƐn
2
Face of all supports satisfying (a) or (b)
(a) slabs with spans not exceeding 10 ft
E EHDPVZKHUHUDWLRRIVXPRIFROXPQVWL൵QHVVHVWREHDP
VWL൵QHVVH[FHHGVDWHDFKHQGRIVSDQ
wuƐn
2
[1]
To calculate negative moments, Ɛn shall be the average of the adjacent clear span lengths.
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![R7.3.2 DOFXODWHGGHÀHFWLRQOLPLWV
7KHEDVLVIRUFDOFXODWHGGHÀHFWLRQVIRURQHZDVODEVLV
the same as that for beams. Refer to R9.3.2 for additional
information.
R7.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV
R7.3.3.1 The basis for a reinforcement strain limit for
one-way slabs is the same as that for beams. Refer to R9.3.3
for additional information.
Table 7.3.1.1—Minimum thickness of solid
nonprestressed one-way slabs
Support condition Minimum h[1]
Simply supported Ɛ
One end continuous Ɛ
Both ends continuous Ɛ
Cantilever Ɛ
[1]
Expression applicable for normalweight concrete and fy = 60,000 psi. For other
cases, minimum hVKDOOEHPRGL¿HGLQDFFRUGDQFHZLWKWKURXJK
as appropriate.
7.3.1.1.1 For fy other than 60,000 psi, the expressions in
Table 7.3.1.1 shall be multiplied by (0.4 + fy/100,000).
7.3.1.1.2 For nonprestressed slabs made of lightweight
concretehavingwcLQWKHUDQJHRIWROEIW3
,theexpressions
in Table 7.3.1.1 shall be multiplied by the greater of (a) and (b):
(a) 1.65 – 0.005wc
(b) 1.09
7.3.1.1.3 For nonprestressed composite slabs made of a
combinationoflightweightandnormalweightconcrete,shored
during construction, and where the lightweight concrete is in
FRPSUHVVLRQWKHPRGL¿HURIVKDOODSSO
7.3.1.27KHWKLFNQHVVRIDFRQFUHWHÀRRU¿QLVKVKDOOEH
permitted to be included in h if it is placed monolithically
ZLWKWKHÀRRUVODERULIWKHÀRRU¿QLVKLVGHVLJQHGWREH
FRPSRVLWHZLWKWKHÀRRUVODELQDFFRUGDQFHZLWK16.4.
7.3.2 DOFXODWHGGHÀHFWLRQOLPLWV
7.3.2.1 For nonprestressed slabs not satisfying 7.3.1 and
IRUSUHVWUHVVHGVODEVLPPHGLDWHDQGWLPHGHSHQGHQWGHÀHF-
tions shall be calculated in accordance with 24.2 and shall
not exceed the limits in 24.2.2.
7.3.2.2 For nonprestressed composite concrete slabs satis-
ILQJGHÀHFWLRQVRFFXUULQJDIWHUWKHPHPEHUEHFRPHV
FRPSRVLWH QHHG QRW EH FDOFXODWHG 'HÀHFWLRQV RFFXUULQJ
before the member becomes composite shall be investigated,
XQOHVVWKHSUHFRPSRVLWHWKLFNQHVVDOVRVDWLV¿HV
7.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV
7.3.3.1 Nonprestressed slabs shall be tension-controlled in
accordance with Table 21.2.2.
7.3.4 6WUHVVOLPLWVLQSUHVWUHVVHGVODEV
7.3.4.13UHVWUHVVHGVODEVVKDOOEHFODVVL¿HGDVODVV87
or C in accordance with 24.5.2.
American Concrete Institute – Copyrighted © Material – www.concrete.org
comp
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CODE COMMENTARY
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![7
One-way
Slabs
7.7.1.3 Splices of deformed reinforcement shall be in
accordance with 25.5.
7.7.1.4 Bundled bars shall be in accordance with 25.6.
7.7.2 5HLQIRUFHPHQWVSDFLQJ
7.7.2.1 Minimum spacing s shall be in accordance with 25.2.
7.7.2.2 For nonprestressed and Class C prestressed slabs,
spacing of bonded longitudinal reinforcement closest to the
tension face shall not exceed s given in 24.3.
7.7.2.3 For nonprestressed and Class T and C prestressed
slabs with unbonded tendons, maximum spacing s of
deformed longitudinal reinforcement shall be the lesser of
3h and 18 in.
7.7.2.4 Maximum spacing, s, of reinforcement required by
7.5.2.3 shall be the lesser of 5h and 18 in.
7.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV
7.7.3.1 Calculated tensile or compressive force in rein-
forcement at each section of the slab shall be developed on
each side of that section.
7.7.3.2 Critical locations for development of reinforce-
ment are points of maximum stress and points along the span
where bent or terminated tension reinforcement is no longer
UHTXLUHGWRUHVLVWÀH[XUH
7.7.3.3 Reinforcement shall extend beyond the point at
ZKLFKLWLVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUHIRUDGLVWDQFH
at least the greater of d and 12db, except at supports of
simply-supported spans and at free ends of cantilevers.
7.7.3.4 RQWLQXLQJ ÀH[XUDO WHQVLRQ UHLQIRUFHPHQW VKDOO
have an embedment length at least Ɛd beyond the point
where bent or terminated tension reinforcement is no longer
UHTXLUHGWRUHVLVWÀH[XUH
7.7.3.5 Flexural tension reinforcement shall not be termi-
QDWHGLQDWHQVLRQ]RQHXQOHVV D E RU F LVVDWLV¿HG
(a) Vu” ࢥVnDWWKHFXWR൵SRLQW
(b) For No. 11 bars and smaller, continuing reinforcement
SURYLGHVGRXEOHWKHDUHDUHTXLUHGIRUÀH[XUHDWWKHFXWR൵
point and Vu” ࢥVn.
(c) Stirrup area in excess of that required for shear is
provided along each terminated bar or wire over a distance
R7.7.2 5HLQIRUFHPHQWVSDFLQJ
R7.7.2.3 Editions of ACI 318 prior to 2019 excluded the
provisions of 7.7.2.3 for prestressed concrete. However, Class
T and C slabs prestressed with unbonded tendons rely solely
on deformed reinforcement for crack control. Consequently,
the requirements of 7.7.2.3 have been extended to apply to
Class T and C slabs prestressed with unbonded tendons.
R7.7.2.4 The spacing limitations for slab reinforcement
DUHEDVHGRQÀDQJHWKLFNQHVVZKLFKIRUWDSHUHGÀDQJHVFDQ
be taken as the average thickness.
R7.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV
Requirements for development of reinforcement in
one-way slabs are similar to those for beams. Refer to R9.7.3
for additional information.
American Concrete Institute – Copyrighted © Material – www.concrete.org
average thic
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or devel
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PART 3: MEMBERS 95
CODE COMMENTARY
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![R8.2.2 Refer to R7.2.1.
R8.2.4 and R8.2.5 'URS SDQHO GLPHQVLRQV VSHFL¿HG LQ
8.2.4 are necessary when reducing the amount of nega-
tive moment reinforcement following 8.5.2.2 or to satisfy
minimum slab thicknesses permitted in 8.3.1.1. If the dimen-
VLRQVDUHOHVVWKDQVSHFL¿HGLQWKHSURMHFWLRQPDEH
used as a shear cap to increase the shear strength of the slab.
For slabs with changes in thickness, it is necessary to check
the shear strength at several sections (Refer to 22.6.4.1(b)).
R8.2.7 RQQHFWLRQVWRRWKHUPHPEHUV
Safety of a slab system requires consideration of the trans-
PLVVLRQ RI ORDG IURP WKH VODE WR WKH FROXPQV E ÀH[XUH
torsion, and shear.
R8.3—Design limits
R8.3.1 0LQLPXPVODEWKLFNQHVV
Theminimumslabthicknessesin8.3.1.1and8.3.1.2areinde-
pendent of loading and concrete modulus of elasticity, both of
ZKLFKKDYHVLJQL¿FDQWH൵HFWVRQGHÀHFWLRQV7KHVHPLQLPXP
thicknesses are not applicable to slabs with unusually heavy
superimposed sustained loads or for concrete with modulus of
HODVWLFLWVLJQL¿FDQWOORZHUWKDQWKDWRIRUGLQDUQRUPDOZHLJKW
FRQFUHWH'HÀHFWLRQVVKRXOGEHFDOFXODWHGIRUVXFKVLWXDWLRQV
8.2.27KHH൵HFWVRIFRQFHQWUDWHGORDGVVODERSHQLQJVDQG
slab voids shall be considered in design.
8.2.36ODEVSUHVWUHVVHGZLWKDQDYHUDJHH൵HFWLYHFRPSUHV-
sive stress less than 125 psi shall be designed as nonpre-
stressed slabs.
8.2.4 A drop panel in a nonprestressed slab, where used
to reduce the minimum required thickness in accordance
with 8.3.1.1 or the quantity of deformed negative moment
reinforcement at a support in accordance with 8.5.2.2, shall
satisfy (a) and (b):
(a) The drop panel shall project below the slab at least
one-fourth of the adjacent slab thickness.
(b) The drop panel shall extend in each direction from the
centerline of support a distance not less than one-sixth the
span length measured from center-to-center of supports in
that direction.
8.2.5 A shear cap, where used to increase the critical
section for shear at a slab-column joint, shall project below
WKHVODEVR൶WDQGH[WHQGKRUL]RQWDOOIURPWKHIDFHRIWKH
column a distance at least equal to the thickness of the
SURMHFWLRQEHORZWKHVODEVR൶W
8.2.6 Materials
8.2.6.1 Design properties for concrete shall be selected to
be in accordance with Chapter 19.
8.2.6.2 Design properties for steel reinforcement shall be
selected to be in accordance with Chapter 20.
8.2.6.3 Materials, design, and detailing requirements for
embedments in concrete shall be in accordance with 20.6.
8.2.7 RQQHFWLRQVWRRWKHUPHPEHUV
8.2.7.1 Beam-column and slab-column joints shall satisfy
Chapter 15.
8.3—Design limits
8.3.1 0LQLPXPVODEWKLFNQHVV
American Concrete Institute – Copyrighted © Material – www.concrete.org
100 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
be
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![R8.3.1.1 The minimum thicknesses in Table 8.3.1.1 are
those that have been developed through the years. Use of
longitudinal reinforcement with fy 80,000 psi may result in
ODUJHUORQJWHUPGHÀHFWLRQVWKDQLQWKHFDVHRIfy 80,000
psi unless associated service stresses calculated for cracked
sections are smaller than 40,000 psi. Careful calculation of
GHÀHFWLRQVVKRXOGEHSHUIRUPHG
R8.3.1.2 For panels having a ratio of long-to-short span
greater than 2, the use of expressions (b) and (d) of Table
8.3.1.2, which give the minimum thickness as a fraction
of the long span, may give unreasonable results. For such
panels, the rules applying to one-way construction in 7.3.1
should be used.
8.3.1.1 For nonprestressed slabs without interior beams
spanning between supports on all sides, having a maximum
ratio of long-to-short span of 2, overall slab thickness h shall
not be less than the limits in Table 8.3.1.1, and shall be at
OHDVWWKHYDOXHLQ D RU E XQOHVVWKHFDOFXODWHGGHÀHFWLRQ
OLPLWVRIDUHVDWLV¿HG
(a) Slabs without drop panels as given in 8.2.4.......... 5 in.
(b) Slabs with drop panels as given in 8.2.4............... 4 in.
For fy H[FHHGLQJ SVL WKH FDOFXODWHG GHÀHFWLRQ
OLPLWVLQVKDOOEHVDWLV¿HGDVVXPLQJDUHGXFHGPRGXOXV
of rupture ′
= 5
r c
f f .
8.3.1.2 For nonprestressed slabs with beams spanning
between supports on all sides, overall slab thickness h shall
satisfy the limits in Table 8.3.1.2, unless the calculated
GHÀHFWLRQOLPLWVRIDUHVDWLV¿HG
Table 8.3.1.2—Minimum thickness of
nonprestressed two-way slabs with beams
spanning between supports on all sides
Įfm
[1]
Minimum h, in.
ĮIP” 8.3.1.1 applies (a)
ĮIP”
Greater
of:
0.8
200,000
36 5 ( 0.2)
y
n
IP
f
⎛ ⎞
+
⎜ ⎟
⎝ ⎠
+ β α −
A
(b)[1],[2]
5.0 (c)
ĮIP 2.0
Greater
of:
0.8
200,000
36 9
y
n
f
⎛ ⎞
+
⎜ ⎟
⎝ ⎠
+ β
A
(d)
3.5 (e)
[1]
ĮIPLVWKHDYHUDJHYDOXHRIĮf for all beams on edges of a panel.
[2]
Ɛn is the clear span in the long direction, measured face-to-face of beams (in.).
[3]
ȕLVWKHUDWLRRIFOHDUVSDQVLQORQJWRVKRUWGLUHFWLRQVRIVODE
Table 8.3.1.1—Minimum thickness of nonprestressed two-way slabs without interior beams (in.)[1]
fy, psi[2]
Without drop panels[3]
With drop panels[3]
Exterior panels
Interior panels
Exterior panels
Interior panels
Without edge beams With edge beams[4]
Without edge beams With edge beams[4]
40,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn
60,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn
80,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn
[1]
Ɛn is the clear span in the long direction, measured face-to-face of supports (in.).
[2]
For fy between the values given in the table, minimum thickness shall be calculated by linear interpolation.
[3]
Drop panels as given in 8.2.4.
[4]
6ODEVZLWKEHDPVEHWZHHQFROXPQVDORQJH[WHULRUHGJHV([WHULRUSDQHOVVKDOOEHFRQVLGHUHGWREHZLWKRXWHGJHEHDPVLIĮf is less than 0.8.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 101
CODE COMMENTARY
8
Two-way
Slabs
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thickness shall be calc
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ated by linear interpol
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on.
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![RPPHQWDURQVL]HH൵HFWIDFWRULVSURYLGHGLQR22.5.5.1
and R22.6.5.2.
R8.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV
R8.6.2.17KHPLQLPXPDYHUDJHH൵HFWLYHSUHVWUHVVRI
psi was used in two-way test panels in the early 1970s to
address punching shear concerns of lightly reinforced slabs.
)RUWKLVUHDVRQWKHPLQLPXPH൵HFWLYHSUHVWUHVVLVUHTXLUHG
to be provided at every cross section.
If the slab thickness varies along the span of a slab or
perpendicular to the span of a slab, resulting in a varying slab
FURVVVHFWLRQWKHSVLPLQLPXPH൵HFWLYHSUHVWUHVVDQGWKH
maximum tendon spacing is required at every cross section
tributary to the tendon or group of tendons along the span,
considering both the thinner and the thicker slab sections. This
may result in higher than the minimum fpc in thinner cross
sections, and tendons spaced at less than the maximum in
thicker cross sections along a span with varying thickness,
GXHWRWKHSUDFWLFDODVSHFWVRIWHQGRQSODFHPHQWLQWKH¿HOG
R8.6.2.2 This provision is a precaution against abrupt
ÀH[XUDO IDLOXUH GHYHORSLQJ LPPHGLDWHO DIWHU FUDFNLQJ $
ÀH[XUDO PHPEHU GHVLJQHG DFFRUGLQJ WR RGH SURYLVLRQV
requires considerable additional load beyond cracking to
UHDFK LWV ÀH[XUDO VWUHQJWK 7KXV FRQVLGHUDEOH GHÀHFWLRQ
would warn that the member strength is approaching. If
WKH ÀH[XUDO VWUHQJWK ZHUH UHDFKHG VKRUWO DIWHU FUDFNLQJ
WKHZDUQLQJGHÀHFWLRQZRXOGQRWRFFXU7UDQVIHURIIRUFH
between the concrete and the prestressed reinforcement,
DQGDEUXSWÀH[XUDOIDLOXUHLPPHGLDWHODIWHUFUDFNLQJGRHV
not occur when the prestressed reinforcement is unbonded
(ACI 423.3R); therefore, this requirement does not apply to
members with unbonded tendons.
R8.6.2.3 Some bonded reinforcement is required by the
Code in prestressed slabs to limit crack width and spacing
at service load when concrete tensile stresses exceed the
modulus of rupture and, for slabs with unbonded tendons, to
HQVXUHÀH[XUDOSHUIRUPDQFHDWQRPLQDOVWUHQJWKUDWKHUWKDQ
performance as a tied arch. Providing the minimum bonded
reinforcement as stipulated in this provision helps to ensure
adequate performance.
The minimum amount of bonded reinforcement in
WZRZDÀDWVODEVVWHPVLVEDVHGRQUHSRUWVEJoint ACI-
ASCE Committee 423 (1958) and ACI 423.3R. Limited
UHVHDUFKDYDLODEOHIRUWZRZDÀDWVODEVZLWKGURSSDQHOV
(Odello and Mehta 1967) indicates that behavior of these
SDUWLFXODUVVWHPVLVVLPLODUWRWKHEHKDYLRURIÀDWSODWHV
)RUXVXDOORDGVDQGVSDQOHQJWKVÀDWSODWHWHVWVVXPPDUL]HG
in Joint ACI-ASCE Committee 423 (1958) and experience
since the 1963 Code was adopted indicate satisfactory perfor-
mance without bonded reinforcement in positive moment
regions where ft” ′
c
f . In positive moment regions where
2 ′
c
f ”ft” ′
c
f , a minimum bonded reinforcement area
8.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV
8.6.2.1)RUSUHVWUHVVHGVODEVWKHH൵HFWLYHSUHVWUHVVIRUFH
Aps fse shall provide a minimum average compressive stress
of 125 psi on the slab section tributary to the tendon or
tendon group. For slabs with varying cross section along
the slab span, either parallel or perpendicular to the tendon
RUWHQGRQJURXSWKHPLQLPXPDYHUDJHH൵HFWLYHSUHVWUHVV
of 125 psi is required at every cross section tributary to the
tendon or tendon group along the span.
8.6.2.2 For slabs with bonded prestressed reinforcement,
total quantity of As and Aps shall be adequate to develop a
factored load at least 1.2 times the cracking load calculated
on the basis of frGH¿QHGLQ19.2.3.
8.6.2.2.1 )RU VODEV ZLWK ERWK ÀH[XUDO DQG VKHDU GHVLJQ
strength at least twice the required strength, 8.6.2.2 need not
EHVDWLV¿HG
8.6.2.3 For prestressed slabs, a minimum area of bonded
deformed longitudinal reinforcement, As,min, shall be provided
in the precompressed tension zone in the direction of the span
under consideration in accordance with Table 8.6.2.3.
Table 8.6.2.3—Minimum bonded deformed
longitudinal reinforcement As,min in two-way slabs
with bonded or unbonded tendons
Region
Calculated ft after all
losses, psi As,min, in.2
Positive moment
2
t c
f f
≤ ′ Not required (a)
2 6
c t c
f f f
≤
′ ′
0.5
c
y
N
f
(b)[1],[2]
Negative moment
at columns
6
t c
f f
≤ ′ 0.00075Acf (c)[2]
[1]
The value of fy shall not exceed 60,000 psi.
[2]
For slabs with bonded tendons, it shall be permitted to reduce As,PLQ by the area of
the bonded prestressed reinforcement located within the area used to determine Nc for
SRVLWLYHPRPHQWRUZLWKLQWKHZLGWKRIVODEGH¿QHGLQ D IRUQHJDWLYHPRPHQW
American Concrete Institute – Copyrighted © Material – www.concrete.org
112 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![R9.3.1.1.1 7KH PRGL¿FDWLRQ IRU fy is approximate, but
should provide conservative results for typical reinforcement
ratios and for values of fy between 40,000 and 100,000 psi.
R9.3.1.1.2 7KH PRGL¿FDWLRQ IRU OLJKWZHLJKW FRQFUHWH
is based on the results and discussions in ACI 213R. No
correction is given for concretes with wc greater than 115
OEIW3
because the correction term would be close to unity in
this range.
R9.3.2 DOFXODWHGGHÀHFWLRQOLPLWV
R9.3.2.2 The limits in Table 9.3.1.1 apply to the entire
depth of nonprestressed composite beams shored during
construction so that, after removal of temporary supports,
the dead load is resisted by the full composite section. In
unshored construction, the beam depth of concern depends
RQLIWKHGHÀHFWLRQEHLQJFRQVLGHUHGRFFXUVEHIRUHRUDIWHU
WKHDWWDLQPHQWRIH൵HFWLYHFRPSRVLWHDFWLRQ
$GGLWLRQDO GHÀHFWLRQV GXH WR H[FHVVLYH FUHHS DQG
shrinkage caused by premature loading should be consid-
ered. This is especially important at early ages when the
moisture content is high and the strength is low.
The transfer of horizontal shear by direct bond is impor-
WDQWLIH[FHVVLYHGHÀHFWLRQIURPVOLSSDJHLVWREHSUHYHQWHG
Table 9.3.1.1—Minimum depth of nonprestressed
beams
Support condition Minimum h[1]
Simply supported Ɛ
One end continuous Ɛ
Both ends continuous Ɛ
Cantilever Ɛ
[1]
Expressions applicable for normalweight concrete and fy = 60,000 psi. For other
cases, minimum hVKDOOEHPRGL¿HGLQDFFRUGDQFHZLWKWKURXJK
as appropriate.
9.3.1.1.1 For fy other than 60,000 psi, the expressions in
Table 9.3.1.1 shall be multiplied by (0.4 + fy/100,000).
9.3.1.1.2 For nonprestressed beams made of lightweight
concrete having wcLQWKHUDQJHRIWROEIW3
, the expres-
sions in Table 9.3.1.1 shall be multiplied by the greater of (a)
and (b):
(a) 1.65 – 0.005wc
(b) 1.09
9.3.1.1.3 For nonprestressed composite beams made of a
combinationoflightweightandnormalweightconcrete,shored
during construction, and where the lightweight concrete is in
FRPSUHVVLRQWKHPRGL¿HURIVKDOODSSO
9.3.1.2 7KH WKLFNQHVV RI D FRQFUHWH ÀRRU ¿QLVK VKDOO
be permitted to be included in h if it is placed monolithi-
FDOOZLWKWKHEHDPRULIWKHÀRRU¿QLVKLVGHVLJQHGWREH
composite with the beam in accordance with 16.4.
9.3.2 DOFXODWHGGHÀHFWLRQOLPLWV
9.3.2.1 For nonprestressed beams not satisfying 9.3.1
and for prestressed beams, immediate and time-dependent
GHÀHFWLRQVVKDOOEHFDOFXODWHGLQDFFRUGDQFHZLWK24.2 and
shall not exceed the limits in 24.2.2.
9.3.2.2 For nonprestressed composite concrete beams satis-
ILQJGHÀHFWLRQVRFFXUULQJDIWHUWKHPHPEHUEHFRPHV
FRPSRVLWH QHHG QRW EH FDOFXODWHG 'HÀHFWLRQV RFFXUULQJ
before the member becomes composite shall be investigated
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PART 3: MEMBERS 129
CODE COMMENTARY
9
Beams
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![9.5.4.3 Longitudinal and transverse reinforcement
required for torsion shall be added to that required for the
Vu, Mu, and Pu that act in combination with the torsion.
9.5.4.4 For prestressed beams, the total area of longitu-
dinal reinforcement, As and Aps, at each section shall be
designed to resist Mu at that section, plus an additional
concentric longitudinal tensile force equal to AƐ fy, based on
Tu at that section.
9.5.4.5 It shall be permitted to reduce the area of longi-
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R9.5.4.3 The requirements for torsional reinforcement
and shear reinforcement are added and stirrups are provided
to supply at least the total amount required. Because the
reinforcement area AvIRUVKHDULVGH¿QHGLQWHUPVRIDOOWKH
legs of a given stirrup while the reinforcement area At for
WRUVLRQLVGH¿QHGLQWHUPVRIRQHOHJRQOWKHDGGLWLRQRI
transverse reinforcement area is calculated as follows:
Total 2
v t v t
A A A
s s s
+
⎛ ⎞
= +
⎜ ⎟
⎠
(R9.5.4.3)
If a stirrup group has more than two legs for shear, only
the legs adjacent to the sides of the beam are included in this
VXPPDWLRQEHFDXVHWKHLQQHUOHJVZRXOGEHLQH൵HFWLYHIRU
resisting torsion.
The longitudinal reinforcement required for torsion is
added at each section to the longitudinal reinforcement
required for bending moment that acts concurrently with the
torsion. The longitudinal reinforcement is then chosen for this
sum, but should not be less than the amount required for the
maximum bending moment at that section if this exceeds the
moment acting concurrently with the torsion. If the maximum
bending moment occurs at one section, such as midspan,
while the maximum torsional moment occurs at another, such
as the face of the support, the total longitudinal reinforce-
ment required may be less than that obtained by adding the
PD[LPXPÀH[XUDOUHLQIRUFHPHQWSOXVWKHPD[LPXPWRUVLRQDO
reinforcement. In such a case, the required longitudinal rein-
forcement is evaluated at several locations.
R9.5.4.4 Torsion causes an axial tensile force in the longi-
tudinal reinforcement balanced by the force in the diagonal
concrete compression struts. In a nonprestressed beam, the
tensile force must be resisted by longitudinal reinforcement
having an axial tensile strength of AƐ fy. This reinforcement
LVLQDGGLWLRQWRWKHUHTXLUHGÀH[XUDOUHLQIRUFHPHQWDQGLV
distributed uniformly inside and around the perimeter of the
closed transverse reinforcement so that the resultant of AƐ fy
acts along the axis of the member.
In a prestressed beam, the same approach (providing
additional reinforcing bars with strength AƐ fy) may be
followed, or overstrength of the prestressed reinforcement
can be used to resist some of the axial force AƐ fy. The stress
in the prestressed reinforcement at nominal strength will
be between fse and fps. A portion of the AƐ fy force can be
resisted by a force of Aps¨fpt in the prestressed reinforce-
ment. The stress required to resist the bending moment can
be calculated as Mu/(ࢥ0.9dpAps). For pretensioned strands,
the stress that can be developed near the free end of the
strand can be calculated using the procedure illustrated in
Fig. R25.4.8.3.
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CODE COMMENTARY
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![R9.7—Reinforcement detailing
R9.7.2 5HLQIRUFHPHQWVSDFLQJ
R9.7.2.3 For relatively deep beams, some reinforcement
should be placed near the vertical faces of the tension zone
to control cracking in the web (Frantz and Breen 1980;
Frosch 2002), as shown in Fig. R9.7.2.3. Without such auxil-
iary reinforcement, the width of the cracks in the web may
H[FHHGWKHFUDFNZLGWKVDWWKHOHYHORIWKHÀH[XUDOWHQVLRQ
reinforcement.
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research has indicated that the spacing rather than bar size is
of primary importance (Frosch 2002). Bar sizes No. 3 to No.
5, or welded wire reinforcement with a minimum area of 0.1
in.2
per foot of depth, are typically provided.
9.7—Reinforcement detailing
9.7.1 General
9.7.1.1 Concrete cover for reinforcement shall be in accor-
dance with 20.5.1.
9.7.1.2 Development lengths of deformed and prestressed
reinforcement shall be in accordance with 25.4.
9.7.1.3 Splices of deformed reinforcement shall be in
accordance with 25.5.
9.7.1.4Along development and lap splice lengths of longi-
tudinal bars with fy•SVL, transverse reinforcement
shall be provided such that Ktr shall not be smaller than 0.5db.
9.7.1.5 Bundled bars shall be in accordance with 25.6.
9.7.2 5HLQIRUFHPHQWVSDFLQJ
9.7.2.1 Minimum spacing s shall be in accordance with 25.2.
9.7.2.2 For nonprestressed and Class C prestressed beams,
spacing of bonded longitudinal reinforcement closest to the
tension face shall not exceed s given in 24.3.
9.7.2.3 For nonprestressed and Class C prestressed beams
with h exceeding 36 in., longitudinal skin reinforcement
shall be uniformly distributed on both side faces of the beam
for a distance h/2 from the tension face. Spacing of skin rein-
forcement shall not exceed s given in 24.3.2, where cc is the
clear cover from the skin reinforcement to the side face. It
shall be permitted to include skin reinforcement in strength
calculations if a strain compatibility analysis is made.
American Concrete Institute – Copyrighted © Material – www.concrete.org
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PART 3: MEMBERS 139
CODE COMMENTARY
9
Beams
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![R9.7.3.3 The moment diagrams customarily used in design
are approximate; some shifting of the location of maximum
moments may occur due to changes in loading, settlement of
supports, lateral loads, or other causes. A diagonal tension
FUDFNLQDÀH[XUDOPHPEHUZLWKRXWVWLUUXSVPDVKLIWWKH
location of the calculated tensile stress approximately a
distance d toward a point of zero moment. If stirrups are
SURYLGHGWKLVH൵HFWLVOHVVVHYHUHDOWKRXJKVWLOOSUHVHQWWR
some extent.
To provide for shifts in the location of maximum moments,
the Code requires the extension of reinforcement a distance
d or 12db beyond the point at which it is calculated to be
QRORQJHUUHTXLUHGWRUHVLVWÀH[XUHH[FHSWDVQRWHGXWR൵
points of bars to meet this requirement are illustrated in
)LJ5,IGL൵HUHQWEDUVL]HVDUHXVHGWKHH[WHQVLRQ
should be in accordance with the diameter of the bar being
terminated.
9.7.3.3 Reinforcement shall extend beyond the point at
ZKLFKLWLVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUHIRUDGLVWDQFH
equal to the greater of d and 12db, except at supports of
simply-supported spans and at free ends of cantilevers.
Section 25.4.2.1, or 9.7.3.8,
or dc for compression when
bottom bars used as
compression reinforcement
Bars a
c
x
c x
c
x
c
x
Bars b
≥ (d or 12db)
≥ d
≥ (d or 12db)
≥ d
P.I.
Diameter of bars a
limited by Section 9.7.3.8.3
at point of inflection
Points of
inflection (P.I.)
Moment
strength
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Moment
strength
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Face of support
Embedment
of bars a ≥ d
≥ d
Mid-span of
member
≥ (d, 12db or n /16)
Moment
Curve
Fig. R9.7.3.2²'HYHORSPHQWRIÀH[XUDOUHLQIRUFHPHQWLQDWSLFDOFRQWLQXRXVEHDP
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 141
CODE COMMENTARY
9
Beams
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![R9.7.3.4 Local peak stresses exist in the remaining bars
ZKHUHYHUDGMDFHQWEDUVDUHFXWR൵LQWHQVLRQUHJLRQV,Q)LJ
R9.7.3.2, an “x” is used to indicate the point where termi-
nated tension reinforcement is no longer required to resist
ÀH[XUH ,I EDUV ZHUH FXW R൵ DW WKLV ORFDWLRQ WKH UHTXLUHG
FXWR൵ SRLQW LV EHRQG ORFDWLRQ ³[´ LQ DFFRUGDQFH ZLWK
9.7.3.3), peak stresses in the continuing bars would reach fy
at “x”. Therefore, the continuing reinforcement is required
to have a full Ɛd extension as indicated.
R9.7.3.5 Reduced shear strength and loss of ductility when
EDUVDUHFXWR൵LQDWHQVLRQ]RQHDVLQ)LJ5KDYH
EHHQUHSRUWHG7KHRGHGRHVQRWSHUPLWÀH[XUDOUHLQIRUFH-
ment to be terminated in a tension zone unless additional
FRQGLWLRQVDUHVDWLV¿HG)OH[XUDOFUDFNVWHQGWRRSHQDWORZ
load levels wherever any reinforcement is terminated in a
tension zone. If the stress in the continuing reinforcement
and the shear strength are each near their limiting values,
diagonal tension cracking tends to develop prematurely
IURPWKHVHÀH[XUDOFUDFNV'LDJRQDOFUDFNVDUHOHVVOLNHO
WR IRUP ZKHUH VKHDU VWUHVV LV ORZ D RU ÀH[XUDO
reinforcement stress is low (9.7.3.5(b)). Diagonal cracks can
be restrained by closely spaced stirrups (9.7.3.5(c)). These
requirements are not intended to apply to tension splices that
are covered by 25.5.
R9.7.3.7Abar bent to the far face of a beam and continued
WKHUHPDEHFRQVLGHUHGH൵HFWLYHLQVDWLVILQJWRWKH
point where the bar crosses the mid-depth of the member.
R9.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW
R9.7.3.8.1 Positive moment reinforcement is extended
into the support to provide for some shifting of the moments
due to changes in loading, settlement of supports, and lateral
loads. It also enhances structural integrity.
For precast beams, tolerances and reinforcement cover
should be considered to avoid bearing on plain concrete
where reinforcement has been discontinued.
R9.7.3.8.2 Development of the positive moment reinforce-
ment at the support is required for beams that are part of the
primary lateral-load-resisting system to provide ductility in
the event of moment reversal.
R9.7.3.8.3 The diameter of the positive moment tension
reinforcement is limited to ensure that the bars are devel-
oped in a length short enough such that the moment capacity
9.7.3.4 RQWLQXLQJ ÀH[XUDO WHQVLRQ UHLQIRUFHPHQW VKDOO
have an embedment length at least Ɛd beyond the point
where bent or terminated tension reinforcement is no longer
UHTXLUHGWRUHVLVWÀH[XUH
9.7.3.5 Flexural tension reinforcement shall not be termi-
QDWHGLQDWHQVLRQ]RQHXQOHVV D E RU F LVVDWLV¿HG
(a) Vu” ࢥVnDWWKHFXWR൵SRLQW
(b) For No. 11 bars and smaller, continuing reinforcement
SURYLGHVGRXEOHWKHDUHDUHTXLUHGIRUÀH[XUHDWWKHFXWR൵
point and Vu” ࢥVn
(c) Stirrup or hoop area in excess of that required for shear
and torsion is provided along each terminated bar or wire
over a distance 3/4dIURPWKHFXWR൵SRLQW([FHVVVWLUUXS
or hoop area shall be at least 60bws/fyt. Spacing s shall not
exceed d ȕb)
9.7.3.6 Adequate anchorage shall be provided for tension
reinforcement where reinforcement stress is not directly
proportional to moment, such as in sloped, stepped, or
tapered beams, or where tension reinforcement is not parallel
to the compression face.
9.7.3.7 Development of tension reinforcement by bending
across the web to be anchored or made continuous with rein-
forcement on the opposite face of beam shall be permitted.
9.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW
9.7.3.8.1 At simple supports, at least one-third of the
maximum positive moment reinforcement shall extend
along the beam bottom into the support at least 6 in., except
for precast beams where such reinforcement shall extend at
least to the center of the bearing length.
9.7.3.8.2 At other supports, at least one-fourth of the
maximum positive moment reinforcement shall extend
along the beam bottom into the support at least 6 in. and, if
the beam is part of the primary lateral-load-resisting system,
shall be anchored to develop fy at the face of the support.
9.7.3.8.3$WVLPSOHVXSSRUWVDQGSRLQWVRILQÀHFWLRQdb
for positive moment tension reinforcement shall be limited
such that ƐdIRUWKDWUHLQIRUFHPHQWVDWLV¿HV D RU E ,IUHLQ-
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142 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![is greater than the applied moment over the entire length
of the beam. As illustrated in the moment diagram of Fig.
R9.7.3.8.3(a), the slope of the moment diagram is Vu, while
the slope of moment development is Mn/Ɛd, where Mn is
WKHQRPLQDOÀH[XUDOVWUHQJWKRIWKHFURVVVHFWLRQ%VL]LQJ
the reinforcement such that the capacity slope Mn/Ɛd equals
or exceeds the demand slope Vu, proper development is
provided. Therefore, Mn/Vu represents the available devel-
opment length. Under favorable support conditions, a 30
percent increase for Mn/Vu is permitted when the ends of the
UHLQIRUFHPHQWDUHFRQ¿QHGEDFRPSUHVVLYHUHDFWLRQ
The application of this provision is illustrated in Fig.
R9.7.3.8.3(b) for simple supports and in Fig. R9.7.3.8.3(c)
IRUSRLQWVRILQÀHFWLRQ)RUH[DPSOHWKHEDUVL]HSURYLGHG
at a simple support is satisfactory only if the corresponding
bar, Ɛd, calculated in accordance with 25.4.2, does not exceed
1.3Mn/Vu + Ɛa.
The ƐaWREHXVHGDWSRLQWVRILQÀHFWLRQLVOLPLWHGWRWKH
H൵HFWLYHGHSWKRIWKHPHPEHUd or 12 bar diameters (12db),
whichever is greater. The Ɛa limitation is provided because
test data are not available to show that a long end anchorage
OHQJWKZLOOEHIXOOH൵HFWLYHLQGHYHORSLQJDEDUWKDWKDV
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of maximum stress.
forcement terminates beyond the centerline of supports by a
standard hook or a mechanical anchorage at least equivalent
WRDVWDQGDUGKRRN D RU E QHHGQRWEHVDWLV¿HG
(a) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVFRQ¿QHG
by a compressive reaction
(b) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVQRWFRQ¿QHG
by a compressive reaction
Mn is calculated assuming all reinforcement at the section is
stressed to fy, and Vu is calculated at the section. At a support,
Ɛa is the embedment length beyond the center of the support.
$WDSRLQWRILQÀHFWLRQƐa is the embedment length beyond the
SRLQWRILQÀHFWLRQOLPLWHGWRWKHJUHDWHURId and 12db.
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PART 3: MEMBERS 143
CODE COMMENTARY
9
Beams
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![Vu
Mn for reinforcement
continuing into support
Vu
1
d
Max. d
1.3Mn /Vu
End anchorage a
Embedment
length Max. d
Mn /Vu
Maximum effective embedment
length limited to d or 12db for a
Note: The 1.3 factor is applicable only if the reaction
confines the ends of the reinforcement
Capacity slope
Mn
d
( )≥ Demand slope (Vu )
d
Mn
Vu
≤
(a) Positive Mu Diagram
(b) Maximum d at simple support
(c) Maximum d for bars “a” at point of inflection
Bars a
P.I.
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9.7.3.8.4 At least one-third of the negative moment rein-
forcement at a support shall have an embedment length
EHRQGWKHSRLQWRILQÀHFWLRQDWOHDVWWKHJUHDWHVWRId, 12db,
and Ɛn/16.
American Concrete Institute – Copyrighted © Material – www.concrete.org
144 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![R10.1—Scope
R10.1.1 Composite structural steel-concrete columns are
not covered in this chapter. Composite columns include both
structural steel sections encased in reinforced concrete and
KROORZVWUXFWXUDOVWHHOVHFWLRQV¿OOHGZLWKFRQFUHWH'HVLJQ
provisions for such composite columns are covered in AISC
360.
R10.3—Design limits
R10.3.1 'LPHQVLRQDOOLPLWV
([SOLFLWPLQLPXPVL]HVIRUFROXPQVDUHQRWVSHFL¿HGWR
permit the use of reinforced concrete columns with small
cross sections in lightly loaded structures, such as low-rise
UHVLGHQWLDODQGOLJKWR൶FHEXLOGLQJV,IVPDOOFURVVVHFWLRQV
are used, there is a greater need for careful workmanship,
DQGVKULQNDJHVWUHVVHVKDYHLQFUHDVHGVLJQL¿FDQFH
R10.3.1.2 In some cases, the gross area of a column is
larger than necessary to resist the factored load. In those
cases, the minimum reinforcement percentage may be
calculated on the basis of the required area rather than the
provided area, but the area of reinforcement cannot be less
than 0.5 percent of the actual cross-sectional area.
10.1—Scope
10.1.1 This chapter shall apply to the design of nonpre-
stressed and prestressed columns, including reinforced
concrete pedestals.
10.1.2 Design of plain concrete pedestals shall be in accor-
dance with Chapter 14.
10.2—General
10.2.1 Materials
10.2.1.1 Design properties for concrete shall be selected to
be in accordance with Chapter 19.
10.2.1.2 Design properties for steel reinforcement shall be
selected to be in accordance with Chapter 20.
10.2.1.3 Materials, design, and detailing requirements for
embedments in concrete shall be in accordance with 20.6.
10.2.2 RQQHFWLRQWRRWKHUPHPEHUV
10.2.2.1 For cast-in-place construction, beam-column and
slab-column joints shall satisfy Chapter 15.
10.2.2.2 For precast construction, connections shall satisfy
the force transfer requirements of 16.2.
10.2.2.3 Connections of columns to foundations shall
satisfy 16.3.
10.3—Design limits
10.3.1 'LPHQVLRQDOOLPLWV
10.3.1.1 For columns with a square, octagonal, or other
shaped cross section, it shall be permitted to base gross area
considered, required reinforcement, and design strength on
a circular section with a diameter equal to the least lateral
dimension of the actual shape.
10.3.1.2 For columns with cross sections larger than
required by considerations of loading, it shall be permitted
to base gross area considered, required reinforcement, and
GHVLJQ VWUHQJWK RQ D UHGXFHG H൵HFWLYH DUHD QRW OHVV WKDQ
one-half the total area. This provision shall not apply to
columns in special moment frames or columns not part of
the seismic-force-resisting system required to be designed in
accordance with Chapter 18.
10.3.1.3 For columns built monolithically with a concrete
ZDOO WKH RXWHU OLPLWV RI WKH H൵HFWLYH FURVV VHFWLRQ RI WKH
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 155
CODE COMMENTARY
10
Columns
all
ling requ
accor
HPE
ns
Ch
c
on, beam-column
r 15.
and
CHAPTER 10—COLUMNS
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![10.7.6.3 Lateral support of longitudinal bars using spirals
10.7.6.3.1 In any story, the bottom of the spiral shall be
located at the top of footing or slab.
10.7.6.3.2 In any story, the top of the spiral shall be located
in accordance with Table 10.7.6.3.2.
Table 10.7.6.3.2 —Spiral extension requirements at
top of column
Framing at column end Extension requirements
Beams or brackets frame into
all sides of the column
Extend to the level of the lowest
horizontal reinforcement in members
supported above.
Beams or brackets do not
frame into all sides of the
column
Extend to the level of the lowest
horizontal reinforcement in members
supported above.
Additional column ties shall extend
above termination of spiral to bottom of
slab, drop panel, or shear cap.
Columns with capitals
Extend to the level at which the diameter
or width of capital is twice that of the
column.
10.7.6.4 /DWHUDOVXSSRUWRIRৼVHWEHQWORQJLWXGLQDOEDUV
10.7.6.4.1 :KHUHORQJLWXGLQDOEDUVDUHR൵VHWKRUL]RQWDO
support shall be provided by ties, hoops, spirals, or parts
RIWKHÀRRUFRQVWUXFWLRQDQGVKDOOEHGHVLJQHGWRUHVLVW
times the horizontal component of the calculated force in the
LQFOLQHGSRUWLRQRIWKHR൵VHWEDU
10.7.6.4.2 If transverse reinforcement is provided to resist
IRUFHVWKDWUHVXOWIURPR൵VHWEHQGVWLHVKRRSVRUVSLUDOV
shall be placed not more than 6 in. from points of bend.
10.7.6.5 Shear
10.7.6.5.1 If required, shear reinforcement shall be
provided using ties, hoops, or spirals.
10.7.6.5.2 Maximum spacing of shear reinforcement shall
be in accordance with Table 10.7.6.5.2.
Table 10.7.6.5.2—Maximum spacing of shear
reinforcement
Vs
Maximum s, in.
Nonprestressed
column
Prestressed
column
4 c w
f b d
≤ ′ Lesser of:
d 3h
24
4 c w
f b d
′ Lesser of:
d 3h
12
R10.7.6.3 Lateral support of longitudinal bars using spirals
R10.7.6.3.2 Refer to R10.7.6.2.2.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 163
CODE COMMENTARY
10
Columns
st
ch the diameter
al is twice tha
colum
ৼVHW
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OO
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ops, spirals, or
HVLJQHGWRUHVLV
t d
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arts
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![11.2.3 Load distribution
11.2.3.1 Unless otherwise demonstrated by an analysis,
WKH KRUL]RQWDO OHQJWK RI ZDOO FRQVLGHUHG DV H൵HFWLYH IRU
resisting each concentrated load shall not exceed the lesser
of the center-to-center distance between loads, and the
EHDULQJ ZLGWK SOXV IRXU WLPHV WKH ZDOO WKLFNQHVV (൵HF-
tive horizontal length for bearing shall not extend beyond
vertical wall joints unless design provides for transfer of
forces across the joints.
11.2.4 ,QWHUVHFWLQJHOHPHQWV
11.2.4.1 Walls shall be anchored to intersecting elements,
VXFKDVÀRRUVDQGURRIVFROXPQVSLODVWHUVEXWWUHVVHVRU
intersecting walls; and to footings.
11.2.4.2 For cast-in-place walls having Pu 0.2fcƍAg, the
SRUWLRQRIWKHZDOOZLWKLQWKHWKLFNQHVVRIWKHÀRRUVVWHP
VKDOOKDYHVSHFL¿HGFRPSUHVVLYHVWUHQJWKDWOHDVW0.8fcƍ of
the wall.
11.3—Design limits
11.3.1 0LQLPXPZDOOWKLFNQHVV
11.3.1.1 Minimum wall thicknesses shall be in accordance
with Table 11.3.1.1. Thinner walls are permitted if adequate
strength and stability can be demonstrated by structural
analysis.
Table 11.3.1.1—Minimum wall thickness h
Wall type Minimum thickness h
Bearing[1]
Greater of:
4 in. (a)
WKHOHVVHURIXQVXSSRUWHGOHQJWK
and unsupported height
(b)
Nonbearing Greater of:
4 in. (c)
WKHOHVVHURIXQVXSSRUWHGOHQJWK
and unsupported height
(d)
Exterior
basement
and
foundation[1]
7.5 in. (e)
[1]
2QODSSOLHVWRZDOOVGHVLJQHGLQDFFRUGDQFHZLWKWKHVLPSOL¿HGGHVLJQPHWKRGRI
11.5.3.
11.4—Required strength
11.4.1 General
11.4.1.1 Required strength shall be calculated in accor-
dance with the factored load combinations in Chapter 5.
11.4.1.2 Required strength shall be calculated in accor-
dance with the analysis procedures in Chapter 6.
R11.2.4 ,QWHUVHFWLQJHOHPHQWV
R11.2.4.1 Walls that do not depend on intersecting elements
for support, do not have to be connected to those elements. It is
not uncommon to separate massive retaining walls from inter-
VHFWLQJZDOOVWRDFFRPPRGDWHGL൵HUHQFHVLQGHIRUPDWLRQV
R11.2.4.27KHIDFWRUUHÀHFWVUHGXFHGFRQ¿QHPHQWLQ
ÀRRUZDOO MRLQWV FRPSDUHG ZLWK ÀRRUFROXPQ MRLQWV XQGHU
gravity loads.
R11.3—Design limits
R11.3.1 0LQLPXPZDOOWKLFNQHVV
R11.3.1.1 The minimum thickness requirements need not
be applied to bearing walls and exterior basement and foun-
dation walls designed by 11.5.2 or analyzed by 11.8.
R11.4—Required strength
R11.4.1 General
American Concrete Institute – Copyrighted © Material – www.concrete.org
166 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
imits
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inimum t
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ty loads.
hall be in accord
ermitted if ade
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ate
R11
R11
R11
be ap
d
—De
3.1 0
3.1.1
ed t
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![11.6.2 If in-plane Vu”ࢥĮcȜ ′
c
f Acv, (a) and (b) shall
EHVDWLV¿HG
(a) ȡƐ shall be at least the greater of the value calculated by
Eq. (11.6.2) and 0.0025, but need not exceed ȡt required
for strength by 11.5.4.3.
ȡƐ• ±hwƐw ȡt±
(b) ȡt shall be at least 0.0025
11.7—Reinforcement detailing
11.7.1 General
11.7.1.1 Concrete cover for reinforcement shall be in
accordance with 20.5.1.
11.7.1.2 Development lengths of deformed and prestressed
reinforcement shall be in accordance with 25.4.
11.7.1.3 Splice lengths of deformed reinforcement shall be
in accordance with 25.5.
11.7.2 6SDFLQJRIORQJLWXGLQDOUHLQIRUFHPHQW
11.7.2.1 Spacing s of longitudinal bars in cast-in-place
walls shall not exceed the lesser of 3h and 18 in. If shear
reinforcement is required for in-plane strength, spacing of
longitudinal reinforcement shall not exceed Ɛw/3.
11.7.2.2 Spacing s of longitudinal bars in precast walls
shall not exceed the lesser of (a) and (b):
(a) 5h
(b) 18 in. for exterior walls or 30 in. for interior walls
If shear reinforcement is required for in-plane strength, s
shall not exceed the smallest of 3h, 18 in., and Ɛw/3.
of curing and develop less shrinkage stress than compa-
rable cast-in-place walls.
R11.6.2 For monotonically loaded walls with low height-
to-length ratios, test data (Barda et al. 1977) indicate that
KRUL]RQWDO VKHDU UHLQIRUFHPHQW EHFRPHV OHVV H൵HFWLYH IRU
shear resistance than vertical reinforcement. This change in
H൵HFWLYHQHVVRIWKHKRUL]RQWDOYHUVXVYHUWLFDOUHLQIRUFHPHQW
is recognized in Eq. (11.6.2); if hw/Ɛw is less than 0.5, the
amount of vertical reinforcement is equal to the amount of
horizontal reinforcement. If hwȡw is greater than 2.5, only
a minimum amount of vertical reinforcement is required
(0.0025sh).
Table 11.6.1—Minimum reinforcement for walls with in-plane Vu ≤ 0.5ࢥĮcȜ ′
c
f Acv
Wall type
Type of nonprestressed
reinforcement Bar/wire size fy, psi
Minimum longitudinal[1]
,
ȡƐ 0LQLPXPWUDQVYHUVHȡt
Cast-in-place
Deformed bars
”1R
• 0.0012 0.0020
60,000 0.0015 0.0025
No. 5 Any 0.0015 0.0025
Welded-wire reinforcement ”:RU' Any 0.0012 0.0020
Precast[2] Deformed bars or welded-wire
reinforcement
Any Any 0.0010 0.0010
[1]
3UHVWUHVVHGZDOOVZLWKDQDYHUDJHH൵HFWLYHFRPSUHVVLYHVWUHVVRIDWOHDVWSVLQHHGQRWPHHWWKHUHTXLUHPHQWIRUPLQLPXPORQJLWXGLQDOUHLQIRUFHPHQWȡƐ.
[2]
In one-way precast, prestressed walls not wider than 12 ft and not mechanically connected to cause restraint in the transverse direction, the minimum reinforcement requirement
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American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 171
CODE COMMENTARY
11
Walls
n Eq. (11.6
l reinforce
ement. If
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![R12.2—General
R12.2.1 As partially illustrated in Fig. R12.1.1, diaphragms
resist forces from several types of actions (Moehle et al. 2010):
(a) Diaphragm in-plane forces—Lateral forces from
load combinations including wind, earthquake, and hori-
]RQWDOÀXLGRUVRLOSUHVVXUHJHQHUDWHLQSODQHVKHDUD[LDO
and bending actions in diaphragms as they span between,
and transfer forces to, vertical elements of the lateral-force-
resisting system. For wind loading, lateral force is gener-
ated by wind pressure acting on building cladding that
is transferred by diaphragms to the vertical elements. For
earthquake loading, inertial forces are generated within the
diaphragm and tributary portions of walls, columns, and
other elements, and then transferred by diaphragms to the
vertical elements. For buildings with subterranean levels,
lateral forces are generated by soil pressure bearing against
the basement walls; in a typical system, the basement walls
VSDQYHUWLFDOOEHWZHHQÀRRUVDOVRVHUYLQJDVGLDSKUDJPV
12.1.2 Diaphragms in structures assigned to Seismic
Design Category D, E, or F shall also satisfy requirements
of 18.12.
12.2—General
12.2.1 Design shall consider forces (a) through (e):
(a) Diaphragm in-plane forces due to lateral loads acting
on the building
(b) Diaphragm transfer forces
(c) Connection forces between the diaphragm and vertical
framing or nonstructural elements
(d) Forces resulting from bracing vertical or sloped
building elements
(e) Diaphragm out-of-plane forces due to gravity and
other loads applied to the diaphragm surface
Below grade
soil pressure
In-plane inertial loads
Gravity loads
Out-of-plane
wind pressure
or inertial loads
Thrust
Thrust
Inclined column
Moment resisting
frame
Distributor
Shear
Transfer in
diaphragm
Transfer slab/
diaphragm
Basement
wall
Structural
(shear) wall
Collector
Diaphragm
Collector
Structural (shear) wall
Fig. R12.1.1²7SLFDOGLDSKUDJPDFWLRQV
American Concrete Institute – Copyrighted © Material – www.concrete.org
176 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![LQ ZKLFK GLDSKUDJP DQG YHUWLFDO HOHPHQW VWL൵QHVVHV KDYH
approximately the same value, buildings with large force
transfers, and parking structures in which ramps connect
EHWZHHQÀRRUVDQGDFWHVVHQWLDOODVEUDFLQJHOHPHQWVZLWKLQ
the building.
For diaphragms constructed of concrete slabs, $6(
SEI 7 permits the assumption of a rigid diaphragm if the
diaphragm aspect ratio falls within a prescribed limit, which
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not prohibit the rigid diaphragm assumption for other condi-
tions, provided the rigid diaphragm assumption is reasonably
consistent with anticipated behavior. Cast-in-place concrete
diaphragms designed with the rigid-diaphragm assumption
have a long history of satisfactory performance even though
WKHPDIDOORXWVLGHWKH$6(6(,LQGH[YDOXHV
R12.4.2.3Forlow-aspect-ratiodiaphragmsthatareentirely
cast-in-place or comprise a cast-in-place topping slab on
precast elements, the diaphragm is often modeled as a rigid
HOHPHQWVXSSRUWHGEÀH[LEOHYHUWLFDOHOHPHQWV+RZHYHU
H൵HFWVRIGLDSKUDJPÀH[LELOLWVKRXOGEHFRQVLGHUHGZKHUH
VXFKH൵HFWVZLOOPDWHULDOOD൵HFWFDOFXODWHGGHVLJQDFWLRQV
6XFKH൵HFWVVKRXOGEHFRQVLGHUHGIRUGLDSKUDJPVWKDWXVH
precast elements, with or without a cast-in-place topping.
Where large transfer forces occur, as outlined in R12.2.1(b),
more realistic design forces can be obtained by modeling
GLDSKUDJPLQSODQHVWL൵QHVV'LDSKUDJPVZLWKORQJVSDQV
large cutout areas, or other irregularities may develop
in-plane deformations that should be considered in design
(refer to Fig. R12.4.2.3a).
For a diaphragm considered rigid in its own plane, and for
semi-rigid diaphragms, the diaphragm internal force distri-
bution can be obtained by modeling it as a horizontal rigid
EHDP VXSSRUWHG RQ VSULQJV UHSUHVHQWLQJ ODWHUDO VWL൵QHVVHV
RIWKHYHUWLFDOHOHPHQWV UHIHUWR)LJ5E (൵HFWV
of in-plane eccentricity between applied forces and vertical
element resistances, resulting in overall building torsion,
should be included in the analysis. Elements of the lateral-
force-resisting system aligned in the orthogonal direction
can participate in resisting diaphragm plan rotation (Moehle
et al. 2010).
12.4.2.3 Any set of reasonable and consistent assumptions
IRUGLDSKUDJPVWL൵QHVVVKDOOEHSHUPLWWHG
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 179
CODE COMMENTARY
12
Diaphragms
OPDWHULDOO
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with or w
r forces o
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reas, or
formations
r to Fig. R12
For a d
cast in
precast element
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[LEL
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![Diaphragm
span,
Diaphragm depth, h
Lateral force
Lateral-force resisting wall at each end
δmax
δwall
Fig. R12.4.2.3a²([DPSOHRIGLDSKUDJPWKDWPLJKWQRWEH
considered rigid in its plane.
Plan
Diaphragm shear
Diaphragm moment
Diaphragm
boundary
Vertical element
and reaction force
Center of
resistance
Lateral load
Fig. R12.4.2.3b²'LDSKUDJPLQSODQHDFWLRQVREWDLQHGE
PRGHOLQJWKHGLDSKUDJPDVDKRUL]RQWDOULJLGEHDPRQÀH[-
ible supports.
American Concrete Institute – Copyrighted © Material – www.concrete.org
180 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![12.4.2.4 Calculation of diaphragm in-plane design
moments, shears, and axial forces shall be consistent with
requirements of equilibrium and with design boundary
conditions. It shall be permitted to calculate design
moments, shears, and axial forces in accordance with one of
(a) through (e):
(a) A rigid diaphragm model if the diaphragm can be
idealized as rigid
E $ÀH[LEOHGLDSKUDJPPRGHOLIWKHGLDSKUDJPFDQEH
LGHDOL]HGDVÀH[LEOH
(c) A bounding analysis in which the design values are the
envelope of values obtained by assuming upper bound and
ORZHUERXQGLQSODQHVWL൵QHVVHVIRUWKHGLDSKUDJPLQWZR
or more separate analyses
G $ ¿QLWH HOHPHQW PRGHO FRQVLGHULQJ GLDSKUDJP
ÀH[LELOLW
(e) A strut-and-tie model in accordance with 23.2
12.5—Design strength
12.5.1 General
12.5.1.1 For each applicable factored load combination,
design strengths of diaphragms and connections shall satisfy
ࢥSn•U,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOOEHFRQVLGHUHG
ࢥ shall be determined in accordance with 21.2.
R12.4.2.4 The rigid diaphragm model is widely used for
diaphragms that are entirely cast-in-place and for diaphragms
that comprise a cast-in-place topping slab on precast
HOHPHQWVSURYLGHGÀH[LEOHFRQGLWLRQVDUHQRWFUHDWHGED
long span, by a large aspect ratio, or by diaphragm irregu-
ODULW)RUPRUHÀH[LEOHGLDSKUDJPVDERXQGLQJDQDOVLVLV
sometimes done in which the diaphragm is analyzed as a
VWL൵RUULJLGHOHPHQWRQÀH[LEOHVXSSRUWVDQGDVDÀH[LEOH
diaphragm on rigid supports, with the design values taken as
the envelope of values from the two analyses. Finite element
models can be suitable for any diaphragm, but are especially
useful for irregularly shaped diaphragms and diaphragms
UHVLVWLQJODUJHWUDQVIHUIRUFHV6WL൵QHVVVKRXOGEHDGMXVWHG
to account for expected concrete cracking under design
loads. For jointed precast concrete diaphragms that rely on
mechanical connectors, it may be necessary to include the
MRLQWVDQGFRQQHFWRUVLQWKH¿QLWHHOHPHQWPRGHO6WUXWDQG
tie models may be used for diaphragm design. The strut-and-
tie models should include considerations of force reversals
that may occur under design load combinations.
R12.5—Design strength
R12.5.1 General
R12.5.1.1 Design actions commonly include in-plane
moment, with or without axial force; in-plane shear; and
axial compression and tension in collectors and other
HOHPHQWVDFWLQJDVVWUXWVRUWLHV6RPHGLDSKUDJPFRQ¿JXUD-
tions may result in additional types of design actions. For
example, a diaphragm vertical step can result in out-of-plane
bending, torsion, or both. The diaphragm is required to be
designed for such actions where they occur in elements that
are part of the load path.
Nominal strengths are prescribed in Chapter 22 for a
diaphragm idealized as a beam or solid element resisting
in-plane moment, axial force, and shear; and in Chapter 23
for a diaphragm or diaphragm segment idealized as a strut-
and-tie system. Collectors and struts around openings can
be designed as compression members subjected to axial
force using provisions of 10.5.2 with the strength reduction
factor for compression-controlled members in 21.2.2. For
axial tension in such members, nominal tensile strength is
As fy, and the strength reduction factor is 0.90 as required for
tension-controlled members in 21.2.2.
Diaphragms are designed under load combinations of 5.3.
Where a diaphragm or part of a diaphragm is subjected to
PXOWLSOHORDGH൵HFWVWKHLQWHUDFWLRQRIWKHORDGH൵HFWVLVWR
be considered. A common example is where a collector is
built within a beam or slab that also resists gravity loads, in
which case the element is designed for combined moment
and axial force. Another example is where a connection is
subjected to simultaneous tension and shear.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 181
CODE COMMENTARY
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![12.5.1.3 Design strengths shall be in accordance with (a),
(b), (c), or (d):
(a) For a diaphragm idealized as a beam whose depth is
equal to the full diaphragm depth, with moment resisted
by boundary reinforcement concentrated at the diaphragm
edges, design strengths shall be in accordance with 12.5.2
through 12.5.4.
(b) For a diaphragm or a diaphragm segment modeled as
a strut-and-tie system, design strengths shall be in accor-
dance with 23.3.
F )RUDGLDSKUDJPLGHDOL]HGZLWKD¿QLWHHOHPHQWPRGHO
design strengths shall be in accordance with Chapter 22.
Nonuniform shear distributions shall be considered in
design for shear. Collectors in such designs shall be
provided to transfer diaphragm shears to the vertical
elements of the lateral-force-resisting system.
(d) For a diaphragm designed by alternative methods, such
methods shall satisfy the requirements of equilibrium and
shall provide design strengths at least equal to required
strengths for all elements in the load path.
12.5.1.4 It shall be permitted to use precompression from
prestressed reinforcement to resist diaphragm forces.
12.5.1.5 If nonprestressed, bonded prestressing reinforce-
ment is designed to resist collector forces, diaphragm shear,
or tension due to in-plane moment, the value of steel stress
used to calculate resistance shall not exceed the lesser of the
VSHFL¿HGLHOGVWUHQJWKDQGSVL
12.5.2 0RPHQWDQGD[LDOIRUFH
12.5.2.1 It shall be permitted to design a diaphragm to
resist in-plane moment and axial force in accordance with
22.3 and 22.4.
R12.5.1.3 'L൵HUHQW GHVLJQ VWUHQJWK UHTXLUHPHQWV DSSO
depending on how the diaphragm load-path is idealized.
Section 12.5.1.3(a) addresses requirements for the
common case where a diaphragm is idealized as a beam
spanning between supports and resisting forces within its
plane, with chord reinforcement at the boundaries to resist
in-plane moment and axial force. If diaphragms are designed
according to this model, then it is appropriate to assume
WKDW VKHDU ÀRZ LV XQLIRUP WKURXJK WKH GLDSKUDJP GHSWK
Diaphragm depth refers to the dimension measured in the
direction of lateral forces within the plane of the diaphragm
(refer to Fig. R12.4.2.3a). If vertical elements of the lateral-
force-resisting system do not extend the full depth of the
diaphragm, then collectors are required to transfer shear
acting along the remaining portions of the diaphragm depth
to the vertical elements. Sections 12.5.2 through 12.5.4 are
based on this model. This design approach is acceptable
even if some of the moment is resisted by precompression
as provided by 12.5.1.4.
Sections 12.5.1.3(b) through (d) permit alternative
methods for design of diaphragms. If diaphragms are
designed to resist moment through distributed chords, or
LIGLDSKUDJPVDUHGHVLJQHGDFFRUGLQJWRVWUHVV¿HOGVGHWHU-
PLQHG E ¿QLWHHOHPHQW DQDOVLV WKHQ QRQXQLIRUP VKHDU
ÀRZVKRXOGEHWDNHQLQWRDFFRXQW
R12.5.1.4,QWKHWSLFDOFDVHRIDSUHVWUHVVHGÀRRUVODE
prestressing is required, at a minimum, to resist the factored
load combination 1.2D + 1.6L, where L may have been
reduced as permitted by the general building code. For
wind or earthquake design, however, the gravity load to be
resisted by prestressing is reduced because the governing
load combination is 1.2D + f1L + (W or E), where f1 is either
1.0 or 0.5 depending on the nature of L. Thus, only a portion
RI WKH H൵HFWLYH SUHVWUHVV LV UHTXLUHG WR UHVLVW WKH UHGXFHG
JUDYLWORDGV7KHUHPDLQGHURIWKHH൵HFWLYHSUHVWUHVVFDQ
be used to resist in-plane diaphragm moments. Additional
moment, if any, is resisted by added reinforcement.
R12.5.1.5 Nonprestressed bonded prestressing reinforce-
ment, either strand or bars, is sometimes used to resist
diaphragm design forces. The imposed limit on assumed
yield strength is to control crack width and joint opening.
The Code does not include provisions for developing
nonprestressed, bonded prestressing reinforcement. Stress
limits for other provided reinforcement are prescribed in
Chapter 20.
R12.5.2 0RPHQWDQGD[LDOIRUFH
R12.5.2.1 This section permits design for moment and
axial force in accordance with the usual assumptions of 22.3
and 22.4, including the assumption that strains vary linearly
through the depth of the diaphragm. In most cases, design
for moment and axial force can be accomplished satisfacto-
American Concrete Institute – Copyrighted © Material – www.concrete.org
182 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![R13.2—General
R13.2.3 (DUWKTXDNHHৼHFWV
R13.2.3.17KHEDVHRIDVWUXFWXUHDVGH¿QHGLQDQDOVLV
does not necessarily correspond to the foundation or ground
OHYHORUWRWKHEDVHRIDEXLOGLQJDVGH¿QHGLQWKHJHQHUDO
building code for planning (for example, for height limits or
¿UHSURWHFWLRQUHTXLUHPHQWV 'HWDLOVRIFROXPQVDQGZDOOV
extending below the base of a structure to the foundation are
required to be consistent with those above the base of the
structure. For additional discussion of the design of founda-
WLRQVIRUHDUWKTXDNHH൵HFWVVHHR18.13.1.
R13.2.4 Slabs-on-ground
Slabs-on-ground often act as a diaphragm to hold the
EXLOGLQJWRJHWKHUDWWKHJURXQGOHYHODQGPLQLPL]HWKHH൵HFWV
of out-of-phase ground motion that may occur over the foot-
print of the building. In these cases, the slab-on-ground
should be adequately reinforced and detailed. As required
in Chapter 26, construction documents should clearly state
that these slabs-on-ground are structural members so as to
prohibit sawcutting of such slabs.
R13.2.6 Design criteria
13.2—General
13.2.1 Materials
13.2.1.1 Design properties for concrete shall be selected to
be in accordance with Chapter 19.
13.2.1.2 Design properties for steel reinforcement shall be
selected to be in accordance with Chapter 20.
13.2.1.3 Materials, design, and detailing requirements for
embedments in concrete shall be in accordance with 20.6.
13.2.2 RQQHFWLRQWRRWKHUPHPEHUV
13.2.2.1 Design and detailing of cast-in-place and precast
column, pedestal, and wall connections to foundations shall
be in accordance with 16.3.
13.2.3 (DUWKTXDNHHৼHFWV
13.2.3.1 Structural members extending below the base of
the structure that are required to transmit forces resulting
IURPHDUWKTXDNHH൵HFWVWRWKHIRXQGDWLRQVKDOOEHGHVLJQHG
in accordance with 18.2.2.3.
13.2.3.2 For structures assigned to Seismic Design Cate-
gory (SDC) C, D, E, or F, foundations resisting earthquake-
induced forces or transferring earthquake-induced forces
between structure and ground shall be designed in accor-
dance with 18.13.
13.2.4 Slabs-on-ground
13.2.4.1 Slabs-on-ground that transmit vertical loads or
lateral forces from other parts of the structure to the ground
shall be designed and detailed in accordance with applicable
provisions of this Code.
13.2.4.2 Slabs-on-ground that transmit lateral forces as
part of the seismic-force-resisting system shall be designed
in accordance with 18.13.
13.2.5 Plain concrete
13.2.5.1 Plain concrete foundations shall be designed in
accordance with Chapter 14.
13.2.6 Design criteria
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 193
CODE COMMENTARY
13
Foundations
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![R13.2.6.1 Permissible soil pressures or permissible deep
foundation strengths are determined by principles of soil
mechanics and in accordance with the general building code.
The size of the base area of a footing on soil or the number and
arrangement of deep foundation members are established by
using allowable geotechnical strength and service-level load
combinations or by using nominal geotechnical strength
with resistance factor and factored load combinations.
Only the calculated end moments at the base of a column
or pedestal require transfer to the footing. The minimum
moment requirement for slenderness considerations given
in 6.6.4.5 need not be considered for transfer of forces and
moments to footings.
R13.2.6.3 To design a footing or pile cap for strength,
the induced reactions due to factored loads applied to the
foundation should be determined. For a single concentri-
cally-loaded spread footing, the soil pressure due to factored
loading is calculated as the factored load divided by the base
area of the footing. For the case of footings or mats with
eccentric loading, applied factored loads may be used to deter-
mine soil pressures. For pile caps or mats supported by deep
foundations, applied factored loads may be used to deter-
mine member reactions. However, the resulting pressures or
reactions may be incompatible with the geotechnical design
resulting in unacceptable subgrade reactions or instability
(Rogowsky and Wight 2010). In such cases, the design should
be adjusted in coordination with the geotechnical engineer.
Only the calculated end moments at the base of a column
or pedestal require transfer to the footing. The minimum
moment requirements for slenderness considerations given
in 6.6.4.5 need not be considered for transfer of forces and
moments to footings.
R13.2.6.4 Foundation design is permitted to be based
directly on fundamental principles of structural mechanics,
provided it can be demonstrated that all strength and service-
DELOLWFULWHULDDUHVDWLV¿HG'HVLJQRIWKHIRXQGDWLRQPD
be achieved through the use of classic solutions based on
a linearly elastic continuum, numerical solutions based on
discrete elements, or yield-line analyses. In all cases, anal-
yses and evaluation of the stress conditions at points of load
application or pile reactions in relation to shear and torsion,
DVZHOODVÀH[XUHVKRXOGEHLQFOXGHG
R13.2.6.5 An example of the application of this provision
is a pile cap similar to that shown in Fig. R13.1.1. Pile caps
may be designed using a three-dimensional strut-and-tie
13.2.6.1 Foundations shall be proportioned for bearing
H൵HFWV VWDELOLW DJDLQVW RYHUWXUQLQJ DQG VOLGLQJ DW WKH
soil-foundation interface in accordance with the general
building code.
13.2.6.2 For one-way shallow foundations, two-way
isolated footings, or two-way combined footings and mat
IRXQGDWLRQVLWLVSHUPLVVLEOHWRQHJOHFWWKHVL]HH൵HFWIDFWRU
VSHFL¿HG LQ 22.5 for one-way shear strength and 22.6 for
two-way shear strength.
13.2.6.3 Foundation members shall be designed to resist
factored loads and corresponding induced reactions except
as permitted by 13.4.2.
13.2.6.4 Foundation systems shall be permitted to be
designed by any procedure satisfying equilibrium and
geometric compatibility.
13.2.6.5 Foundation design in accordance with the strut-
and-tie method, Chapter 23, shall be permitted.
American Concrete Institute – Copyrighted © Material – www.concrete.org
194 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![13.4.1.1 Number and arrangement of deep foundation
members shall be determined such that forces and moments
applied to the foundation do not exceed the permissible deep
foundation strength. Permissible deep foundation strength
shall be determined through principles of soil or rock
mechanics in accordance with the general building code, or
RWKHUUHTXLUHPHQWVDVGHWHUPLQHGEWKHEXLOGLQJR൶FLDO
13.4.1.2 Design of deep foundation members shall be in
accordance with 13.4.2 or 13.4.3.
13.4.2 $OORZDEOHD[LDOVWUHQJWK
13.4.2.1 It shall be permitted to design a deep foundation
member using load combinations for allowable stress design
in $6(6(, , Section 2.4, and the allowable strength
VSHFL¿HGLQ7DEOHLI D DQG E DUHVDWLV¿HG
(a) The deep foundation member is laterally supported for
its entire height
(b) The applied forces cause bending moments in the deep
foundation member less than the moment due to an acci-
dental eccentricity of 5 percent of the member diameter
or width
Table 13.4.2.1—Maximum allowable compressive
strength for deep foundation members
Deep foundation member type
Maximum allowable
compressive strength [1]
Uncased cast-in-place concrete drilled
or augered pile
Pa = 0.3fcƍAg + 0.4fyAs (a)
Cast-in-place concrete pile in rock
or within a pipe, tube, or other
permanent metal casing that does not
satisfy 13.4.2.3
Pa = 0.33fcƍAg + 0.4fyAs
[2]
(b)
Metal cased concrete pile
FRQ¿QHGLQDFFRUGDQFHZLWK
Pa = 0.4fcƍAg (c)
Precast nonprestressed concrete pile Pa = 0.33fcƍAg + 0.4fyAs (d)
Precast prestressed concrete pile Pa = (0.33fcƍ– 0.27fpc)Ag (e)
[1]
Ag applies to the gross cross-sectional area. If a temporary or permanent casing is
used, the inside face of the casing shall be considered the concrete surface.
[2]
As does not include the steel casing, pipe, or tube.
13.4.2.2 ,I D RU E LV QRW VDWLV¿HG D
deep foundation member shall be designed using strength
design in accordance with 13.4.3.
13.4.2.3 Metal cased cast-in-place concrete deep foun-
GDWLRQ PHPEHUV VKDOO EH FRQVLGHUHG WR EH FRQ¿QHG LI D
WKURXJK I DUHVDWLV¿HG
(a) Design shall not use the casing to resist any portion of
the axial load imposed.
(b)Casingshallhaveasealedtipandshallbemandrel-driven.
R13.4.1.1 General discussion on selecting the number and
arrangement of piles, drilled piers, and caissons is provided
in R13.2.6.1.
R13.4.2 $OORZDEOHD[LDOVWUHQJWK
R13.4.2.1 Potential changes to lateral support of the deep
foundation member due to liquefaction, excavation, or other
causes, should be considered.
The values in the Table 13.4.2.1 represent an upper bound
for well understood soil conditions with quality workman-
ship. A lower value for the maximum allowable compressive
strength may be appropriate, depending on soil conditions
and the construction and quality control procedures used.
For auger-grout piles, where grout is placed through the
stem of a hollow-stem auger as it is withdrawn from the soil,
WKHVWUHQJWKFRH൶FLHQWRILVEDVHGRQDVWUHQJWKUHGXF-
tion factor of 0.6. The designer should carefully consider the
reliable grout strength, grout strength testing methods, and
the minimum cross-sectional area of the pile, accounting
for soil conditions and construction procedures. Additional
information is provided in ACI 543R.
R13.4.2.3 The basis for this allowable strength is the
DGGHG VWUHQJWK SURYLGHG WR WKH FRQFUHWH E WKH FRQ¿QLQJ
action of the steel casing. This strength applies only to non-
axial load-bearing steel where the stress in the steel is taken
in hoop tension instead of axial compression. In this Code,
steel pile casing is not to be considered in the design of the
pile to resist a portion of the pile axial load. Provisions for
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 199
CODE COMMENTARY
13
Foundations
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![(c) Thickness of the casing shall not be less than manufac-
turer’s standard gauge No. 14 (0.068 in.).
(d) Casing shall be seamless, or provided with seams of
VWUHQJWKHTXDOWRWKHEDVLFPDWHULDODQGEHRIDFRQ¿JX-
UDWLRQWKDWZLOOSURYLGHFRQ¿QHPHQWWRWKHFDVWLQSODFH
concrete.
(e) Ratio of yield strength of the steel casing to fcƍVKDOOEH
at least 6, and yield strength shall be at least 30,000 psi.
(f) Nominal diameter of the member shall be less than or
equal to 16 in.
13.4.2.4 The use of allowable strengths greater than those
VSHFL¿HGLQ7DEOHVKDOOEHSHUPLWWHGLIDFFHSWHGE
WKHEXLOGLQJR൶FLDOLQDFFRUGDQFHZLWK1.10DQGMXVWL¿HGE
load tests.
13.4.3 Strength design
13.4.3.1 Strength design in accordance with this section is
permitted for all deep foundation members.
13.4.3.2 The strength design of deep foundation members
shall be in accordance with 10.5 using the compressive
strength reduction factors of Table 13.4.3.2 for axial load
without moment, and the strength reduction factors of Table
21.2.1 for tension, shear, and combined axial force and
moment. The provisions of 22.4.2.4 and 22.4.2.5 shall not
apply to deep foundations.
Table 13.4.3.2—Compressive strength reduction
factors ࢥ for deep foundation members
Deep foundation member type
Compressive strength
reduction factors ࢥ
Uncased cast-in-place concrete drilled or
augered pile[1] 0.55 (a)
Cast-in-place concrete pile in rock or within
a pipe, tube,[2]
or other permanent casing that
does not satisfy 13.4.2.3
0.60 (b)
DVWLQSODFHFRQFUHWH¿OOHGVWHHOSLSHSLOH[3]
0.70 (c)
0HWDOFDVHGFRQFUHWHSLOHFRQ¿QHGLQ
accordance with 13.4.2.3
0.65 (d)
Precast-nonprestressed concrete pile 0.65 (e)
Precast-prestressed concrete pile 0.65 (f)
[1]
The factor of 0.55 represents an upper bound for well understood soil conditions
with quality workmanship. A lower value for the strength reduction factor may be
appropriate, depending on soil conditions and the construction and quality control
procedures used.
[2]
For wall thickness of the steel pipe or tube less than 0.25 in.
[3]
Wall thickness of the steel pipe shall be at least 0.25 in.
13.4.4 Cast-in-place deep foundations
13.4.4.1 Cast-in-place deep foundations that are subject to
uplift or where Mu is greater than 0.4Mcr shall be reinforced,
unless enclosed by a structural steel pipe or tube.
members designed to be composite with steel pipe or casing
are covered in AISC 360.
Potential corrosion of the metal casing should be consid-
ered; provision is based on a non-corrosive environment.
R13.4.2.4 Geotechnical and load test requirements for
deep foundation members can be found in the IBC.
R13.4.3 Strength design
R13.4.3.2 The strength design of deep foundation
members is discussed in detail in ACI 543R.
If cast-in-place concrete drilled or augered piles are subject
WR ÀH[XUH VKHDU RU WHQVLRQ ORDGV WKH VWUHQJWK UHGXFWLRQ
factors should be adjusted accordingly, considering the soil
conditions, quality-control procedures that will be imple-
mented, likely workmanship quality, and local experience.
Guidance for adjustment factors is provided in ACI 543R.
R13.4.4 Cast-in-place deep foundations
American Concrete Institute – Copyrighted © Material – www.concrete.org
200 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
ussed in de
oncrete dr
RU WHQVLRQ
djusted ac
-control p
orkmansh
djustment
ection is
deep fo
.5 u
abl
gth
d c
4.
The stren
4.3.2 for axial
ction factors of T
ned axial force
nd 22.4.2.5 shal
ad
ble
and
not
If
WR ÀH[
condit
ment
t-in-
XUH
shou
ns,
lik
4.3.2
rs is
gth
gth
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![13.4.4.2 Portions of deep foundation members in air,
water, or soils not capable of providing adequate restraint
throughout the member length to prevent lateral buckling
shall be designed as columns in accordance with the appli-
cable provisions of Chapter 10.
13.4.5 Precast concrete piles
13.4.5.1 Precast concrete piles supporting buildings
assigned to SDC A or B shall satisfy the requirements of
13.4.5.2 through 13.4.5.6.
13.4.5.2 Longitudinal reinforcement shall be arranged in a
symmetrical pattern.
13.4.5.3 For precast nonprestressed piles, longitudinal
reinforcement shall be provided according to (a) and (b):
(a) Minimum of 4 bars
(b) Minimum area of 0.008Ag
13.4.5.4)RUSUHFDVWSUHVWUHVVHGSLOHVWKHH൵HFWLYHSUHVWUHVV
in the pile shall provide a minimum average compressive
stress in the concrete in accordance with Table 13.4.5.4.
Table 13.4.5.4—Minimum compressive stress in
precast prestressed piles
Pile length, ft Minimum compressive stress, psi
3LOHOHQJWK” 400
3LOHOHQJWK” 550
Pile length 50 700
13.4.5.5 )RU SUHFDVW SUHVWUHVVHG SLOHV WKH H൵HFWLYH
prestress in the pile shall be calculated based on an assumed
total loss of 30,000 psi in the prestressed reinforcement.
13.4.5.6 The longitudinal reinforcement shall be enclosed
by transverse reinforcement according to Table 13.4.5.6(a)
and shall be spaced according to Table 13.4.5.6(b):
Table 13.4.5.6(a)—Minimum transverse
reinforcement size
Least horizontal pile dimension
h, in.
Minimum wire size transverse
reinforcement[1]
h” W4, D4
16 h 20 W4.5, D5
h• W5.5, D6
[1]
If bars are used, minimum of No. 3 bar applies to all values of h.
R13.4.5 Precast concrete piles
R13.4.5.6 The minimum transverse reinforcement
UHTXLUHG LQ WKLV VHFWLRQ LV WSLFDOO VX൶FLHQW IRU GULYLQJ
and handling stresses. These provisions for precast concrete
piles in SDC A and B are based on information from PCI
5HFRPPHQGHG 3UDFWLFH IRU WKH 'HVLJQ 0DQXIDFWXUH DQG
Installation of Prestressed Concrete Piling (1993) and the
PCI Bridge Design Manual, Chapter 20 (2004). Minimum
reinforcement requirements for precast concrete piles
supporting buildings assigned to SDC C, D, E, and F are
GH¿QHGLQ18.13.5.10.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 201
CODE COMMENTARY
13
Foundations
OHVWK
mum
nce
o
mum
able 13.4.5.4.
ssive stress i
pressive stress, p
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![Table 14.5.4.1—Combined flexure and axial
compression
Location Interaction equation
Tension face 5
u u
c
P J
M P
f
S A
− ≤ φ λ ′ (a)
Compression face 1.0
u u
n n
M P
M P
+ ≤
φ φ
(b)
14.5.4.2 For walls of solid rectangular cross section where
Mu”Pu(h/6), Mu need not be considered in design and Pn
is calculated by:
2
0.45 1
32
c
n c g
P f A
h
⎡ ⎤
⎛ ⎞
= −
′ ⎢ ⎥
⎜ ⎟
⎝ ⎠
⎢ ⎥
⎣ ⎦
A
(14.5.4.2)
14.5.5 Shear
14.5.5.1 Vn shall be calculated in accordance with Table
14.5.5.1.
Table 14.5.5.1—Nominal shear strength
Shear action Nominal shear strength Vn
One-way
4
3
c w
f b h
λ ′ (a)
Two-way Lesser of:
2 4
1
3
c o
f b h
⎛ ⎞ ⎛ ⎞
+ λ ′
⎜ ⎟
⎜ ⎟ ⎝ ⎠
⎝ β⎠
[1]
(b)
4
2
3
c o
f b h
⎛ ⎞
λ ′
⎜ ⎟
⎝ ⎠
(c)
[1]
ȕLVWKHUDWLRRIORQJVLGHWRVKRUWVLGHRIFRQFHQWUDWHGORDGRUUHDFWLRQDUHD
14.5.6 Bearing
14.5.6.1 Bn shall be calculated in accordance with Table
14.5.6.1.
R14.5.4.2 If the resultant load falls within the middle third
of the wall thickness, plain concrete walls may be designed
XVLQJ WKH VLPSOL¿HG (T (FFHQWULF ORDGV DQG
lateral forces are used to determine the total eccentricity of
the factored axial force Pu(TXDWLRQ UHÀHFWVWKH
range of braced and restrained end conditions encountered
in wall design. The limitations of 14.2.2.2, 14.3.1.1, and
14.5.1.8 apply whether the wall is proportioned by 14.5.4.1
or by 14.5.4.2.
R14.5.5 Shear
R14.5.5.1 Proportions of plain concrete members usually
are controlled by tensile strength rather than shear strength.
Shear stress (as a substitute for principal tensile stress) rarely
ZLOOFRQWURO+RZHYHUEHFDXVHLWLVGL൶FXOWWRIRUHVHHDOO
possible conditions where shear may have to be investigated,
such as shear keys, Committee 318 maintains the investiga-
tion of this basic stress condition.
The shear requirements for plain concrete assume an
uncracked section. Shear failure in plain concrete will be a
diagonal tension failure, occurring when the principal tensile
stress near the centroidal axis becomes equal to the tensile
strength of the concrete. Because the major portion of the
principal tensile stress results from shear, the Code safe-
guards against tension failure by limiting the permissible
shear at the centroidal axis as calculated from the equation
for a section of homogeneous material:
v = VQIb
where v and V are the shear stress and shear force, respec-
tively, at the section considered; Q is the statical moment
of the area above or below the centroid of the gross section
calculated about the centroidal axis; I is the moment of
inertia of the gross section; and b is the section width where
shear stress is being calculated.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 3: MEMBERS 209
CODE COMMENTARY
14
Plain
Conc.
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![Table 15.4.2.3—Nominal joint shear strength Vn
Column
Beam in
direction of Vu
RQ¿QHPHQWE
transverse beams
according to
15.2.8 Vn, lb[1]
Continuous or
meets 15.2.6
Continuous or
meets 15.2.7
RQ¿QHG 24 c j
f A
λ ′
1RWFRQ¿QHG 20 c j
f A
λ ′
Other
RQ¿QHG 20 c j
f A
λ ′
1RWFRQ¿QHG 15 c j
f A
λ ′
Other
Continuous or
meets 15.2.7
RQ¿QHG 20 c j
f A
λ ′
1RWFRQ¿QHG 15 c j
f A
λ ′
Other
RQ¿QHG 15 c j
f A
λ ′
1RWFRQ¿QHG 12 c j
f A
λ ′
[1]
ȜVKDOOEHIRUOLJKWZHLJKWFRQFUHWHDQGIRUQRUPDOZHLJKWFRQFUHWH
15.4.2.4(൵HFWLYHFURVVVHFWLRQDODUHDZLWKLQDMRLQWAj,
VKDOOEHFDOFXODWHGDVWKHSURGXFWRIMRLQWGHSWKDQGH൵HF-
tive joint width. Joint depth shall be the overall depth of the
column, hLQWKHGLUHFWLRQRIMRLQWVKHDUFRQVLGHUHG(൵HF-
tive joint width shall be the overall width of the column
where the beam is wider than the column. Where the column
LVZLGHUWKDQWKHEHDPH൵HFWLYHMRLQWZLGWKVKDOOQRWH[FHHG
the lesser of (a) and (b):
(a) Beam width plus joint depth
(b) Twice the perpendicular distance from longitudinal
axis of beam to nearest side face of the column
15.5—Transfer of column axial force through the
floor system
15.5.1 If fcƍRIDÀRRUVVWHPLVOHVVWKDQ0.7fcƍ of a column,
WUDQVPLVVLRQRID[LDOIRUFHWKURXJKWKHÀRRUVVWHPVKDOOEH
in accordance with (a), (b), or (c):
D RQFUHWH RI FRPSUHVVLYH VWUHQJWK VSHFL¿HG IRU WKH
FROXPQVKDOOEHSODFHGLQWKHÀRRUVVWHPDWWKHFROXPQ
location. Column concrete shall extend outward at least
IWLQWRWKHÀRRUVVWHPIURPIDFHRIFROXPQIRUWKHIXOO
GHSWK RI WKH ÀRRU VVWHP DQG EH LQWHJUDWHG ZLWK ÀRRU
concrete.
E 'HVLJQVWUHQJWKRIDFROXPQWKURXJKDÀRRUVVWHP
shall be calculated using the lower value of concrete
strength with vertical dowels and transverse reinforce-
ment as required to achieve design strength.
(c) For beam-column joints laterally supported on four
sides by beams of approximately equal depth that satisfy
h = Joint depth in
plane parallel to
reinforcement
generating shear
b
Effective joint
width = lesser of
(b + h) and
(b + 2x)
x
Reinforcement
generating
shear
Effective joint area, Aj
Note: Effective area of joint for forces in each
direction of framing is to be considered
separately.
Plan
x
Column
Fig. R15.4.2²(ৼHFWLYHMRLQWDUHD
R15.5—Transfer of column axial force through the
floor system
7KH UHTXLUHPHQWV RI WKLV VHFWLRQ FRQVLGHU WKH H൵HFW RI
ÀRRU VVWHP FRQFUHWH VWUHQJWK RQ FROXPQ D[LDO VWUHQJWK
(Bianchini et al. 1960 ,IÀRRUVVWHPFRQFUHWHVWUHQJWKLV
less than 70 percent of column concrete strength, methods
in 15.5.1(a) or 15.5.1(b) may be applied to corner or edge
columns. Methods in 15.5.1(a), (b), or (c) may be applied to
interior columns.
Application of the concrete placement procedure
GHVFULEHGLQ D UHTXLUHVWKHSODFLQJRIWZRGL൵HUHQW
FRQFUHWH PL[WXUHV LQ WKH ÀRRU VVWHP7KH RGH UHTXLUHV
that column concrete be placed through the thickness of the
ÀRRUVVWHPDQGWKDWPL[WXUHVEHSODFHGDQGUHPDLQSODVWLF
such that the two can be vibrated so they are well integrated.
Additional inspection may be required for this process. As
required in Chapter 26, it is the responsibility of the licensed
design professional to indicate on the construction docu-
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214 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![16.1—Scope
16.1.1 This chapter shall apply to the design of joints and
connections at the intersection of concrete members and
for load transfer between concrete surfaces, including (a)
through (d):
(a) Connections of precast members
(b) Connections between foundations and either cast-in-
place or precast members
F +RUL]RQWDOVKHDUVWUHQJWKRIFRPSRVLWHFRQFUHWHÀH[-
ural members
(d) Brackets and corbels
16.2—Connections of precast members
16.2.1 General
16.2.1.1 Transfer of forces by means of grouted joints,
shear keys, bearing, anchors, mechanical connectors, steel
reinforcement, reinforced topping, or a combination of
these, shall be permitted.
16.2.1.2 $GHTXDF RI FRQQHFWLRQV VKDOO EH YHUL¿HG E
analysis or test.
16.2.1.3 Connection details that rely solely on friction
caused by gravity loads shall not be permitted.
16.2.1.4 Connections, and regions of members adjacent to
connections, shall be designed to resist forces and accom-
PRGDWHGHIRUPDWLRQVGXHWRDOOORDGH൵HFWVLQWKHSUHFDVW
structural system.
16.2.1.5 Design of connections shall consider structural
H൵HFWV RI UHVWUDLQW RI YROXPH FKDQJH LQ DFFRUGDQFH ZLWK
5.3.6.
16.2.1.6'HVLJQRIFRQQHFWLRQVVKDOOFRQVLGHUWKHH൵HFWV
RIWROHUDQFHVVSHFL¿HGIRUIDEULFDWLRQDQGHUHFWLRQRISUHFDVW
members.
R16.2—Connections of precast members
R16.2.1 General
Connection details should be arranged to minimize the
potential for cracking due to restrained creep, shrinkage, and
WHPSHUDWXUHPRYHPHQWV7KH3UHFDVW3UHVWUHVVHGRQFUHWH
Institute (MNL 123) provides information on recommended
connection details for precast concrete structures.
R16.2.1.1 If two or more connection methods are used to
satisfy the requirements for force transfer, their individual
load-deformation characteristics should be considered to
FRQ¿UPWKDWWKHPHFKDQLVPVZRUNWRJHWKHUDVLQWHQGHG
R16.2.1.4 The structural behavior of precast members may
GL൵HU VXEVWDQWLDOO IURP WKDW RI VLPLODU PHPEHUV WKDW DUH
cast-in-place. Design of connections to minimize or transmit
forces due to shrinkage, creep, temperature change, elastic
GHIRUPDWLRQ GL൵HUHQWLDO VHWWOHPHQW ZLQG DQG HDUWKTXDNH
require particular consideration in precast construction.
R16.2.1.5 Connections should be designed to either permit
WKHGLVSODFHPHQWVRUUHVLVWWKHIRUFHVLQGXFHGEODFNRI¿W
volume changes caused by shrinkage, creep, thermal, and
RWKHUHQYLURQPHQWDOH൵HFWVRQQHFWLRQVLQWHQGHGWRUHVLVW
the forces should do so without loss of strength. Restraint
assumptions should be consistent in all interconnected
members. There are also cases in which the intended force
PDEHLQRQHGLUHFWLRQEXWLWPDD൵HFWWKHVWUHQJWKRI
the connection in another. For example, shrinkage-induced
ORQJLWXGLQDOWHQVLRQLQDSUHFDVWEHDPPDD൵HFWWKHYHUWLFDO
shear strength on the corbel supporting it.
R16.2.1.6 Refer to R26.9.1(a).
CHAPTER 16—CONNECTIONS BETWEEN MEMBERS
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 217
CODE COMMENTARY
16
Connections
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![16.3.6.1 At the base of a precast column, pedestal, or wall,
the connection to the foundation shall satisfy 16.2.4.3 or
16.2.5.2.
16.3.6.2Iftheapplicableloadcombinationsof16.3.3result
in no tension at the base of precast walls, vertical integrity
ties required by 16.2.4.3(b) shall be permitted to be devel-
oped into an adequately reinforced concrete slab-on-ground.
16.4—Horizontal shear transfer in composite
concrete flexural members
16.4.1 General
16.4.1.1 ,Q D FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHU IXOO
transfer of horizontal shear forces shall be provided at
contact surfaces of interconnected elements.
16.4.1.2 Where tension exists across any contact surface
between interconnected concrete elements, horizontal shear
transfer by contact shall be permitted only where transverse
reinforcement is provided in accordance with 16.4.6 and
16.4.7.
16.4.1.3 Surface preparation assumed for design shall be
VSHFL¿HGLQWKHFRQVWUXFWLRQGRFXPHQWV
16.4.2 Required strength
16.4.2.1 Factored forces transferred along the contact
VXUIDFH LQ FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHUV VKDOO EH
calculated in accordance with the factored load combina-
tions in Chapter 5.
16.4.2.2 Required strength shall be calculated in accor-
dance with the analysis procedures in Chapter 6.
16.4.3 Design strength
16.4.3.1 Design strength for horizontal shear transfer
shall satisfy Eq. (16.4.3.1) at all locations along the contact
VXUIDFH LQ D FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHU XQOHVV
LVVDWLV¿HG
ࢥVnh•Vu (16.4.3.1)
where nominal horizontal shear strength Vnh is calculated in
accordance with 16.4.4.
ࢥ shall be determined in accordance with 21.2.
16.4.4 1RPLQDOKRUL]RQWDOVKHDUVWUHQJWK
R16.4—Horizontal shear transfer in composite
concrete flexural members
R16.4.1 General
R16.4.1.1 Full transfer of horizontal shear forces between
segments of composite members can be provided by hori-
zontal shear strength at contact surfaces through interface
shear, properly anchored ties, or both.
R16.4.1.3 Section 26.5.6 requires the licensed design
professional to specify the surface preparation in the
construction documents.
R16.4.4 1RPLQDOKRUL]RQWDOVKHDUVWUHQJWK
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 225
CODE COMMENTARY
16
Connections
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![16.4.4.1 If Vu ࢥ(500bvd), Vnh shall be taken as Vn calcu-
lated in accordance with 22.9, where bv is the width of the
contact surface, and d is in accordance with 16.4.4.3.
16.4.4.2 If Vu ” ࢥ(500bvd), Vnh shall be calculated in
accordance with Table 16.4.4.2, where Av,min is in accor-
dance with 16.4.6, bv is the width of the contact surface, and
d is in accordance with 16.4.4.3.
16.4.4.3 In Table 16.4.4.2, d shall be the distance from
H[WUHPHFRPSUHVVLRQ¿EHUIRUWKHHQWLUHFRPSRVLWHVHFWLRQ
to the centroid of prestressed and nonprestressed longitu-
dinal tension reinforcement, if any, but need not be taken
less than 0.80h for prestressed concrete members.
16.4.4.4 Transverse reinforcement in the previously cast
concrete that extends into the cast-in-place concrete and is
anchored on both sides of the interface shall be permitted to
be included as ties for calculation of Vnh.
16.4.5 $OWHUQDWLYH PHWKRG IRU FDOFXODWLQJ GHVLJQ KRUL-
zontal shear strength
16.4.5.1 As an alternative to 16.4.3.1, factored horizontal
shear Vuh VKDOO EH FDOFXODWHG IURP WKH FKDQJH LQ ÀH[XUDO
compressive or tensile force in any segment of the composite
FRQFUHWHPHPEHUDQG(T VKDOOEHVDWLV¿HGDWDOO
locations along the contact surface:
ࢥVnh•Vuh (16.4.5.1)
Nominal horizontal shear strength Vnh shall be calcu-
lated in accordance with 16.4.4.1 or 16.4.4.2, where area of
contact surface shall be substituted for bvd and Vuh shall be
substituted for Vu. Provisions shall be made to transfer the
change in compressive or tensile force as horizontal shear
force across the interface.
16.4.5.2 Where shear transfer reinforcement is designed
to resist horizontal shear to satisfy Eq. (16.4.5.1), the tie
area to tie spacing ratio along the member shall approxi-
R16.4.4.2 The permitted horizontal shear strengths and the
UHTXLUHPHQWRILQDPSOLWXGHIRULQWHQWLRQDOURXJKQHVV
are based on tests discussed in Kaar et al. (1960), Saemann
and Washa (1964), and Hanson (1960).
R16.4.4.3 In composite prestressed concrete members,
the depth of the tension reinforcement may vary along the
PHPEHU7KHGH¿QLWLRQRId used in Chapter 22 for deter-
mining the vertical shear strength is also appropriate for
determining the horizontal shear strength.
R16.4.5 $OWHUQDWLYHPHWKRGIRUFDOFXODWLQJGHVLJQKRUL-
zontal shear strength
R16.4.5.2 The distribution of horizontal shear stresses
DORQJWKHFRQWDFWVXUIDFHLQDFRPSRVLWHPHPEHUZLOOUHÀHFW
the distribution of shear along the member. Horizontal
Table 16.4.4.2—Nominal horizontal shear strength
Shear transfer
reinforcement Contact surface preparation[1]
Vnh, lb
Av•AYPLQ
Concrete placed against hardened
concrete intentionally roughened to a full
DPSOLWXGHRIDSSUR[LPDWHOLQ
Lesser of:
260 0.6
v yt
v
v
A f
b d
b s
⎛ ⎞
λ +
⎜ ⎟
⎝ ⎠
(a)
500bvd (b)
Concrete placed against hardened
concrete not intentionally roughened
80bvd (c)
Other cases
Concrete placed against hardened
concrete intentionally roughened
80bvd (d)
[1]
Concrete contact surface shall be clean and free of laitance.
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226 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![shear failure will initiate where the horizontal shear stress
is a maximum and will spread to regions of lower stress.
Because the slip at peak horizontal shear resistance is small
for a concrete-to-concrete contact surface, longitudinal
redistribution of horizontal shear resistance is very limited.
Therefore, the spacing of ties along the contact surface
should provide horizontal shear resistance distributed
approximately the same as the distribution of shear stress
along the contact surface.
R16.4.6 0LQLPXPUHLQIRUFHPHQWIRUKRUL]RQWDOVKHDUWUDQVIHU
R16.4.6.1 The requirements for minimum area of shear
transfer reinforcement are based on test data given in Kaar
et al. (1960), Saemann and Washa (1964), Hanson (1960),
*URVV¿HOGDQG%LUQVWLHO DQG0DVW
R16.4.75HLQIRUFHPHQWGHWDLOLQJIRUKRUL]RQWDOVKHDUWUDQVIHU
R16.4.7.3 Proper anchorage of ties extending across the
interface is required to maintain contact along the interface.
R16.5—Brackets and corbels
R16.5.1 General
Brackets and corbels are short cantilevers that tend to act
as simple trusses or deep beams, rather than beams, which
are designed for shear according to 22.5. The corbel shown
in Fig. R16.5.1a and Fig. 16.5.1b may fail by shearing along
the interface between the column and the corbel, yielding of
the tension tie, crushing or splitting of the compression strut,
or localized bearing or shearing failure under the loading
plate. These failure modes are illustrated and discussed in
Elzanaty et al. (1986).
PDWHOUHÀHFWWKHGLVWULEXWLRQRILQWHUIDFHVKHDUIRUFHVLQWKH
FRPSRVLWHFRQFUHWHÀH[XUDOPHPEHU
16.4.5.3 Transverse reinforcement in a previously cast
section that extends into the cast-in-place section and is
anchored on both sides of the interface shall be permitted to
be included as ties for calculation of Vnh.
16.4.6 0LQLPXPUHLQIRUFHPHQWIRUKRUL]RQWDOVKHDUWUDQVIHU
16.4.6.1 Where shear transfer reinforcement is designed
to resist horizontal shear, Av,min shall be the greater of (a)
and (b):
(a) 0.75 w
c
y
b s
f
f
′
(b) 50 w
y
b s
f
16.4.7 5HLQIRUFHPHQWGHWDLOLQJIRUKRUL]RQWDOVKHDUWUDQVIHU
16.4.7.1 Shear transfer reinforcement shall consist of
single bars or wire, multiple leg stirrups, or vertical legs of
welded wire reinforcement.
16.4.7.2 Where shear transfer reinforcement is designed to
resist horizontal shear, longitudinal spacing of shear transfer
reinforcement shall not exceed the lesser of 24 in. and four
times the least dimension of the supported element.
16.4.7.3 Shear transfer reinforcement shall be developed
in interconnected elements in accordance with 25.7.1.
16.5—Brackets and corbels
16.5.1 General
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 227
CODE COMMENTARY
16
Connections
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![R16.5.2 'LPHQVLRQDOOLPLWV
R16.5.2.2 A minimum depth, as shown in Fig. R16.5.1a
and R16.5.1b, is required at the outside edge of the bearing
area so that a premature failure will not occur due to a major
crack propagating from below the bearing area to the sloping
face of the corbel or bracket. Failures of this type have been
observed (Kriz and Raths 1965) in corbels having depths at
the outside edge of the bearing area less than required in
16.5.2.2.
R16.5.2.3 The restriction on the location of the bearing
DUHDLVQHFHVVDUWRHQVXUHGHYHORSPHQWRIWKHVSHFL¿HGLHOG
strength of the primary tension reinforcement near the load.
If the corbel is designed to resist restraint force Nuc, a
bearing plate should be provided and fully anchored to the
primary tension reinforcement (Fig. R16.5.1b).
R16.5.2.4 These limits impose dimensional restrictions on
brackets and corbels necessary to comply with the maximum
shear friction strength allowed on the critical section at the
face of support.
R16.5.2.5 Tests (Mattock et al. 1976a) have shown that
the maximum shear friction strength of lightweight concrete
brackets and corbels is a function of both fcƍ and av/d.
R16.5.3 Required strength
R16.5.3.1 Figure R16.5.1b shows the forces applied to the
corbel. Mu can be calculated as [Vuav + Nuc(h – d)].
R16.5.3.2 In editions of the Code prior to ACI 318-19,
VSHFL¿F SURYLVLRQV IRU UHVWUDLQW IRUFHV DW EHDULQJ FRQQHF-
tions were included only for corbels and brackets. In 2019,
16.2.2.3 and 16.2.2.4 were added to include consideration
of restraint forces at all bearing connections. Consequently
the provisions applicable only to brackets or corbels were
removed and a reference made to 16.2.2.3 or 16.2.2.4.
16.5.2 'LPHQVLRQDOOLPLWV
16.5.2.1(൵HFWLYHGHSWKd for a bracket or corbel shall be
calculated at the face of the support.
16.5.2.2 Overall depth of bracket or corbel at the outside
edge of the bearing area shall be at least 0.5d.
16.5.2.3 No part of the bearing area on a bracket or corbel
shall project farther from the face of support than (a) or (b):
(a) End of the straight portion of the primary tension
reinforcement
(b) Interior face of the transverse anchor bar, if one is
provided
16.5.2.4 For normalweight concrete, the bracket or corbel
dimensions shall be selected such that Vu/ࢥVKDOOQRWH[FHHG
the least of (a) through (c):
(a) 0.2fcƍbwd
(b) (480 + 0.08fcƍ bwd
(c) 1600bwd
16.5.2.5 For lightweight concrete, the bracket or corbel
dimensions shall be selected such that Vuࢥ shall not exceed
the lesser of (a) and (b):
(a) 0.2 0.07 v
c w
a
f b d
d
⎛ ⎞
− ′
⎜ ⎟
⎝ ⎠
(b) 800 280 v
w
a
b d
d
⎛ ⎞
−
⎜ ⎟
⎝ ⎠
16.5.3 Required strength
16.5.3.1 The section at the face of the support shall be
designed to resist simultaneously the factored shear Vu, the
factored restraint force Nuc, and the factored moment Mu.
16.5.3.2 Factored restraint force, Nuc, and shear, Vu, shall
be the maximum values calculated in accordance with the
factored load combinations in Chapter 5. It shall be permitted
to calculate Nuc in accordance with 16.2.2.3 or 16.2.2.4, as
appropriate.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 229
CODE COMMENTARY
16
Connections
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![of reinforcement required to cross the face of the support, as
shown in Fig. R16.5.1b, is the sum of Asc and Ah.
R16.5.6 5HLQIRUFHPHQWGHWDLOLQJ
R16.5.6.3 For brackets and corbels of variable depth
(refer to Fig. R16.5.1a), the stress at ultimate in the rein-
forcement is almost constant at approximately fy from the
face of support to the load point. This is because the hori-
zontal component of the inclined concrete compression
strut is transferred to the primary tension reinforcement at the
location of the vertical load. Therefore, reinforcement should
be fully anchored at its outer end (refer to 16.5.6.3) and in
the supporting column (refer to 16.5.6.4), so as to be able to
GHYHORSLWVVSHFL¿HGLHOGVWUHQJWKIURPWKHIDFHRIVXSSRUW
to the vertical load (refer to Fig. R16.5.6.3a). Satisfactory
anchorage at the outer end can be obtained by bending the
primary tension reinforcement bars in a horizontal loop as
VSHFL¿HGLQERUEZHOGLQJDEDURIHTXDOGLDPHWHU
or a suitably sized angle across the ends of the primary tension
reinforcement bars. The weld detail used successfully in the
corbel tests reported in Mattock et al. (1976a) is shown in Fig.
R16.5.6.3b. Refer to ACI Committee 408 (1966).
An end hook in the vertical plane, with the minimum
GLDPHWHU EHQG LV QRW WRWDOO H൵HFWLYH EHFDXVH D ]RQH RI
unreinforced concrete beneath the point of loading will exist
for loads applied close to the end of the bracket or corbel.
)RUZLGHEUDFNHWV SHUSHQGLFXODUWRWKHSODQHRIWKH¿JXUH
and loads not applied close to the end, U-shaped bars in a
KRUL]RQWDOSODQHSURYLGHH൵HFWLYHHQGKRRNV
dh
See Fig.
R16.5.6.3b
Standard 90- or
180-degree hook
(see Table 25.3.1)
P
Fig. R16.5.6.3a²0HPEHUODUJHOGHSHQGHQWRQVXSSRUWDQG
end anchorages.
16.5.6 5HLQIRUFHPHQWGHWDLOLQJ
16.5.6.1 Concrete cover shall be in accordance with 20.5.1.3.
16.5.6.2 Minimum spacing for deformed reinforcement
shall be in accordance with 25.2.
16.5.6.3 At the front face of a bracket or corbel, primary
tension reinforcement shall be anchored by (a), (b), or (c):
(a) A weld to a transverse bar of at least equal size that is
designed to develop fy of primary tension reinforcement
(b) Bending the primary tension reinforcement back to
form a horizontal loop
(c) Other means of anchorage that develops fy
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 231
CODE COMMENTARY
16
Connections
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![present reduction factor ȜDGHTXDWHOUHSUHVHQWVWKHLQÀX-
ence of lightweight concrete (Shaikh and Yi 1985; Anderson
and Meinheit 2005). Anchor manufacturer data developed
for evaluation reports on post-installed expansion, screw,
undercut, and adhesive anchors indicate that a reduced Ȝ is
needed to provide the necessary safety factor for the respec-
tive design strength. ACI 355.2 and ACI 355.4 provide
SURFHGXUHVZKHUHEDVSHFL¿FYDOXHRIȜa can be used based
on testing, assuming the lightweight concrete is similar to
the reference test material.
R17.3—Design limits
R17.3.1 A limited number of tests of cast-in and post-
installed anchors in high-strength concrete (Primavera et al.
1997) indicate that the design procedures contained in this
chapter become unconservative with increasing concrete
strength, particularly for cast-in anchors in concrete with
compressive strengths in the range of 11,000 to 12,000
psi. Until further tests are available, an upper limit on fcƍ
of 10,000 psi has been imposed for the design of cast-in
anchors. This limitation is consistent with those for shear
strength, torsion strength, and reinforcement development
length in this Code (22.5.3.1, 22.6.3.1, 22.7.2.1, 25.4.1.4).
For some post-installed anchors, the capacity may be nega-
WLYHOD൵HFWHGEYHUKLJKVWUHQJWKFRQFUHWH7KHVHH൵HFWV
DUHDVVRFLDWHGZLWKGL൶FXOWLQIXOOH[SDQGLQJH[SDQVLRQ
anchors, cutting grooves in the sidewall of the predrilled
hole by the screw anchor’s threads, and reduced bond
strength of adhesive anchors. The 8000 psi limit for post-
LQVWDOOHGDQFKRUVUHÀHFWVWKHFXUUHQWFRQFUHWHVWUHQJWKUDQJH
IRUWHVWLQJVSHFL¿HGLQ$,DQG$,7KH
SVLOLPLWPDEHH[FHHGHGLIYHUL¿HGZLWKWHVWV
R17.3.2 The limitation on anchor diameter is based on the
current range of test data. In the 2002 through 2008 editions
of the Code, there were limitations on the diameter and
embedment of anchors to calculate the concrete breakout
strength. These limitations were necessitated by the lack of
test results on anchors with diameters larger than 2 in. and
embedment lengths longer than 24 in. In 2011, limitations
on anchor diameter and embedment length were revised to
limit the diameter to 4 in. based on the results of tension
and shear tests on large-diameter anchors with deep embed-
ments (Lee et al. 2007, 2010). These tests included 4.25 in.
diameter anchors, embedded 45 in., tested in tension and 3
in. diameter anchors tested in shear. The 4 in. diameter limit
was selected to maintain consistency with the largest diam-
eter anchor permitted in ASTM F1554. Other ASTM speci-
¿FDWLRQVSHUPLWXSWRLQGLDPHWHUDQFKRUVKRZHYHUWKH
have not been tested to ensure applicability of the 17.6.2 and
17.7.2 concrete breakout provisions.
permitted to use an alternate value of Ȝa if tests are performed
and evaluated in accordance with ACI 355.2 or ACI 355.4.
Table 17.2.4.1—Modification factor Ȝa for
lightweight concrete
Case Ȝa
[1]
Cast-in and undercut anchor concrete failure Ȝ
Expansion, screw, and adhesive anchor concrete failure Ȝ
Adhesive anchor bond failure per Eq. (17.6.5.2.1) Ȝ
[1]
ȜVKDOOEHLQDFFRUGDQFHZLWK
17.2.5 Anchors shall be installed and inspected in accor-
dance with the requirements of 26.7 and 26.13.
17.3—Design Limits
17.3.1 The value of fcƍ used for calculation purposes in this
chapter shall not exceed 10,000 psi for cast-in anchors and
8000 psi for post-installed anchors. Post-installed anchors
shall not be used in concrete with a strength greater than
8000 psi without testing to verify acceptable performance.
17.3.2 For anchors with diameters da ” LQ, concrete
EUHDNRXWVWUHQJWKUHTXLUHPHQWVVKDOOEHFRQVLGHUHGVDWLV¿HG
by the design procedures of 17.6.2 and 17.7.2.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 235
17
Anchoring
CODE COMMENTARY
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![R17.3.3 ACI 355.4 limits the embedment depth of adhe-
sive anchors to 4da”hef”da, which represents the theo-
retical limits of the bond model (Eligehausen et al. 2006a).
R17.3.4 Screw anchor research by Olsen et al. (2012) is
based on the nominal screw anchor diameter corresponding
WR WKH QRPLQDO GULOO ELW VL]H IRU H[DPSOH D LQ VFUHZ
DQFKRULQVWDOOVLQDKROHGULOOHGEDLQ$16,GULOOELW
7KLV GH¿QLWLRQ RI VFUHZ DQFKRU VL]H LV DSSUR[LPDWHO WKH
diameter of the core or shank of the screw rather than the size
RIWKHODUJHUH[WHUQDOGLDPHWHURIWKHWKUHDG7KLVGH¿QLWLRQ
GL൵HUVIURPWKHGLDPHWHURIVWDQGDUGDQFKRUVZLWKASME
B1.1 threads that have a reduced shaft area and smaller
H൵HFWLYHDUHD7KHH൵HFWLYHDUHDRIWKHVFUHZDQFKRUDVZLWK
other post-installed mechanical anchors, is provided by the
manufacturer.
The Olsen et al. (2012) empirical design model was
derived from a database of tests in cracked and uncracked
concrete on metric-sized screw anchors tested in Europe
and inch-sized anchors tested by independent laboratories in
accordance with ICC-ES AC193.
)RU FRQFUHWH VFUHZ DQFKRUV WKH H൵HFWLYH HPEHGPHQW
depth, hef, is determined as a reduction from the nominal
embedment based on geometric characteristics of the screw.
7KHH൵HFWLYHHPEHGPHQWLVYHUL¿HGGXULQJWKHTXDOL¿FDWLRQ
testing under ACI 355.2 and provided by the manufacturer
IRUXVHLQGHVLJQ8VLQJWKHUHGXFHGH൵HFWLYHHPEHGPHQW
depth with the concrete capacity design (CCD) method is
shown to adequately represent the behavior of concrete
screws in the current concrete screw database and also vali-
GDWHVWKHH൵HFWVDQGOLPLWDWLRQVRIFHUWDLQUHOHYDQWSDUDP-
HWHUVVXFKDVWKHH൵HFWLYHHPEHGPHQWGHSWKDQGVSDFLQJRI
anchors (17.9).
R17.5—Design strength
17.3.3 For adhesive anchors with embedment depths 4da
”hef”da, bond strength requirements shall be considered
VDWLV¿HGEWKHGHVLJQSURFHGXUHRI
17.3.4 For screw anchors with embedment depths 5da”hef
”da, and hef•LQ, concrete breakout strength require-
PHQWVVKDOOEHFRQVLGHUHGVDWLV¿HGEWKHGHVLJQSURFHGXUHV
of 17.6.2 and 17.7.2.
17.3.5 Anchors shall satisfy the edge distances, spacings,
and thicknesses in 17.9 unless supplementary reinforcement
is provided to control splitting failure.
17.4—Required strength
17.4.1 Required strength shall be calculated in accordance
with the factored load combinations in Chapter 5.
17.4.2 For anchors in structures assigned to SDC C, D, E,
and F, the additional requirements of 17.10 shall apply.
17.5—Design strength
17.5.1 For each applicable factored load combination,
design strength of individual anchors and anchor groups
VKDOOVDWLVIࢥSn•U,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOO
be considered in accordance with 17.8.1.
17.5.1.1 Strength reduction factor, ࢥ, shall be determined
in accordance with 17.5.3.
American Concrete Institute – Copyrighted © Material – www.concrete.org
236 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![R17.5.1.2 This section provides requirements for estab-
lishing the strength of anchors in concrete. The various types
of steel and concrete failure modes for anchors are shown in
Fig. R17.5.1.2(a) and R17.5.1.2(b). Comprehensive discus-
sions of anchor failure modes are included in CEB (1997),
Fuchs et al. (1995), Eligehausen and Balogh (1995), and
Cook et al. (1998). Tension failure modes related to concrete
include concrete breakout failure (applicable to all anchor
types), pullout failure (applicable to cast-in anchors, post-
installed expansion, screw, and undercut anchors), side-
face blowout failure (applicable to headed anchors), and
bond failure (applicable to adhesive anchors). Shear failure
modes related to concrete include concrete breakout failure
and concrete pryout (applicable to all anchor types). These
failure modes are described in the deemed-to-comply provi-
sions of 17.6.2, 17.6.3, 17.6.4, 17.6.5, 17.7.2, and 17.7.3.
Any model that complies with the requirements of 17.5.1.2
and 17.5.2.3 can be used to establish the concrete-related
strengths. Additionally, anchor tensile and shear strengths
are limited by the minimum spacings and edge distances
of 17.9 to preclude splitting. The design of post-installed
anchors recognizes that the strength of anchors is sensi-
tive to appropriate installation; installation requirements
are included in Chapter 26. Some post-installed anchors are
less sensitive to installation errors and tolerances. This is
UHÀHFWHGLQYDULRXVࢥIDFWRUVJLYHQLQDQGEDVHGRQ
the assessment criteria of ACI 355.2 and ACI 355.4.
The breakout strength of an unreinforced connection can
EH WDNHQ DV DQ LQGLFDWLRQRI WKH ORDG DW ZKLFK VLJQL¿FDQW
cracking will occur. Such cracking can represent a service-
ability problem if not controlled (refer to R17.7.2.1).
17.5.1.2 Nominal strength for an anchor or anchor groups
shall be based on design models that result in predictions of
strength in substantial agreement with results of comprehen-
sive tests. The materials used in the tests shall be compat-
ible with the materials used in the structure. The nominal
strength shall be based on the 5 percent fractile of the basic
individual anchor strength. For nominal strengths related to
FRQFUHWHVWUHQJWKPRGL¿FDWLRQVIRUVL]HH൵HFWVQXPEHURI
DQFKRUVH൵HFWVRIFORVHVSDFLQJRIDQFKRUVSUR[LPLWWR
edges, depth of the concrete member, eccentric loadings of
DQFKRUJURXSVDQGLQÀXHQFHRIFUDFNLQJVKDOOEHWDNHQLQWR
account. Limits on edge distance and anchor spacing in the
design models shall be consistent with the tests that veri-
¿HGWKHPRGHO6WUHQJWKRIDQFKRUVVKDOOEHEDVHGRQGHVLJQ
models that satisfy 17.5.1.2 for the following:
(a) Steel strength of anchor in tension
(b) Concrete breakout strength of anchor in tension
(c) Pullout strength of a single cast-in anchor and single
post-installed expansion, screw, and undercut anchor in
tension
(d) Concrete side-face blowout strength of headed anchor
in tension
(e) Bond strength of adhesive anchor in tension
(f) Steel strength of anchor in shear
(g) Concrete breakout strength of anchor in shear
(h) Concrete pryout strength of anchor in shear
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 237
17
Anchoring
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![17.5.2 For each applicable factored load combination,
design strength of anchors shall satisfy the criteria in Table
17.5.2.
Table 17.5.2—Design strength requirements of
anchors
Failure mode
Single
anchor
Anchor group[1]
Individual
anchor in a
group
Anchors as a
group
Steel strength in
tension (17.6.1)[2] ࢥNsa•Nua ࢥNsa•Nua,i
Concrete breakout
strength in tension[3]
(17.6.2)
ࢥNcb•Nua ࢥNcbg•Nua,g
Pullout strength in
tension (17.6.3)
ࢥNpn•Nua ࢥNpn•Nua,i
Concrete side-face
blowout strength in
tension (17.6.4)
ࢥNsb•Nua ࢥNsbg•Nua,g
Bond strength of
adhesive anchor in
tension (17.6.5)
ࢥNa•Nua ࢥNag•Nua,g
Steel strength in shear
(17.7.1)
ࢥVsa•Vua ࢥVsa•Vua,i
Concrete breakout
strength in shear[3]
(17.7.2)
ࢥVcb•Vua ࢥVcbg•Vua,g
Concrete pryout strength
in shear (17.7.3)
ࢥVcp•Vua ࢥVcpg•Vua,g
[1]
Design strengths for steel and pullout failure modes shall be calculated for the most
highly stressed anchor in the group.
[2]
Sections referenced in parentheses are pointers to models that are permitted to be
used to evaluate the nominal strengths.
[3]
If anchor reinforcement is provided in accordance with 17.5.2.1, the design strength
of the anchor reinforcement shall be permitted to be used instead of the concrete
breakout strength
17.5.2.1 The design strength of anchor reinforcement shall
be permitted to be used instead of the concrete breakout
VWUHQJWKLI D RU E LVVDWLV¿HG
(a) For tension, if anchor reinforcement is developed in
accordance with Chapter 25 on both sides of the concrete
breakout surface
(b) For shear, if anchor reinforcement is developed in
accordance with Chapter 25 on both sides of the concrete
breakout surface, or encloses and contacts the anchor and
is developed beyond the breakout surface.
17.5.2.1.1 Strength reduction factor ࢥ for anchor rein-
forcement shall be in accordance with 17.5.3.
greater than the 5 percent fractile. The number of tests has to
EHVX൶FLHQWIRUVWDWLVWLFDOYDOLGLWDQGVKRXOGEHFRQVLGHUHG
in the determination of the 5 percent fractile.
R17.5.2 Under combined tension and bending, indi-
YLGXDODQFKRUVLQDJURXSPDEHUHTXLUHGWRUHVLVWGL൵HUHQW
magnitudes of tensile force. Similarly, under combined shear
and torsion, individual anchors in a group may be required
WRUHVLVWGL൵HUHQWPDJQLWXGHVRIVKHDU7DEOHLQFOXGHV
requirements to design single anchors and individual anchors
in a group to safeguard against all potential failure modes.
For steel and pullout failure modes, the most highly stressed
DQFKRULQWKHJURXSVKRXOGEHFKHFNHGWRHQVXUHLWKDVVX൶-
cient strength to resist its required load. For concrete breakout,
the anchors should be checked as a group. Elastic analysis or
plastic analysis of ductile anchors as described in 17.2.1 may
be used to determine the loads resisted by each anchor.
The addition of reinforcement in the direction of the
load to restrain concrete breakout can enhance the strength
and deformation capacity of the anchor connection. Such
enhancement is practical with cast-in anchors such as those
used in precast sections. Klingner et al. (1982), ¿E (2011),
ACI 349, and Eligehausen et al. (2006b) provide informa-
WLRQUHJDUGLQJWKHH൵HFWRIUHLQIRUFHPHQWRQWKHEHKDYLRURI
DQFKRUV7KHH൵HFWRIUHLQIRUFHPHQWLVQRWLQFOXGHGLQWKH
ACI 355.2 and ACI 355.4 anchor acceptance tests or in the
concrete breakout calculation method of 17.6.2 and 17.7.2.
Anchor reinforcement may be provided in accordance with
17.5.2.1 and developed according to Chapter 25 instead of
calculating breakout strength.
R17.5.2.1 For conditions where the factored tensile or
shear force exceeds the concrete breakout strength of the
anchor(s) or if the breakout strength is not evaluated, the
nominal strength can be based on properly developed anchor
reinforcement as illustrated in Fig. R17.5.2.1a for tension
and Fig. R17.5.2.1b(i) and Fig. R17.5.2.1b(ii) for shear.
Because anchor reinforcement is placed below where the
shear is applied (refer to Fig. R17.5.2.1b), the force in the
anchor reinforcement will be larger than the shear force.
Anchor reinforcement is distinguished from supplementary
reinforcement in that it is designed exclusively for the anchor
loads and is intended to preclude concrete breakout. Strut-
and-tie models may be used to design anchor reinforcement.
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Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![Table 17.5.3(a)—Anchor strength governed by steel
Type of steel element
Strength reduction factor ࢥ
Tension (steel) Shear (steel)
Ductile 0.75 0.65
Brittle 0.65 0.60
Table 17.5.3(b)—Anchor strength governed by
concrete breakout, bond, and side-face blowout
Supplementary
reinforcement
Type of
anchor
installation
Anchor
Category[1]
from ACI
355.2 or
ACI 355.4
Strength reduction
factor ࢥ
Tension
(concrete
breakout,
bond, or
side-face
blowout)
Shear
(concrete
breakout)
Supplementary
reinforcement
present
Cast-in
anchors
Not
applicable
0.75
0.75
Post-
installed
anchors
1 0.75
2 0.65
3 0.55
Supplementary
reinforcement
not present
Cast-in
Anchors
Not
applicable
0.70
0.70
Post-
installed
anchors
1 0.65
2 0.55
3 0.45
[1]
Anchor Category 1 indicates low sensitivity to installation and high reliability;
Anchor Category 2 indicates medium sensitivity and medium reliability; Anchor Cate-
gory 3 indicates high sensitivity and lower reliability.
Table 17.5.3(c)—Anchor strength governed by
concrete pullout, or pryout strength
Type of anchor
installation
Anchor
Category[1]
from ACI
355.2 or ACI
355.4
Strength reduction factor ࢥ
Tension
(concrete
pullout)
Shear
(concrete
pryout)
Cast-in anchors Not applicable 0.70
0.70
Post-installed
anchors
1 0.65
2 0.55
3 0.45
[1]
Anchor Category 1 indicates low sensitivity to installation and high reliability;
Anchor Category 2 indicates medium sensitivity and medium reliability; and Anchor
Category 3 indicates high sensitivity and lower reliability.
17.6—Tensile strength
17.6.1 Steel strength of anchors in tension, Nsa
17.6.1.1 Nominal steel strength of anchors in tension as
governed by the steel, Nsa, shall be evaluated based on the
7KHࢥIDFWRUVIRUDQFKRUVWUHQJWKJRYHUQHGEFRQFUHWH
breakout, bond, and side-face blowout in Table 17.5.3(b) are
separated into two groups based on the presence or absence
of supplementary reinforcement. The supplementary rein-
IRUFHPHQWFODVVL¿FDWLRQVRIWKLVWDEOHUHSODFHWKH³RQGL-
tion A” and “Condition B” designations in previous Codes.
Applications with supplementary reinforcement provide
more deformation capacity, permitting the ࢥ-factors to be
increased. An explicit design of supplementary reinforce-
ment for anchor-related forces is not required; however, the
arrangement of supplementary reinforcement should gener-
ally conform to that of the anchor reinforcement shown in Fig.
R17.5.2.1(a) and R17.5.2.1(b)(i) and (ii). Unlike anchor rein-
forcement, full development of supplementary reinforcement
beyond the assumed breakout failure plane is not required.
For concrete breakout in shear for all anchor types and for
brittle concrete failure modes for cast-in anchors, the basic
strength reduction factor for brittle concrete failures (ࢥ
0.70) was chosen based on results of probabilistic studies.
While this factor is greater than the strength reduction factor
of structural plain concrete (ࢥ ), the nominal resistance
expressions used in this chapter and in the test requirements
are based on the 5 percent fractiles; therefore, ࢥ would
be overly conservative. Comparison with other design
procedures and probabilistic studies (Farrow and Klingner
1995) indicated that the choice of ࢥ LVMXVWL¿HG)RU
the same cases with supplementary reinforcement, the value
of ࢥ is compatible with the level of safety for shear
failures in concrete beams, and has been recommended in
the PCI Design Handbook (MNL 120) and by ACI 349.
Tests included in ACI 355.2 and ACI 355.4 to assess
sensitivity to installation procedures determine the Anchor
Categories as given in Table 17.5.3(b) for proprietary post-
installed expansion, screw, undercut, and adhesive anchors.
$,WHVWVIRULQVWDOODWLRQVHQVLWLYLWPHDVXUHH൵HFWVRI
variability in anchor torque during installation, tolerance on
drilled hole size, and energy level used in setting anchors;
for expansion, screw, and undercut anchors intended for use
in cracked concrete, increased crack widths are considered.
$,WHVWVIRULQVWDOODWLRQVHQVLWLYLWDVVHVVWKHLQÀX-
HQFHRIDGKHVLYHPL[LQJDQGWKHLQÀXHQFHRIKROHFOHDQLQJ
LQGUVDWXUDWHGDQGZDWHU¿OOHGXQGHUZDWHUERUHKROHV
R17.6—Tensile strength
R17.6.1 Steel strength of anchors in tension, Nsa
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246 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
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![17.6.2.1.3 If an additional plate or washer is added at the head
of the anchor, it shall be permitted to calculate the projected area
of the failure surface by projecting the failure surface outward
1.5hefIURPWKHH൵HFWLYHSHULPHWHURIWKHSODWHRUZDVKHU7KH
H൵HFWLYH SHULPHWHU VKDOO QRW H[FHHG WKH YDOXH DW D VHFWLRQ
projected outward more than the thickness of the washer or
plate from the outer edge of the head of the anchor.
17.6.2.1.4 ANco is the projected concrete failure area of a
single anchor with an edge distance of at least 1.5hef and
shall be calculated by Eq. (17.6.2.1.4).
ANco = 9hef
2
(17.6.2.1.4)
17.6.2.2 Basic single anchor breakout strength, Nb
17.6.2.2.1 Basic concrete breakout strength of a single
anchor in tension in cracked concrete, Nb, shall be calculated
by Eq. (17.6.2.2.1), except as permitted in 17.6.2.2.3
Nb = kcȜa c
f ′ hef
1.5
(17.6.2.2.1)
R17.6.2.2 Basic single anchor breakout strength, Nb
R17.6.2.2.1 The equation for the basic concrete breakout
strength was derived assuming concrete breakout with an
angle of approximately 35 degrees, considering fracture
mechanics concepts (Fuchs et al. 1995; Eligehausen and
Balogh 1995; Eligehausen and Fuchs 1988; ¿E 2011).
≈ 35°
≈ 35°
6 in.
4 in.
5 in. 9 in. 1.5h’ef
N
5.5 in.
h’ef
N
1.5h’ef
Actual failure
surface
Assumed failure
surface for
limiting hef
Actual failure
surface
Assumed failure
surface for
limiting hef
Point A
5.5 in.
h’ef
Side section
Plan
Actual failure
surface
Assumed failure
surface for
limiting hef
A’Nc
Elevation
The actual hef = 5.5 in. but three edges
are ≤ 1.5hef therefore the limiting value
of hef (shown as h’ef in the figure) is the
larger of ca,max /1.5 and one-third of the
maximum spacing for an anchor group:
h’ef = max (6/1.5, 9/3) = 4 in.
Therefore, use hef = 4 in. for the value
of hef in equations 17.6.2.1 through
17.6.2.5 including the calculation of A’Nc:
A’Nc = (6 + 4)(5 + 9 + [1.5 x 4]) = 200 in.2
Point A shows the intersection of the
assumed failure surface for limiting hef
with the concrete surface.
Fig. R17.6.2.1.2²([DPSOHRIWHQVLRQZKHUHDQFKRUVDUHORFDWHGLQQDUURZPHPEHUV
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250 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![17.6.5.2 Basic single anchor bond strength, Nba
17.6.5.2.1 Basic bond strength of a single adhesive anchor
in tension in cracked concrete, Nba, shall be calculated by
Eq. (17.6.5.2.1)
Nba ȜaIJcrʌdahef (17.6.5.2.1)
17.6.5.2.2 Characteristic bond stress, IJcr, shall be taken as
the 5 percent fractile of results of tests performed and evalu-
ated in accordance with ACI 355.4.
17.6.5.2.3 If analysis indicates cracking at service load
OHYHOVDGKHVLYHDQFKRUVVKDOOEHTXDOL¿HGIRUXVHLQFUDFNHG
concrete in accordance with ACI 355.4.
17.6.5.2.4 For adhesive anchors located in a region of a
concrete member where analysis indicates no cracking at
service load levels, IJuncr shall be permitted to be used in
place of IJcr in Eq. (17.6.5.2.1) and shall be taken as the 5
percent fractile of results of tests performed and evaluated
according to ACI 355.4.
17.6.5.2.5 It shall be permitted to use the minimum char-
acteristic bond stress values in Table 17.6.5.2.5, provided (a)
WKURXJK H DUHVDWLV¿HG
(a) Anchors shall meet the requirements of ACI 355.4
(b) Anchors shall be installed in holes drilled with a rotary
impact drill or rock drill
(c) Concrete compressive strength at time of anchor instal-
lation shall be at least 2500 psi
(d) Concrete age at time of anchor installation shall be at
least 21 days
(e) Concrete temperature at time of anchor installation
shall be at least 50°F
R17.6.5.2 Basic single anchor bond strength, Nba
R17.6.5.2.1 The equation for basic bond strength of
adhesive anchors as given in Eq. (17.6.5.2.1) represents a
uniform bond stress model that has been shown to provide
the best prediction of adhesive anchor bond strength based
RQQXPHULFDOVWXGLHVDQGFRPSDULVRQVRIGL൵HUHQWPRGHOVWR
an international database of experimental results (Cook et
al. 1998). The basic bond strength is valid for bond failures
that occur between the concrete and the adhesive as well as
between the anchor and the adhesive.
R17.6.5.2.2 Characteristic bond stresses should be based
on tests performed in accordance with ACI 355.4 and should
UHÀHFWWKHSDUWLFXODUFRPELQDWLRQRILQVWDOODWLRQDQGXVHFRQGL-
tions anticipated during construction and during anchor service
OLIH,ISURGXFWVSHFL¿FLQIRUPDWLRQLVXQDYDLODEOHDWWKHWLPHRI
design, Table 17.6.5.2.5 provides lower-bound default values.
R17.6.5.2.5 The characteristic bond stresses in Table
17.6.5.2.5 are the minimum values permitted for adhesive
DQFKRUVVWHPVTXDOL¿HGLQDFFRUGDQFHZLWK$,IRU
the tabulated installation and use conditions. Use of these
YDOXHVLVUHVWULFWHGWRWKHFRPELQDWLRQVRIVSHFL¿FFRQGLWLRQV
listed; values for other combinations of installation and use
conditions should not be inferred. If both sustained tension
and earthquake-induced forces are required to be resisted
by the anchors, the applicable factors given in the footnotes
of Table 17.6.5.2.5 should be multiplied together. The table
assumes a concrete age of at least 21 days and a concrete
compressive strength of at least 2500 psi.
The terms “indoor” and “outdoor” as used in Table 17.6.5.2.5
UHIHUWRDVSHFL¿FVHWRILQVWDOODWLRQDQGVHUYLFHHQYLURQPHQWV
Indoor conditions represent anchors installed in dry concrete
with a rotary impact drill or rock drill and subjected to limited
concrete temperature variations over the service life of the
anchor. Outdoor conditions are assumed to occur if, at the time
of installation, the concrete is exposed to weather that might
leave the concrete wet. Anchors installed in outdoor conditions
are also assumed to be subject to greater concrete tempera-
ture variations such as might be associated with freezing and
thawing or elevated temperatures resulting from direct sun
H[SRVXUH:KLOHWKHLQGRRURXWGRRUFKDUDFWHUL]DWLRQLVXVHIXO
for many applications, there may be situations in which a literal
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258 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
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![Table 17.6.5.2.5—Minimum characteristic bond
stresses[1][2]
Installation
and service
environment
Moisture
content of
concrete at
time of anchor
installation
Peak
in-service
temperature
of concrete,
°F IJcr, psi IJuncr, psi
Outdoor
Dry to fully
saturated
175 200 650
Indoor Dry 110 300 1000
[1]
,IDQFKRUGHVLJQLQFOXGHVVXVWDLQHGWHQVLRQPXOWLSOYDOXHVRIIJcrDQGIJuncr by 0.4.
[2]
If anchor design includes earthquake-induced forces for structures assigned to SDC
'(RU)PXOWLSOYDOXHVRIIJcrEDQGIJuncr by 0.4.
interpretation of the terms “indoor” and “outdoor” do not apply.
For example, anchors installed before the building envelope
is completed may involve drilling in saturated concrete. As
such, the minimum characteristic bond stress associated with
the outdoor condition in Table 17.6.5.2.5 applies, regardless of
whether the service environment is “indoor” or “outdoor.”
Rotary impact drills and rock drills produce non-uniform
hole geometries that are generally favorable for bond. Instal-
lation of adhesive anchors in core-drilled holes may result in
substantially lower characteristic bond stresses. Because this
H൵HFWLVKLJKOSURGXFWGHSHQGHQWGHVLJQRIDQFKRUVWREH
installed in core-drilled holes should adhere to the product-
VSHFL¿F FKDUDFWHULVWLF ERQG VWUHVVHV HVWDEOLVKHG WKURXJK
testing in accordance with ACI 355.4.
7KH FKDUDFWHULVWLF ERQG VWUHVVHV DVVRFLDWHG ZLWK VSHFL¿F
adhesive anchor systems are dependent on a number of param-
eters. Consequently, care should be taken to include all param-
eters relevant to the value of characteristic bond stress used in
the design. These parameters include but are not limited to:
(a) Type and duration of loading—bond strength is
reduced for sustained tension
(b) Concrete cracking—bond strength is higher in
uncracked concrete
(c) Anchor size—bond strength is generally inversely
proportional to anchor diameter
(d) Drilling method—bond strength may be lower for
anchors installed in core-drilled holes
(e) Degree of concrete saturation at time of hole drilling
and anchor installation—bond strength may be reduced
due to concrete saturation
(f) Concrete temperature at time of installation—installa-
tion of anchors in cold conditions may result in retarded
adhesive cure and reduced bond strength
(g) Concrete age at time of installation—installation in
early-age concrete may result in reduced bond strength
(refer to R17.2.2)
(h) Peak concrete temperatures during anchor service
OLIH²XQGHU VSHFL¿F FRQGLWLRQV IRU H[DPSOH DQFKRUV LQ
thin concrete members exposed to direct sunlight), elevated
concrete temperatures can result in reduced bond strength
(i) Chemical exposure—anchors used in industrial envi-
ronments may be exposed to increased levels of contami-
nants that can reduce bond strength over time
Anchors tested and assessed underACI 355.4 may in some
FDVHVQRWEHTXDOL¿HGIRUDOORIWKHLQVWDOODWLRQDQGVHUYLFH
environments represented in Table 17.6.5.2.5. Therefore,
where the minimum values given in Table 17.6.5.2.5 are
used for design, the relevant installation and service envi-
URQPHQWVVKRXOGEHVSHFL¿HGLQDFFRUGDQFHZLWK L
M N DQG O DQGRQODQFKRUVWKDWKDYHEHHQTXDOL¿HG
under ACI 355.4 for the installation and service environ-
ments corresponding to the characteristic bond stress taken
IURP7DEOHVKRXOGEHVSHFL¿HG
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PART 4: JOINTS/CONNECTIONS/ANCHORS 259
17
Anchoring
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![ca1
V
ha
1.5ca1
1.5ca1
Avc
Avc = 2(1.5ca1)ha
If ha 1.5ca1
1.5ca1
ca1
V
1.5ca1
ca2
Avc
Avc = 1.5ca1(1.5ca1 + ca2)
If ca2 1.5ca1
ca1
V
ha
1.5ca1
1.5ca1
s1
Avc
Avc = [2(1.5ca1) + s1]ha
If ha 1.5ca1 and s1 3ca1
0.5V
0.5V
ca1,1
ca1,2
s ≥ ca1,1
ha
1.5ca1,1
1.5ca1,1
Avc
If ha 1.5ca1
Avc = 2(1.5ca1,1)ha
Case 1: One assumption of the distribution of
forces indicates that half of the shear force
would be critical on the front anchor and the
projected area. For the calculation of concrete
breakout, ca1 is taken as ca1,1.
If ha 1.5ca1
Avc = 2(1.5ca1,2)ha ca1,1
Avc
1.5ca1,2
1.5ca1,2
ca1,2
ha
s ≥ ca1,1
V
Note: For s ≥ ca1,1, both Case 1 and Case 2 should be evaluated to determine which controls for design except
as noted for anchors welded to a common plate
V
ca1,1
ha
ca1,2
s ca1,1
1.5ca1,1
1.5ca1,1
If ha 1.5ca1
Avc = 2(1.5ca1,1)ha
Case 3: Where s ca1,1, apply the entire shear
load V to the front anchor. This case does not
apply for anchors welded to a common plate.
For the calculation of concrete breakout,
ca1 is taken as ca1,1.
Case 2: Another assumption of the distribution
of forces indicates that the total shear force
would be critical on the rear anchor and its
projected area. Only this assumption needs to
be considered when anchors are welded to a
common plate independent of s. For the
calculation of concrete breakout, ca1 is taken
as ca1,2.
Avc
Fig. R17.7.2.1b—Calculation of Avc for single anchors and anchor groups.
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![17.7.2.1.3 AVco is the projected area for a single anchor in a
deep member with a distance from edges of at least 1.5ca1 in
the direction perpendicular to the shear. It shall be permitted
to calculate AVco by Eq. (17.7.2.1.3), which gives the area of
the base of a half-pyramid with a side length parallel to the
edge of 3ca1 and a depth of 1.5ca1.
AVco = 4.5(ca1)2
(17.7.2.1.3)
17.7.2.1.4 If anchors are located at varying distances from
the edge and the anchors are welded to the attachment so as
to distribute the force to all anchors, it shall be permitted to
evaluate the strength based on the distance to the farthest row
of anchors from the edge. In this case, it shall be permitted
to base the value of ca1 on the distance from the edge to the
axis of the farthest anchor row that is selected as critical, and
all of the shear shall be assumed to be resisted by this critical
anchor row alone.
17.7.2.2 Basic single anchor breakout strength, Vb
17.7.2.2.1 Basic concrete breakout strength of a single
anchor in shear in cracked concrete, Vb, shall not exceed the
lesser of (a) and (b):
(a) ( )
0.2
1.5
1
7 e
b a a c a
a
V d f c
d
⎛ ⎞
⎛ ⎞
= λ ′
⎜ ⎟
⎜ ⎟
⎜ ⎟
⎝ ⎠
⎝ ⎠
A
(17.7.2.2.1a)
where Ɛe is the load-bearing length of the anchor for shear:
Ɛe = hefIRUDQFKRUVZLWKDFRQVWDQWVWL൵QHVVRYHUWKHIXOO
length of embedded section, such as headed studs and post-
installed anchors with one tubular shell over full length of
the embedment depth;
Ɛe = 2da for torque-controlled expansion anchors with a
distance sleeve separated from expansion sleeve;
Ɛe”da in all cases.
(b) Vb Ȝa c
f ′ (ca1)1.5
(17.7.2.2.1b)
17.7.2.2.2 For cast-in headed studs, headed bolts, or
hooked bolts that are continuously welded to steel attach-
ments, basic concrete breakout strength of a single anchor
in shear in cracked concrete, Vb, shall be the lesser of Eq.
(17.7.2.2.1b) and Eq. (17.7.2.2.2) provided that (a) through
G DUHVDWLV¿HG
( )
0.2
1.5
1
8 e
b a a c a
a
V d f c
d
⎛ ⎞
⎛ ⎞
= λ ′
⎜ ⎟
⎜ ⎟
⎜ ⎟
⎝ ⎠
⎝ ⎠
A
(17.7.2.2.2)
where ƐeLVGH¿QHGLQ
(a) Steel attachment thickness is the greater of 0.5daDQGLQ
R17.7.2.2 Basic single anchor breakout strength, Vb
R17.7.2.2.1 Like the concrete breakout tensile strength,
the concrete breakout shear strength does not increase with
the failure surface, which is proportional to (ca1)2
. Instead,
the strength increases proportionally to (ca1)1.5
due to the
VL]H H൵HFW 7KH FRQVWDQW LQ WKH VKHDU VWUHQJWK HTXD-
tion (17.7.2.2.1a) was determined from test data reported
in Fuchs et al. (1995) at the 5 percent fractile adjusted for
cracking.
7KH VWUHQJWK LV DOVR LQÀXHQFHG E WKH DQFKRU VWL൵QHVV
and the anchor diameter (Fuchs et al. 1995; Eligehausen
and Balogh 1995; Eligehausen et al. 1987, 2006b; Elige-
hausen and Fuchs 1988 7KHLQÀXHQFHRIDQFKRUVWL൵QHVV
and diameter is not apparent in large-diameter anchors (Lee
et al. 2010), resulting in a limitation on the shear breakout
strength provided by Eq. (17.7.2.2.1b).
R17.7.2.2.2 For cast-in headed bolts continuously welded
to an attachment, test data (Shaikh and Yi 1985) show that
somewhat higher shear strength exists, possibly due to the
VWL൵ZHOGHGFRQQHFWLRQFODPSLQJWKHEROWPRUHH൵HFWLYHO
than an attachment with an anchor gap. Because of this, the
basic shear breakout strength for such anchors is increased,
but the upper limit of Eq. (17.7.2.2.1b) is imposed because
tests on large-diameter anchors welded to steel attach-
ments are not available to justify a higher value than Eq.
(17.7.2.2.1b). The design of supplementary reinforcement is
discussed in ¿E (2011), Eligehausen et al. (1987, 2006b), and
Eligehausen and Fuchs (1988).
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 267
17
Anchoring
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![performed in accordance with ACI 355.2 or ACI 355.4 shall
be permitted.
17.9.2 Unless determined in accordance with 17.9.3,
minimumspacingparametersshallconformtoTable17.9.2(a).
Table 17.9.2(a)—Minimum spacing and edge
distance requirements
Spacing
parameter
Anchor type
Cast-in anchors Post-installed
expansion
and undercut
anchors
Post-
installed
screw
anchors
Not torqued Torqued
Minimum
anchor
spacing
4da 6da 6da
Greater of
0.6hef and
6da
Minimum
edge distance
6SHFL¿HG
cover
requirements
for
reinforcement
according to
20.5.1.3
6da
Greatest of (a), (b), and (c):
D 6SHFL¿HGFRYHU
requirements for
reinforcement according to
20.5.1.3
(b) Twice the maximum
aggregate size
(c) Minimum edge distance
requirements according to
ACI 355.2 or 355.4, or Table
17.9.2(b) when product
information is absent
Table 17.9.2(b)—Minimum edge distance in
absence of product-specific ACI 355.2 or ACI 355.4
test information
Post-installed anchor type Minimum edge distance
Torque-controlled 8da
Displacement-controlled 10da
Screw 6da
Undercut 6da
Adhesive 6da
17.9.3 For anchors where installation does not produce
a splitting force and that will not be torqued, if the edge
distance or spacing is less than those given in 17.9.2, calcu-
lations shall be performed by substituting for da a lesser
value daƍ that meets the requirements of 17.9.2. Calculated
forces applied to the anchor shall be limited to the values
corresponding to an anchor having a diameter of daƍ.
17.9.4 Value of hef for a post-installed expansion, screw,
or undercut post-installed anchor shall not exceed the greater
be produced in subsequent torquing during connection of
attachments to anchors including cast-in anchors. The primary
source of values for minimum spacings, edge distances, and
thicknesses of post-installed anchors should be the product-
VSHFL¿FWHVWVRIACI 355.2 and ACI 355.4. In some cases,
KRZHYHUVSHFL¿FSURGXFWVDUHQRWNQRZQLQWKHGHVLJQVWDJH
Approximate values are provided for use in design.
R17.9.2 Edge cover for anchors with deep embedments
FDQKDYHDVLJQL¿FDQWH൵HFWRQWKHVLGHIDFHEORZRXWVWUHQJWK
provided in 17.6.4. It is therefore advantageous to increase
edge cover beyond that required in 20.5.1.3 to increase side-
face blowout strength.
Drilling holes for post-installed anchors can cause micro-
cracking. The requirement for edge distance to be at least
WZLFHWKHPD[LPXPDJJUHJDWHVL]HLVWRUHGXFHH൵HFWVRI
such microcracking.
R17.9.3 In some cases, it may be desirable to use a larger-
diameter anchor than the requirements of 17.9.2 permit. In
these cases, it is permissible to use a larger-diameter anchor,
provided the design strength of the anchor is based on a
smaller assumed anchor diameter daƍ.
R17.9.4 Splitting failures are caused by load transfer
between the bolt and the concrete. The limitations on the
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 4: JOINTS/CONNECTIONS/ANCHORS 271
17
Anchoring
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![of ordinary or intermediate systems for nonbuilding struc-
tures in the higher seismic design categories. These are not
the typical applications that were considered in the writing
of this chapter, but wherever the term “ordinary or inter-
mediate moment frame” is used in reference to reinforced
concrete, 18.3 or 18.4 apply.
Table R18.2 summarizes the applicability of the provi-
sions of Chapter 18 as they are typically applied when using
the minimum requirements in the various seismic design
categories. Where special systems are used for structures in
SDC B or C, it is not required to satisfy the requirements
RIDOWKRXJKLWVKRXOGEHYHUL¿HGWKDWPHPEHUVQRW
designated as part of the seismic-force-resisting system will
be stable under design displacements.
Table R18.2—Sections of Chapter 18 to be
satisfied in typical applications[1]
Component
resisting
HDUWKTXDNHH൵HFW
unless otherwise
noted
SDC
A
(None)
B
(18.2.1.3)
C
(18.2.1.4)
D, E, F
(18.2.1.5)
Analysis and design
requirements
None
18.2.2 18.2.2
18.2.2,
18.2.4
Materials None None
18.2.5
through
18.2.8
Frame members 18.3 18.4
18.6 through
18.9
Structural walls and
coupling beams
None None 18.10
Precast structural
walls
None 18.5 18.5[2]
, 18.11
Diaphragms and
trusses
None 18.12 18.12
Foundations None 18.13 18.13
Frame members not
designated as part of
the seismic-force-
resisting system
None
None
18.14
Anchors None 18.2.3 18.2.3
[1]
In addition to requirements of Chapters 1 through 17, 19 through 26, and ACI 318.2,
H[FHSWDVPRGL¿HGEKDSWHU6HFWLRQDOVRDSSOLHVLQ6''(DQG)
[2]
As permitted by the general building code.
The proportioning and detailing requirements in Chapter
DUHEDVHGSUHGRPLQDQWORQ¿HOGDQGODERUDWRUH[SH-
rience with monolithic reinforced concrete building struc-
tures and precast concrete building structures designed
and detailed to behave like monolithic building structures.
Extrapolation of these requirements to other types of cast-in-
place or precast concrete structures should be based on evidence
SURYLGHGE¿HOGH[SHULHQFHWHVWVRUDQDOVLV7KHDFFHSWDQFH
criteria for moment frames given in ACI 374.1 can be used in
conjunction with Chapter 18 to demonstrate that the strength,
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 287
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-289-320.jpg)
![axial force, consistent with the direction of the lateral forces
FRQVLGHUHGUHVXOWLQJLQWKHKLJKHVWÀH[XUDOVWUHQJWK
(b) The maximum shear obtained from design load combi-
nations that include E, with ȍoE substituted for E.
18.3.4 Beam-column joints shall satisfy Chapter 15 with
joint shear Vu calculated on a plane at mid-height of the joint
using tensile and compressive beam forces and column shear
consistent with beam nominal moment strengths Mn.
18.4—Intermediate moment frames
18.4.1 Scope
18.4.1.1 This section shall apply to intermediate moment
frames including two-way slabs without beams forming part
of the seismic-force-resisting system.
18.4.2 %HDPV
18.4.2.1 Beams shall have at least two continuous bars
at both top and bottom faces. Continuous bottom bars shall
have area not less than one-fourth the maximum area of
bottom bars along the span. These bars shall be anchored to
develop fy in tension at the face of support.
18.4.2.2 The positive moment strength at the face of the
joint shall be at least one-third the negative moment strength
provided at that face of the joint. Neither the negative nor the
positive moment strength at any section along the length of
WKHEHDPVKDOOEHOHVVWKDQRQH¿IWKWKHPD[LPXPPRPHQW
strength provided at the face of either joint.
ࢥVn shall be at least the lesser of (a) and (b):
(a) The sum of the shear associated with development of
nominal moment strengths of the beam at each restrained
end of the clear span due to reverse curvature bending and
the shear calculated for factored gravity and vertical earth-
quake loads
(b) The maximum shear obtained from design load
combinations that include E, with E taken as twice that
prescribed by the general building code
18.4.2.4At both ends of the beam, hoops shall be provided
over a length of at least 2h measured from the face of the
VXSSRUWLQJPHPEHUWRZDUGPLGVSDQ7KH¿UVWKRRSVKDOOEH
located not more than 2 in. from the face of the supporting
member. Spacing of hoops shall not exceed the smallest of
(a) through (d):
(a) d/4
(b) Eight times the diameter of the smallest longitudinal
bar enclosed
(c) 24 times the diameter of the hoop bar
R18.4—Intermediate moment frames
The objective of the requirements in 18.4.2.3 and 18.4.3.1
is to reduce the risk of failure in shear in beams and columns
during an earthquake. Two options are provided to deter-
mine the factored shear force.
R18.4.2 %HDPV
According to 18.4.2.3(a), the factored shear force is
determined from a free-body diagram obtained by cutting
through the beam ends, with end moments assumed equal
to the nominal moment strengths acting in reverse curva-
ture bending, both clockwise and counterclockwise. Figure
R18.4.2 demonstrates only one of the two options that are to
be considered for every beam. To determine the maximum
beam shear, it is assumed that its nominal moment strengths
(ࢥ for moment) are developed simultaneously at both
ends of its clear span. As indicated in Fig. R18.4.2, the shear
associated with this condition [(MQƐ + Mnr)/Ɛn] is added
algebraically to the shear due to the factored gravity loads
DQGYHUWLFDOHDUWKTXDNHH൵HFWVWRREWDLQWKHGHVLJQVKHDUIRU
the beam. For the example shown, dead load, live load, and
snow load have been assumed to be uniformly distributed.
7KH¿JXUHDOVRVKRZVWKDWYHUWLFDOHDUWKTXDNHH൵HFWVDUHWR
be included, as is typically required by the general building
code. For example,$6(6(, requires vertical earthquake
H൵HFWV0.2SDS, to be included.
Provision 18.4.2.3(b) bases Vu on the load combination
LQFOXGLQJWKHHDUWKTXDNHH൵HFWE, which should be doubled.
)RUH[DPSOHWKHORDGFRPELQDWLRQGH¿QHGE(T H
would be
U = 1.2D + 2.0E + 1.0L + 0.2S
where ELVWKHYDOXHVSHFL¿HGEWKHJHQHUDOEXLOGLQJFRGH
The factor of 1.0 applied to L is allowed to be reduced to 0.5
in accordance with 5.3.3.
Transverse reinforcement at the ends of the beam is
required to be hoops. In most cases, transverse reinforce-
ment required by 18.4.2.3 for the design shear force will be
more than those required by 18.4.2.4.
Beams may be subjected to axial compressive force due
to prestressing or applied loads. The additional requirements
American Concrete Institute – Copyrighted © Material – www.concrete.org
292 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-294-320.jpg)
![Maximum
spacing between
bars restrained by
legs of crossties
or hoops = 14 in.
Detail A
Detail C
Detail B
A
B
C
Consecutive crossties
engaging the same
longitudinal bars have
their 90-degree hooks on
opposite sides
6db ≥ 3 in.
extension
Crosstie as defined in 25.3.5
6db extension
C
A
Fig. R18.6.4²([DPSOHVRIRYHUODSSLQJKRRSVDQGLOOXVWUD-
WLRQRIOLPLWRQPD[LPXPKRUL]RQWDOVSDFLQJRIVXSSRUWHG
longitudinal bars.
R18.6.5 Shear strength
Unless a beam possesses a moment strength that is on
the order of 3 or 4 times the design moment, it should be
DVVXPHGWKDWLWZLOOLHOGLQÀH[XUHLQWKHHYHQWRIDPDMRU
earthquake. The design shear force should be selected so as
to be a good approximation of the maximum shear that may
develop in a member. Therefore, required shear strength
IRU IUDPH PHPEHUV LV UHODWHG WR ÀH[XUDO VWUHQJWKV RI WKH
designed member rather than to factored shear forces indi-
cated by lateral load analysis. The conditions described by
DUHLOOXVWUDWHGLQ)LJ57KH¿JXUHDOVRVKRZV
WKDWYHUWLFDOHDUWKTXDNHH൵HFWVDUHWREHLQFOXGHGDVLVWSL-
cally required by the general building code. For example,
$6(6(,UHTXLUHVYHUWLFDOHDUWKTXDNHH൵HFWV0.2SDS, to
be included.
Because the actual yield strength of the longitudinal
UHLQIRUFHPHQWPDH[FHHGWKHVSHFL¿HGLHOGVWUHQJWKDQG
because strain hardening of the reinforcement is likely to
(c) For Grade 60, 6db RI WKH VPDOOHVW SULPDU ÀH[XUDO
reinforcing bar excluding longitudinal skin reinforcement
required by 9.7.2.3
(d) For Grade 80, 5db RI WKH VPDOOHVW SULPDU ÀH[XUDO
reinforcing bar excluding longitudinal skin reinforcement
required by 9.7.2.3
18.6.4.5 Where hoops are required, they shall be designed
to resist shear according to 18.6.5.
18.6.4.6 Where hoops are not required, stirrups with
seismic hooks at both ends shall be spaced at a distance not
more than d/2 throughout the length of the beam.
18.6.4.7 In beams having factored axial compressive
force exceeding Ag fcƍ, hoops satisfying 18.7.5.2 through
18.7.5.4 shall be provided along lengths given in 18.6.4.1.
Along the remaining length, hoops satisfying 18.7.5.2 shall
have spacing s not exceeding the least of 6 in., 6db of the
smallest Grade 60 enclosed longitudinal beam bar, and
5db of the smallest Grade 80 enclosed longitudinal beam
bar. Where concrete cover over transverse reinforcement
exceeds 4 in., additional transverse reinforcement having
cover not exceeding 4 in. and spacing not exceeding 12 in.
shall be provided.
18.6.5 Shear strength
18.6.5.1 Design forces
The design shear force Ve shall be calculated from consid-
eration of the forces on the portion of the beam between faces
of the joints. It shall be assumed that moments of opposite
VLJQFRUUHVSRQGLQJWRSUREDEOHÀH[XUDOVWUHQJWKMpr, act at
the joint faces and that the beam is loaded with the factored
gravity and vertical earthquake loads along its span.
18.6.5.2 7UDQVYHUVHUHLQIRUFHPHQW
7UDQVYHUVH UHLQIRUFHPHQW RYHU WKH OHQJWKV LGHQWL¿HG LQ
18.6.4.1 shall be designed to resist shear assuming Vc = 0
when both (a) and (b) occur:
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 303
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-305-320.jpg)
![Table 18.8.4.3—Nominal joint shear strength Vn
Column
Beam in
direction of Vu
RQ¿QHPHQW
by transverse
beams
according to
15.2.8 Vn, lb[1]
Continuous or
meets 15.2.6
Continuous or
meets 15.2.7
RQ¿QHG 20 c j
f A
λ ′
1RWFRQ¿QHG 15 c j
f A
λ ′
Other
RQ¿QHG 15 c j
f A
λ ′
1RWFRQ¿QHG 12 c j
f A
λ ′
Other
Continuous or
meets 15.2.7
RQ¿QHG 15 c j
f A
λ ′
1RWFRQ¿QHG 12 c j
f A
λ ′
Other
RQ¿QHG 12 c j
f A
λ ′
1RWFRQ¿QHG 8 c j
f A
λ ′
[1]
ȜVKDOOEHIRUOLJKWZHLJKWFRQFUHWHDQGIRUQRUPDOZHLJKWFRQFUHWHAj shall
be calculated in accordance with 15.4.2.4.
18.8.5 'HYHORSPHQWOHQJWKRIEDUVLQWHQVLRQ
18.8.5.1 For bar sizes No. 3 through No. 11 terminating in
a standard hook, Ɛdh shall be calculated by Eq. (18.8.5.1), but
Ɛdh shall be at least the greater of 8db and 6 in. for normal-
weight concrete and at least the greater of 10dbDQGLQ
for lightweight concrete.
Ɛdh = fydb Ȝ c
f ′ ) (18.8.5.1)
The value of Ȝ shall be 0.75 for concrete containing light-
weight aggregate and 1.0 otherwise.
7KHKRRNVKDOOEHORFDWHGZLWKLQWKHFRQ¿QHGFRUHRID
column or of a boundary element, with the hook bent into
the joint.
18.8.5.2 For headed deformed bars satisfying 20.2.1.6,
development in tension shall be in accordance with 25.4.4,
by substituting a bar stress of 1.25fy for fy.
columns, when properly dimensioned and reinforced with
ORQJLWXGLQDODQGWUDQVYHUVHEDUVSURYLGHH൵HFWLYHFRQ¿QH-
ment to the joint faces, thus delaying joint strength deteriora-
tion at large deformations (Meinheit and Jirsa 1981).
R18.8.5 'HYHORSPHQWOHQJWKRIEDUVLQWHQVLRQ
R18.8.5.1 Minimum embedment length in tension for
deformed bars with standard hooks is determined using Eq.
(18.8.5.1), which is based on the requirements of 25.4.3.
The embedment length of a bar with a standard hook is the
distance, parallel to the bar, from the critical section (where
the bar is to be developed) to a tangent drawn to the outside
edge of the hook. The tangent is to be drawn perpendicular
to the axis of the bar (refer to Table 25.3.1).
Because Chapter 18 stipulates that the hook is to be
HPEHGGHG LQ FRQ¿QHG FRQFUHWH WKH FRH൶FLHQWV IRU
concrete cover) and 0.8 (for ties) have been incorporated in
the constant used in Eq. (18.8.5.1). The development length
that would be derived directly from 25.4.3 is increased to
UHÀHFWWKHH൵HFWRIORDGUHYHUVDOV)DFWRUVVXFKDVWKHDFWXDO
stress in the reinforcement being more than the yield strength
DQGWKHH൵HFWLYHGHYHORSPHQWOHQJWKQRWQHFHVVDULOVWDUWLQJ
at the face of the joint were implicitly considered in the
formulation of the expression for basic development length
that has been used as the basis for Eq. (18.8.5.1).
The requirement for the hook to project into the joint is to
improve development of a diagonal compression strut across
the joint. The requirement applies to beam and column bars
terminated at a joint with a standard hook.
R18.8.5.2 The factor 1.25 is intended to represent the poten-
tial increase in stresses due to inelastic response, including strain
hardening that may occur in beams of special moment frames.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 313
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![ACI 374.1GH¿QHVDSURWRFROIRUHVWDEOLVKLQJDGHVLJQSURFH-
dure, validated by analysis and laboratory tests, for such
frames. The design procedure should identify the load path
or mechanism by which the frame resists gravity and earth-
TXDNHH൵HFWV7KHWHVWVVKRXOGEHFRQ¿JXUHGWRLQYHVWLJDWH
critical behaviors, and the measured quantities should estab-
lish upper-bound acceptance values for components of the
load path, which may be in terms of limiting stresses, forces,
strains, or other quantities. The design procedure used for the
structure should not deviate from that used to design the test
specimens, and acceptance values should not exceed values
that were demonstrated by the tests to be acceptable. Materials
and components used in the structure should be similar to those
used in the tests. Deviations may be acceptable if the licensed
design professional can demonstrate that those deviations do
QRWDGYHUVHOD൵HFWWKHEHKDYLRURIWKHIUDPLQJVVWHP
ACI 550.3 GH¿QHV GHVLJQ UHTXLUHPHQWV IRU RQH WSH RI
special precast concrete moment frame for use in accordance
with 18.9.2.3.
R18.10—Special structural walls
R18.10.1 Scope
This section contains requirements for the dimensions
and details of special structural walls and all components
including coupling beams and wall piers. Wall piers are
GH¿QHG LQ Chapter 2. Design provisions for vertical wall
segments depend on the aspect ratio of the wall segment
in the plane of the wall (hw/Ɛw), and the aspect ratio of the
horizontal cross section (Ɛw/bw), and generally follow the
descriptions in Table R18.10.1. The limiting aspect ratios for
wall piers are based on engineering judgment. It is intended
WKDWÀH[XUDOLHOGLQJRIWKHYHUWLFDOUHLQIRUFHPHQWLQWKHSLHU
should limit shear demand on the pier.
Table R18.10.1—Governing design provisions for
vertical wall segments[1]
Clear height
of vertical wall
segment/length
of vertical wall
segment, (hw/Ɛw)
Length of vertical wall segment/wall thickness
(Ɛw/bw)
(Ɛw/bw ” 2.5 (Ɛw/bw ”
(Ɛw/bw)
6.0
hwƐw 2.0 Wall Wall Wall
hwƐw•
Wall pier
required to
VDWLVIVSHFL¿HG
column design
requirements;
refer to 18.10.8.1
Wall pier required
WRVDWLVIVSHFL¿HG
column design
requirements
or alternative
requirements; refer
to 18.10.8.1
Wall
[1]
hw is the clear height, Ɛw is the horizontal length, and bw is the width of the web of
the wall segment.
R18.10.2 5HLQIRUFHPHQW
(a) ACI 374.1
(b) Details and materials used in the test specimens shall
be representative of those used in the structure
(c) The design procedure used to proportion the test speci-
PHQV VKDOO GH¿QH WKH PHFKDQLVP E ZKLFK WKH IUDPH
UHVLVWVJUDYLWDQGHDUWKTXDNHH൵HFWVDQGVKDOOHVWDEOLVK
acceptance values for sustaining that mechanism. Portions
of the mechanism that deviate from Code requirements
shall be contained in the test specimens and shall be tested
to determine upper bounds for acceptance values.
18.10—Special structural walls
18.10.1 Scope
18.10.1.1 This section shall apply to special structural
walls, including ductile coupled walls, and all components
of special structural walls including coupling beams and
wall piers forming part of the seismic-force-resisting system.
18.10.1.2 Special structural walls constructed using
precast concrete shall be in accordance with 18.11 in addi-
tion to 18.10.
18.10.2 5HLQIRUFHPHQW
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 317
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![R18.10.3.1 Design shears for structural walls are obtained
from lateral load analysis with appropriate load factors
LQFUHDVHGWRDFFRXQWIRU L ÀH[XUDORYHUVWUHQJWKDWFULWLFDO
sections where yielding of longitudinal reinforcement is
H[SHFWHGDQG LL GQDPLFDPSOL¿FDWLRQGXHWRKLJKHUPRGH
H൵HFWVDVLOOXVWUDWHGLQ)LJ57KHDSSURDFKXVHG
WRGHWHUPLQHWKHDPSOL¿HGVKHDUIRUFHVLVVLPLODUWRWKDWXVHG
in New Zealand Standard 3101 (2006). Because Mn and Mpr
GHSHQGRQD[LDOIRUFHZKLFKYDULHVIRUGL൵HUHQWORDGFRPEL-
QDWLRQVDQGORDGLQJGLUHFWLRQIRUÀDQJHGDQGFRXSOHGZDOOV
the condition producing the largest value of ȍv should be
used. Although the value of 1.5 in 18.10.3.1.2 is greater than
the minimum value obtained for the governing load combina-
tion with a ࢥ factor of 0.9 and a tensile stress of at least 1.25fy
in the longitudinal reinforcement, a value greater than 1.5 may
be appropriate if provided longitudinal reinforcement exceeds
WKDW UHTXLUHG 'QDPLF DPSOL¿FDWLRQ LV QRW VLJQL¿FDQW LQ
walls with hw/Ɛw 2. A limit of 0.007hwcs is imposed on ns to
account for buildings with large story heights. The application
of ȍV to Vu does not preclude the application of a redundancy
factor if required by the general building code.
18.10.3.1 The design shear force Ve shall be calculated by:
Ve ȍvȦvVu”Vu (18.10.3.1)
where Vu, ȍv, and ȦvDUHGH¿QHGLQ
and 18.10.3.1.3, respectively.
18.10.3.1.1 Vu is the shear force obtained from code lateral
load analysis with factored load combinations.
ȍv shall be in accordance with Table
18.10.3.1.2.
Table 18.10.3.1.2—Overstrength factor ȍv at critical
section
Condition ȍv
hwcsƐw 1.5 Greater of
MprMu
[1]
1.5[2]
hwcsƐw” 1.0
[1]
)RUWKHORDGFRPELQDWLRQSURGXFLQJWKHODUJHVWYDOXHRIȍv.
[2]
Unless a more detailed analysis demonstrated a smaller value, but not less than 1.0.
18.10.3.1.3 For walls with hwcs/Ɛw 2.0, Ȧv shall be taken
as 1.0. Otherwise, Ȧv shall be calculated as:
0.9 6
10
1.3 1.8 6
30
s
v s
s
v s
n
n
n
n
ω = + ≤
ω = + ≤
(18.10.3.1.3)
where ns shall not be taken less than the quantity 0.007hwcs.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 321
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-323-320.jpg)
![18.10.4.6 The requirements of 21.2.4.1 shall not apply to
walls or wall piers designed according to 18.10.6.2.
18.10.5 'HVLJQIRUÀH[XUHDQGD[LDOIRUFH
18.10.5.1 Structural walls and portions of such walls
VXEMHFWWRFRPELQHGÀH[XUHDQGD[LDOORDGVVKDOOEHGHVLJQHG
in accordance with 22.4. Concrete and developed longitu-
GLQDOUHLQIRUFHPHQWZLWKLQH൵HFWLYHÀDQJHZLGWKVERXQGDU
HOHPHQWV DQG WKH ZDOO ZHE VKDOO EH FRQVLGHUHG H൵HFWLYH
7KHH൵HFWVRIRSHQLQJVVKDOOEHFRQVLGHUHG
18.10.5.2 Unless a more detailed analysis is performed,
H൵HFWLYHÀDQJHZLGWKVRIÀDQJHGVHFWLRQVVKDOOH[WHQGIURP
the face of the web a distance equal to the lesser of one-half
the distance to an adjacent wall web and 25 percent of the
total wall height above the section under consideration.
one member is imposed to limit the degree of redistribution
of shear force.
Horizontal wall segments in 18.10.4.5 refer to wall
sections between two vertically aligned openings (refer
WR)LJ5 ,WLVLQH൵HFWDYHUWLFDOZDOOVHJPHQW
rotated through 90 degrees.Ahorizontal wall segment is also
referred to as a coupling beam when the openings are aligned
vertically over the building height. When designing a hori-
]RQWDOZDOOVHJPHQWRUFRXSOLQJEHDPȡt refers to vertical
reinforcement and ȡƐ refers to horizontal reinforcement.
Horizontal
wall segment
Vertical
wall segment
Fig. R18.10.4.5—Wall with openings.
R18.10.4.6 Section 21.2.4.1 does not apply because walls
GHVLJQHGDFFRUGLQJWRDUHFRQWUROOHGEÀH[XUDO
LHOGLQJDQGFRGHOHYHOVKHDUIRUFHVKDYHEHHQDPSOL¿HG
R18.10.5 'HVLJQIRUÀH[XUHDQGD[LDOIRUFH
R18.10.5.1 Flexural strength of a wall or wall segment
is determined according to procedures commonly used for
columns. Strength should be determined considering the
applied axial and lateral forces. Reinforcement concentrated
LQERXQGDUHOHPHQWVDQGGLVWULEXWHGLQÀDQJHVDQGZHEV
should be included in the strength calculations based on a
strain compatibility analysis. The foundation supporting the
wall should be designed to resist the wall boundary and web
IRUFHV)RUZDOOVZLWKRSHQLQJVWKHLQÀXHQFHRIWKHRSHQLQJ
RURSHQLQJVRQÀH[XUDODQGVKHDUVWUHQJWKVLVWREHFRQVLG-
ered and a load path around the opening or openings should
EHYHUL¿HGDSDFLWGHVLJQFRQFHSWVDQGWKHVWUXWDQGWLH
method may be useful for this purpose (Taylor et al. 1998).
R18.10.5.2 Where wall sections intersect to form L-,
7RURWKHUFURVVVHFWLRQDOVKDSHVWKHLQÀXHQFHRIWKH
ÀDQJHRQWKHEHKDYLRURIWKHZDOOVKRXOGEHFRQVLGHUHGE
VHOHFWLQJ DSSURSULDWH ÀDQJH ZLGWKV 7HVWV Wallace 1996)
VKRZWKDWH൵HFWLYHÀDQJHZLGWKLQFUHDVHVZLWKLQFUHDVLQJ
GULIWOHYHODQGWKHH൵HFWLYHQHVVRIDÀDQJHLQFRPSUHVVLRQ
GL൵HUVIURPWKDWIRUDÀDQJHLQWHQVLRQ7KHYDOXHXVHGIRU
WKHH൵HFWLYHFRPSUHVVLRQÀDQJHZLGWKKDVOLWWOHH൵HFWRQ
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 323
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-325-320.jpg)
![Equation (18.10.6.2b) is based on the mean top-of-wall
drift capacity at 20 percent loss of lateral strength proposed
by Abdullah and Wallace (2019). The requirement that drift
capacity exceed 1.5 times the drift demand results in a low
probability of strength loss for the design earthquake. The
expression for b in (ii) is derived from Eq. (18.10.6.2b),
assuming values of Vu/(8Acv ′
c
f ) and įu/hwcs of approxi-
mately 1.0 and 0.015, respectively. If b varies over c, an
average or representative value of b should be used. For
H[DPSOHDWWKHÀDQJHGHQGRIDZDOOb should be taken equal
WRWKHH൵HFWLYHÀDQJHZLGWKGH¿QHGLQXQOHVVc
extends into the web, then a weighted average should be
used for b.$WWKHHQGRIDZDOOZLWKRXWDÀDQJHb should be
taken equal to the wall thickness. If the drift capacity does
not exceed the drift demand for a trial design, then changes
to the design are required to increase wall drift capacity,
reduces wall drift demand, or both, such that drift capacity
exceeds drift demand for each wall in a given building.
R18.10.6.3 By this procedure, the wall is considered to
be acted on by gravity loads and the maximum shear and
moment induced by earthquake in a given direction. Under
this loading, the compressed boundary at the critical section
resists the tributary gravity load plus the compressive resul-
tant associated with the bending moment.
Recognizing that this loading condition may be repeated
many times during the strong motion, the concrete is to be
FRQ¿QHGZKHUHWKHFDOFXODWHGFRPSUHVVLYHVWUHVVHVH[FHHG
a nominal critical value equal to 0.2fcƍ. The stress is to be
calculated for the factored forces on the section assuming
linear response of the gross concrete section. The compres-
sive stress of 0.2fcƍ is used as an index value and does
not necessarily describe the actual state of stress that may
GHYHORS DW WKH FULWLFDO VHFWLRQ XQGHU WKH LQÀXHQFH RI WKH
actual inertia forces for the anticipated earthquake intensity.
R18.10.6.4 The horizontal dimension of the special
boundary element is intended to extend at least over the
length where the concrete compressive strain exceeds the
FULWLFDO YDOXH )RU ÀDQJHG ZDOO VHFWLRQV LQFOXGLQJ ER[
shapes, L-shapes, and C-shapes, the calculation to deter-
mine the need for special boundary elements should include
a direction of lateral load consistent with the orthogonal
FRPELQDWLRQVGH¿QHGLQ$6(6(,. The value of c/2 in
18.10.6.4(a) is to provide a minimum length of the special
boundary element. Good detailing practice is to arrange the
ORQJLWXGLQDO UHLQIRUFHPHQW DQG WKH FRQ¿QHPHQW UHLQIRUFH-
ment such that all primary longitudinal reinforcement at the
wall boundary is supported by transverse reinforcement.
A slenderness limit is introduced into the 2014 edition
of this Code based on lateral instability failures of slender
wall boundaries observed in recent earthquakes and tests
(Wallace 2012; Wallace et al. 2012). For walls with large
cover, where spalling of cover concrete would lead to a
18.10.6.3 Structural walls not designed in accordance with
18.10.6.2 shall have special boundary elements at bound-
aries and edges around openings of structural walls where
WKH PD[LPXP H[WUHPH ¿EHU FRPSUHVVLYH VWUHVV FRUUH-
VSRQGLQJWRORDGFRPELQDWLRQVLQFOXGLQJHDUWKTXDNHH൵HFWV
E, exceeds 0.2fcƍ. The special boundary element shall be
permitted to be discontinued where the calculated compres-
sive stress is less than 0.15fcƍ. Stresses shall be calculated for
the factored loads using a linearly elastic model and gross
VHFWLRQSURSHUWLHV)RUZDOOVZLWKÀDQJHVDQH൵HFWLYHÀDQJH
width as given in 18.10.5.2 shall be used.
18.10.6.4 If special boundary elements are required by
RU D WKURXJK N VKDOOEHVDWLV¿HG
(a) The boundary element shall extend horizontally from
WKH H[WUHPH FRPSUHVVLRQ ¿EHU D GLVWDQFH DW OHDVW WKH
greater of c – 0.1Ɛw and c/2, where c is the largest neutral
axis depth calculated for the factored axial force and
nominal moment strength consistent with įu.
E :LGWKRIWKHÀH[XUDOFRPSUHVVLRQ]RQHb, over the
horizontal distance calculated by 18.10.6.4(a), including
ÀDQJHLISUHVHQWVKDOOEHDWOHDVWhu/16.
(c) For walls or wall piers with hw/Ɛw•WKDWDUHH൵HF-
tively continuous from the base of structure to top of
ZDOOGHVLJQHGWRKDYHDVLQJOHFULWLFDOVHFWLRQIRUÀH[XUH
and axial loads, and with c/Ɛw•ZLGWKRIWKHÀH[-
ural compression zone b over the length calculated in
18.10.6.4(a) shall be greater than or equal to 12 in.
G ,QÀDQJHGVHFWLRQVWKHERXQGDUHOHPHQWVKDOOLQFOXGH
WKHH൵HFWLYHÀDQJHZLGWKLQFRPSUHVVLRQDQGVKDOOH[WHQG
at least 12 in. into the web.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 325
CODE COMMENTARY
18
Seismic
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
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![≤ 6 in.
≥ dh or dt
as appropriate
bc1
be
bc2
b
≤ 6 in.
≥ d of the horizontal
web reinforcement
Option with standard hooks or headed reinforcement
(a)
Option with straight developed reinforcement
(b)
Confined
core
Horizontal web reinforcement, Av
Horizontal web
reinforcement, Av
Boundary element
reinforcement, Ash
Fig. R18.10.6.4b²'HYHORSPHQW RI ZDOO KRUL]RQWDO UHLQ-
IRUFHPHQWLQFRQ¿QHGERXQGDUHOHPHQW
American Concrete Institute – Copyrighted © Material – www.concrete.org
328 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-330-320.jpg)
![R18.10.6.5 Cyclic load reversals may lead to buck-
ling of boundary longitudinal reinforcement even in cases
where the demands on the boundary of the wall do not
require special boundary elements. For walls with moderate
amounts of boundary longitudinal reinforcement, ties are
required to inhibit buckling. The longitudinal reinforce-
ment ratio is intended to include only the reinforcement at
the wall boundary, as indicated in Fig. R18.10.6.5. A greater
spacing of ties relative to 18.10.6.4(e) is allowed due to the
lower deformation demands on the walls. Requirements of
18.10.6.5 apply over the entire wall height and are summa-
rized in Fig. R18.10.6.4c for cases where special boundary
elements are required (Moehle et al. 2011).
The addition of hooks or U-stirrups at the ends of hori-
zontal wall reinforcement provides anchorage so that the
UHLQIRUFHPHQWZLOOEHH൵HFWLYHLQUHVLVWLQJVKHDUIRUFHV,W
will also tend to inhibit the buckling of the vertical edge
reinforcement. In walls with low in-plane shear, the devel-
opment of horizontal reinforcement is not necessary.
Limits on spacing of transverse reinforcement are intended
to prevent bar buckling until reversed cyclic strains extend
well into the inelastic range. To achieve similar performance
capability, smaller spacing is required for higher-strength
longitudinal reinforcement.
h
h
x a x
14 boundary
longitudinal bars
Distributed
bars
Ab ρ =
14Ab
h(2x + a)
s
Distributed bars, Ab, at equal spacing s
ρ =
2Ab
hs
Fig. R18.10.6.5²/RQJLWXGLQDO UHLQIRUFHPHQW UDWLRV IRU
typical wall boundary conditions.
R18.10.7 RXSOLQJEHDPV
Coupling beams connecting structural walls can provide
VWL൵QHVVDQGHQHUJGLVVLSDWLRQ,QPDQFDVHVJHRPHWULF
limits result in coupling beams that are deep in relation to
their clear span. Deep coupling beams may be controlled by
VKHDUDQGPDEHVXVFHSWLEOHWRVWUHQJWKDQGVWL൵QHVVGHWH-
rioration under earthquake loading. Test results (Paulay and
Binney 1974; Barney et al. 1980 KDYHVKRZQWKDWFRQ¿QHG
diagonal reinforcement provides adequate resistance in deep
coupling beams.
18.10.6.5 Where special boundary elements are not required
ERU D DQG E VKDOOEHVDWLV¿HG
(a) Except where Vu in the plane of the wall is less than
Ȝ ′
c
f Acv, horizontal reinforcement terminating at the
edges of structural walls without boundary elements shall
have a standard hook engaging the edge reinforcement
or the edge reinforcement shall be enclosed in U-stirrups
having the same size and spacing as, and spliced to, the
horizontal reinforcement.
(b) If the maximum longitudinal reinforcement ratio at the
wall boundary exceeds 400/fy, boundary transverse rein-
forcement shall satisfy 18.7.5.2(a) through (e) over the
distance calculated in accordance with 18.10.6.4(a). The
vertical spacing of transverse reinforcement at the wall
boundary shall be in accordance with Table 18.10.6.5(b).
Table 18.10.6.5(b)—Maximum vertical spacing of
transverse reinforcement at wall boundary
Grade of
SULPDUÀH[XUDO
reinforcing bar
Transverse
reinforcement required
Maximum vertical
spacing of transverse
reinforcement[1]
60
Within the greater of Ɛw
and MuVu above and
below critical sections[2]
Lesser of:
6db
6 in.
Other locations Lesser of:
8db
8 in.
80
Within the greater of Ɛw
and MuVu above and
below critical sections[2]
Lesser of:
5db
6 in.
Other locations Lesser of:
6db
6 in.
100
Within the greater of Ɛw
and MuVu above and
below critical sections[2]
Lesser of:
4db
6 in.
Other locations Lesser of:
6db
6 in.
[1]
In this table, dbLVWKHGLDPHWHURIWKHVPDOOHVWSULPDUÀH[XUDOUHLQIRUFLQJEDU
[2]
ULWLFDOVHFWLRQVDUHGH¿QHGDVORFDWLRQVZKHUHLHOGLQJRIORQJLWXGLQDOUHLQIRUFH-
ment is likely to occur as a result of lateral displacements.
18.10.7 RXSOLQJEHDPV
18.10.7.1 Coupling beams with (Ɛn/h • shall satisfy the
requirements of 18.6, with the wall boundary interpreted as
being a column. The provisions of 18.6.2.1(b) and (c) need
QRWEHVDWLV¿HGLILWFDQEHVKRZQEDQDOVLVWKDWWKHEHDP
has adequate lateral stability.
18.10.7.2 Coupling beams with (Ɛn/h) 2 and with Vu•
Ȝ ′
c
f Acw shall be reinforced with two intersecting groups of
diagonally placed bars symmetrical about the midspan, unless it
FDQEHVKRZQWKDWORVVRIVWL൵QHVVDQGVWUHQJWKRIWKHFRXSOLQJ
American Concrete Institute – Copyrighted © Material – www.concrete.org
330 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
CODE COMMENTARY
Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1
#Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1](https://image.slidesharecdn.com/aci318-19buildingcoderequirementsforstructuralconcrete-230807163753-e1b24ffa/85/ACI-318-19-Building-Code-Requirements-for-Structural-Concrete-pdf-332-320.jpg)
![Direction of
earthquake forces
Direction of
earthquake forces
Required
horizontal
reinforcement
Edge
of wall
hw for
wall pier
w for wall pier
Wall pier
Edge
of wall
Wall pier
Required
horizontal
reinforcement
hw for
wall pier
w for wall pier
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VHJPHQWVDERYHDQGEHORZZDOOSLHUVDWWKHHGJHRIDZDOO
R18.10.9 Ductile coupled walls
The aspect ratio limits and development length require-
ments for ductile coupled walls are intended to induce an
energy dissipation mechanism associated with inelastic
GHIRUPDWLRQUHYHUVDORIFRXSOLQJEHDPV:DOOVWL൵QHVVDQG
VWUHQJWKDWHDFKHQGRIFRXSOLQJEHDPVVKRXOGEHVX൶FLHQW
to develop this intended behavior.
18.10.9 Ductile coupled walls
18.10.9.1 Ductile coupled walls shall satisfy the require-
ments of this section.
18.10.9.2 Individual walls shall satisfy hwcs/Ɛw• and the
applicable provisions of 18.10 for special structural walls.
18.10.9.3 Coupling beams shall satisfy 18.10.7 and (a)
through (c) in the direction considered.
(a) Coupling beams shall have Ɛn/h• at all levels of the
building.
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in at least 90 percent of the levels of the building.
F 7KHUHTXLUHPHQWVRIVKDOOEHVDWLV¿HGDWERWK
ends of all coupling beams.
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 335
CODE COMMENTARY
18
Seismic
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![18.12.1.3 Section 18.12.12 shall apply to structural trusses
forming part of the seismic-force-resisting system in struc-
tures assigned to SDC D, E, or F.
18.12.2 Design forces
18.12.2.1 The earthquake design forces for diaphragms
shall be obtained from the general building code using the
applicable provisions and load combinations.
18.12.3 6HLVPLFORDGSDWK
18.12.3.1 All diaphragms and their connections shall
be designed and detailed to provide for transfer of forces
to collector elements and to the vertical elements of the
seismic-force-resisting system.
18.12.3.2 Elements of a structural diaphragm system that
are subjected primarily to axial forces and used to transfer
VWL൵QHVVDQGGXFWLOLWVRWKHEXLOGLQJUHVSRQGVDVLQWHQGHG
in the design (Wyllie 1987).
R18.12.2 Design forces
R18.12.2.1 In the general building code, earthquake
GHVLJQ IRUFHV IRU ÀRRU DQG URRI GLDSKUDJPV WSLFDOO DUH
not calculated directly during the lateral-force analysis that
provides story forces and story shears. Instead, diaphragm
design forces at each level are calculated by a formula
WKDWDPSOL¿HVWKHVWRUIRUFHVUHFRJQL]LQJGQDPLFH൵HFWV
and includes minimum and maximum limits. These forces
are used with the governing load combinations to design
diaphragms for shear and moment.
For collector elements, the general building code in the
8QLWHG 6WDWHV VSHFL¿HV ORDG FRPELQDWLRQV WKDW DPSOLI
earthquake forces by a factor ȍo 7KH IRUFHV DPSOL¿HG
by ȍo are also used for the local diaphragm shear forces
resulting from the transfer of collector forces, and for local
GLDSKUDJPÀH[XUDOPRPHQWVUHVXOWLQJIURPDQHFFHQWULFLW
RI FROOHFWRU IRUFHV 7KH VSHFL¿F UHTXLUHPHQWV IRU HDUWK-
quake design forces for diaphragms and collectors depend
on which edition of the general building code is used. The
requirements may also vary according to the SDC.
For most concrete buildings subjected to inelastic earth-
quake demands, it is desirable to limit inelastic behavior of
ÀRRU DQG URRI GLDSKUDJPV XQGHU WKH LPSRVHG HDUWKTXDNH
forces and deformations. It is preferable for inelastic behavior
to occur only in the intended locations of the vertical seismic-
force-resisting system that are detailed for ductile response,
such as in beam plastic hinges of special moment frames, or
LQÀH[XUDOSODVWLFKLQJHVDWWKHEDVHRIVWUXFWXUDOZDOOVRULQ
coupling beams. For buildings without long diaphragm spans
between lateral-force-resisting elements, elastic diaphragm
EHKDYLRU LV WSLFDOO QRW GL൶FXOW WR DFKLHYH )RU EXLOGLQJV
ZKHUHGLDSKUDJPVFRXOGUHDFKWKHLUÀH[XUDORUVKHDUVWUHQJWK
before yielding occurs in the vertical seismic-force-resisting
system, the licensed design professional should consider
providing increased diaphragm strength.
For reinforced concrete diaphragms, $6(6(, Sections
12.10.1 and 12.10.2 provide requirements to determine
design forces for reinforced concrete diaphragms. For precast
concrete diaphragms in buildings assigned to SDC C, D, E, or
F, the provisions of $6(6(, Section 12.10.3 apply.
R18.12.3 6HLVPLFORDGSDWK
R18.12.3.2 This provision applies to strut-like elements
that occur around openings, diaphragm edges, or other
American Concrete Institute – Copyrighted © Material – www.concrete.org
PART 5: EARTHQUAKE RESISTANCE 337
CODE COMMENTARY
18
Seismic
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ACI 318-19 Building Code Requirements for Structural Concrete.pdf
- 1. ACI 318-19 An ACI Standard Building Code Requirements for Structural Concrete (ACI 318-19) Commentary on Building Code Requirements for Structural Concrete (ACI 318R-19) Reported by ACI Committee 318 Inch-Pound Units IN-LB
- 3. Building Code Requirements for Structural Concrete (ACI 318-19) An ACI Standard Commentary on Building Code Requirements for Structural Concrete (ACI 318R-19) Reported by ACI Committee 318 Jack P. Moehle, Chair Gregory M. Zeisler, Secretary (Non-voting) VOTING MEMBERS Neal S. Anderson Roger J. Becker John F. Bonacci Dean A. Browning JoAnn P. Browning James R. Cagley Ned M. Cleland Charles W. Dolan Catherine E. French Robert J. Frosch Luis E. Garcia Satyendra Ghosh James R. Harris Terence C. Holland James O. Jirsa Dominic J. Kelly Gary J. Klein Ronald Klemencic William M. Klorman Michael E. Kreger Colin L. Lobo Raymond Lui Paul F. Mlakar Michael C. Mota Lawrence C. Novak Carlos E. Ospina Gustavo J. Parra-Montesinos Randall W. Poston Carin L. Roberts-Wollmann Mario E. Rodriguez David H. Sanders 7KRPDV6FKDH൵HU Stephen J. Seguirant Andrew W. Taylor John W. Wallace James K. Wight Sharon L. Wood Loring A. Wyllie Jr. Fernando Yanez SUBCOMMITTEE MEMBERS Theresa M. Ahlborn F. Michael Bartlett Asit N. Baxi Abdeldjelil Belarbi Allan P. Bommer Sergio F. Brena Jared E. Brewe Nicholas J. Carino Min Yuan Cheng Ronald A. Cook David Darwin Curtis L. Decker -H൵UH-'UDJRYLFK Jason L. Draper Lisa R. Feldman Damon R. Fick David C. Fields Anthony E. Fiorato Rudolph P. Frizzi Wassim M. Ghannoum Harry A. Gleich Zen Hoda R. Brett Holland R. Doug Hooton Kenneth C. Hover I-chi Huang Matias Hube Mary Beth D. Hueste Jose M. Izquierdo-Encarnacion Maria G. Juenger Keith E. Kesner Insung Kim Donald P. Kline Jason J. Krohn Daniel A. Kuchma James M. LaFave Andres Lepage Remy D. Lequesne Ricardo R. Lopez Laura N. Lowes Frank Stephen Malits Leonardo M. Massone Steven L. McCabe Ian S. McFarlane Robert R. McGlohn Donald F. Meinheit Fred Meyer Daniel T. Mullins Clay J. Naito William H. Oliver Viral B. Patel Conrad Paulson Jose A. Pincheira Mehran Pourzanjani Santiago Pujol Jose I. Restrepo Nicolas Rodrigues Andrea J. Schokker Bahram M. Shahrooz John F. Silva Lesley H. Sneed John F. Stanton Bruce A. Suprenant Miroslav Vejvoda W. Jason Weiss Christopher D. White LIAISON MEMBERS Raul D. Bertero* Mario Alberto Chiorino Juan Francisco Correal Daza* Kenneth J. Elwood* Luis B. Fargier-Gabaldon Werner A. F. Fuchs* Patricio Garcia* Raymond Ian Gilbert Wael Mohammed Hassan Angel E. Herrera Augusto H. Holmberg* Hector Monzon-Despang Ernesto Ng Guney Ozcebe Enrique Pasquel* Guillermo Santana* Ahmed B. Shuraim Roberto Stark* Julio Timerman Roman Wan-Wendner * Liaison members serving on various subcommittees. CONSULTING MEMBERS David P. Gustafson Neil M. Hawkins Robert F. Mast Basile G. Rabbat David M. Rogowsky ACI 318-19 supersedes ACI 318-14, was adopted May 3, 2019, and published June 2019. Copyright © 2019, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc- tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.
- 4. First printing: June 2019 ISBN: 978-1-64195-056-5 DOI: 10.14359/51716937 Building Code Requirements for Structural Concrete and Commentary Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI. The technical committees responsible for ACI committee reports and standards strive to avoid ambiguities, omissions, and errors in these documents. In spite of these efforts, the users of ACI documents occasionally find information or requirements that may be subject to more than one interpretation or may be incomplete or incorrect. Users who have suggestions for the improvement of ACI documents are requested to contact ACI via the errata website at http://concrete.org/Publications/ DocumentErrata.aspx. Proper use of this document includes periodically checking for errata for the most up-to-date revisions. ACI committee documents are intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. Individuals who use this publication in any way assume all risk and accept total responsibility for the application and use of this information. All information in this publication is provided “as is” without warranty of any kind, either express or implied, including but not limited to, the implied warranties of merchantability, fitness for a particular purpose or non-infringement. ACI and its members disclaim liability for damages of any kind, including any special, indirect, incidental, or consequential damages, including without limitation, lost revenues or lost profits, which may result from the use of this publication. It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. ACI does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards. Participation by governmental representatives in the work of the American Concrete Institute and in the development of Institute standards does not constitute governmental endorsement of ACI or the standards that it develops. Order information: ACI documents are available in print, by download, through electronic subscription, or reprint, and may be obtained by contacting ACI. ACI codes, specifications, and practices are made available in the ACI Collection of Concrete Codes, Specifications, and Practices. The online subscription to the ACI Collection is always updated, and includes current and historical versions of ACI’s codes and specifications (in both inch-pound and SI units) plus new titles as they are published. The ACI Collection is also available as an eight-volume set of books and a USB drive. American Concrete Institute 38800 Country Club Drive Farmington Hills, MI 48331 Phone: +1.248.848.3700 Fax: +1.248.848.3701 www.concrete.org American Concrete Institute – Copyrighted © Material – www.concrete.org
- 5. PREFACE TO ACI 318-19 The “Building Code Requirements for Structural Concrete” (“Code”) provides minimum requirements for the materials, design, and detailing of structural concrete buildings and, where applicable, nonbuilding structures. This Code was developed by an ANSI-approved consensus process and addresses structural systems, members, and connections, including cast-in-place, precast, shotcrete, plain, nonprestressed, prestressed, and composite construction. Among the subjects covered are: design and construction for strength, serviceability, and durability; load combinations, load factors, and strength reduction factors; struc- WXUDODQDOVLVPHWKRGVGHÀHFWLRQOLPLWVPHFKDQLFDODQGDGKHVLYHDQFKRULQJWRFRQFUHWHGHYHORSPHQWDQGVSOLFLQJRIUHLQ- IRUFHPHQWFRQVWUXFWLRQGRFXPHQWLQIRUPDWLRQ¿HOGLQVSHFWLRQDQGWHVWLQJDQGPHWKRGVWRHYDOXDWHWKHVWUHQJWKRIH[LVWLQJ structures. The Code was substantially reorganized and reformatted in 2014, and this Code continues and expands that same organi- zational philosophy. The principal objectives of the reorganization were to present all design and detailing requirements for structural systems or for individual members in chapters devoted to those individual subjects, and to arrange the chapters in a manner that generally follows the process and chronology of design and construction. Information and procedures that are common to the design of multiple members are located in utility chapters. Additional enhancements implemented in this Code WRSURYLGHJUHDWHUFODULWDQGHDVHRIXVHLQFOXGHWKH¿UVWXVHRIFRORULOOXVWUDWLRQVDQGWKHXVHRIFRORUWRKHOSWKHXVHUQDYLJDWH WKHRGHDQGTXLFNO¿QGWKHLQIRUPDWLRQWKHQHHG6SHFLDOWKDQNVWR%HQWOH6VWHPV,QFRUSRUDWHGIRUXVHRIWKHLU3URRQ- FUHWHVRIWZDUHWRSURGXFHPDQRIWKH¿JXUHVIRXQGLQWKHRPPHQWDU Uses of the Code include adoption by reference in a general building code, and earlier editions have been widely used in this manner. The Code is written in a format that allows such reference without change to its language. Therefore, background details or suggestions for carrying out the requirements or intent of the Code provisions cannot be included within the Code itself. The Commentary is provided for this purpose. Some considerations of the committee in developing the Code are discussed in the Commentary, with emphasis given to the explanation of new or revised provisions. Much of the research data referenced in preparing the Code is cited for the user desiring to study individual questions in greater detail. Other documents that provide suggestions for carrying out the require- ments of the Code are also cited. Technical changes from ACI 318-14 to ACI 318-19 are outlined in the August 2019 issue of Concrete International and are marked in the text of this Code with change bars in the margins. KEYWORDS admixtures; aggregates; anchorage (structural); beam-column frame; beams (supports); caissons; cements; cold weather; columns (supports); combined stress; composite construction (concrete to concrete); compressive strength; concrete; construc- tion documents; construction joints; continuity (structural); contraction joints; cover; curing; deep beams; deep foundations; GHÀHFWLRQV GULOOHG SLHUV HDUWKTXDNHUHVLVWDQW VWUXFWXUHV ÀH[XUDO VWUHQJWK ÀRRUV IRRWLQJV IRUPZRUN FRQVWUXFWLRQ KRW weather; inspection; isolation joints; joints (junctions); joists; lightweight concretes; load tests (structural); loads (forces); mixture proportioning; modulus of elasticity; moments; piles; placing; plain concrete; precast concrete; prestressed concrete; prestressing steels; quality control; reinforced concrete; reinforcing steels; roofs; serviceability; shear strength; shotcrete; spans; splicing; strength analysis; stresses; structural analysis; structural design; structural integrity; structural walls; T-beams; torsion; walls; water; welded wire reinforcement. American Concrete Institute – Copyrighted © Material – www.concrete.org ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE 3
- 6. INTRODUCTION ACI 318-19, “Building Code Requirements for Structural Concrete,” hereinafter called the Code or the 2019 Code, and ACI 318R-19, “Commentary,” are presented in a side- by-side column format. These are two separate but coordi- nated documents, with Code text placed in the left column and the corresponding Commentary text aligned in the right column. Commentary section numbers are preceded by an “R” to further distinguish them from Code section numbers. The two documents are bound together solely for the user’s convenience. Each document carries a separate enforceable and distinct copyright. As the name implies, “Building Code Requirements for Structural Concrete” is meant to be used as part of a legally DGRSWHGEXLOGLQJFRGHDQGDVVXFKPXVWGL൵HULQIRUPDQG VXEVWDQFHIURPGRFXPHQWVWKDWSURYLGHGHWDLOHGVSHFL¿FD- tions, recommended practice, complete design procedures, or design aids. The Code is intended to cover all buildings of the usual types, both large and small. Requirements more stringent than the Code provisions may be desirable for unusual construction. The Code and Commentary cannot replace sound engineering knowledge, experience, and judgment. A building code states only the minimum requirements necessary to provide for public health and safety. The Code is based on this principle. For any structure, the owner or the licensed design professional may require the quality of materials and construction to be higher than the minimum requirements necessary to protect the public as stated in the Code. However, lower standards are not permitted. The Code has no legal status unless it is adopted by the government bodies having the police power to regulate building design and construction. Where the Code has not been adopted, it may serve as a reference to good practice even though it has no legal status. The Code and Commentary are not intended for use in settling disputes between the owner, engineer, archi- tect, contractor, or their agents, subcontractors, material suppliers, or testing agencies. Therefore, the Code cannot GH¿QHWKHFRQWUDFWUHVSRQVLELOLWRIHDFKRIWKHSDUWLHVLQ usual construction. General references requiring compliance ZLWKWKHRGHLQWKHSURMHFWVSHFL¿FDWLRQVVKRXOGEHDYRLGHG because the contractor is rarely in a position to accept responsibility for design details or construction require- ments that depend on a detailed knowledge of the design. Design-build construction contractors, however, typically combine the design and construction responsibility. Gener- ally, the contract documents should contain all of the neces- sary requirements to ensure compliance with the Code. In SDUWWKLVFDQEHDFFRPSOLVKHGEUHIHUHQFHWRVSHFL¿FRGH VHFWLRQV LQ WKH SURMHFW VSHFL¿FDWLRQV 2WKHU$, SXEOLFD- WLRQVVXFKDV³6SHFL¿FDWLRQVIRU6WUXFWXUDORQFUHWH $, ´DUHZULWWHQVSHFL¿FDOOIRUXVHDVFRQWUDFWGRFXPHQWV for construction. The Commentary discusses some of the considerations of Committee 318 in developing the provisions contained in the Code. Emphasis is given to the explanation of new or revised provisions that may be unfamiliar to Code users. In addition, comments are included for some items contained in previous editions of the Code to make the present Commentary inde- SHQGHQW RI WKH SUHYLRXV HGLWLRQV RPPHQWV RQ VSHFL¿F provisions are made under the corresponding chapter and section numbers of the Code. The Commentary is not intended to provide a complete historical background concerning the development of the Code, nor is it intended to provide a detailed résumé of the studies and research data reviewed by the committee in formulating the provisions of the Code. However, references to some of the research data are provided for those who wish to study the background material in depth. The Commentary directs attention to other documents that provide suggestions for carrying out the requirements and intent of the Code. However, those documents and the Commentary are not a part of the Code. The Commentary is intended for the use of individuals ZKR DUH FRPSHWHQW WR HYDOXDWH WKH VLJQL¿FDQFH DQG OLPL- tations of its content and recommendations, and who will accept responsibility for the application of the information it contains. ACI disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to the Commen- tary shall not be made in construction documents. If items found in the Commentary are desired by the licensed design professional to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the licensed design professional. It is recommended to have the materials, processes, quality control measures, and inspections described in this docu- ment tested, monitored, or performed by individuals holding WKHDSSURSULDWH$,HUWL¿FDWLRQRUHTXLYDOHQWZKHQDYDLO- DEOH7KHSHUVRQQHOFHUWL¿FDWLRQSURJUDPVRIWKH$PHULFDQ Concrete Institute and the Post-Tensioning Institute; the plant FHUWL¿FDWLRQ SURJUDPV RI WKH 3UHFDVW3UHVWUHVVHG RQFUHWH Institute, the Post-Tensioning Institute, and the National Ready Mixed Concrete Association; and the Concrete Rein- IRUFLQJ6WHHO,QVWLWXWH¶V9ROXQWDUHUWL¿FDWLRQ3URJUDPIRU Fusion-Bonded Epoxy Coating Applicator Plants are avail- DEOHIRUWKLVSXUSRVH,QDGGLWLRQ³6WDQGDUG6SHFL¿FDWLRQ for Agencies Engaged in Construction Inspection, Testing, RU 6SHFLDO ,QVSHFWLRQ´ $670 ( VSHFL¿HV SHUIRU- mance requirements for inspection and testing agencies. Design reference materials illustrating applications of the Code requirements are listed and described in the back of this document. American Concrete Institute – Copyrighted © Material – www.concrete.org 4 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
- 7. TABLE OF CONTENTS PART 1: GENERAL CHAPTER 1 GENERAL 1.1—Scope of ACI 318, p. 9 1.2—General, p. 9 1.3—Purpose, p. 9 1.4—Applicability, p. 10 1.5—Interpretation, p. 12 ²%XLOGLQJR൶FLDOS 1.7—Licensed design professional, p. 13 1.8—Construction documents and design records, p. 13 1.9—Testing and inspection, p. 14 1.10—Approval of special systems of design, construction, or alternative construction materials, p. 14 CHAPTER 2 NOTATION AND TERMINOLOGY 2.1—Scope, p. 15 2.2—Notation, p. 15 2.3—Terminology, p. 31 CHAPTER 3 REFERENCED STANDARDS 3.1—Scope, p. 47 3.2—Referenced standards, p. 47 CHAPTER 4 STRUCTURAL SYSTEM REQUIREMENTS 4.1—Scope, p. 51 4.2—Materials, p. 51 4.3—Design loads, p. 51 4.4—Structural system and load paths, p. 52 4.5—Structural analysis, p. 54 4.6—Strength, p. 55 4.7—Serviceability, p. 56 4.8—Durability, p. 56 4.9—Sustainability, p. 56 4.10—Structural integrity, p. 56 4.11—Fire resistance, p. 57 ² 5HTXLUHPHQWVIRUVSHFL¿FWSHVRIFRQVWUXFWLRQ p. 57 4.13—Construction and inspection, p. 59 4.14—Strength evaluation of existing structures, p. 59 PART 2: LOADS ANALYSIS CHAPTER 5 LOADS 5.1—Scope, p. 61 5.2—General, p. 61 5.3—Load factors and combinations, p. 62 CHAPTER 6 STRUCTURAL ANALYSIS 6.1—Scope, p. 67 6.2—General, p. 67 6.3—Modeling assumptions, p. 72 6.4—Arrangement of live load, p. 73 ² 6LPSOL¿HGPHWKRGRIDQDOVLVIRUQRQSUHVWUHVVHG continuous beams and one-way slabs, p. 74 ²/LQHDUHODVWLF¿UVWRUGHUDQDOVLVS 6.7—Linear elastic second-order analysis, p. 84 6.8—Inelastic analysis, p. 85 ²$FFHSWDELOLWRI¿QLWHHOHPHQWDQDOVLVS PART 3: MEMBERS CHAPTER 7 ONE-WAY SLABS 7.1—Scope, p. 89 7.2—General, p. 89 7.3—Design limits, p. 89 7.4—Required strength, p. 91 7.5—Design strength, p. 91 7.6—Reinforcement limits, p. 92 7.7—Reinforcement detailing, p. 94 CHAPTER 8 TWO-WAY SLABS 8.1—Scope, p. 99 8.2—General, p. 99 8.3—Design limits, p. 100 8.4—Required strength, p. 103 8.5—Design strength, p. 109 8.6—Reinforcement limits, p. 110 8.7—Reinforcement detailing, p. 113 8.8—Nonprestressed two-way joist systems, p. 125 American Concrete Institute – Copyrighted © Material – www.concrete.org ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE 5
- 8. CHAPTER 9 BEAMS 9.1—Scope, p. 127 9.2—General, p. 127 9.3—Design limits, p. 128 9.4—Required strength, p. 130 9.5—Design strength, p. 133 9.6—Reinforcement limits, p. 135 9.7—Reinforcement detailing, p. 139 9.8—Nonprestressed one-way joist systems, p. 150 9.9—Deep beams, p. 152 CHAPTER 10 COLUMNS 10.1—Scope, p. 155 10.2—General, p. 155 10.3—Design limits, p. 155 10.4—Required strength, p. 156 10.5—Design strength, p. 157 10.6—Reinforcement limits, p. 157 10.7—Reinforcement detailing, p. 158 CHAPTER 11 WALLS 11.1—Scope, p. 165 11.2—General, p. 165 11.3—Design limits, p. 166 11.4—Required strength, p. 166 11.5—Design strength, p. 167 11.6—Reinforcement limits, p. 170 11.7—Reinforcement detailing, p. 171 11.8—Alternative method for out-of-plane slender wall analysis, p. 172 CHAPTER 12 DIAPHRAGMS 12.1—Scope, p. 175 12.2—General, p. 176 12.3—Design limits, p. 177 12.4—Required strength, p. 178 12.5—Design strength, p. 181 12.6—Reinforcement limits, p. 188 12.7—Reinforcement detailing, p. 188 CHAPTER 13 FOUNDATIONS 13.1—Scope, p. 191 13.2—General, p. 193 13.3—Shallow foundations, p. 197 13.4—Deep foundations, p. 199 CHAPTER 14 PLAIN CONCRETE 14.1—Scope, p. 203 14.2—General, p. 204 14.3—Design limits, p. 204 14.4—Required strength, p. 206 14.5—Design strength, p. 207 14.6—Reinforcement detailing, p. 210 PART 4: JOINTS/CONNECTIONS/ANCHORS CHAPTER 15 BEAM-COLUMN AND SLAB-COLUMN JOINTS 15.1—Scope, p. 211 15.2—General, p. 211 15.3—Detailing of joints, p. 212 15.4—Strength requirements for beam-column joints, p. 213 ² 7UDQVIHURIFROXPQD[LDOIRUFHWKURXJKWKHÀRRU system, p. 214 CHAPTER 16 CONNECTIONS BETWEEN MEMBERS 16.1—Scope, p. 217 16.2—Connections of precast members, p. 217 16.3—Connections to foundations, p. 222 16.4—Horizontal shear transfer in composite concrete ÀH[XUDOPHPEHUVS 16.5—Brackets and corbels, p. 227 CHAPTER 17 ANCHORING TO CONCRETE 17.1—Scope, p. 233 17.2—General, p. 234 17.3—Design Limits, p. 235 17.4—Required strength, p. 236 17.5—Design strength, p. 236 17.6—Tensile strength, p. 246 17.7—Shear strength, p. 261 17.8—Tension and shear interaction, p. 270 17.9—Edge distances, spacings, and thicknesses to preclude splitting failure, p. 270 17.10—Earthquake-resistant anchor design requirements, p. 272 17.11—Attachments with shear lugs, p. 277 American Concrete Institute – Copyrighted © Material – www.concrete.org 6 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
- 9. PART 5: EARTHQUAKE RESISTANCE CHAPTER 18 EARTHQUAKE-RESISTANT STRUCTURES 18.1—Scope, p. 285 18.2—General, p. 285 18.3—Ordinary moment frames, p. 291 18.4—Intermediate moment frames, p. 292 18.5—Intermediate precast structural walls, p. 299 18.6—Beams of special moment frames, p. 299 18.7—Columns of special moment frames, p. 305 18.8—Joints of special moment frames, p. 311 18.9—Special moment frames constructed using precast concrete, p. 314 18.10—Special structural walls, p. 317 18.11—Special structural walls constructed using precast concrete, p. 336 18.12—Diaphragms and trusses, p. 336 18.13—Foundations, p. 343 18.14—Members not designated as part of the seismic- force-resisting system, p. 351 PART 6: MATERIALS DURABILITY CHAPTER 19 CONCRETE: DESIGN AND DURABILITY REQUIREMENTS 19.1—Scope, p. 355 19.2—Concrete design properties, p. 355 19.3—Concrete durability requirements, p. 357 19.4—Grout durability requirements, p. 369 CHAPTER 20 STEEL REINFORCEMENT PROPERTIES, DURABILITY, AND EMBEDMENTS 20.1—Scope, p. 371 20.2—Nonprestressed bars and wires, p. 371 20.3—Prestressing strands, wires, and bars, p. 378 20.4—Headed shear stud reinforcement, p. 382 20.5—Provisions for durability of steel reinforcement, p. 382 20.6—Embedments, p. 390 PART 7: STRENGTH SERVICEABILITY CHAPTER 21 STRENGTH REDUCTION FACTORS 21.1—Scope, p. 391 21.2—Strength reduction factors for structural concrete members and connections, p. 391 CHAPTER 22 SECTIONAL STRENGTH 22.1—Scope, p. 397 22.2—Design assumptions for moment and axial strength, p. 397 22.3—Flexural strength, p. 399 ² $[LDOVWUHQJWKRUFRPELQHGÀH[XUDODQGD[LDO strength, p. 400 22.5—One-way shear strength, p. 401 22.6—Two-way shear strength, p. 411 22.7—Torsional strength, p. 420 22.8—Bearing, p. 428 22.9—Shear friction, p. 430 CHAPTER 23 STRUT-AND-TIE METHOD 23.1—Scope, p. 435 23.2—General, p. 436 23.3—Design strength, p. 443 23.4—Strength of struts, p. 443 23.5—Minimum distributed reinforcement, p. 445 23.6—Strut reinforcement detailing, p. 446 23.7—Strength of ties, p. 447 23.8—Tie reinforcement detailing, p. 447 23.9—Strength of nodal zones, p. 448 23.10—Curved-bar nodes, p. 449 23.11—Earthquake-resistant design using the strut-and-tie method, p. 452 CHAPTER 24 SERVICEABILITY 24.1—Scope, p. 455 ²'HÀHFWLRQVGXHWRVHUYLFHOHYHOJUDYLWORDGVS ² 'LVWULEXWLRQRIÀH[XUDOUHLQIRUFHPHQWLQRQHZD slabs and beams, p. 460 24.4—Shrinkage and temperature reinforcement, p. 461 ² 3HUPLVVLEOHVWUHVVHVLQSUHVWUHVVHGFRQFUHWHÀH[XUDO members, p. 463 PART 8: REINFORCEMENT CHAPTER 25 REINFORCEMENT DETAILS 25.1—Scope, p. 467 25.2—Minimum spacing of reinforcement, p. 467 25.3—Standard hooks, seismic hooks, crossties, and minimum inside bend diameters, p. 469 25.4—Development of reinforcement, p. 471 25.5—Splices, p. 488 25.6—Bundled reinforcement, p. 493 25.7—Transverse reinforcement, p. 494 25.8—Post-tensioning anchorages and couplers, p. 504 25.9—Anchorage zones for post-tensioned tendons, p. 505 American Concrete Institute – Copyrighted © Material – www.concrete.org ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE 7
- 10. PART 9: CONSTRUCTION CHAPTER 26 CONSTRUCTION DOCUMENTS AND INSPECTION 26.1—Scope, p. 515 26.2—Design criteria, p. 516 26.3—Member information, p. 517 26.4—Concrete materials and mixture requirements, p. 517 26.5—Concrete production and construction, p. 528 26.6—Reinforcement materials and construction require- ments, p. 535 26.7—Anchoring to concrete, p. 540 26.8—Embedments, p. 542 26.9—Additional requirements for precast concrete, p. 543 26.10—Additional requirements for prestressed concrete, p. 544 26.11—Formwork, p. 546 26.12—Evaluation and acceptance of hardened concrete, p. 548 26.13—Inspection, p. 554 PART 10: EVALUATION CHAPTER 27 STRENGTH EVALUATION OF EXISTING STRUCTURES 27.1—Scope, p. 559 27.2—General, p. 559 27.3—Analytical strength evaluation, p. 560 27.4—Strength evaluation by load test, p. 561 27.5—Monotonic load test procedure, p. 562 27.6—Cyclic load test procedure, p. 564 APPENDICES REFERENCES APPENDIX A DESIGN VERIFICATION USING NONLINEAR RESPONSE HISTORY ANALYSIS A.1—Notation and terminology, p. 567 A.2—Scope, p. 567 A.3—General, p. 568 A.4—Earthquake ground motions, p. 568 A.5—Load factors and combinations, p. 569 A.6—Modeling and analysis, p. 569 $²$FWLRQFODVVL¿FDWLRQDQGFULWLFDOLWS $²(൵HFWLYHVWL൵QHVVS A.9—Expected material strength, p. 573 A.10—Acceptance criteria for deformation-controlled actions, p. 574 A.11—Expected strength for force-controlled actions, p. 576 A.12—Enhanced detailing requirements, p. 577 A.13—Independent structural design review, p. 578 APPENDIX B STEEL REINFORCEMENT INFORMATION APPENDIX C EQUIVALENCE BETWEEN SI-METRIC, MKS-METRIC, AND U.S. CUSTOMARY UNITS OF NONHOMOGENOUS EQUATIONS IN THE CODE COMMENTARY REFERENCES INDEX American Concrete Institute – Copyrighted © Material – www.concrete.org 8 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE
- 11. 1.1—Scope of ACI 318 1.1.1 This chapter addresses (a) through (h): (a) General requirements of this Code (b) Purpose of this Code (c) Applicability of this Code (d) Interpretation of this Code H 'H¿QLWLRQ DQG UROH RI WKH EXLOGLQJ R൶FLDO DQG WKH licensed design professional (f) Construction documents (g) Testing and inspection (h) Approval of special systems of design, construction, or alternative construction materials 1.2—General 1.2.1 ACI 318, “Building Code Requirements for Struc- tural Concrete,” is hereafter referred to as “this Code.” 1.2.2 In this Code, the general building code refers to the building code adopted in a jurisdiction. When adopted, this Code forms part of the general building code. 1.2.3 7KH R൶FLDO YHUVLRQ RI WKLV RGH LV WKH (QJOLVK language version, using inch-pound units, published by the American Concrete Institute. 1.2.4,QFDVHRIFRQÀLFWEHWZHHQWKHR൶FLDOYHUVLRQRIWKLV RGHDQGRWKHUYHUVLRQVRIWKLVRGHWKHR൶FLDOYHUVLRQ governs. 1.2.5 This Code provides minimum requirements for the materials, design, construction, and strength evaluation of structural concrete members and systems in any structure designed and constructed under the requirements of the general building code. 1.2.6 0RGL¿FDWLRQV WR WKLV RGH WKDW DUH DGRSWHG E D particular jurisdiction are part of the laws of that jurisdic- tion, but are not a part of this Code. 1.2.7 If no general building code is adopted, this Code provides minimum requirements for the materials, design, construction, and strength evaluation of members and systems in any structure within the scope of this Code. 1.3—Purpose 1.3.1 The purpose of this Code is to provide for public health and safety by establishing minimum requirements for R1.1—Scope of ACI 318 R1.1.1 This Code includes provisions for the design of concrete used for structural purposes, including plain concrete; concrete containing nonprestressed reinforce- ment, prestressed reinforcement, or both; and anchoring to concrete. This chapter includes a number of provisions that explain where this Code applies and how it is to be interpreted. R1.2—General R1.2.2 The American Concrete Institute recommends that this Code be adopted in its entirety. R1.2.3 Committee 318 develops the Code in English, using inch-pound units. Based on that version, Committee 318 approved three other versions: (a) In English using SI units (ACI 318M) (b) In Spanish using SI units (ACI 318S) (c) In Spanish using inch-pound units (ACI 318SUS). Jurisdictions may adopt ACI 318, ACI 318M, ACI 318S, or ACI 318SUS. R1.2.5 This Code provides minimum requirements and exceeding these minimum requirements is not a violation of the Code. The licensed design professional may specify project require- ments that exceed the minimum requirements of this Code. R1.3—Purpose R1.3.1 This Code provides a means of establishing minimum requirements for the design and construction of American Concrete Institute – Copyrighted © Material – www.concrete.org mittee 318 units. Bas other ver ng SI uni using SI u h using i urisdictions m or ACI s to the hen adopted, this g code. WKLV oun R this Code be ado s, published b he usin 318 ap (a) I (b) nch-p rove Eng Spa 3 C PART 1: GENERAL 9 CODE COMMENTARY 1 General CHAPTER 1—GENERAL
- 12. strength, stability, serviceability, durability, and integrity of concrete structures. 1.3.2 This Code does not address all design considerations. 1.3.3 Construction means and methods are not addressed in this Code. 1.4—Applicability 1.4.1 This Code shall apply to concrete structures designed and constructed under the requirements of the general building code. 1.4.2 Provisions of this Code shall be permitted to be used for the assessment, repair, and rehabilitation of existing structures. 1.4.3Applicable provisions of this Code shall be permitted to be used for structures not governed by the general building code. 1.4.4 The design of thin shells and folded plate concrete structures shall be in accordance with ACI 318.2, “Building Code Requirements for Concrete Thin Shells.” 1.4.5 This Code shall apply to the design of slabs cast on stay-in-place, noncomposite steel decks. structural concrete, as well as for acceptance of design and FRQVWUXFWLRQRIFRQFUHWHVWUXFWXUHVEWKHEXLOGLQJR൶FLDOV or their designated representatives. This Code does not provide a comprehensive statement of all duties of all parties to a contract or all requirements of a contract for a project constructed under this Code. R1.3.2 The minimum requirements in this Code do not replace sound professional judgment or the licensed design SURIHVVLRQDO¶VNQRZOHGJHRIWKHVSHFL¿FIDFWRUVVXUURXQGLQJ DSURMHFWLWVGHVLJQWKHSURMHFWVLWHDQGRWKHUVSHFL¿FRU unusual circumstances to the project. R1.4—Applicability R1.4.2 6SHFL¿F SURYLVLRQV IRU DVVHVVPHQW UHSDLU DQG rehabilitation of existing concrete structures are provided in ACI 562-19([LVWLQJVWUXFWXUHVLQ$,DUHGH¿QHGDV structures that are complete and permitted for use. R1.4.3 Structures such as arches, bins and silos, blast- resistant structures, chimneys, underground utility struc- tures, gravity walls, and shielding walls involve design and FRQVWUXFWLRQUHTXLUHPHQWVWKDWDUHQRWVSHFL¿FDOODGGUHVVHG by this Code. Many Code provisions, however, such as concrete quality and design principles, are applicable for these structures. Recommendations for design and construc- tion of some of these structures are given in the following: • “Code Requirements for Reinforced Concrete Chim- neys and Commentary” (ACI 307-08) • “Standard Practice for Design and Construction of Concrete Silos and Stacking Tubes for Storing Granular Materials” (ACI 313-97) • “Code Requirements for Nuclear Safety-Related Concrete Structures and Commentary” (ACI 349) • “Code for Concrete Containments” (ACI 359) R1.4.5 In its most basic application, the noncomposite steel deck serves as a form, and the concrete slab is designed to resist all loads, while in other applications the concrete slab may be designed to resist only the superimposed loads. The design of a steel deck in a load-resisting application is given in “Standard for Non-Composite Steel Floor Deck” American Concrete Institute – Copyrighted © Material – www.concrete.org existing co WLQJVWUXFW omplete a s such a es, chimn walls, and QUHTXLUHP this Code. M concrete general hall b nd re f th rne SHFL¿F SURY ode shall be perm the general bui tted ng AC structu R1. resis 2-19 es th 3 S t str 2 6 tatio VLR LR 10 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 13. 1.4.6 For one- and two-family dwellings, multiple single- family dwellings, townhouses, and accessory structures to these types of dwellings, the design and construction of cast- in-place footings, foundation walls, and slabs-on-ground in accordance with ACI 332 shall be permitted. 1.4.7 This Code does not apply to the design and installa- tion of concrete piles, drilled piers, and caissons embedded in ground, except as provided in (a) through (c): (a) For portions of deep foundation members in air or water, or in soil incapable of providing adequate lateral restraint to prevent buckling throughout their length (b) For precast concrete piles supporting structures assigned to Seismic Design Categories A and B (13.4) (c) For deep foundation elements supporting structures assigned to Seismic Design Categories C, D, E, and F (Ch. 13, 18.13) 1.4.8 This Code does not apply to design and construction of slabs-on-ground, unless the slab transmits vertical loads or lateral forces from other portions of the structure to the soil. 1.4.9 This Code does not apply to the design and construc- tion of tanks and reservoirs. 1.4.10 This Code does not apply to composite design slabs cast on stay-in-place composite steel deck. Concrete used in the construction of such slabs shall be governed by this Code, where applicable. Portions of such slabs designed as reinforced concrete are governed by this Code. (SDI NC). The SDI standard refers to this Code for the design and construction of the structural concrete slab. R1.4.6 ACI 332 addresses only the design and construc- tion of cast-in-place footings, foundation walls supported on continuous footings, and slabs-on-ground for limited resi- dential construction applications. The 2015 IBC requires design and construction of residen- tial post-tensioned slabs on expansive soils to be in accor- dance with PTI DC10.5-12, which provides requirements for slab-on-ground foundations, including soil investigation, design, and analysis. Guidance for the design and construc- tion of post-tensioned slabs-on-ground that are not on expan- sive soils can be found in ACI 360R. Refer to R1.4.8. R1.4.7 The design and installation of concrete piles fully embedded in the ground is regulated by the general building code. The 2019 edition of the Code contains some provisions that previously were only available in the general building code. In addition to the provisions in this Code, recommen- dations for concrete piles are given in ACI 543R, recom- mendations for drilled piers are given in ACI 336.3R, and recommendations for precast prestressed concrete piles are given in “Recommended Practice for Design, Manufacture, and Installation of Prestressed Concrete Piling” (PCI 1993). Requirements for the design and construction of micropiles DUHQRWVSHFL¿FDOODGGUHVVHGEWKLVRGH R1.4.8 Detailed recommendations for design and FRQVWUXFWLRQ RI VODEVRQJURXQG DQG ÀRRUV WKDW GR QRW transmit vertical loads or lateral forces from other portions of the structure to the soil are given in ACI 360R. This guide presents information on the design of slabs-on-ground, SULPDULOLQGXVWULDOÀRRUV DQGWKHVODEVDGMDFHQWWRWKHP The guide addresses the planning, design, and detailing of the slabs. Background information on the design theories is followed by discussion of the soil support system, loadings, and types of slabs. Design methods are given for structural plain concrete, reinforced concrete, shrinkage-compensating concrete, and post-tensioned concrete slabs. R1.4.9 Requirements and recommendations for the design and construction of tanks and reservoirs are given in ACI 350, ACI 334.1R, and ACI 372R. R1.4.10 In this type of construction, the steel deck serves as the positive moment reinforcement. The design and construction of concrete-steel deck slabs is described in “Standard for Composite Steel Floor Deck-Slabs” (SDI C). The standard refers to the appropriate portions of this Code for the design and construction of the concrete portion of the composite assembly. SDI C also provides guidance for design of composite-concrete-steel deck slabs. The design of negative moment reinforcement to create continuity at American Concrete Institute – Copyrighted © Material – www.concrete.org ns for preca mended Pr Prestresse e design DGGUHVVH ailed re Q RI VODE smit vertical of the st mbers in air or ding ade ughou les ate m Cat that pr code. In addition s for concrete for drilled p A and B (13.4 upporting struc es C, D, E, and F d ures Ch. give and In DUHQR n “R alla men VSHF ons mend iers er PART 1: GENERAL 11 CODE COMMENTARY 1 General
- 14. 1.5—Interpretation 1.5.1 The principles of interpretation in this section shall apply to this Code as a whole unless otherwise stated. 1.5.2 This Code consists of chapters and appendixes, LQFOXGLQJWH[WKHDGLQJVWDEOHV¿JXUHVIRRWQRWHVWRWDEOHV DQG¿JXUHVDQGUHIHUHQFHGVWDQGDUGV 1.5.3 The Commentary consists of a preface, introduction, FRPPHQWDUWH[WWDEOHV¿JXUHVDQGFLWHGSXEOLFDWLRQV7KH Commentary is intended to provide contextual informa- tion, but is not part of this Code, does not provide binding UHTXLUHPHQWVDQGVKDOOQRWEHXVHGWRFUHDWHDFRQÀLFWZLWK or ambiguity in this Code. 1.5.4 This Code shall be interpreted in a manner that DYRLGV FRQÀLFW EHWZHHQ RU DPRQJ LWV SURYLVLRQV 6SHFL¿F provisions shall govern over general provisions. 1.5.5 This Code shall be interpreted and applied in accor- dance with the plain meaning of the words and terms used. 6SHFL¿FGH¿QLWLRQVRIZRUGVDQGWHUPVLQWKLVRGHVKDOOEH used where provided and applicable, regardless of whether other materials, standards, or resources outside of this Code SURYLGHDGL൵HUHQWGH¿QLWLRQ 1.5.6 The following words and terms in this Code shall be interpreted in accordance with (a) through (e): (a) The word “shall” is always mandatory. (b) Provisions of this Code are mandatory even if the word “shall” is not used. (c) Words used in the present tense shall include the future. (d) The word “and” indicates that all of the connected items, conditions, requirements, or events shall apply. (e) The word “or” indicates that the connected items, conditions, requirements, or events are alternatives, at OHDVWRQHRIZKLFKVKDOOEHVDWLV¿HG 1.5.7 In any case in which one or more provisions of this Code are declared by a court or tribunal to be invalid, that UXOLQJVKDOOQRWD൵HFWWKHYDOLGLWRIWKHUHPDLQLQJSURYL- sions of this Code, which are severable. The ruling of a court RUWULEXQDOVKDOOEHH൵HFWLYHRQOLQWKDWFRXUW¶VMXULVGLFWLRQ DQGVKDOOQRWD൵HFWWKHFRQWHQWRULQWHUSUHWDWLRQRIWKLVRGH in other jurisdictions. 1.5.8,IFRQÀLFWVRFFXUEHWZHHQSURYLVLRQVRIWKLVRGHDQG those of standards and documents referenced in Chapter 3, this Code shall apply. supports is a common example where a portion of the slab is designed in conformance with this Code. R1.5—Interpretation R1.5.4 General provisions are broad statements, such as DEXLOGLQJQHHGVWREHVHUYLFHDEOH6SHFL¿FSURYLVLRQVVXFK as explicit reinforcement distribution requirements for crack control, govern over the general provisions. R1.5.5 ACI Concrete Terminology (2018) is the primary resource to help determine the meaning of words or terms WKDWDUHQRWGH¿QHGLQWKHRGH'LFWLRQDULHVDQGRWKHUUHIHU- ence materials commonly used by licensed design profes- sionals may be used as secondary resources. R1.5.7 This Code addresses numerous requirements that FDQ EH LPSOHPHQWHG IXOO ZLWKRXW PRGL¿FDWLRQ LI RWKHU requirements in this Code are determined to be invalid. This severability requirement is intended to preserve this Code and allow it to be implemented to the extent possible following OHJDOGHFLVLRQVD൵HFWLQJRQHRUPRUHRILWVSURYLVLRQV American Concrete Institute – Copyrighted © Material – www.concrete.org ncrete Term termine t QWKHRG mmonly u ed as seco er that YLVLRQV 6SHFL¿F rovisions rpre of QG cab our R DEXLOGLQJQHHGV licit reinforcem ern over the nd applied in a ords and terms LQWKLVRGHVKD egardless of wh outside of this - ed. OEH her de R resour ence m siona 5 A e to QRW ateri may gov gen en 12 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 15. 1.6—Building official 1.6.1$OOUHIHUHQFHVLQWKLVRGHWRWKHEXLOGLQJR൶FLDO shall be understood to mean persons who administer and enforce this Code. 1.6.2$FWLRQVDQGGHFLVLRQVEWKHEXLOGLQJR൶FLDOD൵HFW RQOWKHVSHFL¿FMXULVGLFWLRQDQGGRQRWFKDQJHWKLVRGH 1.6.3 7KH EXLOGLQJ R൶FLDO VKDOO KDYH WKH ULJKW WR RUGHU testing of any materials used in concrete construction to GHWHUPLQHLIPDWHULDOVDUHRIWKHTXDOLWVSHFL¿HG 1.7—Licensed design professional 1.7.1 All references in this Code to the licensed design professional shall be understood to mean the engineer in either 1.7.1.1 or 1.7.1.2. 1.7.1.1 The licensed design professional responsible for, and in charge of, the structural design work. 1.7.1.2$VSHFLDOWHQJLQHHUWRZKRPDVSHFL¿FSRUWLRQRI the structural design work has been delegated subject to the conditions of (a) and (b). (a) The authority of the specialty engineer shall be explic- itly limited to the delegated design work. (b) The portion of design work delegated shall be well GH¿QHG VXFK WKDW UHVSRQVLELOLWLHV DQG REOLJDWLRQV RI WKH parties are apparent. 1.8—Construction documents and design records 1.8.1 The licensed design professional shall provide in the construction documents the information required in Chapter 26 and that required by the jurisdiction. 1.8.2DOFXODWLRQVSHUWLQHQWWRGHVLJQVKDOOEH¿OHGZLWK WKHFRQVWUXFWLRQGRFXPHQWVLIUHTXLUHGEWKHEXLOGLQJR൶- cial. Analyses and designs using computer programs shall be permitted provided design assumptions, user input, and computer-generated output are submitted. Model analysis shall be permitted to supplement calculations. R1.6—Building official R1.6.1%XLOGLQJR൶FLDOLVGH¿QHGLQ2.3. R1.6.2 Only the American Concrete Institute has the authority to alter or amend this Code. R1.7—Licensed design professional R1.7.1/LFHQVHGGHVLJQSURIHVVLRQDOLVGH¿QHGLQ R1.7.1.2(b) A portion of the design work may be dele- gated to a specialty engineer during the design phase or to the contractor in the construction documents. Examples of design work delegated to a specialty engineer or contractor include precast concrete and post-tensioned concrete design. R1.8—Construction documents and design records R1.8.1 The provisions of Chapter 26 for preparing project GUDZLQJVDQGVSHFL¿FDWLRQVDUHLQJHQHUDOFRQVLVWHQWZLWK those of most general building codes. Additional informa- WLRQPDEHUHTXLUHGEWKHEXLOGLQJR൶FLDO R1.8.2 Documented computer output is acceptable instead of manual calculations. The extent of input and output LQIRUPDWLRQ UHTXLUHG ZLOO YDU DFFRUGLQJ WR WKH VSHFL¿F UHTXLUHPHQWVRILQGLYLGXDOEXLOGLQJR൶FLDOV+RZHYHULID computer program has been used, only skeleton data should QRUPDOOEHUHTXLUHG7KLVVKRXOGFRQVLVWRIVX൶FLHQWLQSXW and output data and other information to allow the building R൶FLDO WR SHUIRUP D GHWDLOHG UHYLHZ DQG PDNH FRPSDUL- sons using another program or manual calculations. Input GDWDVKRXOGEHLGHQWL¿HGDVWRPHPEHUGHVLJQDWLRQDSSOLHG loads, and span lengths. The related output data should include member designation and the shears, moments, and reactions at key points in the span. For column design, it LVGHVLUDEOHWRLQFOXGHPRPHQWPDJQL¿FDWLRQIDFWRUVLQWKH output where applicable. The Code permits model analysis to be used to supplement structural analysis and design calculations. Documentation American Concrete Institute – Copyrighted © Material – www.concrete.org ortion of ty engine in the co k delegate ude precast c PDVSHFL¿ n deleg alt des or WLHV ineer shall be ex work egated shall be G REOLJDWLRQV R lic- well KH R1. gated 1.2( o a s PART 1: GENERAL 13 CODE COMMENTARY 1 General
- 16. 1.9—Testing and inspection 1.9.1 Concrete materials shall be tested in accordance with the requirements of Chapter 26. 1.9.2 Concrete construction shall be inspected in accor- dance with the general building code and in accordance with Chapter 26. 1.9.3 Inspection records shall include information in accordance with Chapter 26. 1.10—Approval of special systems of design, construction, or alternative construction materials 1.10.1 Sponsors of any system of design, construction, or alternative construction materials within the scope of this Code, the adequacy of which has been shown by successful use or by analysis or test, but which does not conform to or is not covered by this Code, shall have the right to present the GDWDRQZKLFKWKHLUGHVLJQLVEDVHGWRWKHEXLOGLQJR൶FLDO RUWRDERDUGRIH[DPLQHUVDSSRLQWHGEWKHEXLOGLQJR൶- cial. This board shall be composed of competent engineers and shall have authority to investigate the data so submitted, require tests, and formulate rules governing design and construction of such systems to meet the intent of this Code. 7KHVH UXOHV ZKHQ DSSURYHG E WKH EXLOGLQJ R൶FLDO DQG SURPXOJDWHGVKDOOEHRIWKHVDPHIRUFHDQGH൵HFWDVWKH provisions of this Code. of the model analysis should be provided with the related calculations. Model analysis should be performed by an individual having experience in this technique. R1.10—Approval of special systems of design, construction, or alternative construction materials R1.10.1 New methods of design, new materials, and new uses of materials should undergo a period of development before being covered in a code. Hence, good systems or components might be excluded from use by implication if means were not available to obtain acceptance. )RUVSHFLDOVVWHPVFRQVLGHUHGXQGHUWKLVVHFWLRQVSHFL¿F WHVWV ORDG IDFWRUV GHÀHFWLRQ OLPLWV DQG RWKHU SHUWLQHQW requirements should be set by the board of examiners, and should be consistent with the intent of the Code. The provisions of this section do not apply to model tests used to supplement calculations under 1.8.2 or to strength evaluation of existing structures under Chapter 27. American Concrete Institute – Copyrighted © Material – www.concrete.org VWHPVFRQV V GHÀHFWL d be set b with the f this sec nt calcula xisting st of this wn by successful es not con ve the VHG SRLQ ose st ul mee K uses of before being co onents might be not availabl WKHEXLOGLQJ competent engi he data so subm overning design intent of this C - ers ted, and de. WHVWV requir The used RDG ment be co rovi sup were SHFLD e to to 14 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 17. 2.1—Scope 2.1.17KLVFKDSWHUGH¿QHVQRWDWLRQDQGWHUPLQRORJXVHG in this Code. 2.2—Notation a = depth of equivalent rectangular stress block, in. av = shear span, equal to distance from center of concen- trated load to either: (a) face of support for contin- uous or cantilevered members, or (b) center of support for simply supported members, in. Ab = area of an individual bar or wire, in.2 Abp = area of the attachment base plate in contact with concrete or grout when loaded in compression, in.2 Abrg = net bearing area of the head of stud, anchor bolt, or headed deformed bar, in.2 Ac = area of concrete section resisting shear transfer, in.2 Acf = greater gross cross-sectional area of the two orthog- onal slab-beam strips intersecting at a column of a two-way prestressed slab, in.2 Ach = cross-sectional area of a member measured to the outside edges of transverse reinforcement, in.2 Acp = area enclosed by outside perimeter of concrete cross section, in.2 Acs = cross-sectional area at one end of a strut in a strut- and-tie model, taken perpendicular to the axis of the strut, in.2 Act DUHDRIWKDWSDUWRIFURVVVHFWLRQEHWZHHQWKHÀH[- ural tension face and centroid of gross section, in.2 Acv = gross area of concrete section bounded by web thickness and length of section in the direction of shear force considered in the case of walls, and gross area of concrete section in the case of GLDSKUDJPV*URVVDUHDLVWRWDODUHDRIWKHGH¿QHG section minus area of any openings, in.2 Acw = area of concrete section of an individual pier, hori- zontal wall segment, or coupling beam resisting shear, in.2 Aef,sl H൵HFWLYHEHDULQJDUHDRIVKHDUOXJLQ2 . Af = area of reinforcement in bracket or corbel resisting design moment, in.2 Ag = gross area of concrete section, in.2 For a hollow section, Ag is the area of the concrete only and does not include the area of the void(s) Ah = total area of shear reinforcement parallel to primary tension reinforcement in a corbel or bracket, in.2 Ahs = total cross-sectional area of hooked or headed bars being developed at a critical section, in.2 Aj H൵HFWLYH FURVVVHFWLRQDO DUHD ZLWKLQ D MRLQW LQ D plane parallel to plane of beam reinforcement generating shear in the joint, in.2 AƐ = total area of longitudinal reinforcement to resist torsion, in.2 AƐPLQ = minimum area of longitudinal reinforcement to resist torsion, in.2 R2.2—Notation American Concrete Institute – Copyrighted © Material – www.concrete.org of measured to the inforcem e peri one pe VV ntr of a strut in a icular to the ax RQEHWZHHQWKH f gross section d - of H[- 2 PART 1: GENERAL 15 CODE COMMENTARY 2 Not. Term. CHAPTER 2—NOTATION AND TERMINOLOGY
- 18. An = area of reinforcement in bracket or corbel resisting factored restraint force Nuc, in.2 Anz = area of a face of a nodal zone or a section through a nodal zone, in.2 ANa SURMHFWHGLQÀXHQFHDUHDRIDVLQJOHDGKHVLYHDQFKRU or group of adhesive anchors, for calculation of bond strength in tension, in.2 ANao SURMHFWHG LQÀXHQFH DUHD RI D VLQJOH DGKHVLYH anchor, for calculation of bond strength in tension if not limited by edge distance or spacing, in.2 ANc = projected concrete failure area of a single anchor or group of anchors, for calculation of strength in tension, in.2 ANco = projected concrete failure area of a single anchor, for calculation of strength in tension if not limited by edge distance or spacing, in.2 Ao JURVVDUHDHQFORVHGEWRUVLRQDOVKHDUÀRZSDWK in.2 Aoh = area enclosed by centerline of the outermost closed transverse torsional reinforcement, in.2 Apd = total area occupied by duct, sheathing, and prestressing reinforcement, in.2 Aps = area of prestressed longitudinal tension reinforce- ment, in.2 Apt = total area of prestressing reinforcement, in.2 As = area of nonprestressed longitudinal tension rein- forcement, in.2 Asƍ DUHDRIFRPSUHVVLRQUHLQIRUFHPHQWLQ2 Asc = area of primary tension reinforcement in a corbel or bracket, in.2 Ase,N H൵HFWLYHFURVVVHFWLRQDODUHDRIDQFKRULQWHQVLRQ in.2 Ase,V H൵HFWLYH FURVVVHFWLRQDO DUHD RI DQFKRU LQ VKHDU in.2 Ash = total cross-sectional area of transverse reinforce- ment, including crossties, within spacing s and perpendicular to dimension bc, in.2 Asi = total area of surface reinforcement at spacing si in the i-th layer crossing a strut, with reinforcement at DQDQJOHĮi to the axis of the strut, in.2 AVPLQ PLQLPXPDUHDRIÀH[XUDOUHLQIRUFHPHQWLQ2 Ast = total area of nonprestressed longitudinal reinforce- ment including bars or steel shapes, and excluding prestressing reinforcement, in.2 At = area of one leg of a closed stirrup, hoop, or tie resisting torsion within spacing s, in.2 Ath WRWDOFURVVVHFWLRQDODUHDRIWLHVRUVWLUUXSVFRQ¿QLQJ hooked bars, in.2 Atp = area of prestressing reinforcement in a tie, in.2 Atr = total cross-sectional area of all transverse reinforce- ment within spacing s that crosses the potential plane of splitting through the reinforcement being developed, in.2 Ats = area of nonprestressed reinforcement in a tie, in.2 American Concrete Institute – Copyrighted © Material – www.concrete.org closed in.2 uct, she t, in.2 gitud ng d QIR orcement, in.2 tudinal tension PHQWLQ2 i ein- 16 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 19. Att = total cross-sectional area of ties or stirrups acting as parallel tie reinforcement for headed bars, in.2 Av = area of shear reinforcement within spacing s, in.2 Avd = total area of reinforcement in each group of diag- onal bars in a diagonally reinforced coupling beam, in.2 Avf = area of shear-friction reinforcement, in.2 Avh DUHD RI VKHDU UHLQIRUFHPHQW SDUDOOHO WR ÀH[XUDO tension reinforcement within spacing s2, in.2 AYPLQ = minimum area of shear reinforcement within spacing s, in.2 AVc = projected concrete failure area of a single anchor or group of anchors, for calculation of strength in shear, in.2 AVco = projected concrete failure area of a single anchor, for calculation of strength in shear, if not limited by FRUQHU LQÀXHQFHV VSDFLQJ RU PHPEHU WKLFNQHVV in.2 A1 = loaded area for consideration of bearing, strut, and node strength, in.2 A2 = area of the lower base of the largest frustum of a pyramid, cone, or tapered wedge contained wholly within the support and having its upper base equal to the loaded area. The sides of the pyramid, cone, or tapered wedge shall be sloped one vertical to two horizontal, in.2 b = width of compression face of member, in. bc = cross-sectional dimension of member core measured to the outside edges of the transverse reinforcement composing area Ash, in. bf H൵HFWLYHÀDQJHZLGWKLQ bo = perimeter of critical section for two-way shear in slabs and footings, in. bs = width of strut, in. bsl = width of shear lug, in. bslab H൵HFWLYHVODEZLGWKLQ bt = width of that part of cross section containing the closed stirrups resisting torsion, in. bv = width of cross section at contact surface being investigated for horizontal shear, in. bw = web width or diameter of circular section, in. b1 = dimension of the critical section bo measured in the direction of the span for which moments are deter- mined, in. b2 = dimension of the critical section bo measured in the direction perpendicular to b1, in. Bn = nominal bearing strength, lb Bu = factored bearing load, lb c GLVWDQFHIURPH[WUHPHFRPSUHVVLRQ¿EHUWRQHXWUDO axis, in. cac = critical edge distance required to develop the basic strength as controlled by concrete breakout or bond of a post-installed anchor in tension in uncracked concrete without supplementary reinforcement to control splitting, in. American Concrete Institute – Copyrighted © Material – www.concrete.org in ut, and largest wedg havin e sid be fac sio the pyramid, ed one vertical to member, in. of member h e, wo re PART 1: GENERAL 17 CODE COMMENTARY 2 Not. Term.
- 20. cƍa1 = limiting value of ca1 where anchors are located less than 1.5ca1 from three or more edges, in.; see Fig. R17.7.2.1.2 C = compressive force acting on a nodal zone, lb dburst = distance from the anchorage device to the centroid of the bursting force, Tburst, in. cDPD[ = maximum distance from center of an anchor shaft to the edge of concrete, in. cDPLQ = minimum distance from center of an anchor shaft to the edge of concrete, in. ca1 = distance from the center of an anchor shaft to the edge of concrete in one direction, in. If shear is applied to anchor, ca1 is taken in the direction of the applied shear. If tension is applied to the anchor, ca1 is the minimum edge distance. Where anchors subject to shear are located in narrow sections of limited thickness, see R17.7.2.1.2 ca2 = distance from center of an anchor shaft to the edge of concrete in the direction perpendicular to ca1, in. cb = lesser of: (a) the distance from center of a bar or wire to nearest concrete surface, and (b) one-half the center-to-center spacing of bars or wires being developed, in. cc = clear cover of reinforcement, in. cNa = projected distance from center of an anchor shaft on one side of the anchor required to develop the full bond strength of a single adhesive anchor, in. csl = distance from the centerline of the row of anchors in tension nearest the shear lug to the centerline of the shear lug measured in the direction of shear, in. ct = distance from the interior face of the column to the slab edge measured parallel to c1, but not exceeding c1, in. c1 = dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direc- tion of the span for which moments are being deter- mined, in. c2 = dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direc- tion perpendicular to c1, in. CP = factor relating actual moment diagram to an equiv- alent uniform moment diagram d GLVWDQFHIURPH[WUHPHFRPSUHVVLRQ¿EHUWRFHQWURLG of longitudinal tension reinforcement, in. dƍ GLVWDQFHIURPH[WUHPHFRPSUHVVLRQ¿EHUWRFHQWURLG of longitudinal compression reinforcement, in. da = outside diameter of anchor or shaft diameter of headed stud, headed bolt, or hooked bolt, in. daƍ YDOXHVXEVWLWXWHGIRUda if an oversized anchor is used, in. dagg = nominal maximum size of coarse aggregate, in. db = nominal diameter of bar, wire, or prestressing strand, in. dp GLVWDQFHIURPH[WUHPHFRPSUHVVLRQ¿EHUWRFHQWURLG of prestressed reinforcement, in. American Concrete Institute – Copyrighted © Material – www.concrete.org c s being in. enter hor r sin ter sh d in or l hesive anchor f the row of an g to the centerli direction of shea of the column t ors e of in. he 18 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 21. eanc = eccentricity of the anchorage device or group of devices with respect to the centroid of the cross section, in. dpile = diameter of pile at footing base, in. D H൵HFWRIVHUYLFHGHDGORDG Ds H൵HFWRIVXSHULPSRVHGGHDGORDG Dw H൵HFW RI VHOIZHLJKW GHDG ORDG RI WKH FRQFUHWH structural system eh = distance from the inner surface of the shaft of a J- or L-bolt to the outer tip of the J- or L-bolt, in. eƍ N = distance between resultant tension load on a group of anchors loaded in tension and the centroid of the group of anchors loaded in tension, in.; eƍ N is always positive eƍV = distance between resultant shear load on a group of anchors loaded in shear in the same direction, and the centroid of the group of anchors loaded in shear in the same direction, in.; eƍV is always positive E H൵HFWRIKRUL]RQWDODQGYHUWLFDOHDUWKTXDNHLQGXFHG forces Ec = modulus of elasticity of concrete, psi Ecb = modulus of elasticity of beam concrete, psi Ecs = modulus of elasticity of slab concrete, psi EI ÀH[XUDOVWL൵QHVVRIPHPEHULQ2 -lb (EI)Hৼ H൵HFWLYHÀH[XUDOVWL൵QHVVRIPHPEHULQ2 -lb Ep = modulus of elasticity of prestressing reinforcement, psi Es = modulus of elasticity of reinforcement and struc- tural steel, excluding prestressing reinforcement, psi fcƍ VSHFL¿HGFRPSUHVVLYHVWUHQJWKRIFRQFUHWHSVL c f ′ VTXDUH URRW RI VSHFL¿HG FRPSUHVVLYH VWUHQJWK RI concrete, psi fciƍ VSHFL¿HGFRPSUHVVLYHVWUHQJWKRIFRQFUHWHDWWLPH of initial prestress, psi ci f ′ VTXDUH URRW RI VSHFL¿HG FRPSUHVVLYH VWUHQJWK RI concrete at time of initial prestress, psi fce H൵HFWLYHFRPSUHVVLYHVWUHQJWKRIWKHFRQFUHWHLQD strut or a nodal zone, psi fd VWUHVVGXHWRXQIDFWRUHGGHDGORDGDWH[WUHPH¿EHU of section where tensile stress is caused by exter- nally applied loads, psi fdc = decompression stress; stress in the prestressed rein- forcement if stress is zero in the concrete at the same level as the centroid of the prestressed rein- forcement, psi fpc = compressive stress in concrete, after allowance for all prestress losses, at centroid of cross section resisting externally applied loads or at junction of ZHEDQGÀDQJHZKHUHWKHFHQWURLGOLHVZLWKLQWKH ÀDQJHSVL,QDFRPSRVLWHPHPEHUfpc is the resul- tant compressive stress at centroid of composite VHFWLRQRUDWMXQFWLRQRIZHEDQGÀDQJHZKHUHWKH FHQWURLGOLHVZLWKLQWKHÀDQJHGXHWRERWKSUHVWUHVV American Concrete Institute – Copyrighted © Material – www.concrete.org RI QGXFHG rete, psi eam co slab PE QHV f f r -lb PHPEHULQ2 -lb essing reinforcem orcement and s i ent, c- PART 1: GENERAL 19 CODE COMMENTARY 2 Not. Term.
- 22. and moments resisted by precast member acting alone fpe FRPSUHVVLYHVWUHVVLQFRQFUHWHGXHRQOWRH൵HFWLYH prestress forces, after allowance for all prestress ORVVHVDWH[WUHPH¿EHURIVHFWLRQLIWHQVLOHVWUHVVLV caused by externally applied loads, psi fps VWUHVVLQSUHVWUHVVHGUHLQIRUFHPHQWDWQRPLQDOÀH[- ural strength, psi fpu VSHFL¿HGWHQVLOHVWUHQJWKRISUHVWUHVVLQJUHLQIRUFH- ment, psi fpy VSHFL¿HG LHOG VWUHQJWK RI SUHVWUHVVLQJ UHLQIRUFH- ment, psi fr = modulus of rupture of concrete, psi fs = tensile stress in reinforcement at service loads, excluding prestressed reinforcement, psi fsƍ FRPSUHVVLYHVWUHVVLQUHLQIRUFHPHQWXQGHUIDFWRUHG loads, excluding prestressed reinforcement, psi fse H൵HFWLYHVWUHVVLQSUHVWUHVVHGUHLQIRUFHPHQWDIWHU allowance for all prestress losses, psi ft H[WUHPH¿EHUVWUHVVLQWKHSUHFRPSUHVVHGWHQVLRQ zone calculated at service loads using gross section properties after allowance of all prestress losses, psi futa VSHFL¿HGWHQVLOHVWUHQJWKRIDQFKRUVWHHOSVL fy VSHFL¿HG LHOG VWUHQJWK IRU QRQSUHVWUHVVHG UHLQ- forcement, psi fya VSHFL¿HGLHOGVWUHQJWKRIDQFKRUVWHHOSVL fyt VSHFL¿HG LHOG VWUHQJWK RI WUDQVYHUVH UHLQIRUFH- ment, psi F H൵HFWRIVHUYLFHORDGGXHWRÀXLGVZLWKZHOOGH¿QHG pressures and maximum heights Fnn = nominal strength at face of a nodal zone, lb Fns = nominal strength of a strut, lb Fnt = nominal strength of a tie, lb Fun = factored force on the face of a node, lb Fus = factored compressive force in a strut, lb Fut = factored tensile force in a tie, lb h = overall thickness, height, or depth of member, in. ha = thickness of member in which an anchor is located, measured parallel to anchor axis, in. hef H൵HFWLYHHPEHGPHQWGHSWKRIDQFKRULQ hef,sl = H൵HFWLYHHPEHGPHQWGHSWKRIVKHDUOXJLQ hsl = embedment depth of shear lug, in. hV[ = story height for story [, in. hu = laterally unsupported height at extreme compres- VLRQ¿EHURIZDOORUZDOOSLHULQHTXLYDOHQWWRƐu for compression members fsi = stress in the i-th layer of surface reinforcement, psi hanc = dimension of anchorage device or single group of closely spaced devices in the direction of bursting being considered, in. hƍef = limiting value of hef where anchors are located less than 1.5hef from three or more edges, in.; refer to Fig. R17.6.2.1.2 American Concrete Institute – Copyrighted © Material – www.concrete.org UHFRPSUH loads nce o JWK JWK RI fsi f f = stress FKRUVWHHOSVL QRQSUHVWUHVVHG RUVWHHOSVL HLQ- 20 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 23. hw = height of entire wall from base to top, or clear height of wall segment or wall pier considered, in. hwcs = height of entire structural wall above the critical VHFWLRQIRUÀH[XUDODQGD[LDOORDGVLQ h[ = maximum center-to-center spacing of longitudinal bars laterally supported by corners of crossties or hoop legs around the perimeter of a column or wall boundary element, in. H H൵HFWRIVHUYLFHORDGGXHWRODWHUDOHDUWKSUHVVXUH ground water pressure, or pressure of bulk mate- rials, lb I = moment of inertia of section about centroidal axis, in.4 Ib = moment of inertia of gross section of beam about centroidal axis, in.4 Icr = moment of inertia of cracked section transformed to concrete, in.4 Ie H൵HFWLYH PRPHQW RI LQHUWLD IRU FDOFXODWLRQ RI GHÀHFWLRQLQ4 Ig = moment of inertia of gross concrete section about centroidal axis, neglecting reinforcement, in.4 Is = moment of inertia of gross section of slab about centroidal axis, in.4 Ise = moment of inertia of reinforcement about centroidal axis of member cross section, in.4 k H൵HFWLYHOHQJWKIDFWRUIRUFRPSUHVVLRQPHPEHUV kc FRH൶FLHQWIRUEDVLFFRQFUHWHEUHDNRXWVWUHQJWKLQ tension kcp FRH൶FLHQWIRUSURXWVWUHQJWK kf = concrete strength factor kn FRQ¿QHPHQWH൵HFWLYHQHVVIDFWRU Ktr = transverse reinforcement index, in. Ɛ = span length of beam or one-way slab; clear projec- tion of cantilever, in. Ɛbe = length of boundary element from compression face of member, in. Ɛa = additional embedment length beyond centerline of VXSSRUWRUSRLQWRILQÀHFWLRQLQ Ɛc = length of compression member, measured center- to-center of the joints, in. Ɛcb = arc length of bar bend along centerline of bar, in. Ɛd = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in. Ɛdc = development length in compression of deformed bars and deformed wire, in. Ɛdb = debonded length of prestressed reinforcement at end of member, in. Kt WRUVLRQDO VWL൵QHVV RI PHPEHU PRPHQW SHU XQLW rotation K05 FRH൶FLHQWDVVRFLDWHGZLWKWKHSHUFHQWIUDFWLOH Ɛanc = length along which anchorage of a tie must occur, in. Ɛb = width of bearing, in. American Concrete Institute – Copyrighted © Material – www.concrete.org K te section about nforceme ss sec info sec IR RQ ent about centr in.4 PSUHVVLRQPHPE EUHDNRXWVWUHQJ al V KLQ PART 1: GENERAL 21 CODE COMMENTARY 2 Not. Term.
- 24. Ɛdh = development length in tension of deformed bar or deformed wire with a standard hook, measured from outside end of hook, point of tangency, toward critical section, in. Ɛdt = development length in tension of headed deformed bar, measured from the bearing face of the head toward the critical section, in. Ɛe = load bearing length of anchor for shear, in. ƐH[W = straight extension at the end of a standard hook, in. Ɛn = length of clear span measured face-to-face of supports, in. Ɛo = length, measured from joint face along axis of member, over which special transverse reinforce- ment must be provided, in. Ɛsc = compression lap splice length, in. Ɛst = tension lap splice length, in. Ɛt = span of member under load test, taken as the shorter span for two-way slab systems, in. Span is the lesser of: (a) distance between centers of supports, and (b) clear distance between supports plus thick- ness h of member. Span for a cantilever shall be taken as twice the distance from face of support to cantilever end Ɛtr = transfer length of prestressed reinforcement, in. Ɛu = unsupported length of column or wall, in. Ɛw = length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in. Ɛ1 = length of span in direction that moments are being determined, measured center-to-center of supports, in. Ɛ2 = length of span in direction perpendicular to Ɛ1, measured center-to-center of supports, in. L H൵HFWRIVHUYLFHOLYHORDG Lr H൵HFWRIVHUYLFHURRIOLYHORDG Ma = maximum moment in member due to service loads DWVWDJHGHÀHFWLRQLVFDOFXODWHGLQOE Mc IDFWRUHG PRPHQW DPSOL¿HG IRU WKH H൵HFWV RI member curvature used for design of compression member, in.-lb Mcr = cracking moment, in.-lb Mcre PRPHQWFDXVLQJÀH[XUDOFUDFNLQJDWVHFWLRQGXHWR externally applied loads, in.-lb MPD[ = maximum factored moment at section due to exter- nally applied loads, in.-lb Mn QRPLQDOÀH[XUDOVWUHQJWKDWVHFWLRQLQOE Mnb QRPLQDO ÀH[XUDO VWUHQJWK RI EHDP LQFOXGLQJ VODE where in tension, framing into joint, in.-lb Mnc QRPLQDOÀH[XUDOVWUHQJWKRIFROXPQIUDPLQJLQWR joint, calculated for factored axial force, consis- tent with the direction of lateral forces considered, UHVXOWLQJLQORZHVWÀH[XUDOVWUHQJWKLQOE Mpr SUREDEOH ÀH[XUDO VWUHQJWK RI PHPEHUV ZLWK RU without axial load, determined using the proper- ties of the member at joint faces assuming a tensile M = moment acting on anchor or anchor group, in.-lb American Concrete Institute – Copyrighted © Material – www.concrete.org pports, ports plus thick- a cantile e from res co or d on t inforcement, in or wall, in. h of wall segme on of shear forc moments are b t or in. ng 22 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 25. stress in the longitudinal bars of at least 1.25fy and DVWUHQJWKUHGXFWLRQIDFWRUࢥRILQOE Msa = maximum moment in wall due to service loads, excluding P¨H൵HFWVLQOE Msc = factored slab moment that is resisted by the column at a joint, in.-lb Mu = factored moment at section, in.-lb Mua = moment at midheight of wall due to factored lateral and eccentric vertical loads, not including P¨ H൵HFWVLQOE M1 = lesser factored end moment on a compression member, in.-lb M1ns = factored end moment on a compression member at the end at which M1 acts, due to loads that cause no DSSUHFLDEOHVLGHVZDFDOFXODWHGXVLQJD¿UVWRUGHU elastic frame analysis, in.-lb M1s = factored end moment on compression member at the end at which M1 acts, due to loads that cause DSSUHFLDEOHVLGHVZDFDOFXODWHGXVLQJD¿UVWRUGHU elastic frame analysis, in.-lb M2 = greater factored end moment on a compression member. If transverse loading occurs between supports, M2 is taken as the largest moment occur- ring in member. Value of M2 is always positive, in.-lb M2,PLQ = minimum value of M2, in.-lb M2ns = factored end moment on compression member at the end at which M2 acts, due to loads that cause no DSSUHFLDEOHVLGHVZDFDOFXODWHGXVLQJD¿UVWRUGHU elastic frame analysis, in.-lb M2s = factored end moment on compression member at the end at which M2 acts, due to loads that cause DSSUHFLDEOHVLGHVZDFDOFXODWHGXVLQJD¿UVWRUGHU elastic frame analysis, in.-lb n = number of items, such as, bars, wires, monostrand anchorage devices, or anchors nƐ = number of longitudinal bars around the perimeter of a column core with rectilinear hoops that are later- ally supported by the corner of hoops or by seismic hooks. A bundle of bars is counted as a single bar ns = number of stories above the critical section Na = nominal bond strength in tension of a single adhe- sive anchor, lb Nag = nominal bond strength in tension of a group of adhesive anchors, lb Nb = basic concrete breakout strength in tension of a single anchor in cracked concrete, lb Nba = basic bond strength in tension of a single adhesive anchor, lb Nc = resultant tensile force acting on the portion of the concrete cross section that is subjected to tensile VWUHVVHV GXH WR WKH FRPELQHG H൵HFWV RI VHUYLFH ORDGVDQGH൵HFWLYHSUHVWUHVVOE nt = number of threads per inch N = tension force acting on anchor or anchor group, lb American Concrete Institute – Copyrighted © Material – www.concrete.org se W RUGHU nt on a oading the e o , i on , d is always pos mpression memb o loads that cau e, r at no PART 1: GENERAL 23 CODE COMMENTARY 2 Not. Term.
- 26. Ncb = nominal concrete breakout strength in tension of a single anchor, lb Ncbg = nominal concrete breakout strength in tension of a group of anchors, lb Ncp = basic concrete pryout strength of a single anchor, lb Ncpg = basic concrete pryout strength of a group of anchors, lb Nn = nominal strength in tension, lb Np = pullout strength in tension of a single anchor in cracked concrete, lb Npn = nominal pullout strength in tension of a single anchor, lb Nsa = nominal strength of a single anchor or individual anchor in a group of anchors in tension as governed by the steel strength, lb Nsb = side-face blowout strength of a single anchor, lb Nsbg = side-face blowout strength of a group of anchors, lb Nu = factored axial force normal to cross section occur- ring simultaneously with Vu or Tu; to be taken as positive for compression and negative for tension, lb Nua = factored tensile force applied to anchor or indi- vidual anchor in a group of anchors, lb Nua,g = total factored tensile force applied to anchor group, lb Nua,i = factored tensile force applied to most highly stressed anchor in a group of anchors, lb Nua,s = factored sustained tension load, lb Nuc = factored restraint force applied to a bearing connec- tion acting perpendicular to and simultaneously with Vu, to be taken as positive for tension, lb NXFPD[= maximum restraint force that can be transmitted through the load path of a bearing connection multiplied by the load factor used for live loads in FRPELQDWLRQVZLWKRWKHUIDFWRUHGORDGH൵HFWV pcp = outside perimeter of concrete cross section, in. ph = perimeter of centerline of outermost closed trans- verse torsional reinforcement, in. Pa = maximum allowable compressive strength of a deep foundation member, lb Pc = critical buckling load, lb Pn = nominal axial compressive strength of member, lb PQPD[ = maximum nominal axial compressive strength of a member, lb Pnt = nominal axial tensile strength of member, lb PQWPD[= maximum nominal axial tensile strength of member, lb Po = nominal axial strength at zero eccentricity, lb Ppu = factored prestressing force at anchorage device, lb Ps = unfactored axial load at the design, midheight VHFWLRQLQFOXGLQJH൵HFWVRIVHOIZHLJKWOE Pu = factored axial force; to be taken as positive for compression and negative for tension, lb Pį VHFRQGDUPRPHQWGXHWRLQGLYLGXDOPHPEHUVOHQ- derness, in.-lb American Concrete Institute – Copyrighted © Material – www.concrete.org ed ken as tive for tension, plied p of a rce e ou on l ed to anchor g ed to most h anchors, lb lb b p, ghly 24 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 27. P¨ VHFRQGDUPRPHQWGXHWRODWHUDOGHÀHFWLRQLQOE qu IDFWRUHGORDGSHUXQLWDUHDOEIW2 Q = stability index for a story r = radius of gyration of cross section, in. rb = bend radius at the inside of a bar, in. R FXPXODWLYHORDGH൵HFWRIVHUYLFHUDLQORDG s = center-to-center spacing of items, such as longi- tudinal reinforcement, transverse reinforcement, tendons, or anchors, in. si = center-to-center spacing of reinforcement in the i-th direction adjacent to the surface of the member, in. so = center-to-center spacing of transverse reinforce- ment within the length Ɛo, in. ss = sample standard deviation, psi sw = clear distance between adjacent webs, in. s2 = center-to-center spacing of longitudinal shear or torsional reinforcement, in. S H൵HFWRIVHUYLFHVQRZORDG SDS = 5 percent damped, spectral response acceleration parameter at short periods determined in accor- dance with the general building code Se = moment, shear, or axial force at connection corre- sponding to development of probable strength at intended yield locations, based on the governing mechanism of inelastic lateral deformation, consid- HULQJERWKJUDYLWDQGHDUWKTXDNHH൵HFWV SP = elastic section modulus, in.3 Sn = nominal moment, shear, axial, torsion, or bearing strength Sy = yield strength of connection, based on fy of the connected part, for moment, shear, torsion, or axial force, psi t = wall thickness of hollow section, in. tf WKLFNQHVVRIÀDQJHLQ tsl = thickness of shear lug, in. T FXPXODWLYH H൵HFWV RI VHUYLFH WHPSHUDWXUH FUHHS VKULQNDJH GL൵HUHQWLDO VHWWOHPHQW DQG VKULQNDJH compensating concrete Tcr = cracking torsional moment, in.-lb Tt = total test load, lb Tth = threshold torsional moment, in.-lb Tn = nominal torsional moment strength, in.-lb Tu = factored torsional moment at section, in.-lb U = strength of a member or cross section required to resist factored loads or related internal moments and forces in such combinations as stipulated in this Code vc = stress corresponding to nominal two-way shear strength provided by concrete, psi R = reaction, lb T = tension force acting on a nodal zone in a strut-and- tie model, lb (TLVDOVRXVHGWRGH¿QHWKHFXPXOD- WLYHH൵HFWVRIVHUYLFHWHPSHUDWXUHFUHHSVKULQNDJH GL൵HUHQWLDOVHWWOHPHQWDQGVKULQNDJHFRPSHQVDWLQJ FRQFUHWHLQWKHORDGFRPELQDWLRQVGH¿QHGLQ Tburst = tensile force in general zone acting ahead of the anchorage device caused by spreading of the anchorage force, lb American Concrete Institute – Copyrighted © Material – www.concrete.org eration mined in accor- ng code orce a nt o ns, c la H s, , a d on the gove deformation, co XDNH torsion, or be ng sid- ng PART 1: GENERAL 25 CODE COMMENTARY 2 Not. Term.
- 28. vn = equivalent concrete stress corresponding to nominal two-way shear strength of slab or footing, psi vs = equivalent concrete stress corresponding to nominal two-way shear strength provided by reinforcement, psi vu = maximum factored two-way shear stress calculated around the perimeter of a given critical section, psi vuv = factored shear stress on the slab critical section for two-way action, from the controlling load combi- nation, without moment transfer, psi Vb = basic concrete breakout strength in shear of a single anchor in cracked concrete, lb Vbrg,sl = nominal bearing strength of a shear lug in direction of shear, lb Vc = nominal shear strength provided by concrete, lb Vcb = nominal concrete breakout strength in shear of a single anchor, lb Vcbg = nominal concrete breakout strength in shear of a group of anchors, lb Vcb,sl = nominal concrete breakout strength in shear of attachment with shear lugs, lb Vci = nominal shear strength provided by concrete where diagonal cracking results from combined shear and moment, lb Vcp = nominal concrete pryout strength of a single anchor, lb Vcpg = nominal concrete pryout strength of a group of anchors, lb Vcw = nominal shear strength provided by concrete where diagonal cracking results from high principal tensile stress in web, lb Vd = shear force at section due to unfactored dead load, lb Ve = design shear force for load combinations including HDUWKTXDNHH൵HFWVOE Vi = factored shear force at section due to externally applied loads occurring simultaneously with MPD[, lb Vn = nominal shear strength, lb Vnh = nominal horizontal shear strength, lb Vp YHUWLFDO FRPSRQHQW RI H൵HFWLYH SUHVWUHVV IRUFH DW section, lb Vs = nominal shear strength provided by shear reinforce- ment, lb Vsa = nominal shear strength of a single anchor or indi- vidual anchor in a group of anchors as governed by the steel strength, lb Vu = factored shear force at section, lb Vua = factored shear force applied to a single anchor or group of anchors, lb V = shear force acting on anchor or anchor group, lb V|| = maximum shear force that can be applied parallel to the edge, lb Vŏ = maximum shear force that can be applied perpen- dicular to the edge, lb American Concrete Institute – Copyrighted © Material – www.concrete.org of y concrete, lb trength in kout eak lu pr s f strength in she ed by concrete w combined shea of here nd 26 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 29. Vua,g = total factored shear force applied to anchor group, lb Vua,i = factored shear force applied to most highly stressed anchor in a group of anchors, lb Vuh = factored shear force along contact surface in FRPSRVLWHFRQFUHWHÀH[XUDOPHPEHUOE Vus = factored horizontal shear in a story, lb VX[ = factored shear force at section in the x-direction, lb Vu,y = factored shear force at section in the y-direction, lb VQ[ = shear strength in the x-direction Vn,y = shear strength in the y-direction wc = density, unit weight, of normalweight concrete or HTXLOLEULXPGHQVLWRIOLJKWZHLJKWFRQFUHWHOEIW3 wt H൵HFWLYHWLHZLGWKLQDVWUXWDQGWLHPRGHOLQ wu = factored load per unit length of beam or one-way VODEOELQ wFP = water-cementitious materials ratio W H൵HFWRIZLQGORDG yt = distance from centroidal axis of gross section, neglecting reinforcement, to tension face, in. Į DQJOHGH¿QLQJWKHRULHQWDWLRQRIUHLQIRUFHPHQW Įc FRH൶FLHQW GH¿QLQJ WKH UHODWLYH FRQWULEXWLRQ RI concrete strength to nominal wall shear strength Įf UDWLRRIÀH[XUDOVWL൵QHVVRIEHDPVHFWLRQWRÀH[- XUDOVWL൵QHVVRIDZLGWKRIVODEERXQGHGODWHUDOOE centerlines of adjacent panels, if any, on each side of the beam ĮIP DYHUDJHYDOXHRIĮf for all beams on edges of a panel Įs = constant used to calculate Vc in slabs and footings Į1 = minimum angle between unidirectional distributed reinforcement and a strut ȕ UDWLRRIORQJWRVKRUWGLPHQVLRQVFOHDUVSDQVIRU two-way slabs, sides of column, concentrated load or reaction area; or sides of a footing ȕb UDWLRRIDUHDRIUHLQIRUFHPHQWFXWR൵WRWRWDODUHDRI tension reinforcement at section ȕc FRQ¿QHPHQW PRGL¿FDWLRQ IDFWRU IRU VWUXWV DQG nodes in a strut-and-tie model ȕdns UDWLRXVHGWRDFFRXQWIRUUHGXFWLRQRIVWL൵QHVVRI columns due to sustained axial loads ȕds = the ratio of maximum factored sustained shear within a story to the maximum factored shear in that story associated with the same load combination ȕn IDFWRUXVHGWRDFFRXQWIRUWKHH൵HFWRIWKHDQFKRUDJH RIWLHVRQWKHH൵HFWLYHFRPSUHVVLYHVWUHQJWKRID nodal zone ȕs IDFWRUXVHGWRDFFRXQWIRUWKHH൵HFWRIFUDFNLQJDQG FRQ¿QLQJUHLQIRUFHPHQWRQWKHH൵HFWLYHFRPSUHV- sive strength of the concrete in a strut ws = width of a strut perpendicular to the axis of the strut, in. wt H൵HFWLYHKHLJKWRIFRQFUHWHFRQFHQWULFZLWKDWLH used to dimension nodal zone, in. wWPD[ PD[LPXP H൵HFWLYH KHLJKW RI FRQFUHWH FRQFHQWULF with a tie, in. Wa = service-level wind load, lb Įf = EcbIbEcsIs American Concrete Institute – Copyrighted © Material – www.concrete.org evel wind de bIb I I E cs E I s s s I I eam or one-way als rat ida en QWD H is of gross sec ension face, in. RIUHLQIRUFHPHQ YH FRQWULEXWLR h on, RI Wa W W ser PART 1: GENERAL 27 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 30. ȕ1 = factor relating depth of equivalent rectangular compressive stress block to depth of neutral axis Ȗf = factor used to determine the fraction of Msc trans- IHUUHGEVODEÀH[XUHDWVODEFROXPQFRQQHFWLRQV Ȗp = factor used for type of prestressing reinforcement Ȗs = factor used to determine the portion of reinforce- ment located in center band of footing Ȗv = factor used to determine the fraction of Msc trans- ferred by eccentricity of shear at slab-column connections į PRPHQWPDJQL¿FDWLRQIDFWRUXVHGWRUHÀHFWH൵HFWV of member curvature between ends of a compres- sion member įc = wall displacement capacity at top of wall, in. įs PRPHQWPDJQL¿FDWLRQIDFWRUXVHGIRUIUDPHVQRW EUDFHG DJDLQVW VLGHVZD WR UHÀHFW ODWHUDO GULIW resulting from lateral and gravity loads įu = design displacement, in. ¨cr FDOFXODWHGRXWRISODQHGHÀHFWLRQDWPLGKHLJKWRI wall corresponding to cracking moment Mcr, in. ¨n FDOFXODWHGRXWRISODQHGHÀHFWLRQDWPLGKHLJKWRI ZDOOFRUUHVSRQGLQJWRQRPLQDOÀH[XUDOVWUHQJWKMn, in. ¨o UHODWLYH ODWHUDO GHÀHFWLRQ EHWZHHQ WKH WRS DQG bottom of a story due to Vus, in. ¨fp = increase in stress in prestressed reinforcement due to factored loads, psi ¨fps = stress in prestressed reinforcement at service loads less decompression stress, psi ¨r UHVLGXDOGHÀHFWLRQPHDVXUHGKRXUVDIWHUUHPRYDO RI WKH WHVW ORDG )RU WKH ¿UVW ORDG WHVW UHVLGXDO GHÀHFWLRQLVPHDVXUHGUHODWLYHWRWKHSRVLWLRQRIWKH VWUXFWXUHDWWKHEHJLQQLQJRIWKH¿UVWORDGWHVW)RU WKHVHFRQGORDGWHVWUHVLGXDOGHÀHFWLRQLVPHDVXUHG relative to the position of the structure at the begin- ning of the second load test, in. ¨s RXWRISODQHGHÀHFWLRQGXHWRVHUYLFHORDGVLQ ¨u FDOFXODWHGRXWRISODQHGHÀHFWLRQDWPLGKHLJKWRI wall due to factored loads, in. ¨[ = design story drift of story [, in. ¨1 PD[LPXP GHÀHFWLRQ GXULQJ ¿UVW ORDG WHVW measured 24 hours after application of the full test load, in. ¨2 PD[LPXP GHÀHFWLRQ GXULQJ VHFRQG ORDG WHVW measured 24 hours after application of the full test ORDG'HÀHFWLRQLVPHDVXUHGUHODWLYHWRWKHSRVLWLRQ of the structure at the beginning of the second load test, in. ¨fpt GL൵HUHQFH EHWZHHQ WKH VWUHVV WKDW FDQ EH GHYHO- oped in the prestressed reinforcement at the section under consideration and the stress required to resist factored bending moment at section, MuࢥSVL İcu = maximum usable strain at extreme concrete FRPSUHVVLRQ¿EHU American Concrete Institute – Copyrighted © Material – www.concrete.org ൵HUHQFH E oped in LJKWRI ment Mcr M M , in. FWLRQDWP PLQDOÀ WLRQ to re nfo ZHHQ WKH WRS n. ed reinforcemen ment at service G due ds 28 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 31. İt = net tensile strain in extreme layer of longitu- dinal tension reinforcement at nominal strength, H[FOXGLQJVWUDLQVGXHWRH൵HFWLYHSUHVWUHVVFUHHS shrinkage, and temperature İty = value of net tensile strain in the extreme layer of ORQJLWXGLQDOWHQVLRQUHLQIRUFHPHQWXVHGWRGH¿QHD compression-controlled section ș DQJOHEHWZHHQD[LVRIVWUXWFRPSUHVVLRQGLDJRQDO RUFRPSUHVVLRQ¿HOGDQGWKHWHQVLRQFKRUGRIWKH members Ȝ PRGL¿FDWLRQIDFWRUWRUHÀHFWWKHUHGXFHGPHFKDQ- ical properties of lightweight concrete relative to normalweight concrete of the same compressive strength Ȝa PRGL¿FDWLRQIDFWRUWRUHÀHFWWKHUHGXFHGPHFKDQ- ical properties of lightweight concrete in certain concrete anchorage applications Ȝ¨ PXOWLSOLHU XVHG IRU DGGLWLRQDO GHÀHFWLRQ GXH WR ORQJWHUPH൵HFWV Ȝs = factor used to modify shear strength based on the H൵HFWVRIPHPEHUGHSWKFRPPRQOUHIHUUHGWRDV WKHVL]HH൵HFWIDFWRU ȝ FRH൶FLHQWRIIULFWLRQ ȟ WLPHGHSHQGHQWIDFWRUIRUVXVWDLQHGORDG ȡ UDWLRRIAs to bd ȡƍ UDWLRRIAsƍWRbd ȡƐ = ratio of area of distributed longitudinal reinforce- ment to gross concrete area perpendicular to that reinforcement ȡp = ratio of Aps to bdp ȡs = ratio of volume of spiral reinforcement to total YROXPH RI FRUH FRQ¿QHG E WKH VSLUDO PHDVXUHG out-to-out of spirals ȡt = ratio of area of distributed transverse reinforce- ment to gross concrete area perpendicular to that reinforcement ȡv = ratio of tie reinforcement area to area of contact surface ȡw = ratio of As to bwd ࢥ VWUHQJWKUHGXFWLRQIDFWRU ࢥp = strength reduction factor for moment in preten- sioned member at cross section closest to the end of the member where all strands are fully developed IJcr = characteristic bond stress of adhesive anchor in cracked concrete, psi Ȝ LQ PRVW FDVHV WKH UHGXFWLRQ LQ PHFKDQLFDO SURS- erties is caused by the reduced ratio of tensile- to-compressive strength of lightweight concrete compared to normalweight concrete. There are LQVWDQFHVLQWKHRGHZKHUHȜLVXVHGDVDPRGL- ¿HUWRUHGXFHH[SHFWHGSHUIRUPDQFHRIOLJKWZHLJKW concrete where the reduction is not related directly to tensile strength. Ȣ H[SRQHQWVPEROLQWHQVLOHVKHDUIRUFHLQWHUDFWLRQ equation ࢥK VWL൵QHVVUHGXFWLRQIDFWRU ı ZDOO ERXQGDU H[WUHPH ¿EHU FRQFUHWH QRPLQDO compressive stress, psi American Concrete Institute – Copyrighted © Material – www.concrete.org at KDQ ncrete in certain ns LRQDO she SWK RU ength based o PRQOUHIHUUHG LQHGORDG he RDV PART 1: GENERAL 29 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 32. IJuncr = characteristic bond stress of adhesive anchor in uncracked concrete, psi ȥbrg,sl = shear lug bearing factor used to modify bearing VWUHQJWK RI VKHDU OXJV EDVHG RQ WKH LQÀXHQFH RI axial load ȥc = factor used to modify development length based on concrete strength ȥc,N = breakout cracking factor used to modify tensile VWUHQJWKRIDQFKRUVEDVHGRQWKHLQÀXHQFHRIFUDFNV in concrete ȥc,P = pullout cracking factor used to modify pullout VWUHQJWKRIDQFKRUVEDVHGRQWKHLQÀXHQFHRIFUDFNV in concrete ȥc,V = breakout cracking factor used to modify shear VWUHQJWKRIDQFKRUVEDVHGRQWKHLQÀXHQFHRIFUDFNV in concrete and presence or absence of supplemen- tary reinforcement ȥcp,N = breakout splitting factor used to modify tensile strength of post-installed anchors intended for use in uncracked concrete without supplementary reinforcement to account for the splitting tensile stresses ȥcp,Na = bond splitting factor used to modify tensile strength of adhesive anchors intended for use in uncracked concrete without supplementary reinforcement to account for the splitting tensile stresses due to installation ȥe = factor used to modify development length based on reinforcement coating ȥec,N = breakout eccentricity factor used to modify tensile strength of anchors based on eccentricity of applied loads ȥec,Na = breakout eccentricity factor used to modify tensile strength of adhesive anchors based on eccentricity of applied loads ȥec,V = breakout eccentricity factor used to modify shear strength of anchors based on eccentricity of applied loads ȥed,N EUHDNRXWHGJHH൵HFWIDFWRUXVHGWRPRGLIWHQVLOH strength of anchors based on proximity to edges of concrete member ȥed,Na EUHDNRXWHGJHH൵HFWIDFWRUXVHGWRPRGLIWHQVLOH strength of adhesive anchors based on proximity to edges of concrete member ȥed,V EUHDNRXW HGJH H൵HFW IDFWRU XVHG WR PRGLI VKHDU strength of anchors based on proximity to edges of concrete member ȥg = factor used to modify development length based on grade of reinforcement ȥh,V = breakout thickness factor used to modify shear strength of anchors located in concrete members with ha 1.5ca1 ȥo = factor used to modify development length of hooked DQGKHDGHGEDUVEDVHGRQVLGHFRYHUDQGFRQ¿QHPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org ed for t supplementary r the spli d to ten pp itt eve r use in uncra ntary reinforce ensile stresses d ment length bas d ent e to on 30 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 33. ȥp = factor used to modify development length for headed reinforcement based on parallel tie reinforcement ȥr = factor used to modify development length based on FRQ¿QLQJUHLQIRUFHPHQW ȥs = factor used to modify development length based on reinforcement size ȥt = factor used to modify development length for casting location in tension ȥw = factor used to modify development length for welded deformed wire reinforcement in tension ȍo DPSOL¿FDWLRQIDFWRUWRDFFRXQWIRURYHUVWUHQJWKRI the seismic-force-resisting system determined in accordance with the general building code ȍv = overstrength factor equal to the ratio of MprMu at the wall critical section Ȧv IDFWRUWRDFFRXQWIRUGQDPLFVKHDUDPSOL¿FDWLRQ 2.3—Terminology adhesive—chemical components formulated from organic polymers, or a combination of organic polymers and inorganic materials that cure if blended together. admixture—material other than water, aggregate, FHPHQWLWLRXVPDWHULDOVDQG¿EHUUHLQIRUFHPHQWXVHGDVDQ ingredient, which is added to grout, mortar, or concrete, either before or during its mixing, to modify the freshly mixed, setting, or hardened properties of the mixture. aggregate—granular material, such as sand, gravel, crushed stone, iron blast-furnace slag, or recycled aggre- gates including crushed hydraulic cement concrete, used with a cementing medium to form concrete or mortar. aggregate, lightweight—aggregate meeting the require- ments of ASTM C330 and having a loose bulk density of OEIW3 or less, determined in accordance with ASTM C29. alternative cement—an inorganic cement that can be used as a complete replacement for portland cement or blended hydraulic cement, and that is not covered by applicable spec- L¿FDWLRQVIRUSRUWODQGRUEOHQGHGKGUDXOLFFHPHQWV anchor—a steel element either cast into concrete or post-installed into a hardened concrete member and used to transmit applied loads to the concrete. R2.3—Terminology aggregate—The use of recycled aggregate is addressed LQ WKH RGH LQ 7KH GH¿QLWLRQ RI UHFFOHG PDWHULDOV in ASTM C33 is very broad and is likely to include mate- rials that would not be expected to meet the intent of the provisions of this Code for use in structural concrete. Use of recycled aggregates including crushed hydraulic-cement concrete in structural concrete requires additional precau- tions. See 26.4.1.2.1(c). aggregate, lightweight—In some standards, the term “lightweight aggregate” is being replaced by the term “low- density aggregate.” alternative cements—Alternative cements are described in the references listed in R26.4.1.1.1(b). Refer to 26.4.1.1.1(b) for precautions when using these materials in concrete covered by this Code. anchor—Cast-in anchors include headed bolts, hooked bolts (J- or L-bolt), and headed studs. Post-installed anchors include expansion anchors, undercut anchors, screw anchors, and adhesive anchors; steel elements for adhesive anchors include threaded rods, deformed reinforcing bars, or internally threaded steel sleeves with external deformations. Anchor types are shown in Fig. R2.1. American Concrete Institute – Copyrighted © Material – www.concrete.org he use of 7 33 is very s that would provisio rmulated from organic p nded to tha HUU g xi per l, R2.3 UFHPHQWXVHG mortar, or conc o modify the fr of the mixture. h as sand, gr Q ete, hly el, ag egat PART 1: GENERAL 31 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 34. anchor, adhesive—a post-installed anchor, inserted into hardened concrete with an anchor hole diameter not greater than 1.5 times the anchor diameter, that transfers loads to the concrete by bond between the anchor and the adhesive, and bond between the adhesive and the concrete. anchor, cast-in—headed bolt, headed stud, or hooked bolt installed before placing concrete. anchor, expansion—post-installed anchor, inserted into hardened concrete that transfers loads to or from the concrete by direct bearing or friction, or both. anchor, adhesive—The design model included in Chapter 17 for adhesive anchors is based on the behavior of anchors with hole diameters not exceeding 1.5 times the anchor diameter. Anchors with hole diameters exceeding 1.5 times WKH DQFKRU GLDPHWHU EHKDYH GL൵HUHQWO DQG DUH WKHUHIRUH excluded from the scope of Chapter 17 and ACI 355.4. To limit shrinkage and reduce displacement under load, most adhesive anchor systems require the annular gap to be as QDUURZDVSUDFWLFDOZKLOHVWLOOPDLQWDLQLQJVX൶FLHQWFOHDU- DQFHIRULQVHUWLRQRIWKHDQFKRUHOHPHQWLQWKHDGKHVLYH¿OOHG hole and ensuring complete coverage of the bonded area over the embedded length. The annular gap for reinforcing bars is generally greater than that for threaded rods. The required hole size is provided in the Manufacturer’s Printed Installa- tion Instructions (MPII). anchor, expansion—Expansion anchors may be torque- controlled, where the expansion is achieved by a torque acting on the screw or bolt; or displacement controlled, where the expansion is achieved by impact forces acting on a sleeve or plug and the expansion is controlled by the length of travel of the sleeve or plug. hef hef hef hef hef (A) Cast-in anchors: (a) hex head bolt with washer; (b) L-bolt; (c) J-bolt; and (d) welded headed stud. (B) Post-installed anchors: (a) adhesive anchor; (b) undercut anchor; (c) torque-controlled expansion anchors [(c1) sleeve-type and (c2) stud-type]; (d) drop-in type displacement-controlled expansion anchor; and (e) screw anchor. (a) (c) (b) (d) (a) (c1) (c2) (b) (d) (e) Fig. R2.1––Types of anchors. American Concrete Institute – Copyrighted © Material – www.concrete.org 32 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 35. anchor, horizontal or upwardly inclined—Anchor installed in a hole drilled horizontally or in a hole drilled at any orientation above horizontal. anchor, post-installed—anchor installed in hardened concrete; adhesive, expansion, screw, and undercut anchors are examples of post-installed anchors. anchor, screw—a post-installed threaded, mechanical anchor inserted into hardened concrete that transfers loads to the concrete by engagement of the hardened threads of the screw with the grooves that the threads cut into the sidewall of a predrilled hole during anchor installation. anchor, undercut—post-installed anchor that develops its tensile strength from the mechanical interlock provided by undercutting of the concrete at the embedded end of the anchor. Undercutting is achieved with a special drill before installing the anchor or alternatively by the anchor itself during its installation. anchor group—a number of similar anchors having DSSUR[LPDWHO HTXDO H൵HFWLYH HPEHGPHQW GHSWKV ZLWK spacing s between adjacent anchors such that the projected areas overlap. anchor pullout strength—the strength corresponding to the anchoring device or a major component of the device sliding out from the concrete without breaking out a substan- tial portion of the surrounding concrete. anchorage device—in post-tensioned members, the hard- ware used to transfer force from prestressed reinforcement to the concrete. anchorage device, basic monostrand—anchorage device XVHGZLWKDQVLQJOHVWUDQGRUDVLQJOHLQRUVPDOOHUGLDPHWHU bar that is in accordance with 25.8.1, 25.8.2, and 25.9.3.1(a). anchorage device, basic multistrand—anchorage device used with multiple strands, bars, or wires, or with single bars ODUJHUWKDQLQGLDPHWHUWKDWVDWLV¿HVDQG 25.9.3.1(b). anchorage device, special—anchorage device that satis- ¿HVWHVWVUHTXLUHGLQ F anchor, horizontal or upwardly inclined—Figure R2.2 illustrates the potential hole orientations for horizontal or upwardly inclined anchors. Fig. R2.2––Possible orientations of overhead, upwardly inclined, or horizontal anchors. anchor, screw—The required predrilled hole size for a screw anchor is provided by the anchor manufacturer. anchor group—For all potential failure modes (steel, concrete breakout, pullout, side-face blowout, and pryout), only those anchors susceptible to a particular failure mode should be considered when evaluating the strength associ- ated with that failure mode. anchorage device—Most anchorage devices for post- tensioning are standard manufactured devices available from commercial sources. In some cases, non-standard details or assemblages are developed that combine various wedges and wedge plates for anchoring prestressed reinforcement. Both standard and non-standard anchorage devices may be FODVVL¿HGDVEDVLFDQFKRUDJHGHYLFHVRUVSHFLDODQFKRUDJH GHYLFHVDVGH¿QHGLQWKLVRGHDQG$$6+72/5)'8686 anchorage device, basic—Devices that are so propor- tioned that they can be checked analytically for compli- DQFHZLWKEHDULQJVWUHVVDQGVWL൵QHVVUHTXLUHPHQWVZLWKRXW having to undergo the acceptance-testing program required of special anchorage devices. anchorage device, special—Special anchorage devices are any devices (monostrand or multistrand) that do not meet American Concrete Institute – Copyrighted © Material – www.concrete.org ed group—Fo crete breakou only tho hanical transfers loads ardened t eads c r ins tall ec e a ed tive anch screw anchor is chor that dev al interlock prov embedded end o a special drill b by the anchor ps ded the fore elf PART 1: GENERAL 33 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 36. the relevant PTI or AASHTO LFRDUS bearing stress and, ZKHUH DSSOLFDEOH VWL൵QHVV UHTXLUHPHQWV 0RVW FRPPHU- cially marketed multi-bearing surface anchorage devices are special anchorage devices. As provided in 25.9.3, such devices can be used only if they have been shown experi- mentally to be in compliance with the AASHTO require- ments. This demonstration of compliance will ordinarily be furnished by the device manufacturer. anchorage zone—In post-tensioned members, the portion of the member through which the concentrated prestressing force is transferred to the concrete and distributed more uniformly across the section. Its extent is equal to the largest dimension of the cross section. For anchorage devices located away from the end of a member, the anchorage zone includes the disturbed regions ahead of and behind the anchorage devices. Refer to Fig. R25.9.1.1b. cementitious materials—Cementitious materials permitted for use in this Code are addressed in 26.4.1.1. Fly ash, raw or calcined natural pozzolan, slag cement, and silica fume are considered supplementary cementitious materials. anchorage zone—in post-tensioned members, portion of the member through which the concentrated prestressing forceistransferredtoconcreteanddistributedmoreuniformly across the section; its extent is equal to the largest dimen- sion of the cross section; for anchorage devices located away from the end of a member, the anchorage zone includes the disturbed regions ahead of and behind the anchorage device. attachment—structural assembly, external to the surface of the concrete, that transmits loads to or receives loads from the anchor. B-region—portion of a member in which it is reasonable WRDVVXPHWKDWVWUDLQVGXHWRÀH[XUHYDUOLQHDUOWKURXJK section. base of structure—level at which horizontal earthquake ground motions are assumed to be imparted to a building. This level does not necessarily coincide with the ground level. beam²PHPEHUVXEMHFWHGSULPDULOWRÀH[XUHDQGVKHDU with or without axial force or torsion; beams in a moment frame that forms part of the lateral-force-resisting system are predominantly horizontal members; a girder is a beam. boundary element—portion along wall and diaphragm edge, including edges of openings, strengthened by longitu- dinal and transverse reinforcement. breakout strength, concrete—strength corresponding to a volume of concrete surrounding the anchor or group of anchors separating from the member. EXLOGLQJ R൶FLDO—term used to identify the Authority having jurisdiction or individual charged with administra- tion and enforcement of provisions of the building code. Such terms as building commissioner or building inspector DUHYDULDWLRQVRIWKHWLWOHDQGWKHWHUP³EXLOGLQJR൶FLDO´DV used in this Code, is intended to include those variations, as well as others that are used in the same sense. caisson—see drilled pier. cementitious materials—materials that have cementing value if used in grout, mortar, or concrete, including port- land cement, blended hydraulic cements, expansive cement, ÀDVKUDZRUFDOFLQHGQDWXUDOSR]]RODQVODJFHPHQWDQG silica fume, but excluding alternative cements. collector—element that acts in axial tension or compres- sion to transmit forces between a diaphragm and a vertical element of the lateral-force-resisting system. column—member, usually vertical or predominantly vertical, used primarily to support axial compressive load, but that can also resist moment, shear, or torsion. Columns American Concrete Institute – Copyrighted © Material – www.concrete.org u h it is reasonable YDUOLQH hich o be y LP orsi f arted to a buil ide with the gr WRÀH[XUHDQGV beams in a mo i g. und HDU nt 34 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 37. used as part of a lateral-force-resisting system resist combined axial load, moment, and shear. See also moment frame. column capital—enlargement of the top of a concrete column located directly below the slab or drop panel that is cast monolithically with the column. compliance requirements—construction-related code requirements directed to the contractor to be incorporated into construction documents by the licensed design profes- sional, as applicable. FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHUV²FRQFUHWH ÀH[- ural members of precast or cast-in-place concrete elements, constructed in separate placements but connected so that all elements respond to loads as a unit. compression-controlled section—cross section in which the net tensile strain in the extreme tension reinforcement at nominal strength is less than or equal to the compression- controlled strain limit. compression-controlled strain limit—net tensile strain at balanced strain conditions. concrete—mixture of portland cement or any other FHPHQWLWLRXVPDWHULDO¿QHDJJUHJDWHFRDUVHDJJUHJDWHDQG water, with or without admixtures. concrete,all-lightweight—lightweightconcretecontaining RQOOLJKWZHLJKWFRDUVHDQG¿QHDJJUHJDWHVWKDWFRQIRUPWR ASTM C330. concrete, lightweight—concrete containing lightweight aggregate and having an equilibrium density, as determined by ASTM C567EHWZHHQDQGOEIW3 . concrete, nonprestressed—reinforced concrete with at least the minimum amount of nonprestressed reinforcement and no prestressed reinforcement; or for two-way slabs, with less than the minimum amount of prestressed reinforcement. concrete, normalweight—concrete containing only FRDUVHDQG¿QHDJJUHJDWHVWKDWFRQIRUPWRASTM C33 and KDYLQJDGHQVLWJUHDWHUWKDQOEIW3 . concrete, plain—structural concrete with no reinforce- ment or with less than the minimum amount of reinforce- PHQWVSHFL¿HGIRUUHLQIRUFHGFRQFUHWH concrete, precast—structural concrete element cast else- ZKHUHWKDQLWV¿QDOSRVLWLRQLQWKHVWUXFWXUH concrete, prestressed—reinforced concrete in which internal stresses have been introduced by prestressed rein- forcement to reduce potential tensile stresses in concrete resulting from loads, and for two-way slabs, with at least the minimum amount of prestressed reinforcement. compliance requirements—Although primarily directed to the contractor, the compliance requirements are also commonly used by others involved with the project. concrete, nonprestressed—Nonprestressed concrete usually contains no prestressed reinforcement. Prestressed two-way slabs require a minimum level of compressive VWUHVVLQWKHFRQFUHWHGXHWRH൵HFWLYHSUHVWUHVVLQDFFRUGDQFH with 8.6.2.1. Two-way slabs with less than this minimum level of precompression are required to be designed as nonprestressed concrete. concrete, normalweight—Normalweight concrete typi- FDOOKDVDGHQVLW XQLWZHLJKW EHWZHHQDQGOEIW3 , DQGLVQRUPDOOWDNHQDVWROEIW3 . concrete, plain—The presence of reinforcement, nonpre- stressed or prestressed, does not exclude the member from EHLQJFODVVL¿HGDVSODLQFRQFUHWHSURYLGHGDOOUHTXLUHPHQWV of Chapter 14 DUHVDWLV¿HG concrete, prestressed²ODVVHV RI SUHVWUHVVHG ÀH[- XUDOPHPEHUVDUHGH¿QHGLQ24.5.2.1. Prestressed two-way slabs require a minimum level of compressive stress in WKHFRQFUHWHGXHWRH൵HFWLYHSUHVWUHVVLQDFFRUGDQFHZLWK 8.6.2.1. Although the behavior of a prestressed member with unbonded tendons may vary from that of members with continuously bonded prestressed reinforcement, bonded and unbonded prestressed concrete are combined with nonprestressed concrete under the generic term “reinforced concrete.” Provisions common to both prestressed and American Concrete Institute – Copyrighted © Material – www.concrete.org th , nonpr ally contains two wa rain ement or WHFR s. ghtw HD cre ium concreteconta JDWHVWKDWFRQIRU ntaining lightw nsity, as determ ng PWR ght ed PART 1: GENERAL 35 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 38. concrete, reinforced—structural concrete reinforced with at least the minimum amounts of nonprestressed reinforce- PHQWSUHVWUHVVHGUHLQIRUFHPHQWRUERWKDVVSHFL¿HGLQWKLV Code. concrete, sand-lightweight—lightweight concrete FRQWDLQLQJRQOQRUPDOZHLJKW¿QHDJJUHJDWHWKDWFRQIRUPV to ASTM C33 and lightweight coarse aggregate that conforms to ASTM C330. FRQFUHWH VWHHO ¿EHUUHLQIRUFHG—concrete containing a prescribed amount of dispersed, randomly oriented, discon- WLQXRXVGHIRUPHGVWHHO¿EHUV FRQFUHWH¿OOHG SLSH SLOHV—steel pipe with a closed end that is driven for its full length in contact with the surrounding soil, or a steel pipe with an open end that is driven for its full length and the soil cleaned out; for both LQVWDOODWLRQSURFHGXUHVWKHSLSHLVVXEVHTXHQWO¿OOHGZLWK reinforcement and concrete. FRQFUHWH VWUHQJWK VSHFL¿HG FRPSUHVVLYH fcƍ)— compressive strength of concrete used in design and evalu- ated in accordance with provisions of this Code, psi; wher- ever the quantity fcƍ is under a radical sign, the square root of numerical value only is intended, and the result has units of psi. connection—region of a structure that joins two or more members; a connection also refers to a region that joins members of which one or more is precast. connection, ductile—connection between one or more precast elements that experiences yielding as a result of the earthquake design displacements. connection, strong—connection between one or more precast elements that remains elastic while adjoining members experience yielding as a result of earthquake design displacements. constructiondocuments—writtenandgraphicdocuments DQGVSHFL¿FDWLRQVSUHSDUHGRUDVVHPEOHGIRUGHVFULELQJWKH location, design, materials, and physical characteristics of the elements of a project necessary for obtaining a building permit and construction of the project. contraction joint—formed, sawed, or tooled groove in a concrete structure to create a weakened plane and regu- late the location of cracking resulting from the dimensional FKDQJHRIGL൵HUHQWSDUWVRIWKHVWUXFWXUH FRYHU VSHFL¿HG FRQFUHWH—distance between the outer- most surface of embedded reinforcement and the closest outer surface of the concrete. crosstie—a continuous reinforcing bar having a seismic hook at one end and a hook not less than 90 degrees with at least a 6db extension at the other end. The hooks shall engage peripheral longitudinal bars. The 90-degree hooks nonprestressed concrete are integrated to avoid overlapping DQGFRQÀLFWLQJSURYLVLRQV concrete, reinforced—Includes members satisfying the requirements for nonprestressed and prestressed concrete. concrete, sand-lightweight—By Code terminology, sand-lightweight concrete is lightweight concrete with all RIWKH¿QHDJJUHJDWHUHSODFHGEVDQG7KLVGH¿QLWLRQPD not be in agreement with usage by some material suppliers or contractors where the majority, but not all, of the light- ZHLJKW¿QHVDUHUHSODFHGEVDQG)RUSURSHUDSSOLFDWLRQRI the Code provisions, the replacement limits should be stated, with interpolation if partial sand replacement is used. American Concrete Institute – Copyrighted © Material – www.concrete.org ith the open end that is cleaned o VXEVH ¿HG ete io ra ded PSUHVVLYH f in design and e this Code, psi; w sign, the square d the result has — alu- her- oot its 36 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 39. of two successive crossties engaging the same longitudinal bars shall be alternated end for end. FXWR൵SRLQW—point where reinforcement is terminated. D-region—portion of a member within a distance h of a force discontinuity or a geometric discontinuity. design displacement—total calculated lateral displace- ment expected for the design-basis earthquake. design information²SURMHFWVSHFL¿F LQIRUPDWLRQ WR EH incorporated into construction documents by the licensed design professional, as applicable. design load combination—combination of factored loads and forces. design story drift ratio²UHODWLYH GL൵HUHQFH RI GHVLJQ displacement between the top and bottom of a story, divided by the story height. development length—length of embedded reinforce- ment, including pretensioned strand, required to develop the design strength of reinforcement at a critical section. discontinuity—abrupt change in geometry or loading. distance sleeve—sleeve that encases the center part of an undercut anchor, a torque-controlled expansion anchor, or a displacement-controlled expansion anchor, but does not expand. drilled piers or caissons—cast-in-place concrete foun- dation elements with or without an enlarged base (bell), FRQVWUXFWHGEH[FDYDWLQJDKROHLQWKHJURXQGDQG¿OOLQJ with reinforcement and concrete. Drilled piers or caissons are considered as uncased cast-in-place concrete drilled or augered piles, unless they have permanent steel casing, in which case they are considered as metal cased concrete piles. drop panel—projection below the slab used to reduce the amount of negative reinforcement over a column or the minimum required slab thickness, and to increase the slab shear strength. duct—conduit, plain or corrugated, to accommodate prestressing reinforcement for post-tensioning applications. ductile coupled structural wall—see structural wall, ductile coupled. durability—ability of a structure or member to resist deterioration that impairs performance or limits service life of the structure in the relevant environment considered in design. edge distance—distance from the edge of the concrete surface to the center of the nearest anchor. design displacement—The design displacement is an index of the maximum lateral displacement expected in design for the design-basis earthquake. In documents such as $6(6(, and the International Building Code, the design displacement is calculated using static or dynamic OLQHDUHODVWLFDQDOVLVXQGHUFRGHVSHFL¿HGDFWLRQVFRQVLG- HULQJH൵HFWVRIFUDFNHGVHFWLRQVH൵HFWVRIWRUVLRQH൵HFWV of vertical forces acting through lateral displacements, DQG PRGL¿FDWLRQ IDFWRUV WR DFFRXQW IRU H[SHFWHG LQHODVWLF response. The design displacement generally is greater than the displacement calculated from design-level forces applied to a linear-elastic model of the building. American Concrete Institute – Copyrighted © Material – www.concrete.org ot censed tion of fa DWLYH nd b th ran at m of a story, div embedded reinf quired to develo tical section. d rce- the PART 1: GENERAL 37 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 40. H൵HFWLYH GHSWK RI VHFWLRQ—distance measured from H[WUHPH FRPSUHVVLRQ ¿EHU WR FHQWURLG RI ORQJLWXGLQDO tension reinforcement. H൵HFWLYH HPEHGPHQW GHSWK—overall depth through which the anchor transfers force to or from the surrounding FRQFUHWHH൵HFWLYHHPEHGPHQWGHSWKZLOOQRUPDOOEHWKH depth of the concrete failure surface in tension applications; IRUFDVWLQKHDGHGDQFKRUEROWVDQGKHDGHGVWXGVWKHH൵HF- tive embedment depth is measured from the bearing contact surface of the head. H൵HFWLYHSUHVWUHVV—stress remaining in prestressed rein- forcement after losses in 20.3.2.6 have occurred. H൵HFWLYH VWL൵QHVV²VWL൵QHVV RI D VWUXFWXUDO PHPEHU DFFRXQWLQJIRUFUDFNLQJFUHHSDQGRWKHUQRQOLQHDUH൵HFWV embedments—items embedded in concrete, excluding UHLQIRUFHPHQW DV GH¿QHG LQ Chapter 20 and anchors as GH¿QHG LQ Chapter 17. Reinforcement or anchors welded, bolted or otherwise connected to the embedded item to develop the strength of the assembly, are considered to be part of the embedment. embedments, pipe—embedded pipes, conduits, and sleeves. embedment length—length of embedded reinforcement provided beyond a critical section. equilibrium density—density of lightweight concrete determined in accordance with ASTM C567. expansion sleeve—outer part of an expansion anchor that is forced outward by the center part, either by applied torque or impact, to bear against the sides of the predrilled hole. See also anchor, expansion. extreme tension reinforcement—layer of prestressed or nonprestressed reinforcement that is the farthest from the H[WUHPHFRPSUHVVLRQ¿EHU ¿QLWHHOHPHQWDQDOVLV—a numerical modeling technique in which a structure is divided into a number of discrete elements for analysis. ¿YHSHUFHQWIUDFWLOH—statistical term meaning 90 percent FRQ¿GHQFHWKDWWKHUHLVSHUFHQWSUREDELOLWRIWKHDFWXDO strength exceeding the nominal strength. foundation seismic ties—HOHPHQWV XVHG WR VX൶FLHQWO interconnect foundations to act as a unit. Elements may consist of grade beams, slabs-on-ground, or beams within a slab-on-ground. headed deformed bars—deformed bars with heads attached at one or both ends. H൵HFWLYH HPEHGPHQW GHSWK—(൵HFWLYH HPEHGPHQW depths for a variety of anchor types are shown in Fig. R2.1. For post-installed mechanical anchors, the value hef is obtained from the ACI 355.2 product evaluation report provided by the manufacturer. ¿YHSHUFHQWIUDFWLOH²7KHGHWHUPLQDWLRQRIWKHFRH൶FLHQW K05 associated with the 5 percent fractile, x – K05ss depends on the number of tests, n, used to calculate the sample mean, x , and sample standard deviation, ss. Values of K05 range, for example, from 1.645 for n ’, to 2.010 for n = 40, and 2.568 for n = 10:LWKWKLVGH¿QLWLRQRIWKHSHUFHQWIUDFWLOH the nominal strength in Chapter 17 is the same as the charac- teristic strength in ACI 355.2 and ACI 355.4. headed deformed bars—The bearing area of a headed deformed bar is, for the most part, perpendicular to the bar axis. In contrast, the bearing area of the head of headed stud reinforcement is a nonplanar spatial surface of revolu- tion, as shown in Fig. R20.4.1. The two types of reinforce- PHQWGL൵HULQRWKHUZDV7KHVKDQNVRIKHDGHGVWXGVDUH smooth, not deformed as with headed deformed bars. The American Concrete Institute – Copyrighted © Material – www.concrete.org he d to be ipes, co f em on. ity A o art f ightweight con C56 xpansion ancho er by applied to d ill rete that ue 38 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 41. minimum net bearing area of the head of a headed deformed bar is permitted to be as small as four times the bar area. ,QFRQWUDVWWKHPLQLPXPVWXGKHDGDUHDLVQRWVSHFL¿HGLQ terms of the bearing area, but by the total head area which must be at least 10 times the area of the shank. joint²7KHH൵HFWLYHFURVVVHFWLRQDODUHDRIDMRLQWRID special moment frame, Aj, for shear strength calculations is given in 15.4.2.4. licensed design professional—May also be referred to as “registered design professional” in other documents; a licensed design professional in responsible charge of the design work is often referred to as the “engineer of record” (EOR). headed bolt—cast-in steel anchor that develops its tensile strength from the mechanical interlock provided by either a head or nut at the embedded end of the anchor. headed stud—a steel anchor conforming to the require- ments of AWS D1.1 DQGD൶[HGWRDSODWHRUVLPLODUVWHHO attachment by the stud arc welding process before casting; also referred to as a welded headed stud. headed shear stud reinforcement—reinforcement consisting of individual headed studs or groups of studs, with anchorage provided by a head at each end, or by a head at one end and a common base rail consisting of a steel plate or shape at the other end. hooked bolt—cast-in anchor anchored mainly by bearing of the 90-degree bend (L-bolt) or 180-degree bend (J-bolt) against the concrete, at its embedded end, and having a minimum eh equal to 3da. hoop—closed tie or continuously wound tie, made up of one or several reinforcement elements, each having seismic hooks at both ends. A closed tie shall not be made up of interlocking headed deformed bars. See 25.7.4. inspection²REVHUYDWLRQ YHUL¿FDWLRQ DQG UHTXLUHG GRFX- mentation of the materials, installation, fabrication, erection, or placementofcomponentsandconnectionstodeterminecompli- ance with construction documents and referenced standards. inspection, continuous—the full-time observation, veri- ¿FDWLRQ DQG UHTXLUHG GRFXPHQWDWLRQ RI ZRUN LQ WKH DUHD where the work is being performed. inspection, periodic—the part-time or intermittent obser- YDWLRQYHUL¿FDWLRQDQGUHTXLUHGGRFXPHQWDWLRQRIZRUNLQ the area where the work is being performed. isolation joint—separation between adjoining parts of a concrete structure, usually a vertical plane at a designed location such as to interfere least with performance of the structure, yet such as to allow relative movement in three directions and avoid formation of cracks elsewhere in the concrete, and through which all or part of the bonded rein- forcement is interrupted. jacking force—in prestressed concrete, temporary force exerted by a device that introduces tension into prestressing reinforcement. joint—portion of structure common to intersecting members. licensed design professional—an individual who is OLFHQVHGWRSUDFWLFHVWUXFWXUDOGHVLJQDVGH¿QHGEWKHVWDWX- tory requirements of the professional licensing laws of the state or jurisdiction in which the project is to be constructed, and who is in responsible charge for all or part of the struc- tural design. American Concrete Institute – Copyrighted © Material – www.concrete.org (J bolt) d, and having a y wou ment tie bar L¿ at nec d not be made u e 25.7.4 DQ UHG G abrication, erectio todetermineco d of RFX- , or li- PART 1: GENERAL 39 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 42. load—forces or other actions that result from the weight of all building materials, occupants, and their possessions, HQYLURQPHQWDOH൵HFWVGL൵HUHQWLDOPRYHPHQWDQGUHVWUDLQHG dimensional changes; permanent loads are those loads in which variations over time are rare or of small magnitude; all other loads are variable loads. load, dead—(a) the weights of the members, supported structure, and permanent attachments or accessories that are likely to be present on a structure in service; or (b) loads PHHWLQJVSHFL¿FFULWHULDIRXQGLQWKHJHQHUDOEXLOGLQJFRGH without load factors. load, factored—load, multiplied by appropriate load factors. load, live—(a) load that is not permanently applied to a structure, but is likely to occur during the service life of the structure (excluding environmental loads); or (b) loads PHHWLQJVSHFL¿FFULWHULDIRXQGLQWKHJHQHUDOEXLOGLQJFRGH without load factors. load, roof live—a load on a roof produced: (a) during maintenance by workers, equipment, and materials, and (b) during the life of the structure by movable objects, such as planters or other similar small decorative appurtenances that DUHQRWRFFXSDQFUHODWHGRUORDGVPHHWLQJVSHFL¿FFULWHULD found in the general building code; without load factors. load, self-weight dead—weight of the structural system, including the weight of any bonded concrete topping. load, service—all loads, static or transitory, imposed on a structure or element thereof, during the operation of a facility, without load factors. load, superimposed dead—dead loads other than the self-weight that are present or are considered in the design. ORDG H൵HFWV—forces and deformations produced in structural members by applied loads or restrained volume changes. load path—sequence of members and connections designed to transfer the factored loads and forces in such combinations as are stipulated in this Code, from the point RIDSSOLFDWLRQRURULJLQDWLRQWKURXJKWKHVWUXFWXUHWRWKH¿QDO support location or the foundation. Manufacturer’s Printed Installation Instructions (MPII)—published instructions for the correct installation of an adhesive anchor under all covered installation condi- tions as supplied in the product packaging. metal cased concrete piles—thin-walled steel pipe, steel shell, or spiral-welded metal casing with a closed end that is driven for its full length in contact with the surrounding VRLOOHIWSHUPDQHQWOLQSODFHDQGVXEVHTXHQWO¿OOHGZLWK reinforcement and concrete. modulus of elasticity—ratio of normal stress to corre- sponding strain for tensile or compressive stresses below proportional limit of material. moment frame—frame in which beams, slabs, columns, DQGMRLQWVUHVLVWIRUFHVSUHGRPLQDQWOWKURXJKÀH[XUHVKHDU and axial force; beams or slabs are predominantly horizontal loads²$QXPEHURIGH¿QLWLRQVIRUORDGVDUHJLYHQDVWKH Code contains requirements that are to be met at various load levels. The terms “dead load” and “live load” refer to the unfactored, sometimes called “service” loads speci- ¿HGRUGH¿QHGEWKHJHQHUDOEXLOGLQJFRGH6HUYLFHORDGV (loads without load factors) are to be used where speci- ¿HGLQWKLVRGHWRSURSRUWLRQRULQYHVWLJDWHPHPEHUVIRU adequate serviceability. Loads used to proportion a member IRUDGHTXDWHVWUHQJWKDUHGH¿QHGDVIDFWRUHGORDGV)DFWRUHG loads are service loads multiplied by the appropriate load factors for required strength except wind and earthquake ZKLFKDUHDOUHDGVSHFL¿HGDVVWUHQJWKORDGVLQ$6(6(, 77KH IDFWRUHG ORDG WHUPLQRORJ FODUL¿HV ZKHUH WKH ORDG factors are applied to a particular load, moment, or shear value as used in the Code provisions. ORDGH൵HFWV—Stresses and strains are directly related to IRUFHVDQGGHIRUPDWLRQVDQGDUHFRQVLGHUHGDVORDGH൵HFWV American Concrete Institute – Copyrighted © Material – www.concrete.org in ORDG during materials, and (b) vable obj rative GVP de; igh nd ic du out load factor he structural sy ncrete topping. ansitory, impose the operation em, on a 40 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 43. or nearly horizontal; columns are predominantly vertical or nearly vertical. moment frame, intermediate—cast-in-place beam- column frame or two-way slab-column frame without beams complying with 18.4. moment frame, ordinary—cast-in-place or precast concrete beam-column or slab-column frame complying with 18.3. moment frame, special—cast-in-place beam-column frame complying with 18.2.3 through 18.2.8; and 18.6 through 18.8. A precast beam-column frame complying with 18.2.3 through 18.2.8 and 18.9. net tensile strain—the tensile strain at nominal strength H[FOXVLYH RI VWUDLQV GXH WR H൵HFWLYH SUHVWUHVV FUHHS shrinkage, and temperature. nodal zone—volume of concrete around a node that is assumed to transfer strut-and-tie forces through the node. node—point in a strut-and-tie model where the axes of the struts, ties, and concentrated forces acting on the joint intersect. node, curved bar—the bend region of a continuous rein- IRUFLQJEDU RUEDUV WKDWGH¿QHVDQRGHLQDVWUXWDQGWLH model. one-way construction—members designed to be capable of supporting all loads through bending in a single direction; see also two-way construction. panel, shotcrete mockup—a shotcrete specimen that simulates the size and detailing of reinforcement in a proposed structural member for preconstruction evaluation of the nozzle operator’s ability to encase the reinforcement. panel, shotcrete test—a shotcrete specimen prepared in accordance with ASTM C1140 for evaluation of shotcrete. pedestal—member with a ratio of height-to-least lateral dimension less than or equal to 3 used primarily to support axial compressive load; for a tapered member, the least lateral dimension is the average of the top and bottom dimensions of the smaller side. plastic hinge region—length of frame element over which ÀH[XUDO LHOGLQJ LV LQWHQGHG WR RFFXU GXH WR HDUWKTXDNH design displacements, extending not less than a distance h IURPWKHFULWLFDOVHFWLRQZKHUHÀH[XUDOLHOGLQJLQLWLDWHV post-tensioning—method of prestressing in which prestressing reinforcement is tensioned after concrete has hardened. precast concrete piles—driven piles that may be either prestressed concrete or conventionally reinforced concrete. precompressed tension zone—portion of a prestressed PHPEHU ZKHUH ÀH[XUDO WHQVLRQ FDOFXODWHG XVLQJ JURVV section properties, would occur under service loads if the prestress force was not present. pretensioning—method of prestressing in which prestressing reinforcement is tensioned before concrete is cast. one-way construction—Joists, beams, girders, and some slabs and foundations are considered one-way construction. panel, shotcrete mockup—Shotcrete mockup panels are used for preconstruction evaluation and are either sawed or cored, or both, to evaluate if the reinforcement has been adequately encased. panel, shotcrete test—Shotcrete test panels are typically used to evaluate a shotcrete mixture, to qualify a nozzle RSHUDWRUWRYHULIVXUIDFH¿QLVKDQGWRSURYLGHVSHFLPHQV IRUFRPSUHVVLYHRUÀH[XUDOVWUHQJWKWHVWLQJ American Concrete Institute – Copyrighted © Material – www.concrete.org uction—J ns are con mockup truction e th, to ev encased. anel, shotcre used to he joint of a con D QRG mbe be . —a ng igned to be cap in a single direc crete specimen reinforcement i le on; that a on slabs pan used way d fo , sh r pr PART 1: GENERAL 41 CODE COMMENTARY 2 Not. Term. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 44. projected area—area on the free surface of the concrete member that is used to represent the greater base of the assumed rectilinear failure surface. SURMHFWHG LQÀXHQFH DUHD—rectilinear area on the free surface of the concrete member that is used to calculate the bond strength of adhesive anchors. pryout strength, concrete—strength corresponding to IRUPDWLRQ RI D FRQFUHWH VSDOO EHKLQG VKRUW VWL൵ DQFKRUV displaced in the direction opposite to the applied shear force. reinforcement—steel element or elements embedded in concrete and conforming to 20.2 through 20.4. Prestressed reinforcement in external tendons is also considered reinforcement. reinforcement, anchor—reinforcement used to transfer the design load from the anchors into the structural member. reinforcement, bonded prestressed—pretensioned rein- forcement or prestressed reinforcement in a bonded tendon. reinforcement, deformed—deformed bars, welded bar mats, deformed wire, and welded wire reinforcement conforming to 20.2.1.3, 20.2.1.5, or 20.2.1.7, excluding plain wire. reinforcement, nonprestressed—bonded reinforcement that is not prestressed. reinforcement, plain—bars or wires conforming to 20.2.1.4 RU WKDW GR QRW FRQIRUP WR GH¿QLWLRQ RI deformed reinforcement. reinforcement, prestressed—prestressing reinforcement that has been tensioned to impart forces to concrete. reinforcement, prestressing—high-strength reinforce- ment such as strand, wire, or bar conforming to 20.3.1. reinforcement, supplementary—reinforcement that acts to restrain the potential concrete breakout but is not designed to transfer the design load from the anchors into the struc- tural member. reinforcement, welded deformed steel bar mat—mat conforming to 20.2.1.5 consisting of two layers of deformed bars at right angles to each other welded at the intersections. reinforcement, welded wire—plain or deformed wire fabricated into sheets or rolls conforming to 20.2.1.7. Seismic Design Category²FODVVL¿FDWLRQ DVVLJQHG WR D structure based on its occupancy category and the severity of WKHGHVLJQHDUWKTXDNHJURXQGPRWLRQDWWKHVLWHDVGH¿QHG by the general building code. Also denoted by the abbrevia- tion SDC. seismic-force-resisting system—portion of the structure GHVLJQHGWRUHVLVWHDUWKTXDNHH൵HFWVUHTXLUHGEWKHJHQHUDO reinforcement, anchor—Anchor reinforcement is GHVLJQHGDQGGHWDLOHGVSHFL¿FDOOIRUWKHSXUSRVHRIWUDQV- ferring anchor loads from the anchors into the member. Hair- pins are generally used for this purpose (refer to 17.5.2.1(a) DQG E KRZHYHURWKHUFRQ¿JXUDWLRQVWKDWFDQEH VKRZQWRH൵HFWLYHOWUDQVIHUWKHDQFKRUORDGDUHDFFHSWDEOH reinforcement, deformed—Deformed reinforcement is GH¿QHGDVWKDWPHHWLQJWKHUHLQIRUFHPHQWVSHFL¿FDWLRQVLQ WKLVRGH1RRWKHUUHLQIRUFHPHQWTXDOL¿HV7KLVGH¿QLWLRQ permits accurate statement of development lengths. Bars or wire not meeting the deformation requirements or welded wire reinforcement not meeting the spacing requirements are “plain reinforcement,” for code purposes, and may be used only for spirals. reinforcement, supplementary—Supplementary rein- IRUFHPHQW KDV D FRQ¿JXUDWLRQ DQG SODFHPHQW VLPLODU WR DQFKRU UHLQIRUFHPHQW EXW LV QRW VSHFL¿FDOO GHVLJQHG WR transfer loads from the anchors into the member. Stirrups, as used for shear reinforcement, may fall into this category. American Concrete Institute – Copyrighted © Material – www.concrete.org PHHWLQJWK HUUHLQIRUF atement o he deform t not mee rcement,” to pirals. etensioned rein- t in a bon forme weld 1.5 VKRZQ ment, defor 0.2.1.7, exclu ng WKLV permi wire r are “ GH1 acc t m info ain r orce DVW me me 42 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 45. building code using the applicable provisions and load combinations. seismic hook—hook on a stirrup, hoop, or crosstie having a bend not less than 135 degrees, except that circular hoops shall have a bend not less than 90 degrees; hooks shall have an extension of at least 6db, but not less than 3 in. The hooks shall engage the longitudinal reinforcement and the exten- sion shall project into the interior of the stirrup or hoop. shear cap—projection below the slab used to increase the slab shear strength. shear lug—a steel element welded to an attachment base plate to transfer shear to concrete by bearing. sheathing—material encasing prestressing reinforcement to prevent bonding of the prestressing reinforcement with the surrounding concrete, to provide corrosion protection, and to contain the corrosion-inhibiting coating. shotcrete—mortar or concrete placed pneumatically by high velocity projection from a nozzle onto a surface. shotcrete, dry-mix—shotcrete in which most of the mixing water is added to the concrete ingredients at the nozzle. shotcrete, wet-mix—shotcrete in which the concrete ingredients, including water, are mixed before introduction into the delivery hose. side-face blowout strength, concrete—strength of anchors with deep embedment and thin side-face cover such that spalling occurs on the side face around the embedded head without breakout occurring at the top concrete surface. slab-beam strip—in two-way prestressed slabs, the width RIWKHÀRRUVVWHPLQFOXGLQJERWKWKHVODEDQGEHDPLIDSSOL- cable, bounded laterally by adjacent panel centerlines for an interior slab-beam strip, or by adjacent panel centerline and slab edge for an exterior slab-beam strip. spacing, clear—least dimension between the outermost surfaces of adjacent items. span length—distance between supports. special seismic systems—structural systems that use special moment frames, special structural walls, or both. specialty engineer—a licensed design professional WR ZKRP D VSHFL¿F SRUWLRQ RI WKH GHVLJQ ZRUN KDV EHHQ delegated. specialty insert—predesigned and prefabricated cast-in DQFKRUV VSHFL¿FDOO GHVLJQHG IRU DWWDFKPHQW RI EROWHG RU slotted connections. spiral reinforcement—continuously wound reinforce- ment in the form of a cylindrical helix. steel element, brittle—element with a tensile test elonga- tion of less than 14 percent, or reduction in area of less than 30 percent at failure. steel element, ductile—element with a tensile test elon- gation of at least 14 percent and reduction in area of at least 30 percent; steel element meeting the requirements of ASTM A307 VKDOOEHFRQVLGHUHGGXFWLOHH[FHSWDVPRGL¿HG EIRUHDUWKTXDNHH൵HFWVGHIRUPHGUHLQIRUFLQJEDUVPHHWLQJ sheathing—Typically, sheathing is a continuous, seam- less, high-density polyethylene material extruded directly on the coated prestressing reinforcement. shotcrete—Terms such as gunite and sprayed concrete are sometimes used to refer to shotcrete. specialty insert—Specialty inserts are devices often used for handling, transportation, erection, and anchoring elements; specialty inserts are not within the scope of this Code. steel element, brittle—The 14 percent elongation should EHPHDVXUHGRYHUWKHJDXJHOHQJWKVSHFL¿HGLQWKHDSSUR- priate ASTM standard for the steel. steel element, ductile—The 14 percent elongation VKRXOGEHPHDVXUHGRYHUWKHJDXJHOHQJWKVSHFL¿HGLQWKH appropriate ASTM standard for steel. Due to concerns over IUDFWXUHLQFXWWKUHDGVLWVKRXOGEHYHUL¿HGWKDWWKUHDGHG deformed reinforcing bars satisfy the strength requirements of 25.5.7.1. American Concrete Institute – Copyrighted © Material – www.concrete.org nd the gredients at the in w mix th an e f at ncrete—strength side-face cover round the embe op concrete sur l b of uch ded ce. PART 1: GENERAL 43 CODE COMMENTARY 2 Not. Term.
- 46. the requirements of ASTM A615, A706, or A955 shall be considered as ductile steel elements. stirrup—reinforcement used to resist shear and torsion forces in a member; typically deformed bars, deformed wires, or welded wire reinforcement either single leg or bent into L, U, or rectangular shapes and located perpendicular to, or at an angle to, longitudinal reinforcement. See also tie. strength, design—nominal strength multiplied by a VWUHQJWKUHGXFWLRQIDFWRUࢥ strength, nominal—strength of a member or cross section calculated in accordance with provisions and assumptions of the strength design method of this Code before application of any strength reduction factors. strength, required—strength of a member or cross section required to resist factored loads or related internal moments and forces in such combinations as stipulated in this Code. stretch length—length of anchor, extending beyond concrete in which it is anchored, subject to full tensile load applied to anchor, and for which cross-sectional area is minimum and constant. structural concrete—concrete used for structural purposes, including plain and reinforced concrete. structural diaphragm²PHPEHUVXFKDVDÀRRURUURRI slab, that transmits forces acting in the plane of the member to vertical elements of the lateral-force-resisting system. A structural diaphragm may include chords and collectors as part of the diaphragm. structural integrity—ability of a structure through strength, redundancy, ductility, and detailing of reinforce- ment to redistribute stresses and maintain overall stability if ORFDOL]HGGDPDJHRUVLJQL¿FDQWRYHUVWUHVVRFFXUV structural system—interconnected members designed to meet performance requirements. structural truss—assemblage of reinforced concrete members subjected primarily to axial forces. structural wall—wall proportioned to resist combina- tions of moments, shears, and axial forces in the plane of the wall; a shear wall is a structural wall. structural wall, ductile coupled—a seismic-force- resisting-system complying with 18.10.9. structural wall, ordinary reinforced concrete—a wall complying with Chapter 11. structural wall, ordinary plain concrete—a wall complying with Chapter 14. stirrup—The term “stirrup” is usually applied to trans- verse reinforcement in beams or slabs and the term “ties” or “hoops” to transverse reinforcement in compression members. strength, nominal²1RPLQDORUVSHFL¿HGYDOXHVRIPDWH- rial strengths and dimensions are used in the calculation of nominal strength. The subscript n is used to denote the nominal strengths; for example, nominal axial load strength Pn, nominal moment strength Mn, and nominal shear strength Vn. For additional discussion on the concepts and nomenclature for strength design, refer to the Commentary of Chapter 22. strength, required—The subscript u is used only to denote the required strengths; for example, required axial load strength Pu, required moment strength Mu, and required shear strength Vu, calculated from the applied factored loads and forces. The basic requirement for strength design may EHH[SUHVVHGDVIROORZVGHVLJQVWUHQJWK•UHTXLUHGVWUHQJWK IRUH[DPSOHࢥPn•PuࢥMn•MuࢥVn•Vu. For additional discussion on the concepts and nomenclature for strength design, refer to the Commentary of Chapter 22. stretch length—Length of an anchor over which inelastic elongations are designed to occur under earthquake load- ings. Examples illustrating stretch length are shown in Fig. R17.10.5.3. American Concrete Institute – Copyrighted © Material – www.concrete.org IROORZVGH • Pu P ࢥMn M M concepts Commen Length o designed t s illustrat nternal as stipulated in an su h denote load strength Pu strength Vu V V , calc The basic re , extending be t to full tensile i ond ad IRUH discus stre elong PSOH on refe ch le ons ces. HVVHG qui u 44 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 47. structural wall, intermediate precast—a wall complying with 18.5. structural wall, special—a cast-in-place structural wall in accordance with 18.2.3 through 18.2.8 and 18.10; or a precast structural wall in accordance with 18.2.3 through 18.2.8 and 18.11. strut—compression member in a strut-and-tie model representing the resultant of a parallel or a fan-shaped FRPSUHVVLRQ¿HOG strut, boundary—strut located along the boundary of a member or discontinuity region. strut, interior—strut not located along the boundary of a member or discontinuity region. strut-and-tie model—truss model of a member or of a D-region in such a member, made up of struts and ties connected at nodes and capable of transferring the factored loads to the supports or to adjacent B-regions. tendon—in post-tensioned members, a tendon is a complete assembly consisting of anchorages, prestressing reinforcement, and sheathing with coating for unbonded DSSOLFDWLRQVRUGXFWV¿OOHGZLWKJURXWIRUERQGHGDSSOLFDWLRQV tendon, bonded—tendon in which prestressed reinforce- ment is continuously bonded to the concrete through grouting of ducts embedded within the concrete cross section. tendon, external—a tendon external to the member concrete cross section in post-tensioned applications. tendon, unbonded—tendon in which prestressed rein- forcement is prevented from bonding to the concrete. The prestressing force is permanently transferred to the concrete at the tendon ends by the anchorages only. tension-controlled section—a cross section in which the net tensile strain in the extreme tension steel at nominal strength is greater than or equal to İty + 0.003. tie—(a) reinforcing bar or wire enclosing longitudinal reinforcement; a continuously wound transverse bar or wire in the form of a circle, rectangle, or other polygonal shape without reentrant corners enclosing longitudinal reinforce- ment; see also stirrup, hoop; (b) tension element in a strut- and-tie model. transfer—act of transferring stress in prestressed rein- forcement from jacks or pretensioning bed to concrete member. structural wall, intermediate precast—Requirements of 18.5 are intended to result in an intermediate precast struc- tural wall having minimum strength and toughness equiv- alent to that for an ordinary reinforced concrete structural wall of cast-in-place concrete. A precast concrete wall not satisfying the requirements of 18.5 is considered to have ductility and structural integrity less than that for an inter- mediate precast structural wall. structural wall, special—Requirements of 18.2.3 through 18.2.8 and 18.11 are intended to result in a special precast structural wall having minimum strength and toughness equivalent to that for a special reinforced concrete structural wall of cast-in-place concrete. strut, boundary—A boundary strut is intended to apply WRWKHÀH[XUDOFRPSUHVVLRQ]RQHRIDEHDPZDOORURWKHU member. Boundary struts are not subject to transverse tension and are therefore stronger than interior struts (Fig. R23.2.1). strut, interior—Interior struts are subject to tension, acting perpendicular to the strut in the plane of the model, from shear (Fig. R23.2.1). tendon, external—In new or existing post-tensioned applications, a tendon totally or partially external to the member concrete cross section, or inside a box section, and attached at the anchor device and deviation points. American Concrete Institute – Copyrighted © Material – www.concrete.org R23.2.1). e ong the b mo m e o en me membe and are therefore ut, interior—In ndicular to f a member up of struts and nsferring the fac egions rs, a tendon f ties red a perpe ear ( he he PART 1: GENERAL 45 CODE COMMENTARY 2 Not. Term.
- 48. transfer length—length of embedded pretensioned rein- IRUFHPHQWUHTXLUHGWRWUDQVIHUWKHH൵HFWLYHSUHVWUHVVWRWKH concrete. two-way construction—members designed to be capable of supporting loads through bending in two directions; some slabs and foundations are considered two-way construction. See also one-way construction. uncased cast-in-place concrete drilled or augered piles—piles with or without an enlarged base (bell) that are constructed by either drilling a hole in the ground, or by installing a temporary casing in the ground and cleaning out WKHVRLODQGVXEVHTXHQWO¿OOLQJWKHKROHZLWKUHLQIRUFHPHQW and concrete. wall—a vertical element designed to resist axial load, lateral load, or both, with a horizontal length-to-thickness ratio greater than 3, used to enclose or separate spaces. wall segment—portion of wall bounded by vertical or horizontal openings or edges. wall segment, horizontal—segment of a structural wall, bounded vertically by two openings or by an opening and an edge. wall segment, vertical—segment of a structural wall, bounded horizontally by two openings or by an opening and an edge; wall piers are vertical wall segments. wall pier—a vertical wall segment within a structural wall, bounded horizontally by two openings or by an opening and an edge, with ratio of horizontal length to wall thickness (Ɛw/bw) less than or equal to 6.0, and ratio of clear height to horizontal length (hw/Ɛw) greater than or equal to 2.0. water-cementitious materials ratio—ratio of mass of water, excluding that absorbed by the aggregate, to the mass of cementitious materials in a mixture, stated as a decimal. work²WKH HQWLUH FRQVWUXFWLRQ RU VHSDUDWHO LGHQWL¿DEOH parts thereof that are required to be furnished under the construction documents. yield strength²VSHFL¿HG PLQLPXP LHOG VWUHQJWK RU yield point of reinforcement; yield strength or yield point shall be determined in tension according to applicable $670VWDQGDUGVDVPRGL¿HGEWKLVRGH wall segment, horizontal—A horizontal wall segment is shown in Fig. R18.10.4.5. wall pier—Wall piers are vertical wall segments with dimensions and reinforcement intended to result in shear GHPDQG EHLQJ OLPLWHG E ÀH[XUDO LHOGLQJ RI WKH YHUWLFDO reinforcement in the pier. American Concrete Institute – Copyrighted © Material – www.concrete.org piers ar nforceme WHG E À the pier. al wall, an opening and nt of ning wal seg by o al wall shown in Fig. R ments. t within a struc openings or b zontal length to 0, and ratio of ural an wall ar wal HPDQ reinf pier ons EHL eme 46 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 49. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 47 CODE COMMENTARY 3 Ref. Standards 3.1—Scope 3.1.16WDQGDUGVRUVSHFL¿FVHFWLRQVWKHUHRIFLWHGLQWKLV Code, including Annex, Appendixes, or Supplements where prescribed, are referenced without exception in this Code, XQOHVVVSHFL¿FDOOQRWHGLWHGVWDQGDUGVDUHOLVWHGLQWKH following with their serial designations, including year of adoption or revision. 3.2—Referenced standards 3.2.1 $PHULFDQ$VVRFLDWLRQRI6WDWH+LJKZDDQG7UDQV- SRUWDWLRQ2৽FLDOV $$6+72 /5)'86²/5)' %ULGJH 'HVLJQ 6SHFL¿FDWLRQV WK Edition, 2017, Articles 5.8.4.4.2, 5.8.4.4.3, and 5.8.4.5 /5)'216²/5)' %ULGJH RQVWUXFWLRQ 6SHFL¿FD- tions, Fourth Edition, 2017, Article 10.3.2.3 3.2.2 $PHULFDQRQFUHWH,QVWLWXWH $, ²6SHFL¿FDWLRQV IRU 6WUXFWXUDO RQFUHWH $UWLFOH 4.2.3 318.2-19—Building Code Requirements for Concrete Thin Shells and Commentary 332-14—Residential Code Requirements for Structural Concrete and Commentary ²4XDOL¿FDWLRQ RI 3RVW,QVWDOOHG 0HFKDQLFDO Anchors in Concrete and Commentary ²4XDOL¿FDWLRQ RI 3RVW,QVWDOOHG $GKHVLYH Anchors in Concrete 369.1-17—Standard Requirements for Seismic Evalua- WLRQDQG5HWUR¿WRI([LVWLQJRQFUHWH%XLOGLQJV and Commentary 374.1-05—Acceptance Criteria for Moment Frames Based on Structural Testing ²6SHFL¿FDWLRQ IRU 8QERQGHG 6LQJOH6WUDQG Tendon Materials 437.2-13—Code Requirements for Load Testing of Existing Concrete Structures and Commentary ²'HVLJQ 6SHFL¿FDWLRQ IRU 8QERQGHG 3RVW Tensioned Precast Concrete Special Moment Frames Satis- fying ACI 374.1 and Commentary ²4XDOL¿FDWLRQRI3UHFDVWRQFUHWH'LDSKUDJP Connections and Reinforcement at Joints for Earthquake Loading and Commentary 550.5-18—Code Requirements for the Design of Precast Concrete Diaphragms for Earthquake Motions and Commentary ITG-5.1-07—Acceptance Criteria for Special Unbonded Post-Tensioned Precast Structural Walls Based on Validation Testing ITG-5.2-09—Requirements for Design of a Special Unbonded Post-Tensioned Precast Wall Satisfying ACI ITG-5.1 and Commentary R3.1—Scope R3.1.1 ,QWKLVRGHUHIHUHQFHVWRVWDQGDUGVSHFL¿FDWLRQV RURWKHUPDWHULDODUHWRDVSHFL¿FHGLWLRQRIWKHFLWHGGRFX- ment. This is done by using the complete serial designation for the referenced standard including the title that indicates the subject and year of adoption. All standards referenced in this Code are listed in this chapter, with the title and complete serial designation. In other sections of the Code, referenced standards are abbreviated to include only the serial desig- nation without a title or date. These abbreviated references FRUUHVSRQGWRVSHFL¿FVWDQGDUGVOLVWHGLQWKLVFKDSWHU R3.2—Referenced standards R3.2.1 $PHULFDQ$VVRFLDWLRQRI6WDWH+LJKZDDQG7UDQV- SRUWDWLRQ2৽FLDOV $$6+72 7KUHH DUWLFOHV RI WKH $$6+72 /5)' 6SHFL¿FDWLRQV IRU Highway Bridge Design (AASHTO LRFDUS) and one article RIWKH$$6+72/5)'RQVWUXFWLRQ6SHFL¿FDWLRQV $$6+72 LRFDCONS) are cited in Chapters 2 and 25 of this Code. R3.2.2 $PHULFDQRQFUHWH,QVWLWXWH $, Article 4.2.3 of ACI 301 is referenced for the method of mixture proportioning cited in 26.4.3.1(b). Prior to 2014, the provisions of ACI 318.2 ZHUHVSHFL¿HG in Chapter 19 of the ACI 318 Building Code. ACI 355.2 FRQWDLQVTXDOL¿FDWLRQUHTXLUHPHQWVIRUWHVWLQJ and evaluating post-installed expansion, screw, and undercut anchors for use in both cracked and uncracked concrete. ACI 355.4 FRQWDLQVTXDOL¿FDWLRQUHTXLUHPHQWVIRUWHVWLQJ and evaluating adhesive anchors for use in both cracked and uncracked concrete. ACI 423.7 requires the use of encapsulated tendon systems for applications subject to this Code. CHAPTER 3—REFERENCED STANDARDS
- 50. American Concrete Institute – Copyrighted © Material – www.concrete.org 48 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY 3.2.3 $PHULFDQ6RFLHWRILYLO(QJLQHHUV $6( $6(6(, ²0LQLPXP 'HVLJQ /RDGV IRU %XLOGLQJV and Other Structures, Sections 2.3.2, Load Combinations Including Flood Loads; and 2.3.3, Load Combinations Including Atmospheric Ice Loads 3.2.4 ASTM International $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU :HOGHG Deformed Steel Bar Mats for Concrete Reinforcement A307-14İ ²6WDQGDUG 6SHFL¿FDWLRQ IRU DUERQ 6WHHO Bolts, Studs, and Threaded Rod 60000 PSI Tensile Strength $²6WDQGDUG 7HVW 0HWKRGV DQG 'H¿QLWLRQV IRU Mechanical Testing of Steel Products $$0²6WDQGDUG6SHFL¿FDWLRQIRU/RZ5HOD[- ation, Seven-Wire Steel Strand for Prestressed Concrete $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU 8QFRDWHG Stress-Relieved Steel Wire for Prestressed Concrete, including Supplementary Requirement SI, Low-Relaxation Wire and Relaxation Testing $$0İ ²6WDQGDUG6SHFL¿FDWLRQIRU'HIRUPHG and Plain Carbon-Steel Bars for Concrete Reinforcement $$0²6WDQGDUG6SHFL¿FDWLRQIRU'HIRUPHG and Plain Low-Alloy Steel Bars for Concrete Reinforcement $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU 8QFRDWHG High-Strength Steel Bars for Prestressing Concrete $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU =LQF Coated (Galvanized) Steel Bars for Concrete Reinforcement $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU (SR[ Coated Steel Reinforcing Bars $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU 6WHHO Fibers for Fiber-Reinforced Concrete $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU (SR[ Coated Steel Wire and Welded Wire Reinforcement $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU (SR[ Coated Prefabricated Steel Reinforcing Bars $$0E²6WDQGDUG6SHFL¿FDWLRQIRU'HIRUPHG and Plain Stainless-Steel Bars for Concrete Reinforcement $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU +HDGHG Steel Bars for Concrete Reinforcement, including Annex A1 Requirements for Class HA Head Dimensions $$0²6WDQGDUG 6SHFL¿FDWLRQ IRU 5DLO6WHHO and Axle-Steel Deformed Bars for Concrete Reinforcement $$0E²6WDQGDUG 6SHFL¿FDWLRQ IRU Deformed and Plain Stainless Steel Wire and Welded Wire for Concrete Reinforcement $$0E²6WDQGDUG 6SHFL¿FDWLRQ IRU Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement $$0D²6WDQGDUG 6SHFL¿FDWLRQ IRU 6WHHO Stud Assemblies for Shear Reinforcement of Concrete $$0²6WDQGDUG6SHFL¿FDWLRQIRU=LQFDQG Epoxy Dual-Coated Steel Reinforcing Bars $$0E²6WDQGDUG 6SHFL¿FDWLRQ IRU =LQF Coated (Galvanized) Steel Welded Wire Reinforcement, Plain and Deformed, for Concrete R3.2.3 $PHULFDQ6RFLHWRILYLO(QJLQHHUV $6( 7KHWZRVSHFL¿FVHFWLRQVRI$6(DUHUHIHUHQFHGIRUWKH purposes cited in 5.3.9 and 5.3.10. R3.2.4 ASTM International The ASTM standards listed are the latest editions at the time these code provisions were adopted. ASTM standards are revised frequently relative to the revision cycle for the Code. Current and historical editions of the referenced standards can be obtained from ASTM International. Use of an edition of a standard other than that referenced in the RGHREOLJDWHVWKHXVHUWRHYDOXDWHLIDQGL൵HUHQFHVLQWKH QRQFRQIRUPLQJHGLWLRQDUHVLJQL¿FDQWWRXVHRIWKHVWDQGDUG Many of the ASTM standards are combined standards DV GHQRWHG E WKH GXDO GHVLJQDWLRQ VXFK DV$670$ A36M. For simplicity, these combined standards are refer- enced without the metric (M) designation within the text of the Code and Commentary. In this provision, however, WKHFRPSOHWHGHVLJQDWLRQLVJLYHQEHFDXVHWKDWLVWKHR൶FLDO designation for the standard.
- 51. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 49 CODE COMMENTARY 3 Ref. Standards $$0D²6WDQGDUG 6SHFL¿FDWLRQ IRU Carbon-Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete 0D²6WDQGDUG7HVW0HWKRGIRU%XON'HQVLW (“Unit Weight”) and Voids in Aggregate 0²6WDQGDUG3UDFWLFHIRU0DNLQJDQGXULQJ Concrete Test Specimens in the Field 0²6WDQGDUG 6SHFL¿FDWLRQ IRU RQFUHWH Aggregates 0²6WDQGDUG7HVW0HWKRGIRURPSUHVVLYH Strength of Cylindrical Concrete Specimens 0D²6WDQGDUG 7HVW 0HWKRG IRU 2EWDLQLQJ and Testing Drilled Cores and Sawed Beams of Concrete 0²6WDQGDUG6SHFL¿FDWLRQIRU5HDG0L[HG Concrete C138-17a—Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete 0D²6WDQGDUG 6SHFL¿FDWLRQ IRU 3RUW- land Cement 0²6WDQGDUG 3UDFWLFH IRU 6DPSOLQJ Freshly Mixed Concrete 0²6WDQGDUG7HVW0HWKRGIRU$LURQWHQW of Freshly Mixed Concrete by the Volumetric Method C192-18—Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory 0D²6WDQGDUG7HVW0HWKRGIRU$LURQWHQW of Freshly Mixed Concrete by the Pressure Method 0D ²6WDQGDUG6SHFL¿FDWLRQIRU$LU Entraining Admixtures for Concrete 0D²6WDQGDUG 6SHFL¿FDWLRQ IRU /LJKW- weight Aggregates for Structural Concrete 0²6WDQGDUG7HVW0HWKRGIRU6WDWLF0RGXOXV of Elasticity and Poisson’s Ratio of Concrete in Compression 0²6WDQGDUG 6SHFL¿FDWLRQ IRU KHPLFDO Admixtures for Concrete 0²6WDQGDUG7HVW0HWKRGIRU'HWHUPLQLQJ Density of Structural Lightweight Concrete 0²6WDQGDUG 6SHFL¿FDWLRQ IRU %OHQGHG Hydraulic Cements ²6WDQGDUG 6SHFL¿FDWLRQ IRU RDO )O$VK DQG Raw or Calcined Natural Pozzolan for Use in Concrete 0D²6WDQGDUG 6SHFL¿FDWLRQ IRU RQFUHWH Made by Volumetric Batching and Continuous Mixing 0²6WDQGDUG6SHFL¿FDWLRQIRU([SDQVLYH Hydraulic Cement 0D²6WDQGDUG 6SHFL¿FDWLRQ IRU 6ODJ Cement for Use in Concrete and Mortars 0E²6WDQGDUG7HVW0HWKRGIRU/HQJWK Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution 0İ ²6WDQGDUG6SHFL¿FDWLRQIRUKHP- ical Admixtures for Use in Producing Flowing Concrete C1077-17—Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation
- 52. American Concrete Institute – Copyrighted © Material – www.concrete.org 50 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY 0D ²6WDQGDUG 6SHFL¿FDWLRQ IRU Fiber-Reinforced Concrete C1140-11—Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels ²6WDQGDUG 6SHFL¿FDWLRQ IRU $GPL[WXUHV IRU Shotcrete 0²6WDQGDUG3HUIRUPDQFH6SHFL¿FDWLRQ for Hydraulic Cement 0²6WDQGDUG 7HVW 0HWKRG IRU :DWHU Soluble Chloride in Mortar and Concrete ²6WDQGDUG6SHFL¿FDWLRQIRU6LOLFD)XPH8VHG in Cementitious Mixtures ²6WDQGDUG 6SHFL¿FDWLRQ IRU 0DWHULDOV IRU Shotcrete ²6WDQGDUG 6SHFL¿FDWLRQ IRU 3DFNDJHG Pre-Blended, Dry, Combined Materials for Use in Wet or Dry Shotcrete Application C1580-15—Standard Test Method for Water-Soluble Sulfate in Soil 0 İ ²6WDQGDUG 6SHFL¿FDWLRQ IRU Admixtures to Inhibit Chloride-Induced Corrosion of Rein- forcing Steel in Concrete 0²6WDQGDUG 6SHFL¿FDWLRQ IRU 0L[LQJ Water Used in the Production of Hydraulic Cement Concrete C1604-05(2012)—Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete 0²6WDQGDUG7HVW0HWKRGIRU)OH[XUDO Performance of Fiber-Reinforced Concrete (Using Beam with Third-Point Loading) ²6WDQGDUG 6SHFL¿FDWLRQ IRU *URXQG DOFLXP Carbonate andAggregate Mineral Fillers for use in Hydraulic Cement Concrete D516-16—Standard Test Method for Sulfate Ion in Water D4130-15—Standard Test Method for Sulfate Ion in Brackish Water, Seawater, and Brines 3.2.5 $PHULFDQ:HOGLQJ6RFLHW $:6 ''0²6WUXFWXUDO:HOGLQJRGH±6WHHO ''0 ²6WUXFWXUDO :HOGLQJ RGH ± 5HLQ- forcing Steel
- 53. 4.1—Scope 4.1.1Thischaptershallapplytodesignofstructuralconcrete LQVWUXFWXUHVRUSRUWLRQVRIVWUXFWXUHVGH¿QHGLQChapter 1. 4.2—Materials 4.2.1 Design properties of concrete shall be selected to be in accordance with Chapter 19. 4.2.1.1 Design properties of shotcrete shall conform to the UHTXLUHPHQWVIRUFRQFUHWHH[FHSWDVPRGL¿HGESURYLVLRQV of the Code. 4.2.2 Design properties of reinforcement shall be selected to be in accordance with Chapter 20. 4.3—Design loads 4.3.1 Loads and load combinations considered in design shall be in accordance with Chapter 5. R4.1—Scope This chapter was added to the 2014 Code to introduce structural system requirements. Requirements more strin- gent than the Code provisions may be desirable for unusual construction or construction where enhanced performance is appropriate. The Code and Commentary must be supple- mented with sound engineering knowledge, experience, and judgment. R4.2—Materials Chapter 3 LGHQWL¿HVWKHUHIHUHQFHGVWDQGDUGVSHUPLWWHGIRU design. Chapters 19 and 20 establish properties of concrete and steel reinforcement permitted for design. Chapter 26 presents construction requirements for concrete materials, proportioning, and acceptance of concrete. R4.2.1.1 Shotcrete is considered to behave and have prop- erties similar to concrete unless otherwise noted. Sections ZKHUHXVHRIVKRWFUHWHLVVSHFL¿FDOODGGUHVVHGLQWKLVRGH are shown in Table R4.2.1.1. Additional information on shotcrete can be found in ACI 506R and ACI 506.2. Table R4.2.1.1—Sections in Code with shotcrete provisions Topic covered Section Freezing and thawing 19.3.3.3 through 19.3.3.6 Reinforcement 25.2.7 through 25.2.10, 25.5.1.6, and 25.5.1.7 Where shotcrete is required or permitted 26.3.1, 26.3.2 Materials 26.4.1.2, 26.4.1.4, and 26.4.1.6 Proportioning mixtures 26.4.3 Documentation of mixtures 26.4.4.1 Placement and consolidation 26.5.2.1 Curing 26.5.3 Joints 26.5.6 Evaluation and acceptance 26.12 R4.3—Design loads R4.3.1 The provisions in Chapter 5 are based on $6( SEI 7. The design loads include, but are not limited to, dead loads, live loads, snow loads, wind loads, earth- TXDNH H൵HFWV SUHVWUHVVLQJ H൵HFWV FUDQH ORDGV YLEUDWLRQ impact, shrinkage, temperature changes, creep, expansion of shrinkage-compensating concrete, and predicted unequal VHWWOHPHQWRIVXSSRUWV2WKHUSURMHFWVSHFL¿FORDGVPDEH VSHFL¿HGEWKHOLFHQVHGGHVLJQSURIHVVLRQDO American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 51 CODE COMMENTARY 4 Struct. Systems —Section ing nt ete is require permitted ZKHUH are shown in ete can be foun pro ons Topic ezing Reinf R4.2 CHAPTER 4—STRUCTURAL SYSTEM REQUIREMENTS
- 54. 4.4—Structural system and load paths 4.4.1 The structural system shall include (a) through (g), as applicable: (a) Floor construction and roof construction, including one-way and two-way slabs (b) Beams and joists (c) Columns (d) Walls (e) Diaphragms (f) Foundations (g) Joints, connections, and anchors as required to transmit forces from one component to another 4.4.2 Design of structural members including joints and connections given in 4.4.1 shall be in accordance with Chap- ters 7 through 18. 4.4.3 It shall be permitted to design a structural system comprising structural members not in accordance with 4.4.1 and 4.4.2, provided the structural system is approved in accordance with 1.10.1. 4.4.4 The structural system shall be designed to resist the factored loads in load combinations given in 4.3 without exceeding the appropriate member design strengths, consid- ering one or more continuous load paths from the point of ORDGDSSOLFDWLRQRURULJLQDWLRQWRWKH¿QDOSRLQWRIUHVLVWDQFH 4.4.5 Structural systems shall be designed to accommo- GDWHDQWLFLSDWHGYROXPHFKDQJHDQGGL൵HUHQWLDOVHWWOHPHQW R4.4—Structural system and load paths R4.4.1 Structural concrete design has evolved from emphasizing the design of individual members to designing the structure as an entire system. A structural system consists of structural members, joints, and connections, each SHUIRUPLQJDVSHFL¿FUROHRUIXQFWLRQ$VWUXFWXUDOPHPEHU may belong to one or more structural systems, serving GL൵HUHQW UROHV LQ HDFK VVWHP DQG KDYLQJ WR PHHW DOO WKH detailing requirements of the structural systems of which they are a part. Joints and connections are locations common to intersecting members or are items used to connect one member to another, but the distinction between members, joints, and connections can depend on how the structure is idealized. Throughout this chapter, the term “members” often refers to “structural members, joints, and connections.” Although the Code is written considering that a structural system comprises these members, many alternative arrange- ments are possible because not all structural member types are used in all building structural systems. The selection types RIWKHPHPEHUVWRXVHLQDVSHFL¿FSURMHFWDQGWKHUROHRU roles these member types play is made by the licensed design professional complying with requirements of the Code. R4.4.2 In the chapter for each type of structural member, requirements follow the same general sequence and scope, including general requirements, design limits, required strength, design strength, reinforcement limits, reinforce- ment detailing, and other requirements unique to the type of member. R4.4.3 Some materials, structural members, or systems that may not be recognized in the prescriptive provisions of the Code may still be acceptable if they meet the intent of the Code. Section 1.10.1 outlines the procedures for obtaining approval of alternative materials and systems. R4.4.4 The design should be based on members and connections that provide design strengths not less than the strengths required to transfer the loads along the load path. The licensed design professional may need to study one or more alternative paths to identify weak links along the sequence of elements that constitute each load path. R4.4.5 7KH H൵HFWV RI FROXPQ DQG ZDOO FUHHS DQG shrinkage, restraint of creep and shrinkage in long roof and ÀRRU VVWHPV FUHHS FDXVHG E SUHVWUHVV IRUFHV YROXPH changes caused by temperature variation, as well as poten- tial damage to supporting members caused by these volume changes should be considered in design. Reinforcement, closure strips, or expansion joints are common ways of DFFRPPRGDWLQJ WKHVH H൵HFWV 0LQLPXP VKULQNDJH DQG temperature reinforcement controls cracking to an accept- able level in many concrete structures of ordinary propor- tions and exposures. American Concrete Institute – Copyrighted © Material – www.concrete.org 52 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY hapter for w the sam requirem rength, r nd other 1 4.3 Some that may emb be are us RIWKHPHPEHUV these member ty complying w ncluding joints cordance with C d ap- R requir treng ment 2 In ment ng g , de etail onal p with ith
- 55. 4.4.6 6HLVPLFIRUFHUHVLVWLQJVVWHP 4.4.6.1 Every structure shall be assigned to a Seismic Design Category in accordance with the general building FRGH RU DV GHWHUPLQHG E WKH EXLOGLQJ R൶FLDO LQ DUHDV without a legally adopted building code. 4.4.6.2 Structural systems designated as part of the seismic-force-resisting system shall be restricted to those systems designated by the general building code or as deter- PLQHG E WKH EXLOGLQJ R൶FLDO LQ DUHDV ZLWKRXW D OHJDOO adopted building code. 4.4.6.3 Structural systems assigned to Seismic Design Category A shall satisfy the applicable requirements of this Code. Structures assigned to Seismic Design Category A are not required to be designed in accordance with Chapter 18. 4.4.6.4 Structural systems assigned to Seismic Design Category B, C, D, E, or F shall satisfy the requirements of Chapter 18 in addition to applicable requirements of other chapters of this Code. 4.4.6.5 Structural members assumed not to be part of the seismic-force-resisting system shall be permitted, subject to the requirements of 4.4.6.5.1 and 4.4.6.5.2. 4.4.6.5.1 In structures assigned to Seismic Design Cate- JRU%'(RU)WKHH൵HFWVRIWKRVHVWUXFWXUDOPHPEHUV on the response of the system shall be considered and accom- modated in the structural design. 4.4.6.5.2 In structures assigned to Seismic Design Cate- gory B, C, D, E, or F, the consequences of damage to those structural members shall be considered. 4.4.6.5.3 In structures assigned to Seismic Design Cate- gory D, E, or F, structural members not considered part of 'L൵HUHQWLDO VHWWOHPHQW RU KHDYH PD EH DQ LPSRUWDQW consideration in design. Geotechnical recommendations to DOORZIRUQRPLQDOYDOXHVRIGL൵HUHQWLDOVHWWOHPHQWDQGKHDYH are not normally included in design load combinations for ordinary building structures. R4.4.6 6HLVPLFIRUFHUHVLVWLQJVVWHP R4.4.6.1 Design requirements in the Code are based on the seismic design category to which the structure is assigned. In general, the seismic design category relates to seismic risk level, soil type, occupancy, and building use. Assignment of a building to a seismic design category is under the jurisdic- tion of a general building code rather than this Code. In the absence of a general building code, $6(6(, provides the assignment of a building to a seismic design category. R4.4.6.2 The general building code prescribes, through $6(6(,WKHWSHVRIVWUXFWXUDOVVWHPVSHUPLWWHGDVSDUW of the seismic-force-resisting system based on considerations such as seismic design category and building height. The seismic design requirements for systems assigned to Seismic Design Categories B through F are prescribed in Chapter 18. 2WKHUVVWHPVFDQEHXVHGLIDSSURYHGEWKHEXLOGLQJR൶FLDO R4.4.6.3 Structures assigned to Seismic Design Category A are subject to the lowest seismic hazard. Chapter 18 does not apply. R4.4.6.4 Chapter 18 contains provisions that are appli- cable depending on the seismic design category and on the seismic-force-resisting system used. Not all structural PHPEHU WSHV KDYH VSHFL¿F UHTXLUHPHQWV LQ DOO VHLVPLF design categories. For example, Chapter 18 does not include requirements for structural walls in Seismic Design Catego- ries B and C, but does include special provisions for Seismic Design Categories D, E, and F. R4.4.6.5 In Seismic Design Categories D, E, and F, struc- tural members not considered part of the seismic-force- resisting system are required to be designed to accommodate drifts and forces that occur as the building responds to an earthquake. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 53 CODE COMMENTARY 4 Struct. Systems es B throug EHXVHGLID es assign lowest s of .4.6.4 Chap cable d o those code or as deter- DV ZLWKR ass pli mi d $6( of the seismic-fo as seismic desi gn requirem d to Seismic D requirements o sign Category h ign this re 2WKH A are not a VWHP 6.3 ubjec ly. desi Cate nts nts
- 56. the seismic-force-resisting system shall meet the applicable requirements in Chapter 18. 4.4.6.6 (൵HFWV RI QRQVWUXFWXUDO PHPEHUV VKDOO EH accounted for as described in 18.2.2.1 and consequences of damage to nonstructural members shall be considered. 4.4.6.7 'HVLJQ YHUL¿FDWLRQ RI HDUWKTXDNHUHVLVWDQW concrete structures using nonlinear response history analysis shall be in accordance with Appendix A. 4.4.7 'LDSKUDJPV 4.4.7.1'LDSKUDJPVVXFKDVÀRRURUURRIVODEVVKDOOEH designed to resist simultaneously both out-of-plane gravity loads and in-plane lateral forces in load combinations given in 4.3. 4.4.7.2 Diaphragms and their connections to framing members shall be designed to transfer forces between the diaphragm and framing members. 4.4.7.3 Diaphragms and their connections shall be designed to provide lateral support to vertical, horizontal, and inclined elements. 4.4.7.4 Diaphragms shall be designed to resist applicable lateral loads from soil and hydrostatic pressure and other loads assigned to the diaphragm by structural analysis. 4.4.7.5 Collectors shall be provided where required to transmit forces between diaphragms and vertical elements. 4.4.7.6 Diaphragms that are part of the seismic-force- resisting system shall be designed for the applied forces. In structures assigned to Seismic Design Category D, E, and F, the diaphragm design shall be in accordance with Chapter 18. 4.5—Structural analysis 4.5.1 Analytical procedures shall satisfy compatibility of deformations and equilibrium of forces. 4.5.2 The methods of analysis given in Chapter 6 shall be permitted. R4.4.6.6Although the design of nonstructural elements for HDUWKTXDNHH൵HFWVLVQRWLQFOXGHGLQWKHVFRSHRIWKLVRGH WKHSRWHQWLDOQHJDWLYHH൵HFWVRIQRQVWUXFWXUDOHOHPHQWVRQWKH structural behavior need to be considered in Seismic Design Categories B, C, D, E, and F. Interaction of nonstructural elements with the structural system—for example, the short- FROXPQH൵HFW²KDGOHGWRIDLOXUHRIVWUXFWXUDOPHPEHUVDQG collapse of some structures during earthquakes in the past. R4.4.7 'LDSKUDJPV Floor and roof slabs play a dual role by simultaneously supporting gravity loads and transmitting lateral forces in their own plane as a diaphragm. General requirements for diaphragms are provided in Chapter 12, and roles of the diaphragm described in the Commentary to that chapter. Additional requirements for design of diaphragms in struc- tures assigned to Seismic Design Categories D, E, and F are prescribed in Chapter 18. R4.4.7.5 All structural systems must have a complete load path in accordance with 4.4.4. The load path includes collec- tors where required. R4.5—Structural analysis The role of analysis is to estimate the internal forces and deformations of the structural system and to establish compliance with the strength, serviceability, and stability requirements of the Code. The use of computers in struc- tural engineering has made it feasible to perform analysis of complex structures. The Code requires that the analytical procedure used meets the fundamental principles of equilib- rium and compatibility of deformations, permitting a number of analytical techniques, including the strut-and-tie method required for discontinuity regions, as provided in Chapter 6. American Concrete Institute – Copyrighted © Material – www.concrete.org 54 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY ribed in th ements for ismic De er 18. le DOOEH of-plane gravity d combin eir tr rs eir rt supporting grav own plane as a are provide ections to fra r forces betwee nnections shal i l g the be Add tures a nal sign ed i gms gm p d in i
- 57. 4.6—Strength 4.6.1 Design strength of a member and its joints and connections, in terms of moment, shear, torsional, axial, and bearing strength, shall be taken as the nominal strength Sn multiplied by the applicable strength reduction factor ࢥ. 4.6.2 Structures and structural members shall have design strength at all sections, ࢥSn, greater than or equal to the required strength U calculated for the factored loads and forces in such combinations as required by this Code or the general building code. R4.6—Strength The basic requirement for strength design may be expressed as follows: GHVLJQVWUHQJWK•UHTXLUHGVWUHQJWK ࢥSn•U In the strength design procedure, the level of safety is provided by a combination of factors applied to the loads and strength reduction factors ࢥ applied to the nominal strengths. The strength of a member or cross section, calculated using standard assumptions and strength equations, along with nominal values of material strengths and dimensions, is referred to as nominal strength and is generally designated Sn. Design strength or usable strength of a member or cross section is the nominal strength reduced by the applicable strength reduction factor ࢥ. The purpose of the strength reduction factor is to account for the probability of under- strength due to variations of in-place material strengths and GLPHQVLRQV WKH H൵HFW RI VLPSOLILQJ DVVXPSWLRQV LQ WKH design equations, the degree of ductility, potential failure PRGH RI WKH PHPEHU WKH UHTXLUHG UHOLDELOLW DQG VLJQL¿- cance of failure and existence of alternative load paths for the member in the structure. This Code, or the general building code, prescribes design load combinations, also known as factored load combina- WLRQV ZKLFK GH¿QH WKH ZD GL൵HUHQW WSHV RI ORDGV DUH multiplied (factored) by individual load factors and then combined to obtain a factored load U. The individual load IDFWRUV DQG DGGLWLYH FRPELQDWLRQ UHÀHFW WKH YDULDELOLW LQ magnitude of the individual loads, the probability of simul- taneous occurrence of various loads, and the assumptions and approximations made in the structural analysis when determining required design strengths. A typical design approach, where linear analysis is appli- cable, is to analyze the structure for individual unfactored load cases, and then combine the individual unfactored load cases in a factored load combination to determine the design ORDG H൵HFWV :KHUH H൵HFWV RI ORDGV DUH QRQOLQHDU²IRU example, in foundation uplift—the factored loads are applied simultaneously to determine the nonlinear, factored load H൵HFW7KHORDGH൵HFWVUHOHYDQWIRUVWUHQJWKGHVLJQLQFOXGH moments, shears, torsions, axial forces, bearing forces, and punching shear stresses. Sometimes, design displacements DUHGHWHUPLQHGIRUIDFWRUHGORDGV7KHORDGH൵HFWVUHOHYDQW IRUVHUYLFHGHVLJQLQFOXGHVWUHVVHVDQGGHÀHFWLRQV In the course of applying these principles, the licensed design professional should be aware that providing more strength than required does not necessarily lead to a safer structure because doing so may change the potential failure mode. For example, increasing longitudinal reinforcement area beyond that required for moment strength as derived from analysis without increasing transverse reinforcement could increase the probability of a shear failure occurring American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 55 CODE COMMENTARY 4 Struct. Systems HPEHU WKH nd existen tructure. general b also kno QH WKH Z tored) b o obtain a UV DQG DGGL magnitu reducti strength due to v VLRQV WKH H൵H tions, the d canc the m oad c WLRQV f fa mber Cod mbi ZKLF equa I WK egre gr
- 58. 4.7—Serviceability 4.7.1 Evaluation of performance at service load condi- tions shall consider reactions, moments, shears, torsions, and axial forces induced by prestressing, creep, shrinkage, temperature change, axial deformation, restraint of attached structural members, and foundation settlement. 4.7.2 For structures, structural members, and their connec- tions, the requirements of 4.7.1 shall be deemed to be satis- ¿HG LI GHVLJQHG LQ DFFRUGDQFH ZLWK WKH SURYLVLRQV RI WKH applicable member chapters. 4.8—Durability 4.8.1 Concrete mixtures shall be designed in accordance with the requirements of 19.3.2 and 26.4, considering appli- cable environmental exposure to provide required durability. 4.8.2 Reinforcement shall be protected from corrosion in accordance with 20.5. 4.9—Sustainability 4.9.1 The licensed design professional shall be permitted to specify in the construction documents sustainability requirements in addition to strength, serviceability, and durability requirements of this Code. 4.9.2 The strength, serviceability, and durability require- ments of this Code shall take precedence over sustainability considerations. 4.10—Structural integrity 4.10.1 General 4.10.1.1 Reinforcement and connections shall be detailed WRWLHWKHVWUXFWXUHWRJHWKHUH൵HFWLYHODQGWRLPSURYHRYHUDOO structural integrity. 4.10.2 0LQLPXPUHTXLUHPHQWVIRUVWUXFWXUDOLQWHJULW 4.10.2.1 Structural members and their connections shall be in accordance with structural integrity requirements in Table 4.10.2.1. SULRUWRDÀH[XUDOIDLOXUH([FHVVVWUHQJWKPDEHXQGHVLU- able for structures expected to behave inelastically during earthquakes. R4.7—Serviceability Serviceability refers to the ability of the structural system or structural member to provide appropriate behavior and IXQFWLRQDOLWXQGHUWKHDFWLRQVD൵HFWLQJWKHVVWHP6HUYLFH- DELOLWUHTXLUHPHQWVDGGUHVVLVVXHVVXFKDVGHÀHFWLRQVDQG cracking, among others. Serviceability considerations for vibrations are discussed in R6.6.3.2.2 and R24.1. Except as stated in Chapter 24, service-level load combi- QDWLRQVDUHQRWGH¿QHGLQWKLVRGHEXWDUHGLVFXVVHGLQ Appendix C of $6(6(,$SSHQGL[HVWR$6(6(, are not considered mandatory parts of the standard. R4.8—Durability The environment where the structure will be located will dictate the exposure category for materials selection, design details, and construction requirements to minimize potential for premature deterioration of the structure caused by envi- URQPHQWDOH൵HFWV'XUDELOLWRIDVWUXFWXUHLVDOVRLPSDFWHG by the level of preventative maintenance, which is not addressed in the Code. Chapter 19 provides requirements for protecting concrete against major environmental causes of deterioration. R4.9—Sustainability The Code provisions for strength, serviceability, and durability are minimum requirements to achieve a safe and durable concrete structure. The Code permits the owner or the licensed design professional to specify require- ments higher than the minimums mandated in the Code. Such optional requirements can include higher strengths, PRUHUHVWULFWLYHGHÀHFWLRQOLPLWVHQKDQFHGGXUDELOLWDQG sustainability provisions. R4.10—Structural integrity R4.10.1 General R4.10.1.1 It is the intent of the structural integrity require- ments to improve redundancy and ductility through detailing of reinforcement and connections so that, in the event of damage to a major supporting element or an abnormal loading, the resulting damage will be localized and the structure will have a higher probability of maintaining overall stability. Integrity requirements for selected structural member types are included in the corresponding member chapter in the sections noted. R4.10.2 0LQLPXPUHTXLUHPHQWVIRUVWUXFWXUDOLQWHJULW Structural members and their connections referred to in WKLVVHFWLRQLQFOXGHRQOPHPEHUWSHVWKDWKDYHVSHFL¿F requirements for structural integrity. Notwithstanding, American Concrete Institute – Copyrighted © Material – www.concrete.org 56 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY f preventat ode. des requir onmental ability provision are minimu ble concrete or the appli uired durability. tected s dictate details, and con remature deterio ൵HFWV'XUDE ll b add Cha R4.9 ed in ter 1 maj Sus WDOH leve LOLW OLW
- 59. Table 4.10.2.1—Minimum requirements for structural integrity Member type Section Nonprestressed one-way cast-in-place slabs 7.7.7 Nonprestressed two-way slabs 8.7.4.2 Prestressed two-way slabs 8.7.5.6 Nonprestressed two-way joist systems 8.8.1.6 Cast-in-place beam 9.7.7 Nonprestressed one-way joist system 9.8.1.6 Precast joints and connections 16.2.1.8 4.11—Fire resistance 4.11.16WUXFWXUDOFRQFUHWHPHPEHUVVKDOOVDWLVIWKH¿UH protection requirements of the general building code. 4.11.2 Where the general building code requires a thick- QHVVRIFRQFUHWHFRYHUIRU¿UHSURWHFWLRQJUHDWHUWKDQWKH FRQFUHWH FRYHU VSHFL¿HG LQ 20.5.1, such greater thickness shall govern. 4.12—Requirements for specific types of construction 4.12.1 3UHFDVWFRQFUHWHVVWHPV 4.12.1.1 Design of precast concrete members and connec- tions shall include loading and restraint conditions from initial fabrication to end use in the structure, including form removal, storage, transportation, and erection. 4.12.1.2 Design, fabrication, and construction of precast PHPEHUVDQGWKHLUFRQQHFWLRQVVKDOOLQFOXGHWKHH൵HFWVRI tolerances. detailing requirements for other member types address structural integrity indirectly. R4.11—Fire resistance $GGLWLRQDO JXLGDQFH RQ ¿UH UHVLVWDQFH RI VWUXFWXUDO concrete is provided by ACI 216.1. R4.12—Requirements for specific types of construction This section contains requirements that are related to VSHFL¿FWSHVRIFRQVWUXFWLRQ$GGLWLRQDOUHTXLUHPHQWVWKDW DUHVSHFL¿FWRPHPEHUWSHVDSSHDULQWKHFRUUHVSRQGLQJ member chapters. R4.12.1 3UHFDVWFRQFUHWHVVWHPV All requirements in the Code apply to precast systems and PHPEHUV XQOHVV VSHFL¿FDOO H[FOXGHG ,Q DGGLWLRQ VRPH UHTXLUHPHQWV DSSO VSHFL¿FDOO WR SUHFDVW FRQFUHWH 7KLV VHFWLRQFRQWDLQVVSHFL¿FUHTXLUHPHQWVIRUSUHFDVWVVWHPV 2WKHU VHFWLRQV RI WKLV RGH DOVR SURYLGH VSHFL¿F UHTXLUH- ments, such as required concrete cover, for precast systems. 3UHFDVWVVWHPVGL൵HUIURPPRQROLWKLFVVWHPVLQWKDWWKH type of restraint at supports, the location of supports, and the induced stresses in the body of the member vary during IDEULFDWLRQ VWRUDJH WUDQVSRUWDWLRQ HUHFWLRQ DQG WKH ¿QDO LQWHUFRQQHFWHG FRQ¿JXUDWLRQ RQVHTXHQWO WKH PHPEHU GHVLJQIRUFHVWREHFRQVLGHUHGPDGL൵HULQPDJQLWXGHDQG direction with varying critical sections at various stages of FRQVWUXFWLRQ)RUH[DPSOHDSUHFDVWÀH[XUDOPHPEHUPD EHVLPSOVXSSRUWHGIRUGHDGORDGH൵HFWVEHIRUHFRQWLQXLW at the supporting connections is established and may be a FRQWLQXRXVPHPEHUIRUOLYHRUHQYLURQPHQWDOORDGH൵HFWV due to the moment continuity created by the connections after erection. R4.12.1.2)RUJXLGDQFHRQLQFOXGLQJWKHH൵HFWVRIWROHU- ances, refer to the PCI Design Handbook (PCI MNL 120). American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 57 CODE COMMENTARY 4 Struct. Systems rements f ntains req QVWUXFWLRQ PEHUWS c 3UHFDVWFR All re WKH reater thickness cific con Thi UH VS mem uct sect WS FL¿F r cha —Re
- 60. 4.12.1.3 When precast members are incorporated into a structural system, the forces and deformations occurring in and adjacent to connections shall be included in the design. 4.12.1.4 Where system behavior requires in-plane loads WREHWUDQVIHUUHGEHWZHHQWKHPHPEHUVRIDSUHFDVWÀRRURU ZDOOVVWHP D DQG E VKDOOEHVDWLV¿HG (a) In-plane load paths shall be continuous through both connections and members. (b) Where tension loads occur, a load path of steel or steel reinforcement, with or without splices, shall be provided. 4.12.1.5 Distribution of forces that act perpendicular to the plane of precast members shall be established by analysis or test. 4.12.2 3UHVWUHVVHGFRQFUHWHVVWHPV 4.12.2.1 Design of prestressed members and systems shall be based on strength and on behavior at service conditions at all critical stages during the life of the structure from the WLPHSUHVWUHVVLV¿UVWDSSOLHG 4.12.2.23URYLVLRQVVKDOOEHPDGHIRUH൵HFWVRQDGMRLQLQJ FRQVWUXFWLRQRIHODVWLFDQGSODVWLFGHIRUPDWLRQVGHÀHFWLRQV FKDQJHVLQOHQJWKDQGURWDWLRQVGXHWRSUHVWUHVVLQJ(൵HFWV of temperature change, restraint of attached structural members, foundation settlement, creep, and shrinkage shall also be considered. 4.12.2.3 Stress concentrations due to prestressing shall be considered in design. 4.12.2.4(൵HFWRIORVVRIDUHDGXHWRRSHQGXFWVVKDOOEH considered in computing section properties before grout in post-tensioning ducts has attained design strength. 4.12.2.5 Post-tensioning tendons shall be permitted to be external to any concrete section of a member. Strength and serviceability design requirements of this Code shall be XVHGWRHYDOXDWHWKHH൵HFWVRIH[WHUQDOWHQGRQIRUFHVRQWKH concrete structure. R4.12.1.5 Concentrated and line loads can be distrib- XWHG DPRQJ PHPEHUV SURYLGHG WKH PHPEHUV KDYH VX൶- FLHQWWRUVLRQDOVWL൵QHVVDQGVKHDUFDQEHWUDQVIHUUHGDFURVV MRLQWV 7RUVLRQDOO VWL൵ PHPEHUV VXFK DV KROORZFRUH RU solid slabs will provide better load distribution than torsion- DOOÀH[LEOHPHPEHUVVXFKDVGRXEOHWHHVZLWKWKLQÀDQJHV The actual distribution of the load depends on many factors discussed in detail in LaGue (1971), Johnson and Ghadiali (1972), Pfeifer and Nelson (1983), Stanton (1987, 1992), PCI Manual for the Design of Hollow Core Slabs and Walls (PCI MNL 126), Aswad and Jacques (1992), and the PCI Design Handbook (PCI MNL 120). Large openings can FDXVHVLJQL¿FDQWFKDQJHVLQGLVWULEXWLRQRIIRUFHV R4.12.2 3UHVWUHVVHGFRQFUHWHVVWHPV Prestressing, as used in the Code, may apply to preten- sioning, bonded post-tensioning, or unbonded post- tensioning.All requirements in the Code apply to prestressed VVWHPV DQG PHPEHUV XQOHVV VSHFL¿FDOO H[FOXGHG 7KLV VHFWLRQ FRQWDLQV VSHFL¿F UHTXLUHPHQWV IRU SUHVWUHVVHG concrete systems. Other sections of this Code also provide VSHFL¿FUHTXLUHPHQWVVXFKDVUHTXLUHGFRQFUHWHFRYHUIRU prestressed systems. UHHSDQGVKULQNDJHH൵HFWVPDEHJUHDWHULQSUHVWUHVVHG than in nonprestressed concrete structures because of the prestressing forces and because prestressed structures typi- FDOOKDYHOHVVERQGHGUHLQIRUFHPHQW(൵HFWVRIPRYHPHQWV due to creep and shrinkage may require more attention than is normally required for nonprestressed concrete. These movements may increase prestress losses. Design of externally post-tensioned construction should FRQVLGHUDVSHFWVRIFRUURVLRQSURWHFWLRQDQG¿UHUHVLVWDQFH that are applicable to this structural system. American Concrete Institute – Copyrighted © Material – www.concrete.org 58 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY the Design Aswad an (PCI MN DQJHVLQ HVVHGFRQF he ing, as use ing, bonded tensionin VWH DOOÀ The actual distr ssed in detail in fer and Nel (PC Desig R4 NL Han JQL¿ 2.2 3 Pfe anua son on
- 61. R4.12.3 RPSRVLWHFRQFUHWHÀH[XUDOPHPEHUV This section addresses structural concrete members, either precast or cast-in-place, prestressed or nonprestressed, FRQVLVWLQJRIFRQFUHWHFDVWDWGL൵HUHQWWLPHVLQWHQGHGWRDFW as a composite member when loaded after concrete of the last stage of casting has set. All requirements in the Code DSSO WR WKHVH PHPEHUV XQOHVV VSHFL¿FDOO H[FOXGHG ,Q DGGLWLRQVRPHUHTXLUHPHQWVDSSOVSHFL¿FDOOWRFRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHUV 7KLV VHFWLRQ FRQWDLQV UHTXLUH- PHQWVWKDWDUHVSHFL¿FWRWKHVHHOHPHQWVDQGDUHQRWFRYHUHG in the applicable member chapters. R4.13—Construction and inspection Chapter 26 has been organized to collect into one loca- tion the design information, compliance requirements, and inspection provisions from the Code that should be included in construction documents There may be other information that should be included in construction documents that is not covered in Chapter 26. R4.14—Strength evaluation of existing structures Requirements in Chapter 27 for strength evaluation of existing structures by physical load test address the evalu- ation of structures subjected to gravity loads only. Chapter 27 also covers strength evaluation of existing structures by analytical evaluation, which may be used for gravity as well as other loadings such as earthquake or wind. 4.12.3 RPSRVLWHFRQFUHWHÀH[XUDOPHPEHUV 4.12.3.17KLVRGHVKDOODSSOWRFRPSRVLWHFRQFUHWHÀH[- XUDOPHPEHUVDVGH¿QHGLQChapter 2. 4.12.3.2 Individual members shall be designed for all crit- ical stages of loading. 4.12.3.3 Members shall be designed to support all loads introduced prior to full development of design strength of composite members. 4.12.3.4 Reinforcement shall be detailed to minimize cracking and to prevent separation of individual components of composite members. 4.12.4 6WUXFWXUDOSODLQFRQFUHWHVVWHPV 4.12.4.1 The design of structural plain concrete members, both cast-in-place and precast, shall be in accordance with Chapter 14. 4.13—Construction and inspection 4.13.16SHFL¿FDWLRQVIRUFRQVWUXFWLRQH[HFXWLRQVKDOOEH in accordance with Chapter 26. 4.13.2 Inspection during construction shall be in accor- dance with Chapter 26 and the general building code. 4.14—Strength evaluation of existing structures 4.14.1 Strength evaluation of existing structures shall be in accordance with Chapter 27. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 1: GENERAL 59 CODE COMMENTARY 4 Struct. Systems ruction a been orga ormation, ns from th uments T uded in c pter 26. 14—Streng Requ be mbers, accordance with pect VWUX nst ene H[HFXWLRQVKD on shall be in a uilding code. Ch tion th n con that s EH cor- ter 2 des on p ruct uld —Co Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 62. 60 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 63. 5.1—Scope 5.1.1 This chapter shall apply to selection of load factors and combinations used in design, except as permitted in Chapter 27. 5.2—General 5.2.1 Loads shall include self-weight; applied loads; and H൵HFWV RI SUHVWUHVVLQJ HDUWKTXDNHV UHVWUDLQW RI YROXPH FKDQJHDQGGL൵HUHQWLDOVHWWOHPHQW 5.2.2 Loads and Seismic Design Categories (SDCs) shall be in accordance with the general building code, or deter- PLQHGEWKHEXLOGLQJR൶FLDO R5.2—General R5.2.1 Provisions in the Code are associated with dead, live, wind, and earthquake loads such as those recommended in $6(6(,7KHFRPPHQWDUWR$SSHQGL[RI$6( SEI 7 provides service-level wind loads Wa for serviceability checks; however, these loads are not appropriate for strength design. ,IWKHVHUYLFHORDGVVSHFL¿HGEWKHJHQHUDOEXLOGLQJFRGH GL൵HUIURPWKRVHRI$6(6(,WKHJHQHUDOEXLOGLQJFRGH governs. However, if the nature of the loads contained in a JHQHUDOEXLOGLQJFRGHGL൵HUVFRQVLGHUDEOIURP$6(6(, ORDGVVRPHSURYLVLRQVRIWKLVRGHPDQHHGPRGL¿FDWLRQ WRUHÀHFWWKHGL൵HUHQFH R5.2.2 Seismic Design Categories (SDCs) in this Code DUHDGRSWHGGLUHFWOIURP$6(6(,6LPLODUGHVLJQDWLRQV are used by the International Building Code (2018 IBC) and the National Fire Protection Association (NFPA 5000 2012). The BOCA National Building Code (BOCA 1999) and “The Standard Building Code” (SBC 1999) used seismic perfor- mance categories. The “Uniform Building Code” (IBCO 1997) relates seismic design requirements to seismic zones, whereas editions of ACI 318 prior to 2008 related seismic design requirements to seismic risk levels. Table R5.2.2 correlates SDC to seismic risk terminology used in ACI 318 for several editions before the 2008 edition, and to the various methods of assigning design requirements used in the United States under the various model building codes, WKH $6(6(, VWDQGDUG DQG WKH 1DWLRQDO (DUWKTXDNH Hazard Reduction Program (NEHRP 1994). Design requirements for earthquake-resistant structures in this Code are determined by the SDC to which the structure is assigned. In general, the SDC relates to seismic hazard level, soil type, occupancy, and building use. Assignment of a building to an SDC is under the jurisdiction of the general building code rather than this Code. In the absence of a general building code that prescribes HDUWKTXDNH H൵HFWV DQG VHLVPLF ]RQLQJ LW LV WKH LQWHQW RI Committee 318 that application of provisions for earth- quake-resistant design be consistent with national standards RUPRGHOEXLOGLQJFRGHVVXFKDV$6(6(,,% and NFPA 5000. The model building codes also specify overstrength factors Ÿo that are related to the seismic-force- resisting system used for the structure and design of certain elements. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 2: LOADS ANALYSIS 61 CODE COMMENTARY 5 Loads e Protection nal Buildin Code” (S The “Un ic design of ACI 3 ments to SDC to se for several e various es (SDCs) shall lding cod R5.2.2 Seism GRSWHGGLUHFWOI the Internati The Stand 997) wher d CA d Bu cate elate s ed d by ional ona na CHAPTER 5—LOADS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 64. 5.2.3 Live load reductions shall be permitted in accor- dance with the general building code or, in the absence of a general building code, in accordance with $6(6(,. 5.3—Load factors and combinations 5.3.1 Required strength U shall be at least equal to the H൵HFWVRIIDFWRUHGORDGVLQ7DEOHZLWKH[FHSWLRQVDQG additions in 5.3.3 through 5.3.13. Table 5.3.1—Load combinations Load combination Equation Primary load U = 1.4D (5.3.1a) D U = 1.2D + 1.6L + 0.5(Lr or S or R) (5.3.1b) L U = 1.2D + 1.6(Lr or S or R) + (1.0L or 0.5W) (5.3.1c) Lr or S or R U = 1.2D + 1.0W + 1.0L + 0.5(Lr or S or R) (5.3.1d) W U = 1.2D + 1.0E + 1.0L + 0.2S (5.3.1e) E U = 0.9D + 1.0W (5.3.1f) W U = 0.9D + 1.0E (5.3.1g) E R5.3—Load factors and combinations R5.3.1 The required strength U is expressed in terms of IDFWRUHGORDGV)DFWRUHGORDGVDUHWKHORDGVVSHFL¿HGLQWKH general building code multiplied by appropriate load factors. ,IWKHORDGH൵HFWVVXFKDVLQWHUQDOIRUFHVDQGPRPHQWVDUH linearly related to the loads, the required strength U may be H[SUHVVHGLQWHUPVRIORDGH൵HFWVPXOWLSOLHGEWKHDSSURSULDWH ORDGIDFWRUVZLWKWKHLGHQWLFDOUHVXOW,IWKHORDGH൵HFWVDUH QRQOLQHDUOUHODWHGWRWKHORDGVVXFKDVIUDPH3GHOWDH൵HFWV (Rogowsky and Wight 2010), the loads are factored before GHWHUPLQLQJWKHORDGH൵HFWV7SLFDOSUDFWLFHIRUIRXQGDWLRQ design is discussed in R13.2.6.1 1RQOLQHDU ¿QLWH HOHPHQW analysis using factored load cases is discussed in R6.9.3. 7KH IDFWRU DVVLJQHG WR HDFK ORDG LV LQÀXHQFHG E WKH GHJUHHRIDFFXUDFWRZKLFKWKHORDGH൵HFWXVXDOOFDQEH calculated and the variation that might be expected in the load during the lifetime of the structure. Dead loads, because they are more accurately determined and less variable, are assigned a lower load factor than live loads. Load factors also account for variability in the structural analysis used to calculate moments and shears. 7KHRGHJLYHVORDGIDFWRUVIRUVSHFL¿FFRPELQDWLRQVRI loads. In assigning factors to combinations of loading, some consideration is given to the probability of simultaneous occurrence. While most of the usual combinations of load- ings are included, it should not be assumed that all cases are covered. Due regard is to be given to the sign (positive or nega- tive) in determining U for combinations of loadings, as one WSHRIORDGLQJPDSURGXFHH൵HFWVRIRSSRVLWHVHQVHWRWKDW produced by another type. The load combinations with 0.9D are included for the case where a higher dead load reduces WKHH൵HFWVRIRWKHUORDGV7KHORDGLQJFDVHPDDOVREHFULW- ical for tension-controlled column sections. In such a case, a reduction in compressive axial load or development of tension with or without an increase in moment may result in a critical load combination. Table R5.2.2—Correlation between seismic-related terminology in model codes Code, standard, or resource document and edition Level of seismic risk or assigned seismic performance or design categories as GH¿QHGLQWKHRGH ACI 318-08, ACI 318-11, ACI 318-14, ACI 318-19; IBC of 2000, 2003, 2006, 2009, 2012, 2015, 2018; NFPA 5000 of 2003, 2006, 2009, 2012, 2015, 2018; ASCE 7-98, 7-02, 7-05, 7-10, 7-16; NEHRP 1997, 2000, 2003, 2009, 2015 SDC[1] A, B SDC C SDC D, E, F ACI 318-05 and previous editions Low seismic risk 0RGHUDWHLQWHUPHGLDWHVHLVPLFULVN High seismic risk BOCA National Building Code 1993, 1996, 1999; Standard Building Code 1994, 1997, 1999; ASCE 7-93, 7-95; NEHRP 1991, 1994 SPC[2] A, B SPC C SPC D, E Uniform Building Code 1991, 1994, 1997 Seismic Zone 0, 1 Seismic Zone 2 Seismic Zone 3, 4 [1] 6' VHLVPLFGHVLJQFDWHJRUDVGH¿QHGLQFRGHVWDQGDUGRUUHVRXUFHGRFXPHQW [2] 63 VHLVPLFSHUIRUPDQFHFDWHJRUDVGH¿QHGLQFRGHVWDQGDUGRUUHVRXUFHGRFXPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org 62 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY WVVXFKDV the loads, IORDGH൵H HLGHQWLF WRWKHORD Wight 201 HORDGH൵ discussed in ysis using fac 7KH I ast equal to the ZLWKH[F tio R5 R5.3.1 The re UHGORDGV)DFWR ding code m Equ Prim loa (5.3.1a) D .3.1b) L y linea H[SUHV QRQOLQ (Rog G rela HGLQ WRUV DUO sky buil RDG ultip ti Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 65. Consideration should be given to various combinations of loading to determine the most critical design condition. This is particularly true when strength is dependent on more than RQHORDGH൵HFWVXFKDVVWUHQJWKIRUFRPELQHGÀH[XUHDQG axial load or shear strength in members with axial load. If unusual circumstances require greater reliance on the strength of particular members than circumstances encoun- tered in usual practice, some reduction in the stipulated strength reduction factors ࢥ or increase in the stipulated load factors may be appropriate for such members. Rain load R in Eq. (5.3.1b), (5.3.1c), and (5.3.1d) should account for all likely accumulations of water. Roofs should be GHVLJQHGZLWKVX൶FLHQWVORSHRUFDPEHUWRHQVXUHDGHTXDWH GUDLQDJHDFFRXQWLQJIRUDQORQJWHUPGHÀHFWLRQRIWKHURRI GXHWRWKHGHDGORDGV,IGHÀHFWLRQRIURRIPHPEHUVPD UHVXOWLQSRQGLQJRIZDWHUDFFRPSDQLHGELQFUHDVHGGHÀHF- tion and additional ponding, the design should ensure that this process is self-limiting. Model building codes and design load references refer to earthquake forces at the strength level, and the corre- sponding load factor is 1.0 ($6(6(,; BOCA 1999; SBC 1999; UBC (ICBO 1997); 2018 IBC). In the absence of a general building code that prescribes strength level earth- TXDNHH൵HFWVDKLJKHUORDGIDFWRURQE would be required. 7KHORDGH൵HFWE in model building codes and design load UHIHUHQFHVWDQGDUGVLQFOXGHVWKHH൵HFWRIERWKKRUL]RQWDODQG vertical ground motions (as Eh and Ev, respectively). The H൵HFWIRUYHUWLFDOJURXQGPRWLRQVLVDSSOLHGDVDQDGGLWLRQ WRRUVXEWUDFWLRQIURPWKHGHDGORDGH൵HFW D), and it applies to all structural elements, whether part of the seismic force- UHVLVWLQJVVWHPRUQRWXQOHVVVSHFL¿FDOOH[FOXGHGEWKH general building code. R5.3.3 7KH ORDG PRGL¿FDWLRQ IDFWRU LQ WKLV SURYLVLRQ LV GL൵HUHQW WKDQ WKH OLYH ORDG UHGXFWLRQV EDVHG RQ WKH ORDGHG area that may be allowed in the general building code. The live load reduction, based on loaded area, adjusts the nominal live load (L0LQ$6(6(, WRL. The live load reduction, as VSHFL¿HGLQWKHJHQHUDOEXLOGLQJFRGHFDQEHXVHGLQFRPEL- QDWLRQZLWKWKHORDGIDFWRUVSHFL¿HGLQWKLVSURYLVLRQ 5.3.27KHH൵HFWRIRQHRUPRUHORDGVQRWDFWLQJVLPXOWDQH- ously shall be investigated. 5.3.3 The load factor on live load L in Eq. (5.3.1c), (5.3.1d), and (5.3.1e) shall be permitted to be reduced to 0.5 except for (a), (b), or (c): (a) Garages (b) Areas occupied as places of public assembly (c) Areas where LLVJUHDWHUWKDQOEIW2 5.3.4 If applicable, L shall include (a) through (f): (a) Concentrated live loads (b) Vehicular loads (c) Crane loads (d) Loads on hand rails, guardrails, and vehicular barrier systems H ,PSDFWH൵HFWV I 9LEUDWLRQH൵HFWV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 2: LOADS ANALYSIS 63 CODE COMMENTARY 5 Loads g code that JKHUORDG n model b LQFOXGHV otions (as JURXQGP QIURPWK ural eleme WLQJVVWHP general b to earthquake f ding load factor (ICBO 199 TXDN 7KHO vertic H൵HF ൵HF GH൵ FHVW gro RUYH UBC buil ( 7); ); Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 66. R5.3.5 In $6(6(,, wind loads are consistent with service-level design; a wind load factor of 1.6 is appropriate for use in Eq. (5.3.1d) and (5.3.1f) and a wind load factor of 0.8 is appropriate for use in Eq. (5.3.1c). $6(6(, prescribes wind loads for strength-level design and the wind load factor is 1.0. Design wind speeds for strength-level design are based on storms with mean recurrence intervals of 300, 700, and 1700 years depending on the risk category of the structure. The higher load factors in 5.3.5 apply where service-level wind loads corresponding to a 50-year mean recurrence interval are used for design. R5.3.6 Several strategies can be used to accommodate PRYHPHQWVGXHWRYROXPHFKDQJHDQGGL൵HUHQWLDOVHWWOHPHQW 5HVWUDLQWRIVXFKPRYHPHQWVFDQFDXVHVLJQL¿FDQWPHPEHU forces and moments, such as tension in slabs and shear forces and moments in vertical members. Forces due to T H൵HFWV are not commonly calculated and combined with other load H൵HFWV 5DWKHU GHVLJQV UHO RQ VXFFHVVIXO SDVW SUDFWLFHV using compliant structural members and ductile connections WRDFFRPPRGDWHGL൵HUHQWLDOVHWWOHPHQWDQGYROXPHFKDQJH movement while providing the needed resistance to gravity and lateral loads. Expansion joints and construction closure strips are used to limit volume change movements based on the performance of similar structures. Shrinkage and tempera- WXUHUHLQIRUFHPHQWZKLFKPDH[FHHGWKHUHTXLUHGÀH[XUDO reinforcement, is commonly proportioned based on gross concrete area rather than calculated force. Where structural movements can lead to damage of nonductile elements, calculation of the predicted force should consider the inherent variability of the expected movement and structural response. A long-term study of the volume change behavior of precast concrete buildings (Klein and Lindenberg 2009) UHFRPPHQGVSURFHGXUHVWRDFFRXQWIRUFRQQHFWLRQVWL൵QHVV thermal exposure, member softening due to creep, and other IDFWRUVWKDWLQÀXHQFHT forces. Fintel et al. (1986) provides information on the magni- WXGHVRIYROXPHFKDQJHH൵HFWVLQWDOOVWUXFWXUHVDQGUHFRP- mends procedures for including the forces resulting from WKHVHH൵HFWVLQGHVLJQ 5.3.5 If wind load W is provided at service-level loads, 1.6W shall be used in place of 1.0W in Eq. (5.3.1d) and (5.3.1f), and 0.8W shall be used in place of 0.5W in Eq. (5.3.1c). 5.3.67KHVWUXFWXUDOH൵HFWVRIIRUFHVGXHWRUHVWUDLQWRI YROXPHFKDQJHDQGGL൵HUHQWLDOVHWWOHPHQWT shall be consid- HUHGLQFRPELQDWLRQZLWKRWKHUORDGVLIWKHH൵HFWVRIT can DGYHUVHOD൵HFWVWUXFWXUDOVDIHWRUSHUIRUPDQFH7KHORDG factor for T shall be established considering the uncertainty associated with the likely magnitude of T, the probability WKDWWKHPD[LPXPH൵HFWRIT will occur simultaneously with other applied loads, and the potential adverse consequences LIWKHH൵HFWRIT is greater than assumed. The load factor on T shall not have a value less than 1.0. 5.3.7,IÀXLGORDGF is present, it shall be included in the load combination equations of 5.3.1 in accordance with (a), (b), (c), or (d): (a) If FDFWVDORQHRUDGGVWRWKHH൵HFWVRID, it shall be included with a load factor of 1.4 in Eq. (5.3.1a). (b) If F adds to the primary load, it shall be included with a load factor of 1.2 in Eq. (5.3.1b) through (5.3.1e). F ,I WKH H൵HFW RI F is permanent and counteracts the primary load, it shall be included with a load factor of 0.9 in Eq. (5.3.1g). American Concrete Institute – Copyrighted © Material – www.concrete.org 64 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY s. Expansio limit volum similar str ZKLFKP ommonly er than cal tural mo elements, ld consider moveme H൵ using compliant FRPPRGDWH GL൵ while provid y with se consequences d. The lo 0. strip the pe einfo concr e us orma QIRUF eme e are ent w eral l ng g Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 67. G ,IWKHH൵HFWRIF is not permanent but, when present, counteracts the primary load, F shall not be included in Eq. (5.3.1a) through (5.3.1g). 5.3.8 If lateral earth pressure H is present, it shall be included in the load combination equations of 5.3.1 in accor- dance with (a), (b), or (c): (a) If HDFWVDORQHRUDGGVWRWKHSULPDUORDGH൵HFWLW shall be included with a load factor of 1.6. E ,I WKH H൵HFW RI H is permanent and counteracts the SULPDUORDGH൵HFWLWVKDOOEHLQFOXGHGZLWKDORDGIDFWRU of 0.9. F ,IWKHH൵HFWRIH is not permanent but, when present, FRXQWHUDFWV WKH SULPDU ORDG H൵HFW H shall not be included. 5.3.9,IDVWUXFWXUHLVLQDÀRRG]RQHWKHÀRRGORDGVDQG the appropriate load factors and combinations of $6(6(, 7 shall be used. 5.3.10 If a structure is subjected to forces from atmo- spheric ice loads, the ice loads and the appropriate load IDFWRUVDQGFRPELQDWLRQVRI$6(6(,VKDOOEHXVHG 5.3.11 Required strength U shall include internal load H൵HFWVGXHWRUHDFWLRQVLQGXFHGESUHVWUHVVLQJZLWKDORDG factor of 1.0. 5.3.12 For post-tensioned anchorage zone design, a load factor of 1.2 shall be applied to the maximum prestressing reinforcement jacking force. 5.3.13 /RDG IDFWRUV IRU WKH H൵HFWV RI SUHVWUHVVLQJ XVHG with the strut-and-tie method shall be included in the load combination equations of 5.3.1 in accordance with (a) or (b): (a) A load factor of 1.2 shall be applied to the prestressing H൵HFWVZKHUHWKHSUHVWUHVVLQJH൵HFWVLQFUHDVHWKHQHWIRUFH in struts or ties. (b) A load factor of 0.9 shall be applied to the prestressing H൵HFWVZKHUHWKHSUHVWUHVVLQJH൵HFWVUHGXFHWKHQHWIRUFH in struts or ties. R5.3.8 The required load factors for lateral pressures from VRLO ZDWHU LQ VRLO DQG RWKHU PDWHULDOV UHÀHFW WKHLU YDUL- ability and the possibility that the materials may be removed. The commentary of $6(6(, includes additional useful discussion pertaining to load factors for H. R5.3.9 $UHDV VXEMHFW WR ÀRRGLQJ DUH GH¿QHG E ÀRRG hazard maps, usually maintained by local governmental jurisdictions. R5.3.10 Ice buildup on a structural member increases the DSSOLHGORDGDQGWKHSURMHFWHGDUHDH[SRVHGWRZLQG$6( SEI 7 provides maps of probable ice thicknesses due to freezing rain, with concurrent 3-second gust speeds, for a 50-year return period. R5.3.11 For statically indeterminate structures, the LQWHUQDOORDGH൵HFWVGXHWRUHDFWLRQVLQGXFHGESUHVWUHVVLQJ forces, sometimes referred to as secondary moments, can be VLJQL¿FDQW Bondy 2003; Lin and Thornton 1972; Collins and Mitchell 1997). R5.3.12 The load factor of 1.2 applied to the maximum tendon jacking force results in a design load of about 113 SHUFHQW RI WKH VSHFL¿HG SUHVWUHVVLQJ UHLQIRUFHPHQW LHOG strength, but not more than 96 percent of the nominal tensile strength of the prestressing reinforcement. This compares well with the maximum anchorage capacity, which is at least 95 percent of the nominal tensile strength of the prestressing reinforcement. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 2: LOADS ANALYSIS 65 CODE COMMENTARY 5 Loads GWKHSURMHF maps of p concurre d. statically ൵HFWVGXH etimes refe L¿FDQW Bond and Mitc (, d to and ( sha S hazard jurisdictions. ce buildup o VKDOOEHXVHG clude internal L ad SEI freezi R5 L prov g rai retu 11 10 I ORDG n a a Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 68. 66 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 69. 6.1—Scope 6.1.1 This chapter shall apply to methods of analysis, modeling of members and structural systems, and calcula- WLRQRIORDGH൵HFWV 6.2—General 6.2.1 Members and structural systems shall be permitted to be modeled in accordance with 6.3. 6.2.2 All members and structural systems shall be DQDO]HGWRGHWHUPLQHWKHPD[LPXPORDGH൵HFWVLQFOXGLQJ the arrangements of live load in accordance with 6.4. 6.2.3 Methods of analysis permitted by this chapter shall be (a) through (e): D 7KH VLPSOL¿HG PHWKRG IRU DQDOVLV RI FRQWLQXRXV beams and one-way slabs for gravity loads in 6.5 E /LQHDUHODVWLF¿UVWRUGHUDQDOVLVLQ (c) Linear elastic second-order analysis in 6.7 (d) Inelastic analysis in 6.8 (e) Finite element analysis in 6.9 R6.1—Scope The provisions of this chapter apply to analyses used to GHWHUPLQHORDGH൵HFWVIRUGHVLJQ Section 6.2 provides general requirements that are applicable for all analysis procedures. Section 6.2.4 directs the licensed design professional WR VSHFL¿F DQDOVLV SURYLVLRQV WKDW DUH QRW FRQWDLQHG LQ this chapter. Sections 6.2.4.1 and 6.2.4.2 identify analysis SURYLVLRQVWKDWDUHVSHFL¿FWRWZRZDVODEVDQGZDOOV Section 6.3 addresses modeling assumptions used in establishing the analysis model. Section 6.4 prescribes the arrangements of live loads that are to be considered in the analysis. 6HFWLRQSURYLGHVDVLPSOL¿HGPHWKRGRIDQDOVLVIRU nonprestressed continuous beams and one-way slabs that can be used in place of a more rigorous analysis when the VWLSXODWHGFRQGLWLRQVDUHVDWLV¿HG Section 6.6 includes provisions for a comprehensive linear HODVWLF¿UVWRUGHUDQDOVLV7KHH൵HFWVRIFUDFNHGVHFWLRQV and creep are included in the analysis through the use of H൵HFWLYHVWL൵QHVVHV Section 6.7 includes provisions for linear elastic second- RUGHUDQDOVLV,QFOXVLRQRIWKHH൵HFWVRIFUDFNLQJDQGFUHHS is required. Section 6.8 includes provisions for inelastic analysis. 6HFWLRQLQFOXGHVSURYLVLRQVIRUWKHXVHRIWKH¿QLWH element method. R6.2—General R6.2.3 $ ¿UVWRUGHU DQDOVLV VDWLV¿HV WKH HTXDWLRQV RI equilibrium using the original undeformed geometry of WKHVWUXFWXUH:KHQRQO¿UVWRUGHUUHVXOWVDUHFRQVLGHUHG VOHQGHUQHVV H൵HFWV DUH QRW DFFRXQWHG IRU %HFDXVH WKHVH H൵HFWV FDQ EH LPSRUWDQW SURYLGHV SURFHGXUHV WR calculate both individual member slenderness (Pį H൵HFWV and sidesway (P¨ H൵HFWVIRUWKHRYHUDOOVWUXFWXUHXVLQJWKH ¿UVWRUGHUUHVXOWV $ VHFRQGRUGHU DQDOVLV VDWLV¿HV WKH HTXDWLRQV RI equilibrium using the deformed geometry of the structure. If the second-order analysis uses nodes along compression PHPEHUVWKHDQDOVLVDFFRXQWVIRUVOHQGHUQHVVH൵HFWVGXH to lateral deformations along individual members, as well as sidesway of the overall structure. If the second-order analysis uses nodes at the member intersections only, the analysis FDSWXUHV WKH VLGHVZD H൵HFWV IRU WKH RYHUDOO VWUXFWXUH EXW QHJOHFWVLQGLYLGXDOPHPEHUVOHQGHUQHVVH൵HFWV,QWKLVFDVH WKHPRPHQWPDJQL¿HUPHWKRG LVXVHGWRGHWHUPLQH LQGLYLGXDOPHPEHUVOHQGHUQHVVH൵HFWV American Concrete Institute – Copyrighted © Material – www.concrete.org QFOXVLRQRI des provis GHVSURY al HODVWLF and creep are in YHVWL൵QHVVHV 7 includes p is re Sec leme red. on 6 RQ me on 6 QDOV rov ov PART 2: LOADS ANALYSIS 67 CODE COMMENTARY 6 Analysis CHAPTER 6—STRUCTURAL ANALYSIS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 70. An inelastic analysis i) represents the nonlinear stress- strain response of the materials composing the structure; LL VDWLV¿HVFRPSDWLELOLWRIGHIRUPDWLRQVDQGLLL VDWLV¿HV HTXLOLEULXPLQWKHXQGHIRUPHGFRQ¿JXUDWLRQIRU¿UVWRUGHU DQDOVLVRULQWKHGHIRUPHGFRQ¿JXUDWLRQIRUVHFRQGRUGHU analysis. Finite element analysis was introduced in the 2014 Code to explicitly recognize a widely used analysis method. R6.2.4.1 Code editions from 1971 to 2014 contained provisions for use of the direct design method and the equiv- alent frame method. These methods are well-established and are covered in available texts. These provisions for gravity load analysis of two-way slabs have been removed from the Code because they are considered to be only two of several analysis methods currently used for the design of two-way slabs. The direct design method and the equivalent frame method of the 2014 Code, however, may still be used for the analysis of two-way slabs for gravity loads. R6.2.5 6OHQGHUQHVVHৼHFWV 6HFRQGRUGHU H൵HFWV LQ PDQ VWUXFWXUHV DUH QHJOLJLEOH In these cases, it is unnecessary to consider slenderness H൵HFWVDQGFRPSUHVVLRQPHPEHUVVXFKDVFROXPQVZDOOV or braces, can be designed based on forces determined from ¿UVWRUGHU DQDOVHV 6OHQGHUQHVV H൵HFWV FDQ EH QHJOHFWHG in both braced and unbraced systems, depending on the slenderness ratio (NƐu/r) of the member. The sign convention for M1/M2 has been updated so that M1/M2 is negative if bent in single curvature and positive LIEHQWLQGRXEOHFXUYDWXUH7KLVUHÀHFWVDVLJQFRQYHQWLRQ change from the 2011 Code. 7KH SULPDU GHVLJQ DLG WR HVWLPDWH WKH H൵HFWLYH OHQJWK factor k is the Jackson and Moreland Alignment Charts (Fig. R6.2.5.1), which provide a graphical determination of k for a column of constant cross section in a multi-bay frame (ACI SP-17(09); Column Research Council 1966). Equations (6.2.5.1b) and (6.2.5.1c) are based on Eq. (6.6.4.5.1) assuming that a 5 percent increase in moments due to slenderness is acceptable (MacGregor et al. 1970). 6.2.4 Additional analysis methods that are permitted include 6.2.4.1 through 6.2.4.4. 6.2.4.1 Two-way slabs shall be permitted to be analyzed for gravity loads in accordance with (a) or (b): (a) Direct design method for nonprestressed slabs (b) Equivalent frame method for nonprestressed and prestressed slabs 6.2.4.2 Slender walls shall be permitted to be analyzed in accordance with 11.8 IRURXWRISODQHH൵HFWV 6.2.4.3 Diaphragms shall be permitted to be analyzed in accordance with 12.4.2. 6.2.4.4 A member or region shall be permitted to be analyzed and designed using the strut-and-tie method in accordance with Chapter 23. 6.2.5 6OHQGHUQHVVHৼHFWV 6.2.5.1 6OHQGHUQHVV H൵HFWV VKDOO EH SHUPLWWHG WR EH QHJOHFWHGLI D RU E LVVDWLV¿HG (a) For columns not braced against sidesway 22 u k r ≤ A (6.2.5.1a) (b) For columns braced against sidesway 1 2 u k M M r ≤ + A (6.2.5.1b) and 40 u k r ≤ A (6.2.5.1c) where M1/M2 is negative if the column is bent in single curvature, and positive for double curvature. American Concrete Institute – Copyrighted © Material – www.concrete.org analysi slabs. The direc d of the 2014 C wo-way slab pe IS pe d to be analyz ൵HFWV ed to be analyz n d in of t , s fo f 68 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 71. $VD¿UVWDSSUR[LPDWLRQk may be taken equal to 1.0 in Eq. (6.2.5.1b) and (6.2.5.1c). 7KH VWL൵QHVV RI WKH ODWHUDO EUDFLQJ LV FRQVLGHUHG EDVHG on the principal directions of the framing system. Bracing elements in typical building structures consist of structural walls or lateral braces. Torsional response of the lateral-force- resisting system due to eccentricity of the structural system FDQLQFUHDVHVHFRQGRUGHUH൵HFWVDQGVKRXOGEHFRQVLGHUHG If bracing elements resisting lateral movement of a story KDYHDWRWDOVWL൵QHVVRIDWOHDVWWLPHVWKHJURVVODWHUDO VWL൵QHVVRIWKHFROXPQVLQWKHGLUHFWLRQFRQVLGHUHGLWVKDOO be permitted to consider columns within the story to be braced against sidesway. 6.2.5.2 The radius of gyration, r, shall be permitted to be calculated by (a), (b), or (c): (a) g g I r A = (6.2.5.2) (b) 0.30 times the dimension in the direction stability is being considered for rectangular columns (c) 0.25 times the diameter of circular columns American Concrete Institute – Copyrighted © Material – www.concrete.org PART 2: LOADS ANALYSIS 69 CODE COMMENTARY 6 Analysis 0 50.0 6.0 ∞ ∞ ∞ 10.0 5.0 3.0 2.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 50.0 10.0 5.0 3.0 2.0 1.0 1.0 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.3 0.2 0.1 ΨA ΨA k k ΨB ΨB 100.0 50.0 30.0 20.0 10.0 0 1.0 2.0 3.0 4.0 5.0 9.0 8.0 7.0 6.0 ∞ 100.0 50.0 30.0 20.0 10.0 0 1.0 2.0 3.0 4.0 5.0 9.0 8.0 7.0 20.0 10.0 1.5 1.0 2.0 3.0 4.0 5.0 ∞ (a) Nonsway frames (b) Sway frames Ψ = ratio of Σ(EI /c ) of all columns to Σ(EI /) of beams in a plane at one end of a column = span length of of beam measured center to center of joints Fig. R6.2.5.1²(ৼHFWLYHOHQJWKIDFWRUk. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 72. R6.2.5.3'HVLJQFRQVLGHULQJVHFRQGRUGHUH൵HFWVPDEH EDVHGRQWKHPRPHQWPDJQL¿HUDSSURDFK MacGregor et al. 1970; MacGregor 1993; Ford et al. 1981), an elastic second- order analysis, or a nonlinear second-order analysis. Figure R6.2.5.3 is intended to assist designers with application of the slenderness provisions of the Code. End moments in compression members, such as columns, walls, or braces, should be considered in the design of DGMDFHQWÀH[XUDOPHPEHUV,QQRQVZDIUDPHVWKHH൵HFWVRI magnifying the end moments need not be considered in the GHVLJQRIDGMDFHQWEHDPV,QVZDIUDPHVWKHPDJQL¿HGHQG moments should be considered in designing the adjoining ÀH[XUDOPHPEHUV Several methods have been developed to evaluate VOHQGHUQHVV H൵HFWV LQ FRPSUHVVLRQ PHPEHUV VXEMHFW WR biaxial bending. A review of some of these methods is presented in Furlong et al. (2004). If the weight of a structure is high in proportion to its lateral VWL൵QHVV H[FHVVLYH P¨ H൵HFWV ZKHUH VHFRQGDU PRPHQWV are more than 25 percent of the primary moments, may result. The P¨H൵HFWVZLOOHYHQWXDOOLQWURGXFHVLQJXODULWLHV into the solution to the equations of equilibrium, indicating physical structural instability (Wilson 1997). Analytical research (MacGregor and Hage 1977) on reinforced concrete frames showed that the probability of stability failure increases rapidly when the stability index QGH¿QHG in 6.6.4.4.1, exceeds 0.2, which is equivalent to a secondary- to-primary moment ratio of 1.25. According to $6(6(, 7WKHPD[LPXPYDOXHRIWKHVWDELOLWFRH൶FLHQWș, which LVFORVHWRWKH$,VWDELOLWFRH൶FLHQWQ, is 0.25. The value 0.25 is equivalent to a secondary-to-primary moment ratio of 1.33. Hence, the upper limit of 1.4 on the secondary-to- primary moment ratio was chosen. 6.2.5.3 8QOHVV VOHQGHUQHVV H൵HFWV DUH QHJOHFWHG DV permitted by 6.2.5.1, the design of columns, restraining beams, and other supporting members shall be based on the factored forces and moments considering second-order H൵HFWVLQDFFRUGDQFHZLWKRUMu including VHFRQGRUGHU H൵HFWV VKDOO QRW H[FHHG 1.4Mu GXH WR ¿UVW RUGHUH൵HFWV American Concrete Institute – Copyrighted © Material – www.concrete.org ural instab egor and howed th idly whe s 0.2, wh nt ratio o PYDOXH WKH$,VWD 5 is equivalen of 1 33 VWL൵QH are more than 2 The P¨ P P H൵HFWV tion to the e rese concre n 6.6 to-pr h (M e fr ncre 4.1, ary solu l str qua qu 70 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 73. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 2: LOADS ANALYSIS 71 CODE COMMENTARY 6 Analysis Yes No Analyze columns as nonsway? 6.2.5 or 6.6.4.3 Neglect slenderness? 6.2.5.1 M2nd-order ≤ 1.4M1st-order 6.2.5.3 Yes No Only 1st-order analysis required 6.6 Slenderness effects along column length Moment magnification method - nonsway frames 6.6.4.1 - 6.6.4.5 or 2nd-order analysis R6.7.1.2 or R6.8.1.3 Yes No Slenderness effects at column ends Moment magnification method - sway frames 6.6.4.1 - 6.6.6.4.4, 6.6.4.6 or 2nd-order analysis 6.7 - Elastic or 6.8 - Inelastic Slenderness effects along column length Moment magnification 6.6.4.5 or 2nd-order analysis R6.7.1.2 or R6.8.1.3 Revise structural system Design column for 2nd-order moment Fig. R6.2.5.3—)ORZFKDUWIRUGHWHUPLQLQJFROXPQVOHQGHUQHVVHৼHFWV Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 74. 6.3—Modeling assumptions 6.3.1 General 6.3.1.1 5HODWLYH VWL൵QHVVHV RI PHPEHUV ZLWKLQ VWUXF- tural systems shall be selected based on a reasonable set of assumptions. The assumptions shall be consistent throughout each analysis. 6.3.1.2 To calculate moments and shears caused by gravity loads in columns, beams, and slabs, it shall be permitted to use a model limited to the members in the level being considered and the columns above and below that level. It shall be permitted to assume far ends of columns built inte- JUDOOZLWKWKHVWUXFWXUHWREH¿[HG 6.3.1.37KHDQDOVLVPRGHOVKDOOFRQVLGHUWKHH൵HFWVRI variation of member cross-sectional properties, such as that due to haunches. 6.3.2 7EHDPJHRPHWU 6.3.2.1 For nonprestressed T-beams supporting monolithic RUFRPSRVLWHVODEVWKHH൵HFWLYHÀDQJHZLGWKbf shall include the beam web width bwSOXVDQH൵HFWLYHRYHUKDQJLQJÀDQJH width in accordance with Table 6.3.2.1, where h is the slab thickness and sw is the clear distance to the adjacent web. R6.3—Modeling assumptions R6.3.1 General R6.3.1.16HSDUDWHDQDOVHVZLWKGL൵HUHQWVWL൵QHVVDVVXPS- WLRQV PD EH SHUIRUPHG IRU GL൵HUHQW REMHFWLYHV VXFK DV WR check serviceability and strength criteria or to bound the GHPDQGVRQHOHPHQWVZKHUHVWL൵QHVVDVVXPSWLRQVDUHFULWLFDO ,GHDOO WKH PHPEHU VWL൵QHVVHV EcI and GJ should UHÀHFWWKHGHJUHHRIFUDFNLQJDQGLQHODVWLFDFWLRQWKDWKDV occurred along each member before yielding. However, the FRPSOH[LWLHVLQYROYHGLQVHOHFWLQJGL൵HUHQWVWL൵QHVVHVIRUDOO PHPEHUVRIDIUDPHZRXOGPDNHIUDPHDQDOVHVLQH൶FLHQW in the design process. Simpler assumptions are required to GH¿QHÀH[XUDODQGWRUVLRQDOVWL൵QHVVHV )RU EUDFHG IUDPHV UHODWLYH YDOXHV RI VWL൵QHVV DUH important. A common assumption is to use 0.5Ig for beams and Ig for columns. For sway frames, a realistic estimate of I is desirable and should be used if second-order analyses are performed. Guidance for the choice of I for this case is given in 6.6.3.1. Two conditions determine whether it is necessary to FRQVLGHUWRUVLRQDOVWL൵QHVVLQWKHDQDOVLVRIDJLYHQVWUXF- WXUH WKHUHODWLYHPDJQLWXGHRIWKHWRUVLRQDODQGÀH[XUDO VWL൵QHVVHVDQG ZKHWKHUWRUVLRQLVUHTXLUHGIRUHTXLOLEULXP of the structure (equilibrium torsion) or is due to members twisting to maintain deformation compatibility (compatibility WRUVLRQ ,QWKHFDVHRIHTXLOLEULXPWRUVLRQWRUVLRQDOVWL൵QHVV should be included in the analysis. It is, for example, neces- VDUWRFRQVLGHUWKHWRUVLRQDOVWL൵QHVVHVRIHGJHEHDPV,QWKH FDVHRIFRPSDWLELOLWWRUVLRQWRUVLRQDOVWL൵QHVVXVXDOOLVQRW included in the analysis. This is because the cracked torsional VWL൵QHVVRIDEHDPLVDVPDOOIUDFWLRQRIWKHÀH[XUDOVWL൵QHVV of the members framing into it. Torsion should be considered in design as required in Chapter 9. R6.3.1.3 6WL൵QHVV DQG ¿[HGHQG PRPHQW FRH൶FLHQWV for haunched members may be obtained from the Portland Cement Association (1972). R6.3.2 7EHDPJHRPHWU R6.3.2.1 In ACI 318-11WKHZLGWKRIWKHVODEH൵HFWLYH DVD7EHDPÀDQJHZDVOLPLWHGWRRQHIRXUWKWKHVSDQ7KH Code now allows one-eighth of the span on each side of the beam web. This was done to simplify Table 6.3.2.1 and has negligible impact on designs. American Concrete Institute – Copyrighted © Material – www.concrete.org WLYHPDJQLW ZKHWKHUWR uilibrium deformat RIHTXLOL d in the a UWKHWRUVL PSDWLELOLWW uded in the an VWL൵QHVV should Guidance for th o conditions d VLRQDO VWL൵QH VWL൵Q of the RUVLRQ shou HVD truc to m ,Q be in UWRU WKH VV L V 72 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 75. Table 6.3.2.1—Dimensional limits for effective overhanging flange width for T-beams Flange location (൵HFWLYHRYHUKDQJLQJÀDQJHZLGWKEHRQGIDFH of web Each side of web Least of: 8h sw ln One side of web Least of: 6h sw ln 6.3.2.2 Isolated nonprestressed T-beams in which the ÀDQJHLVXVHGWRSURYLGHDGGLWLRQDOFRPSUHVVLRQDUHDVKDOO KDYHDÀDQJHWKLFNQHVVJUHDWHUWKDQRUHTXDOWR0.5bw and an H൵HFWLYHÀDQJHZLGWKOHVVWKDQRUHTXDOWR4bw. 6.3.2.3 For prestressed T-beams, it shall be permitted to use the geometry provided by 6.3.2.1 and 6.3.2.2. 6.4—Arrangement of live load 6.4.1 )RU WKH GHVLJQ RI ÀRRUV RU URRIV WR UHVLVW JUDYLW loads, it shall be permitted to assume that live load is applied only to the level under consideration. 6.4.2 For one-way slabs and beams, it shall be permitted to assume (a) and (b): (a) Maximum positive Mu near midspan occurs with factored L on the span and on alternate spans (b) Maximum negative Mu at a support occurs with factored L on adjacent spans only 6.4.3 For two-way slab systems, factored moments shall be calculated in accordance with 6.4.3.1, 6.4.3.2, or 6.4.3.3, and shall be at least the moments resulting from factored L applied simultaneously to all panels. 6.4.3.1 If the arrangement of L is known, the slab system shall be analyzed for that arrangement. 6.4.3.2 If L is variable and does not exceed 0.75D, or the nature of L is such that all panels will be loaded simultane- ously, it shall be permitted to assume that maximum Mu at R6.3.2.3 The empirical provisions of 6.3.2.1 and 6.3.2.2 ZHUH GHYHORSHG IRU QRQSUHVWUHVVHG 7EHDPV 7KH ÀDQJH widthsin6.3.2.1and6.3.2.2shouldbeusedunlessexperience has proven that variations are safe and satisfactory. Although many standard prestressed products in use today do not VDWLVI WKH H൵HFWLYH ÀDQJH ZLGWK UHTXLUHPHQWV RI and 6.3.2.2, they demonstrate satisfactory performance. 7KHUHIRUH GHWHUPLQDWLRQ RI DQ H൵HFWLYH ÀDQJH ZLGWK IRU prestressed T-beams is left to the experience and judgment of the licensed design professional. It is not always considered conservative in elastic analysis and design considerations to XVHWKHPD[LPXPÀDQJHZLGWKDVSHUPLWWHGLQ R6.4—Arrangement of live load R6.4.2 The most demanding sets of design forces should EHHVWDEOLVKHGELQYHVWLJDWLQJWKHH൵HFWVRIOLYHORDGSODFHG in various critical patterns. American Concrete Institute – Copyrighted © Material – www.concrete.org prestressed YH ÀDQJH demonstr QDWLRQ RI s is left to n profess elastic a [LPXPÀDQ R6 4—A tted to 3.2.2. R ZHUH GHYHORSHG sin6.3.2.1and6 hat variation VDWLV and 6 prestr the li WKH .2.2 UH sed nsed ven t tand s ar ar PART 2: LOADS ANALYSIS 73 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 76. all sections occurs with factored L applied simultaneously to all panels. 6.4.3.3)RUORDGLQJFRQGLWLRQVRWKHUWKDQWKRVHGH¿QHGLQ 6.4.3.1 or 6.4.3.2, it shall be permitted to assume (a) and (b): (a) Maximum positive Mu near midspan of panel occurs with 75 percent of factored L on the panel and alternate panels (b) Maximum negative Mu at a support occurs with 75 percent of factored L on adjacent panels only 6.5—Simplified method of analysis for nonprestressed continuous beams and one-way slabs 6.5.1 It shall be permitted to calculate Mu and Vu due to gravity loads in accordance with this section for continuous beams and one-way slabs satisfying (a) through (e): (a) Members are prismatic (b) Loads are uniformly distributed (c) L”D (d) There are at least two spans (e) The longer of two adjacent spans does not exceed the shorter by more than 20 percent 6.5.2 Mu due to gravity loads shall be calculated in accor- dance with Table 6.5.2. R6.4.3.3 The use of only 75 percent of the full factored live load for maximum moment loading patterns is based on the fact that maximum negative and maximum positive live load moments cannot occur simultaneously and that redistribution of maximum moments is thus possible before IDLOXUHRFFXUV7KLVSURFHGXUHLQH൵HFWSHUPLWVVRPHORFDO overstress under the full factored live load if it is distributed in the prescribed manner, but still ensures that the design strength of the slab system after redistribution of moment is not less than that required to resist the full factored dead and live loads on all panels. R6.5—Simplified method of analysis for nonprestressed continuous beams and one-way slabs R6.5.2 The approximate moments and shears give reasonable values for the stated conditions if the continuous beams and one-way slabs are part of a frame or continuous construction. Because the load patterns that produce critical YDOXHVIRUPRPHQWVLQFROXPQVRIIUDPHVGL൵HUIURPWKRVH for maximum negative moments in beams, column moments should be evaluated separately. American Concrete Institute – Copyrighted © Material – www.concrete.org The appro nable value beams a e to n for continuous ) through but ns nt nt does not excee the 74 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Table 6.5.2—Approximate moments for nonprestressed continuous beams and one-way slabs Moment Location Condition Mu Positive End span Discontinuous end integral with support wuƐn 2 Discontinuous end unrestrained wuƐn 2 Interior spans All wuƐn 2 Negative[1] Interior face of exterior support Member built integrally with supporting spandrel beam wuƐn 2 Member built integrally with supporting column wuƐn 2 ([WHULRUIDFHRI¿UVWLQWHULRUVXSSRUW Two spans wuƐn 2 More than two spans wuƐn 2 Face of other supports All wuƐn 2 Face of all supports satisfying (a) or (b) (a) slabs with spans not exceeding 10 ft E EHDPVZKHUHUDWLRRIVXPRIFROXPQVWL൵QHVVHVWREHDP VWL൵QHVVH[FHHGVDWHDFKHQGRIVSDQ wuƐn 2 [1] To calculate negative moments, Ɛn shall be the average of the adjacent clear span lengths. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 77. 6.5.3 Moments calculated in accordance with 6.5.2 shall not be redistributed. 6.5.4 Vu due to gravity loads shall be calculated in accor- dance with Table 6.5.4. Table 6.5.4—Approximate shears for nonprestressed continuous beams and one-way slabs Location Vu ([WHULRUIDFHRI¿UVWLQWHULRUVXSSRUW 1.15wuƐn Face of all other supports wuƐn 6.5.5 Floor or roof level moments shall be resisted by distributing the moment between columns immediately DERYHDQGEHORZWKHJLYHQÀRRULQSURSRUWLRQWRWKHUHODWLYH FROXPQVWL൵QHVVHVFRQVLGHULQJFRQGLWLRQVRIUHVWUDLQW 6.6—Linear elastic first-order analysis 6.6.1 General 6.6.1.16OHQGHUQHVVH൵HFWVVKDOOEHFRQVLGHUHGLQDFFRU- dance with 6.6.4, unless they are allowed to be neglected by 6.2.5.1. 6.6.1.2 Redistribution of moments calculated by an elastic ¿UVWRUGHU DQDOVLV VKDOO EH SHUPLWWHG LQ DFFRUGDQFH ZLWK 6.6.5. 6.6.2 0RGHOLQJRIPHPEHUVDQGVWUXFWXUDOVVWHPV 6.6.2.1 Floor or roof level moments shall be resisted by distributing the moment between columns immediately DERYHDQGEHORZWKHJLYHQÀRRULQSURSRUWLRQWRWKHUHODWLYH FROXPQVWL൵QHVVHVDQGFRQVLGHULQJFRQGLWLRQVRIUHVWUDLQW 6.6.2.2 For frames or continuous construction, consider- DWLRQVKDOOEHJLYHQWRWKHH൵HFWRIÀRRUDQGURRIORDGSDWWHUQV on transfer of moment to exterior and interior columns, and of eccentric loading due to other causes. 6.6.2.3 It shall be permitted to simplify the analysis model by the assumptions of (a), (b), or both: (a) Solid slabs or one-way joist systems built integrally with supports, with clear spans not more than 10 ft, shall be permitted to be analyzed as continuous members on knife-edge supports with spans equal to the clear spans of the member and width of support beams otherwise neglected. R6.5.5 This section is provided to make certain that moments are included in column design. The moment refers WRWKHGL൵HUHQFHEHWZHHQWKHHQGPRPHQWVRIWKHPHPEHUV framing into the column and exerted at the column centerline. R6.6—Linear elastic first-order analysis R6.6.1 General R6.6.1.1 :KHQ XVLQJ OLQHDU HODVWLF ¿UVWRUGHU DQDOVLV VOHQGHUQHVVH൵HFWVDUHFDOFXODWHGXVLQJWKHPRPHQWPDJQL- ¿HU DSSURDFK MacGregor et al. 1970; MacGregor 1993; Ford et al. 1981). R6.6.2 0RGHOLQJRIPHPEHUVDQGVWUXFWXUDOVVWHPV R6.6.2.1 This section is provided to make certain that moments are included in column design if members have been proportioned using 6.5.1 and 6.5.2. The moment refers WRWKHGL൵HUHQFHEHWZHHQWKHHQGPRPHQWVRIWKHPHPEHUV framing into the column and exerted at the column centerline. R6.6.2.3 A common feature of modern frame analysis software is the assumption of rigid connections. Section 6.6.2.3(b) is intended to apply to intersecting elements in frames, such as beam-column joints. American Concrete Institute – Copyrighted © Material – www.concrete.org HQ XVLQJ O VDUHFDOFX cGregor e R6 6 DOOE e al ent WW R6.6—Linear e 6 1 General d to be neglecte culated by an e y tic VOHQ ¿HU DS QHVV URDF al. 1 1.1 PART 2: LOADS ANALYSIS 75 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 78. (b) For frames or continuous construction, it shall be permitted to assume the intersecting member regions are rigid. 6.6.3 Section properties 6.6.3.1 Factored load analysis 6.6.3.1.1 Moment of inertia and cross-sectional area of members shall be calculated in accordance with Tables 6.6.3.1.1(a) or 6.6.3.1.1(b), unless a more rigorous analysis is used. If sustained lateral loads are present, I for columns and walls shall be divided by (ȕds), where ȕds is the ratio of maximum factored sustained shear within a story to the maximum factored shear in that story associated with the same load combination. Table 6.6.3.1.1(a)—Moments of inertia and cross- sectional areas permitted for elastic analysis at factored load level Member and condition Moment of inertia Cross- sectional area for axial deformations Cross- sectional area for shear deformations Columns 0.70Ig 1.0Ag bwh Walls Uncracked 0.70Ig Cracked 0.35Ig Beams 0.35Ig )ODWSODWHVDQGÀDWVODEV 0.25Ig R6.6.3 Section properties R6.6.3.1 Factored load analysis )RUODWHUDOORDGDQDOVLVHLWKHUWKHVWL൵QHVVHVSUHVHQWHGLQ 6.6.3.1.1 or 6.6.3.1.2 can be used. These provisions both use YDOXHVWKDWDSSUR[LPDWHWKHVWL൵QHVVIRUUHLQIRUFHGFRQFUHWH building systems loaded to near or beyond the yield level, and have been shown to produce reasonable correlation with both experimental and detailed analytical results (Moehle 1992; Lepage 1998). For earthquake-induced loading, the XVHRIRUPDUHTXLUHDGHÀHFWLRQDPSOL- ¿FDWLRQ IDFWRU WR DFFRXQW IRU LQHODVWLF GHIRUPDWLRQV ,Q JHQHUDOIRUH൵HFWLYHVHFWLRQSURSHUWLHVEc may be calcu- ODWHG RU VSHFL¿HG LQ DFFRUGDQFH ZLWK 19.2.2, the shear modulus may be taken as 0.4Ec, and areas may be taken as given in Table 6.6.3.1.1(a). R6.6.3.1.1 The values of I and A have been chosen from the results of frame tests and analyses, and include an DOORZDQFHIRUWKHYDULDELOLWRIWKHFDOFXODWHGGHÀHFWLRQV The moments of inertia are taken from MacGregor and Hage (1977)ZKLFKDUHPXOWLSOLHGEDVWL൵QHVVUHGXFWLRQIDFWRU ࢥK = 0.875 (refer to R6.6.4.5.2). For example, the moment of inertia for columns is 0.875(0.80Ig) = 0.70Ig. The moment of inertia of T-beams should be based on WKHH൵HFWLYHÀDQJHZLGWKGH¿QHGLQRU,WLV JHQHUDOOVX൶FLHQWODFFXUDWHWRWDNHIg of a T-beam as 2Ig for the web, 2(bwh3 /12). If the factored moments and shears from an analysis based on the moment of inertia of a wall, taken equal to 0.70Ig, LQGLFDWH WKDW WKH ZDOO ZLOO FUDFN LQ ÀH[XUH EDVHG RQ WKH modulus of rupture, the analysis should be repeated with I = 0.35Ig in those stories where cracking is predicted using factored loads. The values of the moments of inertia were derived for nonprestressed members. For prestressed members, the PRPHQWV RI LQHUWLD PD GL൵HU GHSHQGLQJ RQ WKH DPRXQW location, and type of reinforcement, and the degree of FUDFNLQJ SULRU WR UHDFKLQJ XOWLPDWH ORDG 7KH VWL൵QHVV values for prestressed concrete members should include an DOORZDQFHIRUWKHYDULDELOLWRIWKHVWL൵QHVVHV 7KHHTXDWLRQVLQ7DEOH E SURYLGHPRUHUH¿QHG values of I considering axial load, eccentricity, reinforcement ratio, and concrete compressive strength as presented in Khuntia and Ghosh (2004a,b 7KH VWL൵QHVVHV SURYLGHG in these references are applicable for all levels of loading, LQFOXGLQJ VHUYLFH DQG XOWLPDWH DQG FRQVLGHU D VWL൵QHVV reduction factor ࢥK comparable to that for the moment of inertias included in Table 6.6.3.1.1(a). For use at load levels American Concrete Institute – Copyrighted © Material – www.concrete.org e values o me tests YDULDELOLW rtia are ta PXOWLSOLHG to R6.6.4. mns is 0. ment of in H൵HFWLYHÀDQ JHQHUDOO and d in es ds sh t ODWH modulus may be in Table 6.6.3.1 dance with T ore rigorous ana rese colu where is the within a story t i s ysis mns atio he the DOORZ (1977 ࢥK = K ults FH I men ZKL 875 ( 3.1. ) 76 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 79. Table 6.6.3.1.1(b)—Alternative moments of inertia for elastic analysis at factored load Member Alternative value of I for elastic analysis Minimum I Maximum Columns and walls 0.35Ig 0.80 25 1 0.5 st u u g g u o A M P I A P h P + − − ⎛ ⎞ ⎛ ⎞ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ 0.875Ig %HDPVÀDW plates, and ÀDWVODEV 0.25Ig (0.10 25 ) 1.2 0.2 w g b I d + ρ − ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ 0.5Ig 1RWHV)RUFRQWLQXRXVÀH[XUDOPHPEHUVI shall be permitted to be taken as the average of values obtained for the critical positive and negative moment sections. Pu and Mu shall be calculated from the load combination under consideration, or the combination of Pu and Mu that produces the least value of I. 6.6.3.1.2 For factored lateral load analysis, it shall be permitted to assume I = 0.5Ig for all members or to calculate IEDPRUHGHWDLOHGDQDOVLVFRQVLGHULQJWKHH൵HFWLYHVWL൵- ness of all members under the loading conditions. 6.6.3.1.3 For factored lateral load analysis of two-way slab systems without beams, which are designated as part of the seismic-force-resisting system, I for slab members shall EHGH¿QHGEDPRGHOWKDWLVLQVXEVWDQWLDODJUHHPHQWZLWK results of comprehensive tests and analysis and I of other frame members shall be in accordance with 6.6.3.1.1 and 6.6.3.1.2. 6.6.3.2 Service load analysis 6.6.3.2.1,PPHGLDWHDQGWLPHGHSHQGHQWGHÀHFWLRQVGXH to gravity loads shall be calculated in accordance with 24.2. other than ultimate, Pu and Mu should be replaced with their appropriate values at the desired load level. R6.6.3.1.2 7KH ODWHUDO GHÀHFWLRQ RI D VWUXFWXUH XQGHU IDFWRUHG ODWHUDO ORDGV FDQ EH VXEVWDQWLDOO GL൵HUHQW IURP that calculated using linear analysis, in part because of the LQHODVWLFUHVSRQVHRIWKHPHPEHUVDQGWKHGHFUHDVHLQH൵HFWLYH VWL൵QHVV6HOHFWLRQRIWKHDSSURSULDWHH൵HFWLYHVWL൵QHVVIRU reinforced concrete frame members has dual purposes: 1) WRSURYLGHUHDOLVWLFHVWLPDWHVRIODWHUDOGHÀHFWLRQDQG WR GHWHUPLQHGHÀHFWLRQLPSRVHGDFWLRQVRQWKHJUDYLWVVWHP of the structure. A detailed nonlinear analysis of the structure ZRXOGDGHTXDWHOFDSWXUHWKHVHWZRH൵HFWV$VLPSOHZD WR HVWLPDWH DQ HTXLYDOHQW QRQOLQHDU ODWHUDO GHÀHFWLRQ XVLQJOLQHDUDQDOVLVLVWRUHGXFHWKHPRGHOHGVWL൵QHVVRI the concrete members in the structure. The type of lateral ORDG DQDOVLV D൵HFWV WKH VHOHFWLRQ RI DSSURSULDWH H൵HFWLYH VWL൵QHVV YDOXHV )RU DQDOVHV ZLWK ZLQG ORDGLQJ ZKHUH it is desirable to prevent nonlinear action in the structure, H൵HFWLYHVWL൵QHVVHVUHSUHVHQWDWLYHRISUHLHOGEHKDYLRUPD be appropriate. For earthquake-induced loading, the level of nonlinear deformation depends on the intended structural performance and earthquake recurrence interval. 9DULQJ GHJUHHV RI FRQ¿GHQFH FDQ EH REWDLQHG IURP D simple linear analysis based on the computational rigor XVHGWRGH¿QHWKHH൵HFWLYHVWL൵QHVVRIHDFKPHPEHU7KLV VWL൵QHVVFDQEHEDVHGRQWKHVHFDQWVWL൵QHVVWRDSRLQWDWRU beyond yield or, if yielding is not expected, to a point before yield occurs. R6.6.3.1.3 Analysis of buildings with two-way slab systems without beams requires that the model represents the transfer of lateral loads between vertical members. The PRGHOVKRXOGUHVXOWLQSUHGLFWLRQRIVWL൵QHVVLQVXEVWDQWLDO agreement with results of comprehensive tests and analysis. Several acceptable models have been proposed to accomplish this objective (Vanderbilt and Corley 1983; Hwang and Moehle 2000; Dovich and Wight 2005). R6.6.3.2 Service load analysis American Concrete Institute – Copyrighted © Material – www.concrete.org FWLRQLPSRV detailed no FDSWXUHWK TXLYDOHQW LV LVWR U mbers in t ൵HFWV WK OXHV )RU desirable to H൵HFWLY LQHODVWL VWL൵QHVV6HOHFWL rced concrete f HDOLVWLF HVWLP of th ZRXOG XVLQJ the c ruct DGHT PDWH QHDU crete GHU QHG DWH DWH PART 2: LOADS ANALYSIS 77 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 80. 6.6.3.2.2 It shall be permitted to calculate immediate ODWHUDOGHÀHFWLRQVXVLQJDPRPHQWRILQHUWLDRIWLPHVI GH¿QHGLQRUXVLQJDPRUHGHWDLOHGDQDOVLVEXWWKH value shall not exceed Ig. 6.6.4 6OHQGHUQHVVHৼHFWVPRPHQWPDJQL¿FDWLRQPHWKRG 6.6.4.18QOHVVLVVDWLV¿HGFROXPQVDQGVWRULHVLQ structures shall be designated as being nonsway or sway. Analysis of columns in nonsway frames or stories shall be in accordance with 6.6.4.5. Analysis of columns in sway frames or stories shall be in accordance with 6.6.4.6. 6.6.4.2 The cross-sectional dimensions of each member XVHGLQDQDQDOVLVVKDOOEHZLWKLQSHUFHQWRIWKHVSHFL¿HG member dimensions in construction documents or the anal- VLVVKDOOEHUHSHDWHG,IWKHVWL൵QHVVHVRI7DEOH E are used in an analysis, the assumed member reinforcement UDWLRVKDOODOVREHZLWKLQSHUFHQWRIWKHVSHFL¿HGPHPEHU reinforcement in construction documents. 6.6.4.3 It shall be permitted to analyze columns and stories LQVWUXFWXUHVDVQRQVZDIUDPHVLI D RU E LVVDWLV¿HG R6.6.3.2.2 $QDOVHV RI GHÀHFWLRQV YLEUDWLRQV DQG building periods are needed at various service (unfactored) load levels (Grossman 1987, 1990) to determine the perfor- mance of the structure in service. The moments of inertia of the structural members in the service load analyses should be representative of the degree of cracking at the various service load levels investigated. Unless a more accurate estimate of the degree of cracking at service load level is DYDLODEOHLWLVVDWLVIDFWRUWRXVH WLPHVWKH moments of inertia provided in 6.6.3.1, not to exceed Ig, for service load analyses. Serviceability considerations for vibrations are discussed in R24.1. R6.6.4 6OHQGHUQHVVHৼHFWVPRPHQWPDJQL¿FDWLRQPHWKRG R6.6.4.1 This section describes an approximate design SURFHGXUH WKDW XVHV WKH PRPHQW PDJQL¿HU FRQFHSW WR DFFRXQWIRUVOHQGHUQHVVH൵HFWV0RPHQWVFDOFXODWHGXVLQJ D ¿UVWRUGHU IUDPH DQDOVLV DUH PXOWLSOLHG E D PRPHQW PDJQL¿HUWKDWLVDIXQFWLRQRIWKHIDFWRUHGD[LDOORDGPu and the critical buckling load Pc for the column. For the sway FDVHWKHPRPHQWPDJQL¿HULVDIXQFWLRQRIWKHVXPRIPu of the story and the sum of Pc of the sway-resisting columns in the story considered. Nonsway and sway frames are WUHDWHGVHSDUDWHO$¿UVWRUGHUIUDPHDQDOVLVLVDQHODVWLF DQDOVLV WKDW H[FOXGHV WKH LQWHUQDO IRUFH H൵HFWV UHVXOWLQJ IURPGHÀHFWLRQV 7KH PRPHQW PDJQL¿HU GHVLJQ PHWKRG UHTXLUHV WKH designer to distinguish between nonsway frames, which are designed according to 6.6.4.5, and sway frames, which are designed according to 6.6.4.6. Frequently this can be done by FRPSDULQJWKHWRWDOODWHUDOVWL൵QHVVRIWKHFROXPQVLQDVWRU to that of the bracing elements. A compression member, such as a column, wall, or brace, may be assumed nonsway if it is located in a story in which the bracing elements (structural walls, shear trusses, or other types of lateral bracing) KDYH VXFK VXEVWDQWLDO ODWHUDO VWL൵QHVV WR UHVLVW WKH ODWHUDO GHÀHFWLRQVRIWKHVWRUWKDWDQUHVXOWLQJODWHUDOGHÀHFWLRQLV QRWODUJHHQRXJKWRD൵HFWWKHFROXPQVWUHQJWKVXEVWDQWLDOO If not readily apparent without calculations, 6.6.4.3 provides two possible ways of determining if sway can be neglected. R6.6.4.3,Q D DVWRULQDIUDPHLVFODVVL¿HGDV nonsway if the increase in the lateral load moments resulting from P¨H൵HFWVGRHVQRWH[FHHGSHUFHQWRIWKH¿UVWRUGHU moments (MacGregor and Hage 1977). Section 6.6.4.3(b) provides an alternative method of determining if a frame is American Concrete Institute – Copyrighted © Material – www.concrete.org the sum of idered. N $¿UVWRUG GHV WKH L PDJQL¿HU tinguish b ccording to gned accordi FRPSDU n sway 6.6.4.6. D ¿ PDJQL¿HUWKDWLV itical buckling RPHQW PDJQ in t WUHDWHG URPG 7K story VHSD WKD ÀHF PRP HP tory ¿HU ¿H 78 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 81. (a) The increase in column end moments due to second- RUGHUH൵HFWVGRHVQRWH[FHHGSHUFHQWRIWKH¿UVWRUGHU end moments (b) Q in accordance with 6.6.4.4.1 does not exceed 0.05 6.6.4.4 Stability properties 6.6.4.4.1 The stability index for a story, Q, shall be calcu- lated by: u o us c P Q V Σ Δ = A (6.6.4.4.1) where ™Pu and Vus are the total factored vertical load and horizontal story shear, respectively, in the story being eval- uated, and ¨o LV WKH ¿UVWRUGHU UHODWLYH ODWHUDO GHÀHFWLRQ between the top and the bottom of that story due to Vus. 6.6.4.4.2 The critical buckling load Pc shall be calculated by: 2 2 ( ) ( ) eff c u EI P k π = A (6.6.4.4.2) 6.6.4.4.37KHH൵HFWLYHOHQJWKIDFWRUk shall be calculated using Ec in accordance with 19.2.2 and I in accordance with 6.6.3.1.1. For nonsway members, k shall be permitted to be taken as 1.0, and for sway members, k shall be at least 1.0. 6.6.4.4.4 For columns, (EI)Hৼ shall be calculated in accor- dance with (a), (b), or (c): (a) 0.4 ( ) 1 c g eff dns E I EI = + β (6.6.4.4.4a) (b) (0.2 ) ( ) 1 c g s se eff dns E I E I EI + = + β (6.6.4.4.4b) (c) ( ) 1 c eff dns E I EI = + β (6.6.4.4.4c) FODVVL¿HGDVQRQVZDEDVHGRQWKHVWDELOLWLQGH[IRUDVWRU Q. In calculating Q, ™Pu should correspond to the lateral loading case for which ™Pu is greatest. A frame may contain both nonsway and sway stories. ,IWKHODWHUDOORDGGHÀHFWLRQVRIWKHIUDPHDUHFDOFXODWHG using service loads and the service load moments of inertia given in 6.6.3.2.2, it is permissible to calculate Q in Eq. (6.6.4.4.1) using 1.2 times the sum of the service gravity ORDGVWKHVHUYLFHORDGVWRUVKHDUDQGWLPHVWKH¿UVW RUGHUVHUYLFHORDGVWRUGHÀHFWLRQV R6.6.4.4 Stability properties R6.6.4.4.2 In calculating the critical axial buckling load, WKHSULPDUFRQFHUQLVWKHFKRLFHRIDVWL൵QHVV(EI)Hৼ that UHDVRQDEO DSSUR[LPDWHV WKH YDULDWLRQV LQ VWL൵QHVV GXH WR cracking, creep, and nonlinearity of the concrete stress-strain curve. Section 6.6.4.4.4 may be used to calculate (EI)Hৼ. R6.6.4.4.37KHH൵HFWLYHOHQJWKIDFWRUIRUDFRPSUHVVLRQ member, such as a column, wall, or brace, considering braced behavior, ranges from 0.5 to 1.0. It is recommended that a k value of 1.0 be used. If lower values are used, the calculation of k should be based on analysis of the frame using I values given in 6.6.3.1.1. The Jackson and Moreland Alignment Charts (Fig. R6.2.5.1) can be used to estimate appropriate values of k (ACI SP-17(09); Column Research Council 1966). R6.6.4.4.4 The numerators of Eq. (6.6.4.4.4a) to F UHSUHVHQW WKH VKRUWWHUP FROXPQ VWL൵QHVV Equation (6.6.4.4.4b) was derived for small eccentricity ratios and high levels of axial load. Equation (6.6.4.4.4a) LVDVLPSOL¿HGDSSUR[LPDWLRQWR(T E DQGLVOHVV accurate (Mirza 1990). For improved accuracy, (EI)Hৼ can be approximated using Eq. (6.6.4.4.4c). Creep due to sustained loads will increase the ODWHUDO GHÀHFWLRQV RI D FROXPQ DQG KHQFH WKH PRPHQW PDJQL¿FDWLRQUHHSH൵HFWVDUHDSSUR[LPDWHGLQGHVLJQE UHGXFLQJWKHVWL൵QHVV(EI)Hৼ used to calculate Pc and, hence, į, by dividing the short-term EI provided by the numerator of Eq. (6.6.4.4.4a) through (6.6.4.4.4c) by ( ȕdns). For American Concrete Institute – Copyrighted © Material – www.concrete.org culating t QLVWKHF [LPDWHV W , and non ion 6.6.4.4 red verti , in th UHOD of g ory due to Vus V V Pc P P shall be calcu ated WKHSU UHDVR 4.4. PDU EO PART 2: LOADS ANALYSIS 79 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 82. where ȕdns shall be the ratio of maximum factored sustained axial load to maximum factored axial load associated with the same load combination and I in Eq. (6.6.4.4.4c) is calcu- lated according to Table 6.6.3.1.1(b) for columns and walls. 6.6.4.5 0RPHQWPDJQL¿FDWLRQPHWKRG1RQVZDIUDPHV 6.6.4.5.1 The factored moment used for design of columns and walls, McVKDOOEHWKH¿UVWRUGHUIDFWRUHGPRPHQWM2 DPSOL¿HGIRUWKHH൵HFWVRIPHPEHUFXUYDWXUH Mc įM2 (6.6.4.5.1) 6.6.4.5.20DJQL¿FDWLRQIDFWRUįVKDOOEHFDOFXODWHGE 1.0 1 0.75 P u c C P P δ = ≥ − (6.6.4.5.2) 6.6.4.5.3 Cm shall be in accordance with (a) or (b): (a) For columns without transverse loads applied between supports 1 2 0.6 0.4 P M C M = − (6.6.4.5.3a) where M1/M2 is negative if the column is bent in single curvature, and positive if bent in double curvature. M1 corresponds to the end moment with the lesser absolute value. (b) For columns with transverse loads applied between supports. CP = 1.0 (6.6.4.5.3b) VLPSOL¿FDWLRQLWFDQEHDVVXPHGWKDWȕdns = 0.6. In this case, Eq. (6.6.4.4.4a) becomes (EI)Hৼ = 0.25EcIg. In reinforced concrete columns subject to sustained loads, creep transfers some of the load from the concrete to the longitudinal reinforcement, increasing the reinforcement stresses. In the case of lightly reinforced columns, this load transfer may cause the compression reinforcement to yield SUHPDWXUHOUHVXOWLQJLQDORVVLQWKHH൵HFWLYHEI.Accordingly, both the concrete and longitudinal reinforcement terms in Eq. (6.6.4.4.4b) are reduced to account for creep. R6.6.4.5 0RPHQWPDJQL¿FDWLRQPHWKRG1RQVZDIUDPHV R6.6.4.5.27KHIDFWRULQ(T LVWKHVWL൵QHVV reduction factor ࢥK, which is based on the probability of understrength of a single isolated slender column. Studies reported in Mirza et al. (1987) LQGLFDWH WKDW WKH VWL൵QHVV reduction factor ࢥK and the cross-sectional strength reduction ࢥ factors do not have the same values. These studies suggest WKH VWL൵QHVV UHGXFWLRQ IDFWRU ࢥK for an isolated column should be 0.75 for both tied and spiral columns. In the case of DPXOWLVWRUIUDPHWKHFROXPQDQGIUDPHGHÀHFWLRQVGHSHQG on the average concrete strength, which is higher than the strength of the concrete in the critical single understrength column. For this reason, the value of ࢥK implicit in I values in 6.6.3.1.1 is 0.875. R6.6.4.5.3 The factor Cm is a correction factor relating the actual moment diagram to an equivalent uniform moment GLDJUDP7KHGHULYDWLRQRIWKHPRPHQWPDJQL¿HUDVVXPHV that the maximum moment is at or near midheight of the column. If the maximum moment occurs at one end of the column, design should be based on an equivalent uniform moment CmM2 that leads to the same maximum moment at or QHDUPLGKHLJKWRIWKHFROXPQZKHQPDJQL¿HG MacGregor et al. 1970). The sign convention for M1/M2 has been updated to follow the right hand rule convention; hence, M1/M2 is negative if bent in single curvature and positive if bent in double FXUYDWXUH7KLVUHÀHFWVDVLJQFRQYHQWLRQFKDQJHIURPWKH 2011 Code. In the case of columns that are subjected to transverse loading between supports, it is possible that the maximum moment will occur at a section away from the end of the member. If this occurs, the value of the largest calculated moment occurring anywhere along the member should be used for the value of M2 in Eq. (6.6.4.5.1). Cm is to be taken as 1.0 for this case. American Concrete Institute – Copyrighted © Material – www.concrete.org za et al. ( and the cr ve the sam LRQ IDFWR oth tied a HWKHFROX concrete the concr mn. For this in 6 6 3 DOFXODWHGE c P ≥ R6.6.4.5.27K tion factor ࢥK, h of a sing redu ࢥ fact should DPX on fa s do ൵QHV be 0. WRU reng d in e is i 80 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 83. 6.6.4.5.4 M2 in Eq. (6.6.4.5.1) shall be at least M2,min calcu- lated according to Eq. (6.6.4.5.4) about each axis separately. M2PLQ = Pu(0.6 + 0.03h) (6.6.4.5.4) If M2,min exceeds M2, Cm shall be taken equal to 1.0 or calculated based on the ratio of the calculated end moments M1/M2, using Eq. (6.6.4.5.3a). 6.6.4.6 0RPHQWPDJQL¿FDWLRQPHWKRG6ZDIUDPHV 6.6.4.6.1 Moments M1 and M2 at the ends of an individual column shall be calculated by (a) and (b). (a) M1 = M1nsįsM1s (6.6.4.6.1a) (b) M2 = M2nsįsM2s (6.6.4.6.1b) 6.6.4.6.2 7KH PRPHQW PDJQL¿HU įs shall be calculated by (a), (b), or (c). If įs exceeds 1.5, only (b) or (c) shall be permitted: (a) 1 1 1 s Q δ = ≥ − (6.6.4.6.2a) (b) 1 1 1 0.75 s u c P P δ = ≥ Σ − Σ (6.6.4.6.2b) (c) Second-order elastic analysis where ™Pu is the summation of all the factored vertical loads in a story and ™Pc is the summation for all sway- resisting columns in a story. Pc is calculated using Eq. (6.6.4.4.2) with k determined for sway members from 6.6.4.4.3 and (EI)HৼIURPZLWKȕds substituted for ȕdns. R6.6.4.5.4 In the Code, slenderness is accounted for by magnifying the column end moments. If the factored column moments are small or zero, the design of slender columns should be based on the minimum eccentricity provided in Eq. (6.6.4.5.4). It is not intended that the minimum eccentricity be applied about both axes simultaneously. The factored column end moments from the structural analysis are used in Eq. (6.6.4.5.3a) in determining the ratio M1/M2 for the column when the design is based on the minimum eccentricity. This eliminates what would otherwise be a discontinuity between columns with calculated eccentricities less than the minimum eccentricity and columns with calculated eccentricities equal to or greater than the minimum eccentricity. R6.6.4.6 0RPHQWPDJQL¿FDWLRQPHWKRG6ZDIUDPHV R6.6.4.6.1 The analysis described in this section deals only ZLWKSODQHIUDPHVVXEMHFWHGWRORDGVFDXVLQJGHÀHFWLRQVLQWKDW SODQH,IWKHODWHUDOORDGGHÀHFWLRQVLQYROYHVLJQL¿FDQWWRUVLRQDO GLVSODFHPHQWWKHPRPHQWPDJQL¿FDWLRQLQWKHFROXPQVIDUWKHVW from the center of twist may be underestimated by the moment PDJQL¿HUSURFHGXUH,QVXFKFDVHVDWKUHHGLPHQVLRQDOVHFRQG order analysis should be used. R6.6.4.6.2 7KUHH GL൵HUHQW PHWKRGV DUH DOORZHG IRU FDOFXODWLQJWKHPRPHQWPDJQL¿HU7KHVHDSSURDFKHVLQFOXGH the Q method, the sum of P concept, and second-order elastic analysis. (a) Q method: The iterative P¨ analysis for second-order moments can EH UHSUHVHQWHG E DQ LQ¿QLWH VHULHV 7KH VROXWLRQ RI WKLV series is given by Eq. (6.6.4.6.2a) (MacGregor and Hage 1977). Lai and MacGregor (1983) show that Eq. (6.6.4.6.2a) closely predicts the second-order moments in a sway frame until įs exceeds 1.5. The P¨ PRPHQW GLDJUDPV IRU GHÀHFWHG FROXPQV DUH FXUYHGZLWK¨UHODWHGWRWKHGHÀHFWHGVKDSHRIWKHFROXPQV Equation (6.6.4.6.2a) and most commercially available second-order frame analyses have been derived assuming that the P¨ moments result from equal and opposite forces of P¨Ɛc applied at the bottom and top of the story. These forces give a straight-line P¨ moment diagram. The curved P¨ moment diagrams lead to lateral displacements on the order of 15 percent larger than those from the straight-line P¨ PRPHQW GLDJUDPV7KLV H൵HFW FDQ EH LQFOXGHG LQ (T (6.6.4.6.2a) by writing the denominator as (1 – 1.15Q) rather than (1 – Q). The 1.15 factor has been omitted from Eq. (6.6.4.6.2a) for simplicity. ,I GHÀHFWLRQV KDYH EHHQ FDOFXODWHG XVLQJ VHUYLFH ORDGV Q in Eq. (6.6.4.6.2a) should be calculated in the manner explained in R6.6.4.3. The QIDFWRUDQDOVLVLVEDVHGRQGHÀHFWLRQVFDOFXODWHG usingtheIvaluesfrom6.6.3.1.1,whichincludetheequivalent American Concrete Institute – Copyrighted © Material – www.concrete.org XUH,QVXFK ld be used GL൵HUH PHQWPDJ sum of P P ) Q method: The i QL¿ 1 ZLWKSO SODQH,IWKHODWHUD FHPHQWWKHPRP ter of twist m s shall be calcu nly (b) or (c) sha ated be orde FDOFXO the Q alys 4.6. LQJ etho e cen HUSUR ay b y PART 2: LOADS ANALYSIS 81 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 84. 6.6.4.6.3 Flexural members shall be designed for the total PDJQL¿HGHQGPRPHQWVRIWKHFROXPQVDWWKHMRLQW 6.6.4.6.46HFRQGRUGHUH൵HFWVVKDOOEHFRQVLGHUHGDORQJ the length of columns in sway frames. It shall be permitted WRDFFRXQWIRUWKHVHH൵HFWVXVLQJZKHUHCm is calcu- lated using M1 and M2 from 6.6.4.6.1. 6.6.5 5HGLVWULEXWLRQ RI PRPHQWV LQ FRQWLQXRXV ÀH[XUDO PHPEHUV 6.6.5.1 Except where approximate values for moments are used in accordance with 6.5, where moments have been RIDVWL൵QHVVUHGXFWLRQIDFWRUࢥK. These I values lead to a 20 WRSHUFHQWRYHUHVWLPDWLRQRIWKHODWHUDOGHÀHFWLRQVWKDW FRUUHVSRQGVWRDVWL൵QHVVUHGXFWLRQIDFWRUࢥK between 0.80 and 0.85 on the P¨ moments. As a result, no additional ࢥ factor is needed. Once the moments are established using Eq. (6.6.4.6.2a), selection of the cross sections of the columns involves the strength reduction factors ࢥ from 21.2.2. (b) Sum of P concept: 7RFKHFNWKHH൵HFWVRIVWRUVWDELOLWįs is calculated as an averaged value for the entire story based on use of ™Pu™Pc. 7KLVUHÀHFWVWKHLQWHUDFWLRQRIDOOVZDUHVLVWLQJFROXPQVLQ the story on the P¨H൵HFWVEHFDXVHWKHODWHUDOGHÀHFWLRQRI all columns in the story should be equal in the absence of torsional displacements about a vertical axis. In addition, it is possible that a particularly slender individual column in DVZDIUDPHFRXOGKDYHVXEVWDQWLDOPLGKHLJKWGHÀHFWLRQV HYHQLIDGHTXDWHOEUDFHGDJDLQVWODWHUDOHQGGHÀHFWLRQVE other columns in the story. Such a column is checked using 6.6.4.6.4. The 0.75 in the denominator of Eq. (6.6.4.6.2b) is a VWL൵QHVVUHGXFWLRQIDFWRUࢥK, as explained in R6.6.4.5.2. In the calculation of (EI)Hৼ, ȕds will normally be zero for a sway frame because the lateral loads are generally of short GXUDWLRQ6ZDGHÀHFWLRQVGXHWRVKRUWWHUPORDGVVXFKDV ZLQGRUHDUWKTXDNHDUHDIXQFWLRQRIWKHVKRUWWHUPVWL൵QHVV of the columns following a period of sustained gravity load. )RUWKLVFDVHWKHGH¿QLWLRQRIȕds in 6.6.3.1.1 gives ȕds = 0. In the unusual case of a sway frame where the lateral loads are sustained, ȕds will not be zero. This might occur if a building on a sloping site is subjected to earth pressure on one side but not on the other. R6.6.4.6.3 The strength of a sway frame is governed by stability of the columns and the degree of end restraint provided by the beams in the frame. If plastic hinges form in the restraining beam, as the structure approaches a failure mechanism, its axial strength is drastically reduced. This VHFWLRQ UHTXLUHV WKH UHVWUDLQLQJ ÀH[XUDO PHPEHUV WR KDYH HQRXJK VWUHQJWK WR UHVLVW WKH WRWDO PDJQL¿HG FROXPQ HQG moments at the joint. R6.6.4.6.4 The maximum moment in a compression member, such as a column, wall, or brace, may occur between its ends. While second-order computer analysis SURJUDPV PD EH XVHG WR HYDOXDWH PDJQL¿FDWLRQ RI WKH HQG PRPHQWV PDJQL¿FDWLRQ EHWZHHQ WKH HQGV PD QRW be accounted for unless the member is subdivided along LWV OHQJWK 7KH PDJQL¿FDWLRQ PD EH HYDOXDWHG XVLQJ WKH procedure outlined in 6.6.4.5. R6.6.5 5HGLVWULEXWLRQRIPRPHQWVLQFRQWLQXRXVÀH[XUDO PHPEHUV Redistribution of moments is dependent on adequate ductility in plastic hinge regions. These plastic hinge regions American Concrete Institute – Copyrighted © Material – www.concrete.org cause the l ÀHFWLRQVG DUHDIXQ wing a p HGH¿QLWL al case of ned, ȕds on a slopin ide but not 6.6. The 0.75 in VVUHGXFWLRQID culation of ( GXUD ZLQGR )RU = 0 Q6Z HDUW olum KLVF the ca fram ࢥK EI) I EI) I I 82 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 85. calculated in accordance with 6.8, or where moments in two-way slabs are determined using pattern loading speci- ¿HGLQUHGXFWLRQRIPRPHQWVDWVHFWLRQVRIPD[LPXP negative or maximum positive moment calculated by elastic theory shall be permitted for any assumed loading arrange- PHQWLI D DQG E DUHVDWLV¿HG (a) Flexural members are continuous (b) İt• at the section at which moment is reduced 6.6.5.2 For prestressed members, moments include those due to factored loads and those due to reactions induced by prestressing. 6.6.5.3 At the section where the moment is reduced, redis- tribution shall not exceed the lesser of İt percent and 20 percent. 6.6.5.4 The reduced moment shall be used to calculate redistributed moments at all other sections within the spans such that static equilibrium is maintained after redistribution of moments for each loading arrangement. 6.6.5.5 Shears and support reactions shall be calculated in accordance with static equilibrium considering the redistrib- uted moments for each loading arrangement. develop at sections of maximum positive or negative moment and cause a shift in the elastic moment diagram. The usual result is a reduction in the values of maximum negative moments in the support regions and an increase in the values of positive moments between supports from those calculated by elastic analysis. However, because negative moments are typically determined for one loading arrangement and positive moments for another (6.4.3 provides an exception for certain loading conditions), economies in reinforcement can sometimes be realized by reducing maximum elastic positive moments and increasing negative moments, thus narrowing the envelope of maximum negative and positive moments at any section in the span (Bondy 2003). Plastic hinges permit utilization of the full capacity of more cross VHFWLRQVRIDÀH[XUDOPHPEHUDWXOWLPDWHORDGV The Code permissible redistribution is shown in Fig. R6.6.5. Using conservative values of limiting concrete strains and lengths of plastic hinges derived from extensive WHVWVÀH[XUDOPHPEHUVZLWKVPDOOURWDWLRQFDSDFLWLHVZHUH analyzed for redistribution of moments up to 20 percent, depending on the reinforcement ratio. As shown, the permissible redistribution percentages are conservative relative to the calculated percentages available for both fy = 60 ksi and 80 ksi. Studies by Cohn (1965) and Mattock (1959) support this conclusion and indicate that cracking and GHÀHFWLRQRIEHDPVGHVLJQHGIRUUHGLVWULEXWLRQRIPRPHQWV DUHQRWVLJQL¿FDQWOJUHDWHUDWVHUYLFHORDGVWKDQIRUEHDPV designed by the distribution of moments according to elastic theory. Also, these studies indicate that adequate rotational capacity for the redistribution of moments allowed by the Code is available if the members satisfy 6.6.5.1. The provisions for redistribution of moments apply equally to prestressed members (Mast 1992). Theelasticdeformationscausedbyanonconcordanttendon change the amount of inelastic rotation required to obtain a given amount of redistribution of moments. Conversely, for a beam with a given inelastic rotational capacity, the amount by which the moment at the support may be varied is changed by an amount equal to the secondary moment at the support due to prestressing. Thus, the Code requires that secondary moments caused by reactions generated by prestressing forces be included in determining design moments. Redistribution of moments as permitted by 6.6.5 is not appropriate where approximate values of bending moments DUHXVHGVXFKDVSURYLGHGEWKHVLPSOL¿HGPHWKRGRI. Redistribution of moments is also not appropriate for two-way slab systems that are analyzed using the pattern loadings given in 6.4.3.3. These loadings use only 75 percent of the full factored live load, which is based on considerations of moment redistribution. American Concrete Institute – Copyrighted © Material – www.concrete.org calculated p ksi. Studie conclusio GHVLJQHG JUHDWHU istribution hese stud or the redis de is available The late within the spans ed after r gemen acti um ar WHVWVÀ analyzed for red ding on the r redistributi hall be calculat sidering the redi men n rib- = 6 (1959 DUHQR desig i an upp RQR VLJQ d by ible to t on n PART 2: LOADS ANALYSIS 83 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 86. 6.7—Linear elastic second-order analysis 6.7.1 General 6.7.1.1 A linear elastic second-order analysis shall FRQVLGHUWKHLQÀXHQFHRID[LDOORDGVSUHVHQFHRIFUDFNHG UHJLRQVDORQJWKHOHQJWKRIWKHPHPEHUDQGH൵HFWVRIORDG GXUDWLRQ7KHVHFRQVLGHUDWLRQVDUHVDWLV¿HGXVLQJWKHFURVV VHFWLRQDOSURSHUWLHVGH¿QHGLQ Percent change in moment Net tensile strain, εt 0.020 0 0.005 0.010 0.015 0.025 0 5 10 15 20 25 Calculated percentage available f y = 8 0 k s i Permissible redistribution allowed by 6.6.5.3 Minimum permissible net tensile strain = 0.0075 f y = 6 0 k s i ℓ/d = 23 b/d = 1/5 Fig. R6.6.5²3HUPLVVLEOH UHGLVWULEXWLRQ RI PRPHQWV IRU PLQLPXPURWDWLRQFDSDFLW R6.7—Linear elastic second-order analysis R6.7.1 General In linear elastic second-order analyses, the deformed geometry of the structure is included in the equations of equilibrium so that P¨H൵HFWVDUHGHWHUPLQHG7KHVWUXFWXUH LVDVVXPHGWRUHPDLQHODVWLFEXWWKHH൵HFWVRIFUDFNLQJDQG FUHHSDUHFRQVLGHUHGEXVLQJDQH൵HFWLYHVWL൵QHVVEI. In FRQWUDVWOLQHDUHODVWLF¿UVWRUGHUDQDOVLVVDWLV¿HVWKHHTXD- tions of equilibrium using the original undeformed geom- etry of the structure and estimates P¨H൵HFWVEPDJQLILQJ the column-end sway moments using Eq. (6.6.4.6.2a) or (6.6.4.6.2b). R6.7.1.17KHVWL൵QHVVHVEI used in an analysis for strength GHVLJQ VKRXOG UHSUHVHQW WKH VWL൵QHVVHV RI WKH PHPEHUV immediately prior to failure. This is particularly true for a VHFRQGRUGHUDQDOVLVWKDWVKRXOGSUHGLFWWKHODWHUDOGHÀHFWLRQV at loads approaching ultimate. The EI values should not be based solely on the moment-curvature relationship for the most highly loaded section along the length of each member. Instead, they should correspond to the moment-end rotation relationship for a complete member. To allow for variability in the actual member properties in the analysis, the member properties used in analysis should EH PXOWLSOLHG E D VWL൵QHVV UHGXFWLRQ IDFWRU ࢥK less than 7KH FURVVVHFWLRQDO SURSHUWLHV GH¿QHG LQ DOUHDG LQFOXGHWKLVVWL൵QHVVUHGXFWLRQIDFWRU7KHVWL൵QHVVUHGXFWLRQ factor ࢥK may be taken as 0.875. Note that the overall VWL൵QHVV LV IXUWKHU UHGXFHG FRQVLGHULQJ WKDW WKH PRGXOXV of elasticity of the concrete, EcLVEDVHGRQWKHVSHFL¿HG FRQFUHWHFRPSUHVVLYHVWUHQJWKZKLOHWKHVZDGHÀHFWLRQV American Concrete Institute – Copyrighted © Material – www.concrete.org astic sec second- structure that P¨ P P H WRUHPDLQ SDUHFRQVLG FRQWUDVW -or R6.6.5²3HUPL 5 5 WDWLRQ FDSD nalysis R6. R6. In geom Lin 1 G near ry o PUR LW W 84 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 87. 6.7.1.26OHQGHUQHVVH൵HFWVDORQJWKHOHQJWKRIDFROXPQ shall be considered. It shall be permitted to calculate these H൵HFWVXVLQJ 6.7.1.3 The cross-sectional dimensions of each member XVHGLQDQDQDOVLVWRFDOFXODWHVOHQGHUQHVVH൵HFWVVKDOOEH ZLWKLQ SHUFHQW RI WKH VSHFL¿HG PHPEHU GLPHQVLRQV LQ construction documents or the analysis shall be repeated. 6.7.1.4 Redistribution of moments calculated by an elastic second-order analysis shall be permitted in accordance with 6.6.5. 6.7.2 Section properties 6.7.2.1 Factored load analysis 6.7.2.1.1 It shall be permitted to use section properties calculated in accordance with 6.6.3.1. 6.7.2.2 Service load analysis 6.7.2.2.1,PPHGLDWHDQGWLPHGHSHQGHQWGHÀHFWLRQVGXH to gravity loads shall be calculated in accordance with 24.2. 6.7.2.2.2 Alternatively, it shall be permitted to calculate LPPHGLDWHGHÀHFWLRQVXVLQJDPRPHQWRILQHUWLDRIWLPHV I given in 6.6.3.1, or calculated using a more detailed anal- ysis, but the value shall not exceed Ig. 6.8—Inelastic analysis 6.8.1 General 6.8.1.1 An inelastic analysis shall consider material QRQOLQHDULW $Q LQHODVWLF ¿UVWRUGHU DQDOVLV VKDOO VDWLVI HTXLOLEULXP LQ WKH XQGHIRUPHG FRQ¿JXUDWLRQ$Q LQHODVWLF second-order analysis shall satisfy equilibrium in the GHIRUPHGFRQ¿JXUDWLRQ 6.8.1.2 An inelastic analysis procedure shall have been shown to result in calculation of strength and deformations that are in substantial agreement with results of physical tests of reinforced concrete components, subassemblages, or structural systems exhibiting response mechanisms consis- tent with those expected in the structure being designed. are a function of the average concrete strength, which is typically higher. R6.7.1.2 The maximum moment in a compression member may occur between its ends. In computer analysis programs, columns may be subdivided using QRGHV DORQJ WKHLU OHQJWK WR HYDOXDWH VOHQGHUQHVV H൵HFWV between the ends. If the column is not subdivided along LWVOHQJWKVOHQGHUQHVVH൵HFWVPDEHHYDOXDWHGXVLQJWKH QRQVZD PRPHQW PDJQL¿HU PHWKRG VSHFL¿HG LQ with member-end moments from the second-order elastic analysis as input. Second-order analysis already accounts for the relative displacement of member ends. R6.7.2 Section properties R6.7.2.2 Service load analysis R6.7.2.2.2 Refer to R6.6.3.2.2. R6.8—Inelastic analysis R6.8.1 General R6.8.1.10DWHULDOQRQOLQHDULWPDEHD൵HFWHGEPXOWLSOH factors including duration of loads, shrinkage, and creep. R6.8.1.2 Substantial agreement should be demonstrated at characteristic points on the reported response. The char- acteristic points selected should depend on the purpose of the analysis, the applied loads, and the response phenomena exhibited by the component, subassemblage, or structural system. For nonlinear analysis to support design under American Concrete Institute – Copyrighted © Material – www.concrete.org properties .7.2.2 Servi ated by an elastic ed in acco is d to e section prop es R 2 Se PART 2: LOADS ANALYSIS 85 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 88. service-level loading, characteristic points should represent loads and deformations less than those corresponding to yielding of reinforcement. For nonlinear analysis to support design or assess response under design-level loading, char- acteristic points should represent loads and deformations less than those corresponding to yielding of reinforcement as well as points corresponding to yielding of reinforce- ment and onset of strength loss. Strength loss need not be represented if design loading does not extend the response into the strength-loss range. Typically, inelastic analysis to VXSSRUWGHVLJQVKRXOGHPSORVSHFL¿HGPDWHULDOVWUHQJWKV and mean values of other material properties and component VWL൵QHVVHV1RQOLQHDUUHVSRQVHKLVWRUDQDOVLVWRYHULIWKH design of earthquake-resistant concrete structures should employ expected material strengths, expected material prop- HUWLHVDQGH[SHFWHGFRPSRQHQWVWL൵QHVVHVDVVSHFL¿HGLQ A.6.2. R6.8.1.3 Refer to R6.7.1.2. R6.8.1.5Section6.6.5allowsforredistributionofmoments calculated using elastic analysis to account for inelastic response of the system. Moments calculated by inelastic analysis explicitly account for inelastic response; therefore, further redistribution of moments is not appropriate. R6.9—Acceptability of finite element analysis R6.9.1 This section was introduced in the 2014 Code to explicitly recognize a widely used analysis method. R6.9.2 The licensed design professional should ensure that an appropriate analysis model is used for the particular problem of interest. This includes selection of computer software program, element type, model mesh, and other modeling assumptions. $ODUJHYDULHWRI¿QLWHHOHPHQWDQDOVLVFRPSXWHUVRIWZDUH programs are available, including those that perform static, dynamic, elastic, and inelastic analyses. The element types used should be capable of determining the response required. Finite element models may have beam-column elements that model structural framing members, such as beams and columns, along with plane stress elements; plate elements; and shell elements, brick HOHPHQWV RU ERWK WKDW DUH XVHG WR PRGHO WKH ÀRRU VODEV mat foundations, diaphragms, walls, and connections. The model mesh size selected should be capable of determining 6.8.1.3 8QOHVV VOHQGHUQHVV H൵HFWV DUH SHUPLWWHG WR EH neglected in accordance with 6.2.5.1, an inelastic analysis VKDOO VDWLVI HTXLOLEULXP LQ WKH GHIRUPHG FRQ¿JXUDWLRQ ,W VKDOOEHSHUPLWWHGWRFDOFXODWHVOHQGHUQHVVH൵HFWVDORQJWKH length of a column using 6.6.4.5. 6.8.1.4 The cross-sectional dimensions of each member XVHGLQDQDQDOVLVWRFDOFXODWHVOHQGHUQHVVH൵HFWVVKDOOEH ZLWKLQ SHUFHQW RI WKH VSHFL¿HG PHPEHU GLPHQVLRQV LQ construction documents or the analysis shall be repeated. 6.8.1.5 Redistribution of moments calculated by an inelastic analysis shall not be permitted. 6.9—Acceptability of finite element analysis 6.9.1 )LQLWH HOHPHQW DQDOVLV WR GHWHUPLQH ORDG H൵HFWV shall be permitted. 6.9.27KH¿QLWHHOHPHQWPRGHOVKDOOEHDSSURSULDWHIRULWV intended purpose. American Concrete Institute – Copyrighted © Material – www.concrete.org Section6.6 ulated using respons R EH nelastic analysis PHG FRQ¿ GHUQH dim HV ¿H aly ons of each me UQHVVH൵HFWVVKD HPEHU HQVLR hall be repeate ber OEH V LQ 86 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 89. WKHVWUXFWXUDOUHVSRQVHLQVX൶FLHQWGHWDLO7KHXVHRIDQVHW RIUHDVRQDEOHDVVXPSWLRQVIRUPHPEHUVWL൵QHVVLVDOORZHG R6.9.3 )RU DQ LQHODVWLF ¿QLWH HOHPHQW DQDOVLV WKH rules of linear superposition do not apply. To determine the ultimate member inelastic response, for example, it is not correct to analyze for service loads and subsequently combine the results linearly using load factors. A separate inelastic analysis should be performed for each factored load combination. 6.9.3 For inelastic analysis, a separate analysis shall be performed for each factored load combination. 6.9.47KHOLFHQVHGGHVLJQSURIHVVLRQDOVKDOOFRQ¿UPWKDW the results are appropriate for the purposes of the analysis. 6.9.5 The cross-sectional dimensions of each member used in an analysis shall be within 10 percent of the speci- ¿HGPHPEHUGLPHQVLRQVLQFRQVWUXFWLRQGRFXPHQWVRUWKH analysis shall be repeated. 6.9.6 Redistribution of moments calculated by an inelastic analysis shall not be permitted. American Concrete Institute – Copyrighted © Material – www.concrete.org d by an inelastic PART 2: LOADS ANALYSIS 87 CODE COMMENTARY 6 Analysis Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 90. American Concrete Institute – Copyrighted © Material – www.concrete.org 88 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 91. 7 One-way Slabs 7.1—Scope 7.1.1 This chapter shall apply to the design of nonpre- VWUHVVHGDQGSUHVWUHVVHGVODEVUHLQIRUFHGIRUÀH[XUHLQRQH direction, including: (a) Solid slabs (b) Slabs cast on stay-in-place, noncomposite steel deck (c) Composite slabs of concrete elements constructed in separate placements but connected so that all elements resist loads as a unit (d) Precast, prestressed hollow-core slabs 7.2—General 7.2.17KHH൵HFWVRIFRQFHQWUDWHGORDGVVODERSHQLQJVDQG voids within the slab shall be considered in design. 7.2.2 Materials 7.2.2.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 7.2.2.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 7.2.2.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 7.2.3 RQQHFWLRQWRRWKHUPHPEHUV 7.2.3.1 For cast-in-place construction, beam-column and slab-column joints shall satisfy Chapter 15. 7.2.3.2 For precast construction, connections shall satisfy the force transfer requirements of 16.2. 7.3—Design limits 7.3.1 0LQLPXPVODEWKLFNQHVV 7.3.1.1 For solid nonprestressed slabs not supporting or attached to partitions or other construction likely to be GDPDJHGEODUJHGHÀHFWLRQVRYHUDOOVODEWKLFNQHVVh shall not be less than the limits in Table 7.3.1.1, unless the calcu- ODWHGGHÀHFWLRQOLPLWVRIDUHVDWLV¿HG R7.1—Scope R7.1.1 The design and construction of composite slabs on steel deck is described in “Standard for Composite Steel )ORRU'HFN±6ODEV´ SDI C). Provisions for one-way joist systems are provided in Chapter 9. R7.2—General R7.2.1 Concentrated loads and slab openings create local moments and shears and may cause regions of one-way VODEV WR KDYH WZRZD EHKDYLRU 7KH LQÀXHQFH RI RSHQ- ings through the slab and voids within the slab (for example GXFWV RQÀH[XUDODQGVKHDUVWUHQJWKDVZHOODVGHÀHFWLRQV is to be considered, including evaluating the potential for critical sections created by the openings and voids. R7.3—Design limits R7.3.1 0LQLPXPVODEWKLFNQHVV The basis for minimum thickness for one-way slabs is the same as that for beams. Refer to R9.3.1 for additional information. American Concrete Institute – Copyrighted © Material – www.concrete.org con 19 st C is to b critical sections shall be select einforcement sha er 20. to be PART 3: MEMBERS 89 CODE COMMENTARY CHAPTER 7—ONE-WAY SLABS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 92. R7.3.2 DOFXODWHGGHÀHFWLRQOLPLWV 7KHEDVLVIRUFDOFXODWHGGHÀHFWLRQVIRURQHZDVODEVLV the same as that for beams. Refer to R9.3.2 for additional information. R7.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV R7.3.3.1 The basis for a reinforcement strain limit for one-way slabs is the same as that for beams. Refer to R9.3.3 for additional information. Table 7.3.1.1—Minimum thickness of solid nonprestressed one-way slabs Support condition Minimum h[1] Simply supported Ɛ One end continuous Ɛ Both ends continuous Ɛ Cantilever Ɛ [1] Expression applicable for normalweight concrete and fy = 60,000 psi. For other cases, minimum hVKDOOEHPRGL¿HGLQDFFRUGDQFHZLWKWKURXJK as appropriate. 7.3.1.1.1 For fy other than 60,000 psi, the expressions in Table 7.3.1.1 shall be multiplied by (0.4 + fy/100,000). 7.3.1.1.2 For nonprestressed slabs made of lightweight concretehavingwcLQWKHUDQJHRIWROEIW3 ,theexpressions in Table 7.3.1.1 shall be multiplied by the greater of (a) and (b): (a) 1.65 – 0.005wc (b) 1.09 7.3.1.1.3 For nonprestressed composite slabs made of a combinationoflightweightandnormalweightconcrete,shored during construction, and where the lightweight concrete is in FRPSUHVVLRQWKHPRGL¿HURIVKDOODSSO 7.3.1.27KHWKLFNQHVVRIDFRQFUHWHÀRRU¿QLVKVKDOOEH permitted to be included in h if it is placed monolithically ZLWKWKHÀRRUVODERULIWKHÀRRU¿QLVKLVGHVLJQHGWREH FRPSRVLWHZLWKWKHÀRRUVODELQDFFRUGDQFHZLWK16.4. 7.3.2 DOFXODWHGGHÀHFWLRQOLPLWV 7.3.2.1 For nonprestressed slabs not satisfying 7.3.1 and IRUSUHVWUHVVHGVODEVLPPHGLDWHDQGWLPHGHSHQGHQWGHÀHF- tions shall be calculated in accordance with 24.2 and shall not exceed the limits in 24.2.2. 7.3.2.2 For nonprestressed composite concrete slabs satis- ILQJGHÀHFWLRQVRFFXUULQJDIWHUWKHPHPEHUEHFRPHV FRPSRVLWH QHHG QRW EH FDOFXODWHG 'HÀHFWLRQV RFFXUULQJ before the member becomes composite shall be investigated, XQOHVVWKHSUHFRPSRVLWHWKLFNQHVVDOVRVDWLV¿HV 7.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV 7.3.3.1 Nonprestressed slabs shall be tension-controlled in accordance with Table 21.2.2. 7.3.4 6WUHVVOLPLWVLQSUHVWUHVVHGVODEV 7.3.4.13UHVWUHVVHGVODEVVKDOOEHFODVVL¿HGDVODVV87 or C in accordance with 24.5.2. American Concrete Institute – Copyrighted © Material – www.concrete.org comp orm th QF i ghtconcrete,s tweight concrete KDOO ÀRRU¿QLVK VKD ed s in EH 90 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 93. 7 One-way Slabs R7.4—Required strength R7.4.3 Factored shear R7.4.3.2 The requirements for the selection of the critical section for shear in one-way slabs are the same as those for beams. Refer to R9.4.3.2 for additional information. R7.5—Design strength R7.5.1 General R7.5.1.1 Refer to R9.5.1.1. R7.5.2 0RPHQW 7.3.4.2 Stresses in prestressed slabs immediately after transfer and at service loads shall not exceed the permissible stresses in 24.5.3 and 24.5.4. 7.4—Required strength 7.4.1 General 7.4.1.1 Required strength shall be calculated in accor- dance with the factored load combinations in Chapter 5. 7.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. 7.4.1.3)RUSUHVWUHVVHGVODEVH൵HFWVRIUHDFWLRQVLQGXFHG by prestressing shall be considered in accordance with 5.3.11. 7.4.2 )DFWRUHGPRPHQW 7.4.2.1 For slabs built integrally with supports, Mu at the support shall be permitted to be calculated at the face of support. 7.4.3 Factored shear 7.4.3.1 For slabs built integrally with supports, Vu at the support shall be permitted to be calculated at the face of support. 7.4.3.2 Sections between the face of support and a crit- ical section located d from the face of support for nonpre- stressed slabs or h/2 from the face of support for prestressed slabs shall be permitted to be designed for Vu at that critical VHFWLRQLI D WKURXJK F DUHVDWLV¿HG (a) Support reaction, in direction of applied shear, intro- duces compression into the end region of the slab (b) Loads are applied at or near the top surface of the slab (c) No concentrated load occurs between the face of support and critical section 7.5—Design strength 7.5.1 General 7.5.1.1 For each applicable factored load combina- WLRQ GHVLJQ VWUHQJWK DW DOO VHFWLRQV VKDOO VDWLVI ࢥSn • U LQFOXGLQJ D DQG E ,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOO be considered. D ࢥMn•Mu E ࢥVn•Vu ࢥ shall be determined in accordance with 21.2. 7.5.2 0RPHQW 7.5.2.1 Mn shall be calculated in accordance with 22.3. American Concrete Institute – Copyrighted © Material – www.concrete.org equiremen ar in one er to R9.4 ctored shea the e face of support. ally be fac supports, Vu V V a ulated at the fa support and a R7 e of it- 3.2 3 F PART 3: MEMBERS 91 CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 94. R7.5.2.3 This provision applies only where a T-beam is parallel to the span of a one-way slab. For example, this beam might be used to support a wall or concentrated load that the slab alone cannot support. In that case, the primary slab reinforcement is parallel to the beam and the perpen- dicular reinforcement is usually sized for temperature and shrinkage. The reinforcement required by this provision is intended to consider “unintended” negative moments that may develop over the beam that exceed the requirements for temperature and shrinkage reinforcement alone. R7.6—Reinforcement limits R7.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG slabs R7.6.1.1 The required area of deformed or welded wire UHLQIRUFHPHQW XVHG DV PLQLPXP ÀH[XUDO UHLQIRUFHPHQW is the same as provided for shrinkage and temperature in 24.4.3.2. However, whereas shrinkage and temperature rein- forcement is permitted to be distributed between the two IDFHVRIWKHVODEDVGHHPHGDSSURSULDWHIRUVSHFL¿FFRQGL- WLRQVPLQLPXPÀH[XUDOUHLQIRUFHPHQWVKRXOGEHSODFHGDV close as practicable to the face of the concrete in tension due to applied loads. R7.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV 7KH UHTXLUHPHQWV IRU PLQLPXP ÀH[XUDO UHLQIRUFH- ment for prestressed one-way slabs are the same as those for prestressed beams. Refer to R9.6.2 for additional information. 7.5.2.2 For prestressed slabs, external tendons shall be FRQVLGHUHG DV XQERQGHG WHQGRQV LQ FDOFXODWLQJ ÀH[XUDO VWUHQJWKXQOHVVWKHH[WHUQDOWHQGRQVDUHH൵HFWLYHOERQGHG to the concrete section along the entire length. 7.5.2.3,ISULPDUÀH[XUDOUHLQIRUFHPHQWLQDVODEWKDWLV FRQVLGHUHGWREHD7EHDPÀDQJHLVSDUDOOHOWRWKHORQJLWX- dinal axis of the beam, reinforcement perpendicular to the longitudinal axis of the beam shall be provided in the top of the slab in accordance with (a) and (b). This provision does not apply to joist construction. (a) Slab reinforcement perpendicular to the beam shall be designed to resist the factored load on the overhanging slab width assumed to act as a cantilever. E 2QOWKHH൵HFWLYHRYHUKDQJLQJVODEZLGWKLQDFFRU- dance with 6.3.2 need be considered. 7.5.3 Shear 7.5.3.1 Vn shall be calculated in accordance with 22.5. 7.5.3.2 For composite concrete slabs, horizontal shear strength Vnh shall be calculated in accordance with 16.4. 7.6—Reinforcement limits 7.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG slabs 7.6.1.1$PLQLPXPDUHDRIÀH[XUDOUHLQIRUFHPHQWAs,min, of 0.0018Ag shall be provided. 7.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV 7.6.2.1 For slabs with bonded prestressed reinforcement, total quantity of As and Aps shall be adequate to develop a factored load at least 1.2 times the cracking load calculated on the basis of fr as given in 19.2.3. 7.6.2.2 )RU VODEV ZLWK ERWK ÀH[XUDO DQG VKHDU GHVLJQ strength at least twice the required strength, 7.6.2.1 need not EHVDWLV¿HG 7.6.2.3 For slabs with unbonded tendons, the minimum area of bonded deformed longitudinal reinforcement, As,min, shall be: AVPLQ•Act (7.6.2.3) American Concrete Institute – Copyrighted © Material – www.concrete.org ment lim ÀH[XUDO The requi RUFHPHQW is the s rdance w ete s in a IRU ance with 16.4 QWLQ SUHVWU R7. s slabs G VHG Rein 1 0 92 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 95. 7 One-way Slabs R7.6.3 0LQLPXPVKHDUUHLQIRUFHPHQW The basis for minimum shear reinforcement for one-way slabs is the same as that for beams. Refer to R9.6.3 for addi- tional information. R7.6.3.1 Solid slabs and footings have less stringent minimum shear reinforcement requirements than beams because there is a possibility of load sharing between weak and strong areas. However, research (Angelakos et al. 2001; Lubell et al. 2004; Brown et al. 2006) has shown that deep, lightly reinforced one-way slabs, particularly if constructed with high-strength concrete or concrete having a small coarse aggregate size, may fail at shears less than Vc calculated from Eq. (22.5.5.1). One-way slabs subjected to concen- trated loads are more likely to exhibit this vulnerability. Results of tests on precast, prestressed hollow-core units (Becker and Buettner 1985; Anderson 1978) with h ” 12.5 in. have shown shear strengths greater than those calcu- lated by Eq. (22.5.6.3.1a) and Eq. (22.5.6.3.2). Results of tests on hollow-core units with h 12.5 in. have shown that web-shear strengths in end regions can be less than VWUHQJWKVFDOFXODWHGE(T ,QFRQWUDVWÀH[XUH shear strengths in the deeper hollow-core units equaled or exceeded strengths calculated by Eq. (22.5.6.3.1a). R7.6.3.2 The basis for the testing-based strength evalua- tion for one-way slabs is the same as that for beams. Refer to R9.6.3.3 for additional information. R7.6.40LQLPXPVKULQNDJHDQGWHPSHUDWXUHUHLQIRUFHPHQW R7.6.4.2 In prestressed monolithic beam-and-slab construction, at least one shrinkage and temperature tendon is required between beams, even if the beam tendons alone provide at least 100 psi average compressive stress as required by 24.4.4.1 RQWKHJURVVFRQFUHWHDUHDDVGH¿QHGLQ 7.6.4.2.1. A tendon of any size is permissible as long as all RWKHUUHTXLUHPHQWVRIDQGDUHVDWLV¿HG$SSOL- cation of the provisions of 7.6.4.2 and 7.7.6.3 to monolithic, cast-in-place, post-tensioned, beam-and-slab construction is illustrated in Fig. R7.6.4.2. Tendons used for shrinkage and temperature reinforcement should be positioned as close as practicable to the mid-depth where Act is the area of that part of the cross section between WKHÀH[XUDOWHQVLRQIDFHDQGWKHFHQWURLGRIWKHJURVVVHFWLRQ 7.6.3 0LQLPXPVKHDUUHLQIRUFHPHQW 7.6.3.1 A minimum area of shear reinforcement, Av,min, shall be provided in all regions where Vu ࢥVc. For precast prestressed hollow-core slabs with untopped h 12.5 in., Av,min shall be provided in all regions where Vu 0.5ࢥVcw. 7.6.3.2 If shown by testing that the required Mn and Vn can EHGHYHORSHGQHHGQRWEHVDWLV¿HG6XFKWHVWVVKDOO VLPXODWHH൵HFWVRIGL൵HUHQWLDOVHWWOHPHQWFUHHSVKULQNDJH and temperature change, based on a realistic assessment of WKHVHH൵HFWVRFFXUULQJLQVHUYLFH 7.6.3.3 If shear reinforcement is required, Av,min shall be in accordance with 9.6.3.4. 7.6.4 0LQLPXPVKULQNDJHDQGWHPSHUDWXUHUHLQIRUFHPHQW 7.6.4.1 Reinforcement shall be provided to resist shrinkage and temperature stresses in accordance with 24.4. 7.6.4.2 If prestressed shrinkage and temperature reinforce- ment in accordance with 24.4.4 is used, 7.6.4.2.1 through 7.6.4.2.3 shall apply. 7.6.4.2.1 For monolithic, cast-in-place, post-tensioned beam-and-slab construction, gross concrete area shall consist of the total beam area including the slab thickness and the slab area within half the clear distance to adjacent EHDP ZHEV ,W VKDOO EH SHUPLWWHG WR LQFOXGH WKH H൵HFWLYH force in beam tendons in the calculation of total prestress force acting on gross concrete area. American Concrete Institute – Copyrighted © Material – www.concrete.org 2.5.6.3.1a) ore units ngths in E(T the deepe hs calculat The basis for one-way R9 6 3 H trated l Results of tes er and Buettne own shear test that w shear exce ho b-sh VFD reng d st e sh y Eq tren re PART 3: MEMBERS 93 CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 96. 7.6.4.2.2 If slabs are supported on walls or not cast mono- lithically with beams, gross concrete area is the slab section tributary to the tendon or tendon group. 7.6.4.2.3 At least one tendon is required in the slab between faces of adjacent beams or walls. 7.7—Reinforcement detailing 7.7.1 General 7.7.1.1 Concrete cover for reinforcement shall be in accor- dance with 20.5.1. 7.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4. of the slab. In cases where the shrinkage and temperature tendons are used for supporting the principal tendons, varia- tions from the slab centroid are permissible; however, the resultant of the shrinkage and temperature tendons should not fall outside the middle third of the slab thickness. 7KHH൵HFWVRIVODEVKRUWHQLQJVKRXOGEHHYDOXDWHGWRHQVXUH WKHH൵HFWLYHQHVVRIWKHSUHVWUHVVLQJ,QPRVWFDVHVWKHORZ OHYHORISUHVWUHVVLQJUHFRPPHQGHGVKRXOGQRWFDXVHGL൶FXO- ties in a properly detailed structure. Additional attention may EHUHTXLUHGZKHUHWKHUPDOH൵HFWVEHFRPHVLJQL¿FDQW R7.7—Reinforcement detailing American Concrete Institute – Copyrighted © Material – www.concrete.org 94 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY 6 ft maximum per 7.7.6.3.1 (typ.). Refer to 7.7.6.3.2 for additional reinforcement required when spacing exceeds 4.5 ft. Beam tendons L1/2 L1 L2 L2/2 Beam web width Beam and slab tendons within the orange area must provide 100 psi minimum average compressive stress in the orange area (gross area tributary to each beam). Plan Section A-A A A Slab shrinkage and temperature tendons Fig. R7.6.4.2²6HFWLRQWKURXJKEHDPVFDVWPRQROLWKLFDOOZLWKVODE Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 97. 7 One-way Slabs 7.7.1.3 Splices of deformed reinforcement shall be in accordance with 25.5. 7.7.1.4 Bundled bars shall be in accordance with 25.6. 7.7.2 5HLQIRUFHPHQWVSDFLQJ 7.7.2.1 Minimum spacing s shall be in accordance with 25.2. 7.7.2.2 For nonprestressed and Class C prestressed slabs, spacing of bonded longitudinal reinforcement closest to the tension face shall not exceed s given in 24.3. 7.7.2.3 For nonprestressed and Class T and C prestressed slabs with unbonded tendons, maximum spacing s of deformed longitudinal reinforcement shall be the lesser of 3h and 18 in. 7.7.2.4 Maximum spacing, s, of reinforcement required by 7.5.2.3 shall be the lesser of 5h and 18 in. 7.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV 7.7.3.1 Calculated tensile or compressive force in rein- forcement at each section of the slab shall be developed on each side of that section. 7.7.3.2 Critical locations for development of reinforce- ment are points of maximum stress and points along the span where bent or terminated tension reinforcement is no longer UHTXLUHGWRUHVLVWÀH[XUH 7.7.3.3 Reinforcement shall extend beyond the point at ZKLFKLWLVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUHIRUDGLVWDQFH at least the greater of d and 12db, except at supports of simply-supported spans and at free ends of cantilevers. 7.7.3.4 RQWLQXLQJ ÀH[XUDO WHQVLRQ UHLQIRUFHPHQW VKDOO have an embedment length at least Ɛd beyond the point where bent or terminated tension reinforcement is no longer UHTXLUHGWRUHVLVWÀH[XUH 7.7.3.5 Flexural tension reinforcement shall not be termi- QDWHGLQDWHQVLRQ]RQHXQOHVV D E RU F LVVDWLV¿HG (a) Vu” ࢥVnDWWKHFXWR൵SRLQW (b) For No. 11 bars and smaller, continuing reinforcement SURYLGHVGRXEOHWKHDUHDUHTXLUHGIRUÀH[XUHDWWKHFXWR൵ point and Vu” ࢥVn. (c) Stirrup area in excess of that required for shear is provided along each terminated bar or wire over a distance R7.7.2 5HLQIRUFHPHQWVSDFLQJ R7.7.2.3 Editions of ACI 318 prior to 2019 excluded the provisions of 7.7.2.3 for prestressed concrete. However, Class T and C slabs prestressed with unbonded tendons rely solely on deformed reinforcement for crack control. Consequently, the requirements of 7.7.2.3 have been extended to apply to Class T and C slabs prestressed with unbonded tendons. R7.7.2.4 The spacing limitations for slab reinforcement DUHEDVHGRQÀDQJHWKLFNQHVVZKLFKIRUWDSHUHGÀDQJHVFDQ be taken as the average thickness. R7.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV Requirements for development of reinforcement in one-way slabs are similar to those for beams. Refer to R9.7.3 for additional information. American Concrete Institute – Copyrighted © Material – www.concrete.org average thic UHLQIRUFHP or devel similar to an nformatio forcemen 18 in LQ c sla Class T 7.2.4 The spac ÀDQJH WKLFN UHVWUHVVHGVODEV essive force in all be develope ein- on R7. Req one-w 3 )O irem y sla HGRQ n as QHV QH PART 3: MEMBERS 95 CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 98. 3/4dIURPWKHFXWR൵SRLQW([FHVVVWLUUXSDUHDVKDOOEHQRW less than 60bws/fyt. Spacing s shall not exceed d ȕb). 7.7.3.6 Adequate anchorage shall be provided for tension reinforcement where reinforcement stress is not directly proportional to moment, such as in sloped, stepped, or tapered slabs, or where tension reinforcement is not parallel to the compression face. 7.7.3.7 In slabs with spans not exceeding 10 ft, welded wire reinforcement, with wire size not exceeding W5 or D5, shall be permitted to be curved from a point near the top of slab over the support to a point near the bottom of slab at midspan, provided such reinforcement is continuous over, or developed at, the support. 7.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW 7.7.3.8.1 At simple supports, at least one-third of the maximum positive moment reinforcement shall extend along the slab bottom into the support, except for precast slabs where such reinforcement shall extend at least to the center of the bearing length. 7.7.3.8.2 At other supports, at least one-fourth of the maximum positive moment reinforcement shall extend along the slab bottom into the support at least 6 in. 7.7.3.8.3$WVLPSOHVXSSRUWVDQGSRLQWVRILQÀHFWLRQdb for positive moment tension reinforcement shall be limited such that ƐdIRUWKDWUHLQIRUFHPHQWVDWLV¿HV D RU E ,IUHLQ- forcement terminates beyond the centerline of supports by a standard hook or a mechanical anchorage at least equivalent WRDVWDQGDUGKRRN D RU E QHHGQRWEHVDWLV¿HG (a) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVFRQ¿QHG by a compressive reaction (b) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVQRWFRQ¿QHG by a compressive reaction Mn is calculated assuming all reinforcement at the section is stressed to fy and Vu is calculated at the section. At a support, Ɛa is the embedment length beyond the center of the VXSSRUW$WDSRLQWRILQÀHFWLRQƐa is the embedment length EHRQGWKHSRLQWRILQÀHFWLRQOLPLWHGWRWKHJUHDWHURId and 12db. 7.7.3.8.4 At least one-third of the negative moment rein- forcement at a support shall have an embedment length EHRQGWKHSRLQWRILQÀHFWLRQDWOHDVWWKHJUHDWHVWRId, 12db, and Ɛn/16. 7.7.4 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV R7.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW Requirements for termination of reinforcement in one-way slabs are similar to those for beams. Refer to R9.7.3.8 for additional information. R7.7.4 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV American Concrete Institute – Copyrighted © Material – www.concrete.org a of the nt shall extend rt, excep all ex a re up G Requ slabs are simil onal informatio st one-fourth o ement shall ex at least 6 in. I L the end 96 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 99. 7 One-way Slabs 7.7.4.1 External tendons shall be attached to the member LQDPDQQHUWKDWPDLQWDLQVWKHVSHFL¿HGHFFHQWULFLWEHWZHHQ the tendons and the concrete centroid through the full range RIDQWLFLSDWHGPHPEHUGHÀHFWLRQV 7.7.4.2 If nonprestressed reinforcement is required to VDWLVIÀH[XUDOVWUHQJWKWKHGHWDLOLQJUHTXLUHPHQWVRI VKDOOEHVDWLV¿HG 7.7.4.3 7HUPLQDWLRQRISUHVWUHVVHGUHLQIRUFHPHQW 7.7.4.3.1 Post-tensioned anchorage zones shall be designed and detailed in accordance with 25.9. 7.7.4.3.2 Post-tensioning anchorages and couplers shall be designed and detailed in accordance with 25.8. 7.7.4.4 7HUPLQDWLRQ RI GHIRUPHG UHLQIRUFHPHQW LQ VODEV with unbonded tendons 7.7.4.4.1 Length of deformed reinforcement required by 7.6.2.3 shall be in accordance with (a) and (b): (a) At least Ɛn/3 in positive moment areas and be centered in those areas (b) At least Ɛn/6 on each side of the face of support 7.7.5 6KHDUUHLQIRUFHPHQW 7.7.5.1 If shear reinforcement is required, transverse rein- forcement shall be detailed according to 9.7.6.2. 7.7.6 6KULQNDJHDQGWHPSHUDWXUHUHLQIRUFHPHQW 7.7.6.1 Shrinkage and temperature reinforcement in accor- GDQFHZLWKVKDOOEHSODFHGSHUSHQGLFXODUWRÀH[XUDO reinforcement. 7.7.6.2 1RQSUHVWUHVVHGUHLQIRUFHPHQW 7.7.6.2.1 Spacing of deformed shrinkage and temperature reinforcement shall not exceed the lesser of 5h and 18 in. 7.7.6.3 3UHVWUHVVHGUHLQIRUFHPHQW 7.7.6.3.1 Spacing of slab tendons required by 7.6.4.2 and the distance between face of beam or wall to the nearest slab tendon shall not exceed 6 ft. 7.7.6.3.2 If spacing of slab tendons exceeds 4.5 ft, addi- tional deformed shrinkage and temperature reinforcement conforming to 24.4.3 shall be provided parallel to the tendons, except 24.4.3.4 QHHGQRWEHVDWLV¿HG,QFDOFXODWLQJ the area of additional reinforcement, it shall be permitted to take the gross concrete area in 24.4.3.2 as the slab area R7.7.4.4 7HUPLQDWLRQRIGHIRUPHGUHLQIRUFHPHQWLQVODEV with unbonded tendons Requirements for termination of deformed reinforcement in one-way slabs with unbonded tendons are the same as those for beams. Refer to R9.7.4.4 for additional information. R7.7.6 6KULQNDJHDQGWHPSHUDWXUHUHLQIRUFHPHQW R7.7.6.3 3UHVWUHVVHGUHLQIRUFHPHQW R7.7.6.3.2 Widely spaced tendons result in non-uniform compressive stresses near the slab edges. The additional reinforcement is to reinforce regions near the slab edge that may be inadequately compressed. Placement of this rein- forcement is illustrated in Fig. R7.7.6.3.2. American Concrete Institute – Copyrighted © Material – www.concrete.org Refer to R orcement (a) an om of with quirements for t slabs with eas and be cen ace of support d way r bea unb nb PART 3: MEMBERS 97 CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 100. between faces of beams. This shrinkage and temperature reinforcement shall extend from the slab edge for a distance not less than the slab tendon spacing. 7.7.7 6WUXFWXUDO LQWHJULW UHLQIRUFHPHQW LQ FDVWLQSODFH one-way slabs 7.7.7.1 Longitudinal structural integrity reinforcement consisting of at least one-quarter of the maximum positive moment reinforcement shall be continuous. 7.7.7.2 Longitudinal structural integrity reinforcement at noncontinuous supports shall be anchored to develop fy at the face of the support. 7.7.7.3 If splices are necessary in continuous structural integrity reinforcement, the reinforcement shall be spliced near supports. Splices shall be mechanical or welded in accordance with 25.5.7 or Class B tension lap splices in accordance with 25.5.2. R7.7.7 6WUXFWXUDOLQWHJULWUHLQIRUFHPHQWLQFDVWLQSODFH one-way slabs Positive moment structural integrity reinforcement for one-way slabs is intended to be similar to that for beams. Refer to R9.7.7 for a discussion of structural integrity rein- forcement for beams. American Concrete Institute – Copyrighted © Material – www.concrete.org 98 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY s 4.5 ft s s Length ≥ s Added shrinkage and temperature reinforcement A A Plan Section A-A Beam Tendon Shrinkage and temperature tendon Fig. R7.7.6.3.2²3ODQ YLHZ DW VODE HGJH VKRZLQJ DGGHG VKULQNDJH DQG WHPSHUDWXUH UHLQIRUFHPHQW Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 101. 8.1—Scope 8.1.1 This chapter shall apply to the design of nonpre- VWUHVVHG DQG SUHVWUHVVHG VODEV UHLQIRUFHG IRU ÀH[XUH LQ two directions, with or without beams between supports, including (a) through (d): (a) Solid slabs (b) Slabs cast on stay-in-place, noncomposite steel deck (c) Composite slabs of concrete elements constructed in separate placements but connected so that all elements resist loads as a unit (d) Two-way joist systems in accordance with 8.8 8.2—General 8.2.1 A slab system shall be permitted to be designed by any procedure satisfying equilibrium and geometric compatibility, provided that design strength at every section is at least equal to required strength, and all serviceability UHTXLUHPHQWVDUHVDWLV¿HG7KHGLUHFWGHVLJQPHWKRGRUWKH equivalent frame method is permitted. R8.1—Scope The design methods given in this chapter are based on analysis of the results of an extensive series of tests (Burns and Hemakom 1977; Gamble et al. 1969; Gerber and Burns 1971; Guralnick and LaFraugh 1963; Hatcher et al. 1965, 1969; Hawkins 1981; Jirsa et al. 1966; PTI DC20.8; Smith and Burns 1974; Scordelis et al. 1959; Vanderbilt et al. 1969; Xanthakis and Sozen 1963) and the well-established performance records of various slab systems. The funda- mental design principles are applicable to all planar struc- WXUDOVVWHPVVXEMHFWHGWRWUDQVYHUVHORDGV6HYHUDOVSHFL¿F design rules, as well as historical precedents, limit the types of structures to which this chapter applies. General slab systems that may be designed according to this chapter LQFOXGH ÀDW VODEV ÀDW SODWHV WZRZD VODEV DQG ZD൷H slabs. Slabs with paneled ceilings are two-way, wide-band, beam systems. Slabs-on-ground that do not transmit vertical loads from other parts of the structure to the soil are excluded. For slabs with beams, the explicit design procedures of this chapter apply only when the beams are located at the edges of the panel and when the beams are supported by FROXPQVRURWKHUHVVHQWLDOOQRQGHÀHFWLQJVXSSRUWVDWWKH corners of the panel. Two-way slabs with beams in one direction, with both slab and beams supported by girders in the other direction, may be designed under the general requirements of this chapter. Such designs should be based XSRQDQDOVLVFRPSDWLEOHZLWKWKHGHÀHFWHGSRVLWLRQRIWKH supporting beams and girders. For slabs supported on walls, the explicit design proce- GXUHVLQWKLVFKDSWHUWUHDWWKHZDOODVDEHDPRILQ¿QLWHVWL൵- ness; therefore, each wall should support the entire length of an edge of the panel (refer to 8.4.1.7). Walls of width less than a full panel length can be treated as columns. R8.2—General R8.2.1 This section permits a design to be based directly on fundamental principles of structural mechanics, provided it can be demonstrated explicitly that all strength and service- DELOLWFULWHULDDUHVDWLV¿HG7KHGHVLJQRIWKHVODEPDEH achieved through the combined use of classic solutions based on a linearly elastic continuum, numerical solutions based on discrete elements, or yield-line analyses, including, in all cases, evaluation of the stress conditions around the VXSSRUWVLQUHODWLRQWRVKHDUWRUVLRQDQGÀH[XUHDVZHOODV WKHH൵HFWVRIUHGXFHGVWL൵QHVVRIHOHPHQWVGXHWRFUDFNLQJ and support geometry. The design of a slab system involves more than its analysis; any deviations in physical dimensions RIWKHVODEIURPFRPPRQSUDFWLFHVKRXOGEHMXVWL¿HGRQWKH basis of knowledge of the expected loads and the reliability of the calculated stresses and deformations of the structure. The direct design method and the equivalent frame method are limited in application to orthogonal frames subject to gravity loads only. CHAPTER 8—TWO-WAY SLABS American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 99 CODE COMMENTARY 8 Two-way Slabs HU HVVHQWLDO nel. Two- h slab an on, may s chapter PSDWLEOHZ ms and g s supported HVLQWKLVFKDS ness; th other p For slabs with hapter apply on e panel and corn direct requir XSRQ of n, w other ment QDOV f th V RU wh wh
- 102. R8.2.2 Refer to R7.2.1. R8.2.4 and R8.2.5 'URS SDQHO GLPHQVLRQV VSHFL¿HG LQ 8.2.4 are necessary when reducing the amount of nega- tive moment reinforcement following 8.5.2.2 or to satisfy minimum slab thicknesses permitted in 8.3.1.1. If the dimen- VLRQVDUHOHVVWKDQVSHFL¿HGLQWKHSURMHFWLRQPDEH used as a shear cap to increase the shear strength of the slab. For slabs with changes in thickness, it is necessary to check the shear strength at several sections (Refer to 22.6.4.1(b)). R8.2.7 RQQHFWLRQVWRRWKHUPHPEHUV Safety of a slab system requires consideration of the trans- PLVVLRQ RI ORDG IURP WKH VODE WR WKH FROXPQV E ÀH[XUH torsion, and shear. R8.3—Design limits R8.3.1 0LQLPXPVODEWKLFNQHVV Theminimumslabthicknessesin8.3.1.1and8.3.1.2areinde- pendent of loading and concrete modulus of elasticity, both of ZKLFKKDYHVLJQL¿FDQWH൵HFWVRQGHÀHFWLRQV7KHVHPLQLPXP thicknesses are not applicable to slabs with unusually heavy superimposed sustained loads or for concrete with modulus of HODVWLFLWVLJQL¿FDQWOORZHUWKDQWKDWRIRUGLQDUQRUPDOZHLJKW FRQFUHWH'HÀHFWLRQVVKRXOGEHFDOFXODWHGIRUVXFKVLWXDWLRQV 8.2.27KHH൵HFWVRIFRQFHQWUDWHGORDGVVODERSHQLQJVDQG slab voids shall be considered in design. 8.2.36ODEVSUHVWUHVVHGZLWKDQDYHUDJHH൵HFWLYHFRPSUHV- sive stress less than 125 psi shall be designed as nonpre- stressed slabs. 8.2.4 A drop panel in a nonprestressed slab, where used to reduce the minimum required thickness in accordance with 8.3.1.1 or the quantity of deformed negative moment reinforcement at a support in accordance with 8.5.2.2, shall satisfy (a) and (b): (a) The drop panel shall project below the slab at least one-fourth of the adjacent slab thickness. (b) The drop panel shall extend in each direction from the centerline of support a distance not less than one-sixth the span length measured from center-to-center of supports in that direction. 8.2.5 A shear cap, where used to increase the critical section for shear at a slab-column joint, shall project below WKHVODEVR൶WDQGH[WHQGKRUL]RQWDOOIURPWKHIDFHRIWKH column a distance at least equal to the thickness of the SURMHFWLRQEHORZWKHVODEVR൶W 8.2.6 Materials 8.2.6.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 8.2.6.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 8.2.6.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 8.2.7 RQQHFWLRQVWRRWKHUPHPEHUV 8.2.7.1 Beam-column and slab-column joints shall satisfy Chapter 15. 8.3—Design limits 8.3.1 0LQLPXPVODEWKLFNQHVV American Concrete Institute – Copyrighted © Material – www.concrete.org 100 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY be increase oint, QWDOO ual e thickness o l b he Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 103. R8.3.1.1 The minimum thicknesses in Table 8.3.1.1 are those that have been developed through the years. Use of longitudinal reinforcement with fy 80,000 psi may result in ODUJHUORQJWHUPGHÀHFWLRQVWKDQLQWKHFDVHRIfy 80,000 psi unless associated service stresses calculated for cracked sections are smaller than 40,000 psi. Careful calculation of GHÀHFWLRQVVKRXOGEHSHUIRUPHG R8.3.1.2 For panels having a ratio of long-to-short span greater than 2, the use of expressions (b) and (d) of Table 8.3.1.2, which give the minimum thickness as a fraction of the long span, may give unreasonable results. For such panels, the rules applying to one-way construction in 7.3.1 should be used. 8.3.1.1 For nonprestressed slabs without interior beams spanning between supports on all sides, having a maximum ratio of long-to-short span of 2, overall slab thickness h shall not be less than the limits in Table 8.3.1.1, and shall be at OHDVWWKHYDOXHLQ D RU E XQOHVVWKHFDOFXODWHGGHÀHFWLRQ OLPLWVRIDUHVDWLV¿HG (a) Slabs without drop panels as given in 8.2.4.......... 5 in. (b) Slabs with drop panels as given in 8.2.4............... 4 in. For fy H[FHHGLQJ SVL WKH FDOFXODWHG GHÀHFWLRQ OLPLWVLQVKDOOEHVDWLV¿HGDVVXPLQJDUHGXFHGPRGXOXV of rupture ′ = 5 r c f f . 8.3.1.2 For nonprestressed slabs with beams spanning between supports on all sides, overall slab thickness h shall satisfy the limits in Table 8.3.1.2, unless the calculated GHÀHFWLRQOLPLWVRIDUHVDWLV¿HG Table 8.3.1.2—Minimum thickness of nonprestressed two-way slabs with beams spanning between supports on all sides Įfm [1] Minimum h, in. ĮIP” 8.3.1.1 applies (a) ĮIP” Greater of: 0.8 200,000 36 5 ( 0.2) y n IP f ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ + β α − A (b)[1],[2] 5.0 (c) ĮIP 2.0 Greater of: 0.8 200,000 36 9 y n f ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ + β A (d) 3.5 (e) [1] ĮIPLVWKHDYHUDJHYDOXHRIĮf for all beams on edges of a panel. [2] Ɛn is the clear span in the long direction, measured face-to-face of beams (in.). [3] ȕLVWKHUDWLRRIFOHDUVSDQVLQORQJWRVKRUWGLUHFWLRQVRIVODE Table 8.3.1.1—Minimum thickness of nonprestressed two-way slabs without interior beams (in.)[1] fy, psi[2] Without drop panels[3] With drop panels[3] Exterior panels Interior panels Exterior panels Interior panels Without edge beams With edge beams[4] Without edge beams With edge beams[4] 40,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn 60,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn 80,000 Ɛn Ɛn Ɛn Ɛn Ɛn Ɛn [1] Ɛn is the clear span in the long direction, measured face-to-face of supports (in.). [2] For fy between the values given in the table, minimum thickness shall be calculated by linear interpolation. [3] Drop panels as given in 8.2.4. [4] 6ODEVZLWKEHDPVEHWZHHQFROXPQVDORQJH[WHULRUHGJHV([WHULRUSDQHOVVKDOOEHFRQVLGHUHGWREHZLWKRXWHGJHEHDPVLIĮf is less than 0.8. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 101 CODE COMMENTARY 8 Two-way Slabs LIĮf Į is less th f r panels h n 2, the us 1.2, which g of the l Ɛ Ɛn Ɛ Ɛn Ɛ Ɛ easu , m [WH -to-face of supports (i thickness shall be calc HV([WHULRUSDQHOVVKD ated by linear interpol EHFRQVLGHUHGWREHZ on. RXWHG Ɛ Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 104. R8.3.1.3 The Code does not specify an additional thick- ness for wearing surfaces subjected to unusual conditions of wear. The need for added thickness for unusual wear is left to the discretion of the licensed design professional. $ FRQFUHWH ÀRRU ¿QLVK PD EH FRQVLGHUHG IRU VWUHQJWK purposes only if it is cast monolithically with the slab. A VHSDUDWHFRQFUHWH¿QLVKLVSHUPLWWHGWREHLQFOXGHGLQWKH structural thickness if composite action is provided in accor- dance with 16.4. R8.3.2 DOFXODWHGGHÀHFWLRQOLPLWV R8.3.2.1 )RU SUHVWUHVVHG ÀDW VODEV FRQWLQXRXV RYHU WZR or more spans in each direction, the span-thickness ratio JHQHUDOOVKRXOGQRWH[FHHGIRUÀRRUVDQGIRUURRIV these limits may be increased to 48 and 52, respectively, if FDOFXODWLRQV YHULI WKDW ERWK VKRUW DQG ORQJWHUP GHÀHF- tion, camber, and vibration frequency and amplitude are not objectionable. 6KRUW DQG ORQJWHUP GHÀHFWLRQ DQG FDPEHU VKRXOG EH calculated and checked against serviceability requirements of the structure. R8.3.2.2 If any portion of a composite member is prestressed, or if the member is prestressed after the components have been cast, the provisions of 8.3.2.1 apply DQG GHÀHFWLRQV DUH WR EH FDOFXODWHG )RU QRQSUHVWUHVVHG FRPSRVLWHPHPEHUVGHÀHFWLRQVQHHGWREHFDOFXODWHGDQG compared with the limiting values in Table 24.2.2, only when the thickness of the member or the precast part of the member is less than the minimum thickness given in Table 8.3.1.1. In unshored construction, the thickness of concern GHSHQGVRQZKHWKHUWKHGHÀHFWLRQEHIRUHRUDIWHUWKHDWWDLQ- PHQWRIH൵HFWLYHFRPSRVLWHDFWLRQLVEHLQJFRQVLGHUHG R8.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV R8.3.3.1 The basis for a reinforcement strain limit for two-way slabs is the same as that for beams. Refer to R9.3.3 for additional information. 8.3.1.2.1 At discontinuous edges of slabs conforming to DQHGJHEHDPZLWKĮf• shall be provided, or the minimum thickness required by (b) or (d) of Table 8.3.1.2 shall be increased by at least 10 percent in the panel with a discontinuous edge. 8.3.1.37KHWKLFNQHVVRIDFRQFUHWHÀRRU¿QLVKVKDOOEH permitted to be included in h if it is placed monolithically ZLWKWKHÀRRUVODERULIWKHÀRRU¿QLVKLVGHVLJQHGWREH FRPSRVLWHZLWKWKHÀRRUVODELQDFFRUGDQFHZLWK16.4. 8.3.1.4 If single- or multiple-leg stirrups are used as shear UHLQIRUFHPHQWWKHVODEWKLFNQHVVVKDOOEHVX൶FLHQWWRVDWLVI the requirements for d in 22.6.7.1. 8.3.2 DOFXODWHGGHÀHFWLRQOLPLWV 8.3.2.1,PPHGLDWHDQGWLPHGHSHQGHQWGHÀHFWLRQVVKDOOEH calculated in accordance with 24.2 and shall not exceed the limits in 24.2.2 for two-way slabs given in (a) through (c): (a) Nonprestressed slabs not satisfying 8.3.1 (b) Nonprestressed slabs without interior beams spanning between the supports on all sides and having a ratio of long-to-short span exceeding 2.0 (c) Prestressed slabs 8.3.2.2 For nonprestressed composite concrete slabs VDWLVILQJRUGHÀHFWLRQVRFFXUULQJDIWHUWKH PHPEHUEHFRPHVFRPSRVLWHQHHGQRWEHFDOFXODWHG'HÀHF- tions occurring before the member becomes composite shall be investigated, unless the precomposite thickness also satis- ¿HVRU 8.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGVODEV 8.3.3.1 Nonprestressed slabs shall be tension-controlled in accordance with Table 21.2.2. 8.3.4 6WUHVVOLPLWVLQSUHVWUHVVHGVODEV 8.3.4.1 Prestressed slabs shall be designed as Class U with ft” ′ c f . Other stresses in prestressed slabs immedi- American Concrete Institute – Copyrighted © Material – www.concrete.org 102 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY SUHVWUHVVHG each dire RWH[FHHG increase WKDW ERW vibration G ORQJWH ulated and c of the st 3 2 DOFXODWHG SHQG 4.2 bs sat out hall not excee n in (a) through ng 8.3 rior beams span i or m JHQHUD DOFXO tion, e ): ng e sp VK mits LRQV mbe 2.1 Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 105. R8.4—Required strength R8.4.1 General R8.4.1.2 To determine service and factored moments as well as shears in prestressed slab systems, numerical anal- VLVLVUHTXLUHGUDWKHUWKDQVLPSOL¿HGDSSURDFKHVVXFKDVWKH direct design method. The equivalent frame method of anal- ysis as contained in the 2014 edition of the Code is a numer- ical method that has been shown by tests of large structural models to satisfactorily predict factored moments and shears in prestressed slab systems (Smith and Burns 1974; Burns and Hemakom 1977; Hawkins 1981; PTI DC20.8; Gerber and Burns 1971; Scordelis et al. 1959). The referenced research also shows that analysis using prismatic sections or RWKHUDSSUR[LPDWLRQVRIVWL൵QHVVPDSURYLGHHUURQHRXVDQG unsafe results. Moment redistribution for prestressed slabs is permitted in accordance with 6.6.5. PTI DC20.8 provides guidance for prestressed concrete slab systems. R8.4.1.7$SDQHOLQFOXGHVDOOÀH[XUDOHOHPHQWVEHWZHHQ column centerlines. Thus, the column strip includes the beam, if any. R8.4.1.8 For monolithic or fully composite construction, WKHEHDPVLQFOXGHSRUWLRQVRIWKHVODEDVÀDQJHV7ZRH[DP- ples of the rule are provided in Fig. R8.4.1.8. ately after transfer and at service loads shall not exceed the permissible stresses in 24.5.3 and 24.5.4. 8.4—Required strength 8.4.1 General 8.4.1.1 Required strength shall be calculated in accor- dance with the factored load combinations in Chapter 5. 8.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures given in Chapter 6. 8.4.1.3)RUSUHVWUHVVHGVODEVH൵HFWVRIUHDFWLRQVLQGXFHG by prestressing shall be considered in accordance with 5.3.11. 8.4.1.4 For a slab system supported by columns or walls, dimensions c1, c2, and Ɛn VKDOO EH EDVHG RQ DQ H൵HFWLYH VXSSRUWDUHD7KHH൵HFWLYHVXSSRUWDUHDLVWKHLQWHUVHFWLRQRI the bottom surface of the slab, or drop panel or shear cap if present, with the largest right circular cone, right pyramid, or tapered wedge whose surfaces are located within the column and the capital or bracket and are oriented no greater than 45 degrees to the axis of the column. 8.4.1.5 A column strip is a design strip with a width on each side of a column centerline equal to the lesser of 0.25Ɛ2 and 0.25Ɛ1. A column strip shall include beams within the strip, if present. 8.4.1.6 A middle strip is a design strip bounded by two column strips. 8.4.1.7 A panel is bounded by column, beam, or wall centerlines on all sides. 8.4.1.8 For monolithic or fully composite construction supporting two-way slabs, a beam includes that portion of slab, on each side of the beam extending a distance equal to the projection of the beam above or below the slab, whichever is greater, but not greater than four times the slab thickness. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 103 CODE COMMENTARY 8 Two-way Slabs ccordance ressed con if and research also sho DSSUR[LPDWLRQV ts. Moment H ed t RIUHDFWLRQVLQG cordance with 5 l guid FHG 11. e fo resu itted red ed Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 106. 8.4.1.9 Combining the results of a gravity load analysis with the results of a lateral load analysis shall be permitted. 8.4.2 )DFWRUHGPRPHQW 8.4.2.1 For slabs built integrally with supports, Mu at the support shall be permitted to be calculated at the face of support. 8.4.2.2 )DFWRUHGVODEPRPHQWUHVLVWHGEWKHFROXPQ 8.4.2.2.1 If gravity, wind, earthquake, or other loads cause a transfer of moment between the slab and column, a frac- tion of Msc, the factored slab moment resisted by the column DWDMRLQWVKDOOEHWUDQVIHUUHGEÀH[XUHLQDFFRUGDQFHZLWK 8.4.2.2.2 through 8.4.2.2.5. 8.4.2.2.2 The fraction of factored slab moment resisted by the column, Ȗf Msc, shall be assumed to be transferred by ÀH[XUHZKHUHȖf shall be calculated by: 1 2 1 2 1 3 f b b γ = ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ (8.4.2.2.2) 8.4.2.2.37KHH൵HFWLYHVODEZLGWKbslabIRUUHVLVWLQJȖf Msc shall be the width of column or capital plus a distance on each side in accordance with Table 8.4.2.2.3. hf hf bw bw hb hb hb ≤ 4hf bw + 2hb ≤ bw + 8hf Fig. R8.4.1.8²([DPSOHVRIWKHSRUWLRQRIVODEWREHLQFOXGHG ZLWKWKHEHDPXQGHU R8.4.2 )DFWRUHGPRPHQW R8.4.2.2 )DFWRUHGVODEPRPHQWUHVLVWHGEWKHFROXPQ R8.4.2.2.1 This section is concerned primarily with slab systems without beams. R8.4.2.2.3 Unless measures are taken to resist the torsional and shear stresses, all reinforcement resisting that part of the PRPHQWWREHWUDQVIHUUHGWRWKHFROXPQEÀH[XUHVKRXOG American Concrete Institute – Copyrighted © Material – www.concrete.org 104 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 107. Table 8.4.2.2.3—Dimensional limits for effective slab width Distance on each side of column or capital Without drop panel or shear cap Lesser 1.5h of slab Distance to edge of slab With drop panel or shear cap Lesser 1.5h of drop or cap Distance to edge of the drop or cap plus 1.5h of slab 8.4.2.2.4 For nonprestressed slabs, where the limita- tions on vuv and İtLQ7DEOHDUHVDWLV¿HGȖf shall be SHUPLWWHGWREHLQFUHDVHGWRWKHPD[LPXPPRGL¿HGYDOXHV provided in Table 8.4.2.2.4, where vc is calculated in accor- dance with 22.6.5. be placed between lines that are one and one-half the slab or drop panel thickness, 1.5h, on each side of the column. R8.4.2.2.4 6RPHÀH[LELOLWLQGLVWULEXWLRQRIMsc trans- IHUUHG E VKHDU DQG ÀH[XUH DW ERWK H[WHULRU DQG LQWHULRU columns is possible. Interior, exterior, and corner columns refer to slab-column connections for which the critical perimeter for rectangular columns has four, three, and two sides, respectively. At exterior columns, for Msc resisted about an axis parallel to the edge, the portion of moment transferred by eccen- tricity of shear Ȗv Msc may be reduced, provided that the factored shear at the column (excluding the shear produced by moment transfer) does not exceed 75 percent of the shear strength ࢥvc DV GH¿QHG LQ 22.6.5.1 for edge columns, or 50 percent for corner columns. Tests (Moehle 1988; ACI 352.1R LQGLFDWH WKDW WKHUH LV QR VLJQL¿FDQW LQWHUDFWLRQ between shear and Msc at the exterior column in such cases. Note that as ȖvMsc is decreased, Ȗf Msc is increased. $WLQWHULRUFROXPQVVRPHÀH[LELOLWLQGLVWULEXWLQJMsc WUDQVIHUUHGEVKHDUDQGÀH[XUHLVSRVVLEOHEXWZLWKPRUH severe limitations than for exterior columns. For inte- rior columns, MscWUDQVIHUUHGEÀH[XUHLVSHUPLWWHGWREH increased up to 25 percent, provided that the factored shear (excluding the shear caused by the moment transfer) at the interior columns does not exceed 40 percent of the shear strength ࢥvcDVGH¿QHGLQ If the factored shear for a slab-column connection is large, the slab-column joint cannot always develop all of the rein- IRUFHPHQWSURYLGHGLQWKHH൵HFWLYHZLGWK7KHPRGL¿FDWLRQV for interior slab-column connections in this provision are permitted only where the reinforcement required to develop Ȗf MscZLWKLQWKHH൵HFWLYHZLGWKKDVDQHWWHQVLOHVWUDLQİt not less than İty + 0.008, where the value of İty is determined in 21.2.27KHXVHRI(T ZLWKRXWWKHPRGL¿FDWLRQ permitted in this provision will generally indicate overstress conditions on the joint. This provision is intended to improve ductile behavior of the slab-column joint. If reversal of moments occurs at opposite faces of an interior column, both top and bottom reinforcement should be concentrated within WKHH൵HFWLYHZLGWK$UDWLRRIWRSWRERWWRPUHLQIRUFHPHQWRI approximately 2 has been observed to be appropriate. Before the 2019 Code, the strain limits on İt in Table 8.4.2.2.4 were constants of 0.004 and 0.010. Beginning with the 2019 Code, to accommodate nonprestressed reinforcement American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 105 CODE COMMENTARY 8 Two-way Slabs t the colum er) does no ¿QHG LQ ner colum KDW WKHUH d Msc M M at th Msc M M is dec RUFROXPQ VIHUUHGEVK severe sides, r At exterior co edge, the port ear Ȗv Msc M M m by m streng 52.1R betw ment ࢥv ent LQ n she of sh d she may ay Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 108. 8.4.2.2.5 Concentration of reinforcement over the column by closer spacing or additional reinforcement shall be used WR UHVLVW PRPHQW RQ WKH H൵HFWLYH VODE ZLGWK GH¿QHG LQ 8.4.2.2.2 and 8.4.2.2.3. 8.4.2.2.6 The fraction of Msc not calculated to be resisted EÀH[XUHVKDOOEHDVVXPHGWREHUHVLVWHGEHFFHQWULFLWRI shear in accordance with 8.4.4.2. 8.4.3 Factored one-way shear 8.4.3.1 For slabs built integrally with supports, Vu at the support shall be permitted to be calculated at the face of support. 8.4.3.2 Sections between the face of support and a critical section located d from the face of support for nonprestressed slabs and h/2 from the face of support for prestressed slabs shall be permitted to be designed for Vu at that critical section LI D WKURXJK F DUHVDWLV¿HG (a) Support reaction, in direction of applied shear, intro- duces compression into the end regions of the slab. (b) Loads are applied at or near the top surface of the slab. (c) No concentrated load occurs between the face of support and critical section. 8.4.4 Factored two-way shear of higher grades, these limits are replaced by the expressions İty + 0.003 and İty + 0.008UHVSHFWLYHO7KH¿UVWH[SUHV- sion is the same expression as used for the limit on İt for FODVVL¿FDWLRQRIWHQVLRQFRQWUROOHGPHPEHUVLQ7DEOH this expression is further described in Commentary R21.2.2. The second expression provides a limit on İt with Grade 60 reinforcement that is approximately the same value as the former constant of 0.010. R8.4.4 Factored two-way shear The calculated shear stresses in the slab around the column are required to conform to the requirements of 22.6. Table 8.4.2.2.4—Maximum modified values of Ȗf for nonprestressed two-way slabs Column location Span direction vuv İt (within bslab) 0D[LPXPPRGL¿HGȖf Corner column Either direction ”ࢥvc •İty + 0.003 1.0 Edge column Perpendicular to the edge ”ࢥvc •İty + 0.003 1.0 Parallel to the edge ”ࢥvc •İty + 0.008 1 2 1.25 1.0 2 1 3 b b ≤ ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ Interior column Either direction ”ࢥvc •İty + 0.008 1 2 1.25 1.0 2 1 3 b b ≤ + ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ American Concrete Institute – Copyrighted © Material – www.concrete.org 106 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY nfo re FW ” ࢥv •İty + 0.0 nt over the co cement shall be DE Z H¿QH d n sed G LQ Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 109. 8.4.4.1 Critical section 8.4.4.1.1 Slabs shall be evaluated for two-way shear in the vicinity of columns, concentrated loads, and reaction areas at critical sections in accordance with 22.6.4. 8.4.4.1.2 Slabs reinforced with stirrups or headed shear stud reinforcement shall be evaluated for two-way shear at critical sections in accordance with 22.6.4.2. 8.4.4.2 Factored two-way shear stress due to shear and IDFWRUHGVODEPRPHQWUHVLVWHGEWKHFROXPQ 8.4.4.2.1 For two-way shear with factored slab moment resisted by the column, factored shear stress vu shall be calculated at critical sections in accordance with 8.4.4.1. Factored shear stress vu corresponds to a combination of vuv and the shear stress produced by ȖvMsc, where Ȗv is given in 8.4.4.2.2 and Msc is given in 8.4.2.2.1. 8.4.4.2.2 The fraction of Msc transferred by eccentricity of shear, ȖvMsc, shall be applied at the centroid of the critical section in accordance with 8.4.4.1, where: Ȗv ±Ȗf (8.4.4.2.2) 8.4.4.2.3 The factored shear stress resulting from ȖvMsc shall be assumed to vary linearly about the centroid of the critical section in accordance with 8.4.4.1. R8.4.4.2 Factored two-way shear stress due to shear and IDFWRUHGVODEPRPHQWUHVLVWHGEWKHFROXPQ R8.4.4.2.2 Hanson and Hanson (1968) found that where moment is transferred between a column and a slab, 60 percent of the moment should be considered transferred by ÀH[XUHDFURVVWKHSHULPHWHURIWKHFULWLFDOVHFWLRQGH¿QHGLQ 22.6.4.1, and 40 percent by eccentricity of the shear about the centroid of the critical section. For rectangular columns, WKHSRUWLRQRIWKHPRPHQWWUDQVIHUUHGEÀH[XUHLQFUHDVHV as the width of the face of the critical section resisting the moment increases, as given by Eq. (8.4.2.2.2). Most of the data in Hanson and Hanson (1968) were obtained from tests of square columns. Limited information is available for round columns; however, these can be approximated as square columns having the same cross-sectional area. R8.4.4.2.3 The stress distribution is assumed as illustrated in Fig. R8.4.4.2.3 for an interior or exterior column. The perimeter of the critical section, ABCD, is determined in accordance with 22.6.4.1. The factored shear stress vuv and factored slab moment resisted by the column Msc are deter- mined at the centroidal axis c-c of the critical section. The maximum factored shear stress may be calculated from: , v sc AB u AB uv c M c v v J γ = + or , v sc u CD uv c M cCD v v J γ = − where Ȗv is given by Eq. (8.4.4.2.2). For an interior column, Jc may be calculated by: Jc = property of assumed critical section analogous to polar moment of inertia American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 107 CODE COMMENTARY 8 Two-way Slabs sferred bet ment shou HULPHWHUR rcent by critical se HPRPHQW f the face creases, as Most of the dat from tes iven in sferre the 4.1, ± Hanson an e: 8.4.4 2.2) perc ÀH[XU the ce WKHS of t DFUR , an roid LRQ 4.2. t is d H H Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 110. 3 3 2 1 1 2 1 ( ) ( ) ( )( ) 6 6 2 d c d c d d d c d c d + + + + = + + Similar equations may be developed for Jc for columns located at the edge or corner of a slab. The fraction of Msc not transferred by eccentricity of the VKHDUVKRXOGEHWUDQVIHUUHGEÀH[XUHLQDFFRUGDQFHZLWK 8.4.2.2. A conservative method assigns the fraction trans- IHUUHG E ÀH[XUH RYHU DQ H൵HFWLYH VODE ZLGWK GH¿QHG LQ 8.4.2.2.3. Often, column strip reinforcement is concentrated near the column to accommodate Msc. Available test data (Hanson and Hanson 1968) seem to indicate that this prac- tice does not increase shear strength but may be desirable to LQFUHDVHWKHVWL൵QHVVRIWKHVODEFROXPQMXQFWLRQ Test data (Hawkins 1981) indicate that the moment transfer strength of a prestressed slab-to-column connection can be calculated using the procedures of 8.4.2.2 and 8.4.4.2. Where shear reinforcement has been used, the critical section beyond the shear reinforcement generally has a polyg- onal shape (Fig. R8.7.6(d) and (e)). Equations for calculating shear stresses on such sections are given in ACI 421.1R. D A B C c c c c c c c c D C A B C Column L L L L Column C c2 + d c2 + d c1 + d cCD cAB cCD cAB c1 + d /2 Critical section Critical section Interior column Edge column vu,CD vu,AB vuv Shear stress Shear stress V Msc V Msc vu,CD vu,AB vuv Fig. R8.4.4.2.3²$VVXPHGGLVWULEXWLRQRIVKHDUVWUHVV American Concrete Institute – Copyrighted © Material – www.concrete.org 108 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 111. R8.5—Design strength R8.5.1 General R8.5.1.1 Refer to R9.5.1.1. R8.5.3 Shear R8.5.3.1'L൵HUHQWLDWLRQVKRXOGEHPDGHEHWZHHQDORQJ and narrow slab acting as a beam, and a slab subject to two-way action where failure may occur by punching along a truncated cone or pyramid around a concentrated load or reaction area. 8.5—Design strength 8.5.1 General 8.5.1.1 For each applicable factored load combination, GHVLJQVWUHQJWKVKDOOVDWLVIࢥSn•U, including (a) through G ,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOOEHFRQVLGHUHG D ࢥMn•Mu at all sections along the span in each direction E ࢥMn•Ȗf Msc within bslabDVGH¿QHGLQ F ࢥVn•Vu at all sections along the span in each direction for one-way shear G ࢥvn•vuDWWKHFULWLFDOVHFWLRQVGH¿QHGLQIRU two-way shear 8.5.1.2 ࢥVKDOOEHLQDFFRUGDQFHZLWK21.2. 8.5.2 0RPHQW 8.5.2.1 Mn shall be calculated in accordance with 22.3. 8.5.2.2 In calculating Mn for nonprestressed slabs with a drop panel, the thickness of the drop panel below the slab shall not be assumed to be greater than one-fourth the distance from the edge of drop panel to the face of column or column capital. 8.5.2.3 In calculating Mn for prestressed slabs, external tendons shall be considered as unbonded unless the external WHQGRQVDUHH൵HFWLYHOERQGHGWRWKHVODEDORQJLWVHQWLUH length. 8.5.3 Shear 8.5.3.1 Design shear strength of slabs in the vicinity of columns, concentrated loads, or reaction areas shall be the more severe of 8.5.3.1.1 and 8.5.3.1.2. 8.5.3.1.1 For one-way shear, where each critical section to be investigated extends in a plane across the entire slab width, Vn shall be calculated in accordance with 22.5. 8.5.3.1.2 For two-way shear, vn shall be calculated in accordance with 22.6. 8.5.3.2 For composite concrete slabs, horizontal shear strength Vnh shall be calculated in accordance with 16.4. 8.5.4 2SHQLQJVLQVODEVVWHPV 8.5.4.1 Openings of any size shall be permitted in slab systems if shown by analysis that all strength and service- DELOLWUHTXLUHPHQWVLQFOXGLQJWKHOLPLWVRQGHÀHFWLRQVDUH VDWLV¿HG American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 109 CODE COMMENTARY 8 Two-way Slabs R8 5 . restressed e drop grea pan r p nbo W the face of co essed slabs, ext d unless the ext O mn rnal nal Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 112. R8.6—Reinforcement limits R8.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG slabs R8.6.1.1 The required area of deformed or welded wire UHLQIRUFHPHQW XVHG DV PLQLPXP ÀH[XUDO UHLQIRUFHPHQW LV the same as that required for shrinkage and temperature in 24.4.3.2. However, whereas shrinkage and temperature rein- forcement is permitted to be distributed between the two IDFHVRIWKHVODEDVGHHPHGDSSURSULDWHIRUVSHFL¿FFRQGL- WLRQVPLQLPXPÀH[XUDOUHLQIRUFHPHQWVKRXOGEHSODFHGDV close as practicable to the face of the concrete in tension due to applied loads. Figure R8.6.1.1 illustrates the arrangement of minimum reinforcement required near the top of a two-way slab VXSSRUWLQJXQLIRUPJUDYLWORDG7KHEDUFXWR൵SRLQWVDUH based on the requirements shown in Fig. 8.7.4.1.3. To improve crack control and to intercept potential punching shear cracks with tension reinforcement, the licensed design professional should consider specifying continuous reinforcement in each direction near both faces of thick two-way slabs, such as transfer slabs, podium slabs, and mat foundations. Also refer to R8.7.4.1.3. 8.5.4.2 As an alternative to 8.5.4.1, openings shall be permitted in slab systems without beams in accordance with (a) through (d). (a) Openings of any size shall be permitted in the area common to intersecting middle strips, but the total quan- tity of reinforcement in the panel shall be at least that required for the panel without the opening. (b) At two intersecting column strips, not more than one- eighth the width of column strip in either span shall be interrupted by openings. A quantity of reinforcement at least equal to that interrupted by an opening shall be added on the sides of the opening. (c) At the intersection of one column strip and one middle strip, not more than one-fourth of the reinforcement in either strip shall be interrupted by openings. A quantity of reinforcement at least equal to that interrupted by an opening shall be added on the sides of the opening. (d) If an opening is located closer than 4h from the periphery of a column, concentrated load or reaction area, 22.6.4.3 VKDOOEHVDWLV¿HG 8.6—Reinforcement limits 8.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG slabs 8.6.1.1$PLQLPXPDUHDRIÀH[XUDOUHLQIRUFHPHQWAs,min of 0.0018AgRUDVGH¿QHGLQVKDOOEHSURYLGHGQHDU the tension face of the slab in the direction of the span under consideration. American Concrete Institute – Copyrighted © Material – www.concrete.org 110 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY rcement l PÀH[XUDO quired are HG DV PLQ at require owever, w ement is per IDFHV RI the or reaction area, IRUF ÀH[ LQQRQSUHVWU UHLQIRUFHPHQWA DOOEHSURYLGHG f h R slabs R8. UHLQI G G ,min DU 1 0 1.1 HPH Rei Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 113. Centerline bay Fig. R8.6.1.1²$UUDQJHPHQW RI PLQLPXP UHLQIRUFHPHQW near the top of a two-way slab. R8.6.1.2 Tests on interior column-to-slab connections with lightly reinforced slabs with and without shear reinforcement (Peiris and Ghali 2012; Hawkins and Ospina 2017; Widi- anto et al. 2009; Muttoni 2008; Dam et al. 2017) have shown WKDWLHOGLQJRIWKHVODEÀH[XUDOWHQVLRQUHLQIRUFHPHQWLQWKH vicinity of the column or loaded area leads to increased local rotations and opening of any inclined crack existing within the slab. In such cases, sliding along the inclined crack can cause DÀH[XUHGULYHQSXQFKLQJIDLOXUHDWDVKHDUIRUFHOHVVWKDQWKH strength calculated by the two-way shear equations of Table 22.6.5.2 for slabs without shear reinforcement and less than the strength calculated in accordance with 22.6.6.3 for slabs with shear reinforcement. 7HVWVRIVODEVZLWKÀH[XUDOUHLQIRUFHPHQWOHVVWKDQAs,min have shown that shear reinforcement does not increase the punching shear strength. However, shear reinforcement PD LQFUHDVH SODVWLF URWDWLRQV SULRU WR WKH ÀH[XUHGULYHQ punching failure (Peiris and Ghali 2012). Inclined cracking develops within the depth of the slab at a shear stress of approximately ȜsȜ ′ c f . At higher shear VWUHVVHVWKHSRVVLELOLWRIDÀH[XUHGULYHQSXQFKLQJIDLOXUH increases if As,min LVQRWVDWLV¿HGAs,min was developed for an interior column, such that the factored shear force on the critical section for shear equals the shear force associated with local yielding at the column faces. To derive Eq. (8.6.1.2) the shear force associated with local yielding was taken as 8As,min fyd/bslab for an interior column connection (Hawkins and Ospina 2017) and generalized as (Įs/5)As,min fyd/bslab to account for edge and corner conditions. As,min also needs to be provided at the periphery of drop panels and shear caps. 8.6.1.2 If vuv ! ࢥȜsȜ ′ c f on the critical section for two-way shear surrounding a column, concentrated load, or reaction area, As,min, provided over the width bslab, shall satisfy Eq. (8.6.1.2) , 5 uv slab o V PLQ s y v b b A f = φα (8.6.1.2) where bslab LVWKHZLGWKVSHFL¿HGLQĮs is given in 22.6.5.3ࢥLVWKHYDOXHIRUVKHDUDQGȜs is given in 22.5.5.1.3. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 111 CODE COMMENTARY 8 Two-way Slabs Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 114. RPPHQWDURQVL]HH൵HFWIDFWRULVSURYLGHGLQR22.5.5.1 and R22.6.5.2. R8.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV R8.6.2.17KHPLQLPXPDYHUDJHH൵HFWLYHSUHVWUHVVRI psi was used in two-way test panels in the early 1970s to address punching shear concerns of lightly reinforced slabs. )RUWKLVUHDVRQWKHPLQLPXPH൵HFWLYHSUHVWUHVVLVUHTXLUHG to be provided at every cross section. If the slab thickness varies along the span of a slab or perpendicular to the span of a slab, resulting in a varying slab FURVVVHFWLRQWKHSVLPLQLPXPH൵HFWLYHSUHVWUHVVDQGWKH maximum tendon spacing is required at every cross section tributary to the tendon or group of tendons along the span, considering both the thinner and the thicker slab sections. This may result in higher than the minimum fpc in thinner cross sections, and tendons spaced at less than the maximum in thicker cross sections along a span with varying thickness, GXHWRWKHSUDFWLFDODVSHFWVRIWHQGRQSODFHPHQWLQWKH¿HOG R8.6.2.2 This provision is a precaution against abrupt ÀH[XUDO IDLOXUH GHYHORSLQJ LPPHGLDWHO DIWHU FUDFNLQJ $ ÀH[XUDO PHPEHU GHVLJQHG DFFRUGLQJ WR RGH SURYLVLRQV requires considerable additional load beyond cracking to UHDFK LWV ÀH[XUDO VWUHQJWK 7KXV FRQVLGHUDEOH GHÀHFWLRQ would warn that the member strength is approaching. If WKH ÀH[XUDO VWUHQJWK ZHUH UHDFKHG VKRUWO DIWHU FUDFNLQJ WKHZDUQLQJGHÀHFWLRQZRXOGQRWRFFXU7UDQVIHURIIRUFH between the concrete and the prestressed reinforcement, DQGDEUXSWÀH[XUDOIDLOXUHLPPHGLDWHODIWHUFUDFNLQJGRHV not occur when the prestressed reinforcement is unbonded (ACI 423.3R); therefore, this requirement does not apply to members with unbonded tendons. R8.6.2.3 Some bonded reinforcement is required by the Code in prestressed slabs to limit crack width and spacing at service load when concrete tensile stresses exceed the modulus of rupture and, for slabs with unbonded tendons, to HQVXUHÀH[XUDOSHUIRUPDQFHDWQRPLQDOVWUHQJWKUDWKHUWKDQ performance as a tied arch. Providing the minimum bonded reinforcement as stipulated in this provision helps to ensure adequate performance. The minimum amount of bonded reinforcement in WZRZDÀDWVODEVVWHPVLVEDVHGRQUHSRUWVEJoint ACI- ASCE Committee 423 (1958) and ACI 423.3R. Limited UHVHDUFKDYDLODEOHIRUWZRZDÀDWVODEVZLWKGURSSDQHOV (Odello and Mehta 1967) indicates that behavior of these SDUWLFXODUVVWHPVLVVLPLODUWRWKHEHKDYLRURIÀDWSODWHV )RUXVXDOORDGVDQGVSDQOHQJWKVÀDWSODWHWHVWVVXPPDUL]HG in Joint ACI-ASCE Committee 423 (1958) and experience since the 1963 Code was adopted indicate satisfactory perfor- mance without bonded reinforcement in positive moment regions where ft” ′ c f . In positive moment regions where 2 ′ c f ”ft” ′ c f , a minimum bonded reinforcement area 8.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV 8.6.2.1)RUSUHVWUHVVHGVODEVWKHH൵HFWLYHSUHVWUHVVIRUFH Aps fse shall provide a minimum average compressive stress of 125 psi on the slab section tributary to the tendon or tendon group. For slabs with varying cross section along the slab span, either parallel or perpendicular to the tendon RUWHQGRQJURXSWKHPLQLPXPDYHUDJHH൵HFWLYHSUHVWUHVV of 125 psi is required at every cross section tributary to the tendon or tendon group along the span. 8.6.2.2 For slabs with bonded prestressed reinforcement, total quantity of As and Aps shall be adequate to develop a factored load at least 1.2 times the cracking load calculated on the basis of frGH¿QHGLQ19.2.3. 8.6.2.2.1 )RU VODEV ZLWK ERWK ÀH[XUDO DQG VKHDU GHVLJQ strength at least twice the required strength, 8.6.2.2 need not EHVDWLV¿HG 8.6.2.3 For prestressed slabs, a minimum area of bonded deformed longitudinal reinforcement, As,min, shall be provided in the precompressed tension zone in the direction of the span under consideration in accordance with Table 8.6.2.3. Table 8.6.2.3—Minimum bonded deformed longitudinal reinforcement As,min in two-way slabs with bonded or unbonded tendons Region Calculated ft after all losses, psi As,min, in.2 Positive moment 2 t c f f ≤ ′ Not required (a) 2 6 c t c f f f ≤ ′ ′ 0.5 c y N f (b)[1],[2] Negative moment at columns 6 t c f f ≤ ′ 0.00075Acf (c)[2] [1] The value of fy shall not exceed 60,000 psi. [2] For slabs with bonded tendons, it shall be permitted to reduce As,PLQ by the area of the bonded prestressed reinforcement located within the area used to determine Nc for SRVLWLYHPRPHQWRUZLWKLQWKHZLGWKRIVODEGH¿QHGLQ D IRUQHJDWLYHPRPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org 112 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY GHYHORSLQJ GHVLJQHG ble additi WUHQJWK he memb JWK ZHUH ÀHFWLRQ he concret DEUXSWÀH[X not occ thicker GXHWRWKHSUDFWLF This provis restres l be the 2.3 K d s ing load calcu UDO DQ HDU G gth, 8.6.2.2 nee ÀH[ requir would WKH À d LJQ ot PH co WV À warn XUDO 2.2 IDLO on n Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 115. proportioned to resist Nc according to Eq. (8.6.2.3(b)) is required. The tensile force Nc is calculated at service load on the basis of an uncracked, homogeneous section. 5HVHDUFKRQXQERQGHGSRVWWHQVLRQHGWZRZDÀDWVODE systems (Joint ACI-ASCE Committee 423 1958, 1974; ACI 423.3R; Odello and Mehta 1967) shows that bonded rein- forcement in negative moment regions, proportioned on the basis of 0.075 percent of the cross-sectional area of the slab- EHDPVWULSSURYLGHVVX൶FLHQWGXFWLOLWDQGUHGXFHVFUDFN width and spacing. The same area of bonded reinforcement is required in slabs with either bonded or unbonded tendons. The minimum bonded reinforcement area required by Eq. (8.6.2.3(c)) is a minimum area independent of grade of rein- IRUFHPHQWRUGHVLJQLHOGVWUHQJWK7RDFFRXQWIRUGL൵HUHQW adjacent tributary spans, this equation is given on the basis RIVODEEHDPVWULSVDVGH¿QHGLQ2.3. For rectangular slab panels, this equation is conservatively based on the greater of the cross-sectional areas of the two intersecting slab- beam strips at the column. This ensures that the minimum percentage of reinforcement recommended by research is provided in both directions. Concentration of this rein- forcement in the top of the slab directly over and immedi- ately adjacent to the column is important. Research also shows that where low tensile stresses occur at service loads, satisfactory behavior has been achieved at factored loads without bonded reinforcement. However, the Code requires minimum bonded reinforcement regardless of service load VWUHVVOHYHOVWRKHOSHQVXUHÀH[XUDOFRQWLQXLWDQGGXFWLOLW and to limit crack widths and spacing due to overload, WHPSHUDWXUHRUVKULQNDJH5HVHDUFKRQSRVWWHQVLRQHGÀDW plate-to-column connections is reported in Smith and Burns (1974), Burns and Hemakom (1977), Hawkins (1981), PTI TAB.1, and Foutch et al. (1990). Unbonded post-tensioned members do not inherently provide large capacity for energy dissipation under severe earthquake loadings because the member response is primarily elastic. For this reason, unbonded post-tensioned structural members reinforced in accordance with the provi- sions of this section should be assumed to resist only vertical loads and to act as horizontal diaphragms between energy- dissipating elements under earthquake loadings of the PDJQLWXGHGH¿QHGLQ18.2.1. R8.7—Reinforcement detailing 8.7—Reinforcement detailing 8.7.1 General 8.7.1.1 Concrete cover for reinforcement shall be in accor- dance with 20.5.1. 8.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4. 8.7.1.3 Splice lengths of deformed reinforcement shall be in accordance with 25.5. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 113 CODE COMMENTARY 8 Two-way Slabs e top of the the colum ow tensile or has be nforceme d reinforc KHOSHQV mit crack w SHUDWXUHRU plate to of the beam strips at th ntage of reinfo in both dire ately shows withou mini djace hat w tory bon m b ded ent in ctio ti
- 116. R8.7.2 )OH[XUDOUHLQIRUFHPHQWVSDFLQJ R8.7.2.2 The requirement that the center-to-center spacing of the reinforcement be not more than two times the slab thickness applies only to the reinforcement in solid slabs, DQGQRWWRUHLQIRUFHPHQWLQMRLVWVRUZD൷HVODEV7KLVOLPL- tation is to ensure slab action, control cracking, and provide for the possibility of loads concentrated on small areas of the slab. Refer also to R24.3. R8.7.2.37KLVVHFWLRQSURYLGHVVSHFL¿FJXLGDQFHFRQFHUQLQJ tendon distribution that will permit the use of banded tendon distributions in one direction. This method of tendon distribu- tion has been shown to provide satisfactory performance by structural research (Burns and Hemakom 1977). R8.7.3 Corner restraint in slabs R8.7.3.1 Unrestrained corners of two-way slabs tend to lift when loaded. If this lifting tendency is restrained by edge walls or beams, bending moments result in the slab. This section requires reinforcement to resist these moments and FRQWUROFUDFNLQJ5HLQIRUFHPHQWSURYLGHGIRUÀH[XUHLQWKH primary directions may be used to satisfy this requirement. Refer to Fig. R8.7.3.1. 8.7.1.4 Bundled bars shall be detailed in accordance with 25.6. 8.7.2 )OH[XUDOUHLQIRUFHPHQWVSDFLQJ 8.7.2.1 Minimum spacing s shall be in accordance with 25.2. 8.7.2.2 For nonprestressed solid slabs, maximum spacing s of deformed longitudinal reinforcement shall be the lesser of 2h and 18 in. at critical sections, and the lesser of 3h and 18 in. at other sections. 8.7.2.3 For prestressed slabs with uniformly distributed loads, maximum spacing s of tendons or groups of tendons in at least one direction shall be the lesser of 8h and 5 ft. 8.7.2.4 Concentrated loads and openings shall be consid- ered in determining tendon spacing. 8.7.3 Corner restraint in slabs 8.7.3.1 At exterior corners of slabs supported by edge walls or where one or more edge beams have a value of Įf greater than 1.0, reinforcement at top and bottom of slab shall be designed to resist Mu per unit width due to corner H൵HFWVHTXDOWRWKHPD[LPXPSRVLWLYHMu per unit width in the slab panel. 8.7.3.1.1)DFWRUHGPRPHQWGXHWRFRUQHUH൵HFWVMu, shall be assumed to be about an axis perpendicular to the diagonal from the corner in the top of the slab and about an axis parallel to the diagonal from the corner in the bottom of the slab. 8.7.3.1.2 Reinforcement shall be provided for a distance LQ HDFK GLUHFWLRQ IURP WKH FRUQHU HTXDO WR RQH¿IWK WKH longer span. 8.7.3.1.3 Reinforcement shall be placed parallel to the diagonal in the top of the slab and perpendicular to the diag- onal in the bottom of the slab. Alternatively, reinforcement shall be placed in two layers parallel to the sides of the slab in both the top and bottom of the slab. American Concrete Institute – Copyrighted © Material – www.concrete.org 114 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY straint in ained co If this lifti s, bendin uires reinf WUROFUDFNLQJ primary tion ha structural researc openin ng. bs of e b t s supported by s have a value b R8. R8. lift w dge Įf Į 3 Co 3.1 n loa Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 117. (LLong)/5 LLong LShort (LLong)/5 (LLong)/5 LLong LShort (LLong)/5 As top per 8.7.3 B-1 B-1 B-2 As bottom per 8.7.3 As per 8.7.3 top and bottom OPTION 1 OPTION 2 Notes: 1. Applies where B-1 or B-2 has αf 1.0 2. Max. bar spacing 2h, where h = slab thickness B-2 Fig. R8.7.3.1²6ODEFRUQHUUHLQIRUFHPHQW R8.7.4 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV R8.7.4.1 7HUPLQDWLRQRIUHLQIRUFHPHQW R8.7.4.1.1 and R8.7.4.1.2 Bending moments in slabs at VSDQGUHOEHDPVPDYDUVLJQL¿FDQWO,IVSDQGUHOEHDPVDUH EXLOWVROLGOLQWRZDOOVWKHVODEDSSURDFKHVFRPSOHWH¿[LW Without an integral wall, the slab could approach being simply supported, depending on the torsional rigidity of the spandrel beam or slab edge. These requirements provide for unknown conditions that might normally occur in a structure. 8.7.4 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGVODEV 8.7.4.1 7HUPLQDWLRQRIUHLQIRUFHPHQW 8.7.4.1.1 Where a slab is supported on spandrel beams, columns, or walls, anchorage of reinforcement perpendic- ular to a discontinuous edge shall satisfy (a) and (b): (a) Positive moment reinforcement shall extend to the edge of slab and have embedment, straight or hooked, at least 6 in. into spandrel beams, columns, or walls American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 115 CODE COMMENTARY 8 Two-way Slabs Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 118. R8.7.4.1.3 The minimum lengths and extensions of rein- forcement expressed as a fraction of the clear span in Fig. 8.7.4.1.3 were developed for slabs of ordinary proportions supporting gravity loads. These minimum lengths and H[WHQVLRQVRIEDUVPDQRWEHVX൶FLHQWWRLQWHUFHSWSRWHQ- tial punching shear cracks in thick two-way slabs such as transfer slabs, podium slabs, and mat foundations. Therefore, the Code requires extensions for at least half of the column strip top bars to be at least 5d. For slabs with drop panels, dLVWKHH൵HFWLYHGHSWKZLWKLQWKHGURSSDQHO,QWKHVHWKLFN two-way slabs, continuous reinforcement in each direction near both faces is desirable to improve structural integrity, FRQWUROFUDFNLQJDQGUHGXFHFUHHSGHÀHFWLRQV$VLOOXVWUDWHG in Fig. R8.7.4.1.3, punching shear cracks, which can develop at angles as low as approximately 20 degrees, may not be intercepted by the tension reinforcement in thick slabs if this reinforcement does not extend to at least 5d beyond the face of the support. The 5d bar extension requirement governs where Ɛn/h is less than approximately 15. For moments resulting from combined lateral and gravity loadings, these PLQLPXPOHQJWKVDQGH[WHQVLRQVPDQRWEHVX൶FLHQW %HQWEDUVDUHVHOGRPXVHGDQGDUHGL൶FXOWWRSODFHSURS- erly. Bent bars, however, are permitted provided they comply with 8.7.4.1.3(c). Further guidance on the use of bent bar systems can be found in 13.4.8 of the 1983 Code. (b) Negative moment reinforcement shall be bent, hooked, or otherwise anchored into spandrel beams, columns, or walls, and shall be developed at the face of support 8.7.4.1.2 Where a slab is not supported by a spandrel beam or wall at a discontinuous edge, or where a slab cantilevers beyond the support, anchorage of reinforcement shall be permitted within the slab. 8.7.4.1.3 For slabs without beams, reinforcement exten- sions shall be in accordance with (a) through (c): (a) Reinforcement lengths shall be at least in accordance with Fig. 8.7.4.1.3, and if slabs act as primary members resisting lateral loads, reinforcement lengths shall be at least those required by analysis. (b) If adjacent spans are unequal, extensions of nega- tive moment reinforcement beyond the face of support in accordance with Fig. 8.7.4.1.3 shall be based on the longer span. (c) Bent bars shall be permitted only where the depth-to- span ratio permits use of bends of 45 degrees or less. American Concrete Institute – Copyrighted © Material – www.concrete.org 116 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY 3, punching as approxi ension rei not exten e 5d bar d ss than a combine HQJWKVDQG HQWEDUVDUH erly Be dLVWKH d two-way slabs, both faces is de NLQJ DQG UHG longer y where t f 45 d at an interc of the wher s as ted eme upp Ɛn Ɛ /h FUDF R8.7 XFH XF Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 119. Minimum As at section 50% 50% 100% 100% Remainder Remainder 0.30n 0.33n 0.20n 0.20n 6 in. At least two bars or wires shall conform to 8.7.4.2 0.20n 0.20n Not less than 5d 0.30n 0.33n 6 in. c1 c1 c1 6 in. Not less than 5d Strip Column strip Location Middle strip Without drop panels With drop panels Top Bottom 0.22n 0.22n 0.22n 0.22n 6 in. Max. 0.15n Max. 0.15n 6 in. Center to center span Exterior support (No slab continuity) C L Face of support Clear span - n Center to center span Face of support Clear span - n Exterior support (No slab continuity) C L C L Interior support (Continuity provided) Top Bottom Continuous bars Splices shall be permitted in this region Fig. 8.7.4.1.3²0LQLPXPH[WHQVLRQVIRUGHIRUPHGUHLQIRUFHPHQWLQWZRZDVODEVZLWKRXWEHDPV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 117 CODE COMMENTARY 8 Two-way Slabs Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 120. R8.7.4.2 Structural integrity R8.7.4.2.1 and R8.7.4.2.2 The continuous column strip bottom reinforcement provides the slab some residual ability to span to the adjacent supports should a single support be damaged. The two continuous column strip bottom bars or wires through the column may be termed “integrity rein- forcement,” and are provided to give the slab some residual strength following a single punching shear failure at a single support (Mitchell and Cook 1984). Joint ACI-ASCE Committee 352 (ACI 352.1R) provides further guidance on the design of integrity reinforcement in slab-column connec- tions. Similar provisions for slabs with unbonded tendons are provided in 8.7.5.6. R8.7.5 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV R8.7.5.2 Bonded reinforcement should be adequately anchored to develop the required strength to resist factored loads. The requirements of 7.7.3 are intended to provide adequate anchorage for tensile or compressive forces devel- RSHG LQ ERQGHG UHLQIRUFHPHQW E ÀH[XUH XQGHU IDFWRUHG 8.7.4.2 Structural integrity 8.7.4.2.1 All bottom deformed bars or deformed wires within the column strip, in each direction, shall be contin- uous or spliced using mechanical or welded splices in accor- dance with 25.5.7 or Class B tension lap splices in accor- dance with 25.5.2. Splices shall be located in accordance with Fig. 8.7.4.1.3. 8.7.4.2.2 At least two of the column strip bottom bars or wires in each direction shall pass within the region bounded by the longitudinal reinforcement of the column and shall be anchored at exterior supports. 8.7.5 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGVODEV 8.7.5.1 External tendons shall be attached to the slab in a PDQQHUWKDWPDLQWDLQVWKHVSHFL¿HGHFFHQWULFLWEHWZHHQWKH tendons and the concrete centroid through the full range of DQWLFLSDWHGPHPEHUGHÀHFWLRQV 8.7.5.2 If bonded deformed longitudinal reinforcement LVUHTXLUHGWRVDWLVIÀH[XUDOVWUHQJWKRUIRUWHQVLOHVWUHVV conditions in accordance with Eq. (8.6.2.3(b)), the detailing requirements of 7.7.3 VKDOOEHVDWLV¿HG h 0.3n 5d 0.3n 5d h Potential punching shear crack is intercepted by top reinforcement terminating 0.3n from column face (a) Ordinary Slab Extension of top reinforcement beyond 0.3n to 5d from column is required to intercept potential punching shear crack (b) Thick Slab Fig. R8.7.4.1.3—Punching shear cracks in ordinary and thick slabs. American Concrete Institute – Copyrighted © Material – www.concrete.org 118 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 121. loads in accordance with 22.3.2, or by tensile stresses at service load in accordance with Eq. (8.6.2.3(b)). R8.7.5.5 7HUPLQDWLRQRIGHIRUPHGUHLQIRUFHPHQWLQVODEV with unbonded tendons R8.7.5.5.1 The minimum lengths apply for bonded rein- IRUFHPHQWUHTXLUHGEEXWQRWUHTXLUHGIRUÀH[XUDO strength in accordance with 22.3.2. Research (Odello and Mehta 1967) on continuous spans shows that these minimum lengths provide adequate behavior under service load and factored load conditions. R8.7.5.6 Structural integrity R8.7.5.6.1 Prestressing tendons that pass through the slab-column joint at any location over the depth of the slab suspend the slab following a punching shear failure, provided the tendons are continuous through or anchored within the region bounded by the longitudinal reinforcement of the column and are prevented from bursting through the top surface of the slab (ACI 352.1R). R8.7.5.6.2 Between column or shear cap faces, structural integrity tendons should pass below the orthogonal tendons from adjacent spans so that vertical movements of the integ- rity tendons are restrained by the orthogonal tendons. Where tendons are distributed in one direction and banded in the RUWKRJRQDOGLUHFWLRQWKLVUHTXLUHPHQWFDQEHVDWLV¿HGE¿UVW placing the integrity tendons for the distributed tendon direc- tion and then placing the banded tendons. Where tendons are 8.7.5.3 Bonded longitudinal reinforcement required by Eq. (8.6.2.3(c)) shall be placed in the top of the slab, and shall be in accordance with (a) through (c): (a) Reinforcement shall be distributed between lines that are 1.5h outside opposite faces of the column support. (b)At least four deformed bars, deformed wires, or bonded strands shall be provided in each direction. (c) Maximum spacing s between bonded longitudinal reinforcement shall not exceed 12 in. 8.7.5.4 7HUPLQDWLRQRISUHVWUHVVHGUHLQIRUFHPHQW 8.7.5.4.1 Post-tensioned anchorage zones shall be designed and detailed in accordance with 25.9. 8.7.5.4.2 Post-tensioning anchorages and couplers shall be designed and detailed in accordance with 25.8. 8.7.5.5 7HUPLQDWLRQ RI GHIRUPHG UHLQIRUFHPHQW LQ VODEV with unbonded tendons 8.7.5.5.1 Length of deformed reinforcement required by 8.6.2.3 shall be in accordance with (a) and (b): (a) In positive moment areas, length of reinforcement shall be at least Ɛn/3 and be centered in those areas (b) In negative moment areas, reinforcement shall extend at least Ɛn/6 on each side of the face of support 8.7.5.6 Structural integrity 8.7.5.6.1 Except as permitted in 8.7.5.6.3, at least two WHQGRQVZLWKLQGLDPHWHURUODUJHUVWUDQGVKDOOEHSODFHG in each direction at columns in accordance with (a) or (b): (a) Tendons shall pass through the region bounded by the longitudinal reinforcement of the column. (b) Tendons shall be anchored within the region bounded by the longitudinal reinforcement of the column, and the anchorage shall be located beyond the column centroid and away from the anchored span. 8.7.5.6.2 Outside of the column and shear cap faces, the two structural integrity tendons required by 8.7.5.6.1 shall pass under any orthogonal tendons in adjacent spans. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 119 CODE COMMENTARY 8 Two-way Slabs PLQDWLRQRI dons inimum E dance wit n continu ovide adeq red load con ith couplers shall be 25.8 PHG d with l orcement require and (b with IRUFHP stren by bond 5.5. HQWU in 5.5 Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 122. distributed in both directions, weaving of tendons is neces- sary and use of 8.7.5.6.3 may be an easier approach. R8.7.5.6.3 In some prestressed slabs, tendon layout FRQVWUDLQWVPDNHLWGL൶FXOWWRSURYLGHWKHVWUXFWXUDOLQWHJ- rity tendons required by 8.7.5.6.1. In such situations, the structural integrity tendons can be replaced by deformed bar bottom reinforcement (ACI 352.1R). R8.7.6 6KHDUUHLQIRUFHPHQW±VWLUUXSV Research (Hawkins 1974; Broms 1990; Yamada et al. 1991; Hawkins et al. 1975; ACI 421.1R) has shown that shear reinforcement consisting of properly anchored bars or wires and single- or multiple-leg stirrups, or closed stir- rups, can increase the punching shear resistance of slabs. The spacing limits given in 8.7.6.3 correspond to slab shear UHLQIRUFHPHQWGHWDLOVWKDWKDYHEHHQVKRZQWREHH൵HFWLYH Section 25.7.1 gives anchorage requirements for stirrup-type shear reinforcement that should also be applied for bars or wires used as slab shear reinforcement. It is essential that this shear reinforcement engage longitudinal reinforcement at both the top and bottom of the slab, as shown for typical details in Fig. R8.7.6(a) to (c). Anchorage of shear reinforce- PHQWDFFRUGLQJWRWKHUHTXLUHPHQWVRILVGL൶FXOWLQ slabs thinner than 10 in. Shear reinforcement consisting of vertical bars mechanically anchored at each end by a plate or head capable of developing the yield strength of the bars has been used successfully (ACI 421.1R). In a slab-column connection for which moment transfer is negligible, the shear reinforcement should be symmetrical about the centroid of the critical section (Fig. R8.7.6(d)). 8.7.5.6.3 Slabs with tendons not satisfying 8.7.5.6.1 shall be permitted if bonded bottom deformed reinforcement is provided in each direction in accordance with 8.7.5.6.3.1 through 8.7.5.6.3.3. 8.7.5.6.3.1 Minimum bottom deformed reinforcement As in each direction shall be the larger of (a) and (b). The value of fy shall be limited to a maximum of 80,000 psi: (a) 2 4.5 c s y f c d A f ′ = (8.7.5.6.3.1a) (b) 2 300 s y c d A f = (8.7.5.6.3.1b) where c2 is measured at the column faces through which the reinforcement passes. 8.7.5.6.3.2 Bottom deformed reinforcement calculated in 8.7.5.6.3.1 shall pass within the region bounded by the longi- tudinal reinforcement of the column and shall be anchored at exterior supports. 8.7.5.6.3.3 Bottom deformed reinforcement shall be anchored to develop fy beyond the column or shear cap face. 8.7.6 6KHDUUHLQIRUFHPHQW±VWLUUXSV 8.7.6.1 Single-leg, simple-U, multiple-U, and closed stir- rups shall be permitted as shear reinforcement. 8.7.6.2 Stirrup anchorage and geometry shall be in accor- dance with 25.7.1. 8.7.6.3 If stirrups are provided, location and spacing shall be in accordance with Table 8.7.6.3. Table 8.7.6.3—First stirrup location and spacing limits Direction of measurement Description of measurement Maximum distance or spacing, in. Perpendicular to column face Distance from column IDFHWR¿UVWVWLUUXS d Spacing between stirrups d Parallel to column face Spacing between vertical legs of stirrups 2d American Concrete Institute – Copyrighted © Material – www.concrete.org 120 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY 6.3.1b) faces th rei re um ment calculat bounded by the l d shall be anchor n ngi- d at Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 123. 6SDFLQJ OLPLWV GH¿QHG LQ DUH DOVR VKRZQ LQ )LJ R8.7.6(d) and (e). At edge columns or for interior connections where moment WUDQVIHULVVLJQL¿FDQWFORVHGVWLUUXSVDUHUHFRPPHQGHGLQ a pattern as symmetrical as possible. Although the average shear stresses on faces AD and BC of the exterior column in Fig. R8.7.6(e) are lower than on face AB, the closed stirrups extending from faces AD and BC provide some torsional strength along the edge of the slab. 6db (3 in. min.) 45 deg max. Refer to 25.3 Refer to 25.3 ≤ 2d ≥ 12db Refer to 25.3 (a) single-leg stirrup or bar (b) multiple-leg stirrup or bar (c) closed stirrup Fig. R8.7.6(a)-(c)²6LQJOHRUPXOWLSOHOHJVWLUUXSWSHVODE VKHDUUHLQIRUFHPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 121 CODE COMMENTARY 8 Two-way Slabs Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 124. d/2 d/2 d/2 d/2 Critical section through slab shear reinforcement (first line of stirrup legs) Critical section outside slab shear reinforcement Plan ≤ 2d ≤ d/2 Elevation Column d Slab s ≤ d/2 Fig. R8.7.6(d)²$UUDQJHPHQW RI VWLUUXS VKHDU UHLQIRUFH- PHQWLQWHULRUFROXPQ American Concrete Institute – Copyrighted © Material – www.concrete.org 122 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 125. d/2 Plan ≤ 2d ≤ d/2 Elevation Column d Slab s ≤ d/2 A D B C d/2 Slab edge Critical section outside slab shear reinforcement Critical section through slab shear reinforcement (first line of stirrup legs) d/2 Fig. R8.7.6(e)²$UUDQJHPHQW RI VWLUUXS VKHDU UHLQIRUFH- PHQWHGJHFROXPQ R8.7.7 6KHDUUHLQIRUFHPHQW±KHDGHGVWXGV Using headed stud assemblies as shear reinforcement in slabs requires specifying the stud shank diameter, the spacing of the studs, and the height of the assemblies for the particular applications. Tests (ACI 421.1R) show that vertical studs mechani- cally anchored as close as possible to the top and bottom of VODEVDUHH൵HFWLYHLQUHVLVWLQJSXQFKLQJVKHDU7KHERXQGV RIWKHRYHUDOOVSHFL¿HGKHLJKWDFKLHYHWKLVREMHFWLYHZKLOH providing a reasonable tolerance in specifying that height, as shown in Fig. R20.5.1.3.5. Compared with a leg of a stirrup having bends at the ends, a stud head exhibits smaller slip and, thus, results in smaller shear crack widths. The improved performance results in increased limits for shear strength and spacing between periph- eral lines of headed shear stud reinforcement. Typical arrange- ments of headed shear stud reinforcement are shown in Fig. R8.7.7. The critical section beyond the shear reinforcement 8.7.7 6KHDUUHLQIRUFHPHQW±KHDGHGVWXGV 8.7.7.1 Headed shear stud reinforcement shall be permitted if placed perpendicular to the plane of the slab. 8.7.7.1.1 The overall height of the shear stud assembly shall be at least the thickness of the slab minus the sum of (a) through (c): D RQFUHWHFRYHURQWKHWRSÀH[XUDOUHLQIRUFHPHQW (b) Concrete cover on the base rail F 2QHKDOI WKH EDU GLDPHWHU RI WKH ÀH[XUDO WHQVLRQ reinforcement American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 123 CODE COMMENTARY 8 Two-way Slabs Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 126. 8.7.7.1.2 Headed shear stud reinforcement location and spacing shall be in accordance with Table 8.7.7.1.2. generally has a polygonal shape. Equations for calculating shear stresses on such sections are given in ACI 421.1R. R8.7.7.1.2 7KH VSHFL¿HG VSDFLQJV EHWZHHQ SHULSKHUDO OLQHV RI VKHDU UHLQIRUFHPHQW DUH MXVWL¿HG E H[SHULPHQWV (ACI 421.1R). The clear spacing between the heads of the VWXGVVKRXOGEHDGHTXDWHWRSHUPLWSODFLQJRIWKHÀH[XUDO reinforcement. d /2 ≤ d /2 (typ.) ≤ 2d (typ.) s d /2 d /2 d /2 ≤ 2d (typ.) ≤ 2d (typ.) s s d /2 d /2 ≤ d /2 (typ.) ≤ d /2 (typ.) A A Studs with base rail Av = cross-sectional area of studs on any peripheral line Av = cross-sectional area of studs on a peripheral line Interior column Shear critical sections Outermost peripheral line of studs Shear critical sections Shear critical sections Section A-A Edge column Corner column Outermost peripheral line of studs Outermost peripheral line of studs Slab edges Fig. R8.7.7²7SLFDODUUDQJHPHQWVRIKHDGHGVKHDUVWXGUHLQIRUFHPHQWDQGFULWLFDOVHFWLRQV American Concrete Institute – Copyrighted © Material – www.concrete.org 124 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 127. 8.8—Nonprestressed two-way joist systems 8.8.1 General 8.8.1.1 Nonprestressed two-way joist construction consists of a monolithic combination of regularly spaced ribs and a top slab designed to span in two orthogonal directions. 8.8.1.2 Width of ribs shall be at least 4 in. at any location along the depth. 8.8.1.3 Overall depth of ribs shall not exceed 3.5 times the minimum width. 8.8.1.4 Clear spacing between ribs shall not exceed 30 in. 8.8.1.5 Vc shall be permitted to be taken as 1.1 times the values calculated in 22.5. 8.8.1.6 For structural integrity, at least one bottom bar in each joist shall be continuous and shall be anchored to develop fy at the face of supports. 8.8.1.7 Reinforcement area perpendicular to the ribs shall satisfy slab moment strength requirements, considering load concentrations, and shall be at least the shrinkage and temperature reinforcement area in accordance with 24.4. R8.8—Nonprestressed two-way joist systems R8.8.1 General The empirical limits established for nonprestressed rein- IRUFHG FRQFUHWH MRLVW ÀRRUV DUH EDVHG RQ VXFFHVVIXO SDVW performance of joist construction using standard joist forming systems. For prestressed joist construction, this section may be used as a guide. R8.8.1.4 A limit on the maximum spacing of ribs is required because of the provisions permitting higher shear strengths and less concrete cover for the reinforcement for these relatively small, repetitive members. R8.8.1.57KHLQFUHDVHLQVKHDUVWUHQJWKLVMXVWL¿HGRQWKH basis of: 1) satisfactory performance of joist construction GHVLJQHGZLWKKLJKHUFDOFXODWHGVKHDUVWUHQJWKVSHFL¿HGLQ previous Codes, which allowed comparable shear stresses; and 2) potential for redistribution of local overloads to adja- cent joists. Table 8.7.7.1.2—Shear stud location and spacing limits Direction of measurement Description of measurement Condition Maximum distance or spacing, in. Perpendicular to column face Distance from column face to ¿UVWSHULSKHUDOOLQHRIVKHDUVWXGV All d Constant spacing between peripheral lines of shear studs Nonprestressed slab with vu”ࢥ c f ′ 3d Nonprestressed slab with vu!ࢥ c f ′ d Prestressed slabs conforming to 22.6.5.4 3d Parallel to column face Spacing between adjacent shear studs on peripheral line nearest to column face All 2d American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 125 CODE COMMENTARY 8 Two-way Slabs used as a gu he way f r o o l The IRUFHG FRQFUHW mance of jois tems. For construction con rly spaced ribs a onal directions. ists nd a sy may pres re Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 128. 8.8.1.8 Two-way joist construction not satisfying the limi- tations of 8.8.1.1 through 8.8.1.4 shall be designed as slabs and beams. 8.8.2 -RLVWVVWHPVZLWKVWUXFWXUDO¿OOHUV 8.8.2.1,ISHUPDQHQWEXUQHGFODRUFRQFUHWHWLOH¿OOHUVRI material having a unit compressive strength at least equal to fcƍ in the joists are used, 8.8.2.1.1 and 8.8.2.1.2 shall apply. 8.8.2.1.16ODEWKLFNQHVVRYHU¿OOHUVVKDOOEHDWOHDVWWKH greater of one-twelfth the clear distance between ribs and 1.5 in. 8.8.2.1.2 For calculation of shear and negative moment strength, it shall be permitted to include the vertical shells of ¿OOHUVLQFRQWDFWZLWKWKHULEV2WKHUSRUWLRQVRI¿OOHUVVKDOO not be included in strength calculations. 8.8.3 -RLVWVVWHPVZLWKRWKHU¿OOHUV 8.8.3.1,I¿OOHUVQRWFRPSOLQJZLWKRUUHPRYDEOH forms are used, slab thickness shall be at least the greater of one-twelfth the clear distance between ribs and 2 in. 8.9—Lift-slab construction 8.9.1 In slabs constructed with lift-slab methods where it is impractical to pass the tendons required by 8.7.5.6.1 or the bottom bars required by 8.7.4.2 or 8.7.5.6.3 through the column, at least two post-tensioned tendons or two bonded bottom bars or wires in each direction shall pass through the lifting collar as close to the column as practicable, and be continuous or spliced using mechanical or welded splices in accordance with 25.5.7 or Class B tension lap splices in accordance with 25.5.2. At exterior columns, the reinforce- ment shall be anchored at the lifting collar. American Concrete Institute – Copyrighted © Material – www.concrete.org 126 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY be ZLWK all b etw th ns 2 bs and 2 in. lab methods wh ired by 8.7.5.6 6 3 e it or Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 129. 9.1—Scope 9.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed beams, including: (a) Composite beams of concrete elements constructed in separate placements but connected so that all elements resist loads as a unit (b) One-way joist systems in accordance with 9.8 (c) Deep beams in accordance with 9.9 9.2—General 9.2.1 Materials 9.2.1.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 9.2.1.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 9.2.1.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 9.2.2 RQQHFWLRQWRRWKHUPHPEHUV 9.2.2.1 For cast-in-place construction, beam-column and slab-column joints shall satisfy Chapter 15. 9.2.2.2 For precast construction, connections shall satisfy the force transfer requirements of 16.2. 9.2.3 Stability 9.2.3.1 If a beam is not continuously laterally braced, (a) DQG E VKDOOEHVDWLV¿HG (a) Spacing of lateral bracing shall not exceed 50 times the OHDVWZLGWKRIFRPSUHVVLRQÀDQJHRUIDFH (b) Spacing of lateral bracing shall take into account H൵HFWVRIHFFHQWULFORDGV 9.2.3.2 In prestressed beams, buckling of thin webs and ÀDQJHVVKDOOEHFRQVLGHUHG,IWKHUHLVLQWHUPLWWHQWFRQWDFW between prestressed reinforcement and an oversize duct, member buckling between contact points shall be considered. 9.2.4 7EHDPFRQVWUXFWLRQ R9.1—Scope R9.1.1 Composite structural steel-concrete beams are not covered in this chapter. Design provisions for such composite beams are covered in AISC 360. R9.2—General R9.2.3 Stability R9.2.3.1 Tests (Hansell and Winter 1959; Sant and Blet- zacker 1961) have shown that laterally unbraced reinforced concrete beams, even when very deep and narrow, will not fail prematurely by lateral buckling, provided the beams are loaded without lateral eccentricity that causes torsion. Laterally unbraced beams are frequently loaded eccentri- cally or with slight inclination. Stresses and deformations by such loading become detrimental for narrow, deep beams with long unsupported lengths. Lateral supports spaced closer than 50b may be required for such loading conditions. R9.2.3.2 In post-tensioned members where the prestressed reinforcement has intermittent contact with an oversize duct, the member can buckle due to the axial prestressing force, DV WKH PHPEHU FDQ GHÀHFW ODWHUDOO ZKLOH WKH SUHVWUHVVHG reinforcement does not. If the prestressed reinforcement is in continuous contact with the member being prestressed or is part of an unbonded tendon with the sheathing not excessively larger than the prestressed reinforcement, the prestressing force cannot buckle the member. R9.2.4 7EHDPFRQVWUXFWLRQ American Concrete Institute – Copyrighted © Material – www.concrete.org .2.3 Stabili requirements for ordance EHUV nstr C n, 6 n, beam-column r 15 ections shall sa and fy PART 3: MEMBERS 127 CODE COMMENTARY 9 Beams CHAPTER 9—BEAMS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 130. R9.2.4.1 For monolithic or fully composite construction, WKHEHDPLQFOXGHVDSRUWLRQRIWKHVODEDVÀDQJHV R9.2.4.3 Refer to R7.5.2.3. R9.2.4.4 Two examples of the section to be considered in torsional design are provided in Fig. R9.2.4.4. hf hf bw bw hb hb hb ≤ 4hf bw + 2hb ≤ bw + 8hf Fig. R9.2.4.4²([DPSOHVRIWKHSRUWLRQRIVODEWREHLQFOXGHG ZLWKWKHEHDPIRUWRUVLRQDOGHVLJQ R9.3—Design limits R9.3.1 0LQLPXPEHDPGHSWK R9.3.1.1 For application of this provision to composite concrete beams, refer to R9.3.2.2. 9.2.4.1,Q7EHDPFRQVWUXFWLRQÀDQJHDQGZHEFRQFUHWH shall be placed monolithically or made composite in accor- dance with 16.4. 9.2.4.2(൵HFWLYHÀDQJHZLGWKVKDOOEHLQDFFRUGDQFHZLWK 6.3.2. 9.2.4.3)RU7EHDPÀDQJHVZKHUHWKHSULPDUÀH[XUDOVODE reinforcement is parallel to the longitudinal axis of the beam, UHLQIRUFHPHQWLQWKHÀDQJHSHUSHQGLFXODUWRWKHORQJLWXGLQDO axis of the beam shall be in accordance with 7.5.2.3. 9.2.4.4 For torsional design according to 22.7, the over- KDQJLQJÀDQJHZLGWKXVHGWRFDOFXODWHAcp, Ag, and pcp shall be in accordance with (a) and (b): D 7KHRYHUKDQJLQJÀDQJHZLGWKVKDOOLQFOXGHWKDWSRUWLRQ of slab on each side of the beam extending a distance equal to the projection of the beam above or below the slab, whichever is greater, but not greater than four times the slab thickness. E 7KHRYHUKDQJLQJÀDQJHVVKDOOEHQHJOHFWHGLQFDVHV where the parameter Acp 2 /pcp for solid sections or Ag 2 pcp IRUKROORZVHFWLRQVFDOFXODWHGIRUDEHDPZLWKÀDQJHVLV less than that calculated for the same beam ignoring the ÀDQJHV 9.3—Design limits 9.3.1 0LQLPXPEHDPGHSWK 9.3.1.1 For nonprestressed beams not supporting or attached to partitions or other construction likely to be GDPDJHG E ODUJH GHÀHFWLRQV RYHUDOO EHDP GHSWKh shall satisfy the limits in Table 9.3.1.1, unless the calculated GHÀHFWLRQOLPLWVRIDUHVDWLV¿HG American Concrete Institute – Copyrighted © Material – www.concrete.org 128 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 131. R9.3.1.1.1 7KH PRGL¿FDWLRQ IRU fy is approximate, but should provide conservative results for typical reinforcement ratios and for values of fy between 40,000 and 100,000 psi. R9.3.1.1.2 7KH PRGL¿FDWLRQ IRU OLJKWZHLJKW FRQFUHWH is based on the results and discussions in ACI 213R. No correction is given for concretes with wc greater than 115 OEIW3 because the correction term would be close to unity in this range. R9.3.2 DOFXODWHGGHÀHFWLRQOLPLWV R9.3.2.2 The limits in Table 9.3.1.1 apply to the entire depth of nonprestressed composite beams shored during construction so that, after removal of temporary supports, the dead load is resisted by the full composite section. In unshored construction, the beam depth of concern depends RQLIWKHGHÀHFWLRQEHLQJFRQVLGHUHGRFFXUVEHIRUHRUDIWHU WKHDWWDLQPHQWRIH൵HFWLYHFRPSRVLWHDFWLRQ $GGLWLRQDO GHÀHFWLRQV GXH WR H[FHVVLYH FUHHS DQG shrinkage caused by premature loading should be consid- ered. This is especially important at early ages when the moisture content is high and the strength is low. The transfer of horizontal shear by direct bond is impor- WDQWLIH[FHVVLYHGHÀHFWLRQIURPVOLSSDJHLVWREHSUHYHQWHG Table 9.3.1.1—Minimum depth of nonprestressed beams Support condition Minimum h[1] Simply supported Ɛ One end continuous Ɛ Both ends continuous Ɛ Cantilever Ɛ [1] Expressions applicable for normalweight concrete and fy = 60,000 psi. For other cases, minimum hVKDOOEHPRGL¿HGLQDFFRUGDQFHZLWKWKURXJK as appropriate. 9.3.1.1.1 For fy other than 60,000 psi, the expressions in Table 9.3.1.1 shall be multiplied by (0.4 + fy/100,000). 9.3.1.1.2 For nonprestressed beams made of lightweight concrete having wcLQWKHUDQJHRIWROEIW3 , the expres- sions in Table 9.3.1.1 shall be multiplied by the greater of (a) and (b): (a) 1.65 – 0.005wc (b) 1.09 9.3.1.1.3 For nonprestressed composite beams made of a combinationoflightweightandnormalweightconcrete,shored during construction, and where the lightweight concrete is in FRPSUHVVLRQWKHPRGL¿HURIVKDOODSSO 9.3.1.2 7KH WKLFNQHVV RI D FRQFUHWH ÀRRU ¿QLVK VKDOO be permitted to be included in h if it is placed monolithi- FDOOZLWKWKHEHDPRULIWKHÀRRU¿QLVKLVGHVLJQHGWREH composite with the beam in accordance with 16.4. 9.3.2 DOFXODWHGGHÀHFWLRQOLPLWV 9.3.2.1 For nonprestressed beams not satisfying 9.3.1 and for prestressed beams, immediate and time-dependent GHÀHFWLRQVVKDOOEHFDOFXODWHGLQDFFRUGDQFHZLWK24.2 and shall not exceed the limits in 24.2.2. 9.3.2.2 For nonprestressed composite concrete beams satis- ILQJGHÀHFWLRQVRFFXUULQJDIWHUWKHPHPEHUEHFRPHV FRPSRVLWH QHHG QRW EH FDOFXODWHG 'HÀHFWLRQV RFFXUULQJ before the member becomes composite shall be investigated XQOHVVWKHSUHFRPSRVLWHGHSWKDOVRVDWLV¿HV American Concrete Institute – Copyrighted © Material – www.concrete.org EH correct OEIW3 because th nge. r of (a) co nor the ite beams made eightconcrete,sh tweight concrete DOODSSO of a ored s in PART 3: MEMBERS 129 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 132. Shear keys provide a means of transferring shear but will not be engaged until slippage occurs. R9.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGEHDPV R9.3.3.1 7KH H൵HFW RI WKLV OLPLWDWLRQ LV WR UHVWULFW WKH reinforcement ratio in nonprestressed beams to mitigate EULWWOHÀH[XUDOEHKDYLRULQFDVHRIDQRYHUORDG7KLVOLPLWD- tion does not apply to prestressed beams. Before the 2019 RGH D PLQLPXP VWUDLQ OLPLW RI ZDV VSHFL¿HG IRU QRQSUHVWUHVVHGÀH[XUDOPHPEHUV%HJLQQLQJZLWKWKH Code, this limit is revised to require that the section be tension-controlled. R9.4—Required strength R9.4.3 Factored shear R9.4.3.2 The closest inclined crack to the support of the beam in Fig. R9.4.3.2a will extend upward from the face of the support reaching the compression zone approximately d from the face of the support. If loads are applied to the top of the beam, the stirrups across this crack need only resist the shear force due to loads acting beyond d (right free body in Fig. R9.4.3.2a). The loads applied to the beam between the face of the support and the point d away from the face 9.3.3 5HLQIRUFHPHQWVWUDLQOLPLWLQQRQSUHVWUHVVHGEHDPV 9.3.3.1 Nonprestressed beams with Pu 0.10fcƍAg shall be tension controlled in accordance with Table 21.2.2. 9.3.4 6WUHVVOLPLWVLQSUHVWUHVVHGEHDPV 9.3.4.13UHVWUHVVHGEHDPVVKDOOEHFODVVL¿HGDVODVV87 or C in accordance with 24.5.2. 9.3.4.2 Stresses in prestressed beams immediately after transfer and at service loads shall not exceed permissible stresses in 24.5.3 and 24.5.4. 9.4—Required strength 9.4.1 General 9.4.1.1 Required strength shall be calculated in accor- dance with the factored load combinations in Chapter 5. 9.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. 9.4.1.3)RUSUHVWUHVVHGEHDPVH൵HFWVRIUHDFWLRQVLQGXFHG by prestressing shall be considered in accordance with 5.3.11. 9.4.2 )DFWRUHGPRPHQW 9.4.2.1 For beams built integrally with supports, Mu at the support shall be permitted to be calculated at the face of support. 9.4.3 Factored shear 9.4.3.1 For beams built integrally with supports, Vu at the support shall be permitted to be calculated at the face of support. 9.4.3.2 Sections between the face of support and a critical section located d from the face of support for nonprestressed beams and h/2 from the face of support for prestressed beams shall be permitted to be designed for Vu at that critical VHFWLRQLI D WKURXJK F DUHVDWLV¿HG (a) Support reaction, in direction of applied shear, intro- duces compression into the end region of the beam American Concrete Institute – Copyrighted © Material – www.concrete.org strength mmediately after t exceed hal mbi calculated in a ns in Chapter 5 R9. cor- Req 130 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 133. are transferred directly to the support by compression in the web above the crack. Accordingly, the Code permits design for a maximum factored shear Vu at a distance d from the support for nonprestressed beams and at a distance h/2 for prestressed beams. In Fig. R9.4.3.2b, loads are shown acting near the bottom of a beam. In this case, the critical section is taken at the face of the support. Loads acting near the support should be transferred across the inclined crack extending upward from the support face. The shear force acting on the critical section should include all loads applied below the potential inclined crack. Typical support conditions where the shear force at a distance d from the support may be used include: (a) Beams supported by bearing at the bottom of the beam, such as shown in Fig. R9.4.3.2(c) (b) Beams framing monolithically into a column, as illus- trated in Fig. R9.4.3.2(d) Typical support conditions where the critical section is taken at the face of support include: (a) Beams framing into a supporting member in tension, such as shown in Fig. R9.4.3.2(e). Shear within the connection should also be investigated and special corner reinforcement should be provided. (b) Beams for which loads are not applied at or near the top, as previously discussed and as shown in Fig. R9.4.3.2b. (c) Beams loaded such that the shear at sections between the support and a distance dIURPWKHVXSSRUWGL൵HUVUDGL- cally from the shear at distance d. This commonly occurs in brackets and in beams where a concentrated load is located close to the support, as shown in Fig. R9.4.3.2(f). V M R d T T C C Critical section ∑Avfyt Fig. R9.4.3.2a²)UHHERGGLDJUDPVRIWKHHQGRIDEHDP (b) Loads are applied at or near the top surface of the beam (c) No concentrated load occurs between the face of support and critical section American Concrete Institute – Copyrighted © Material – www.concrete.org ould also b hould be p ich loads a ussed an d such tha a distanc he shear a ts and in cated close t Typi taken at the face Beams framing hown in F re (b) B (c) the orcem eam eviou eam uppo as ectio ig. g PART 3: MEMBERS 131 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 134. 9.4.4 Factored torsion 9.4.4.1 Unless determined by a more detailed analysis, it shall be permitted to take the torsional loading from a slab as uniformly distributed along the beam. 9.4.4.2 For beams built integrally with supports, Tu at the support shall be permitted to be calculated at the face of support. 9.4.4.3 Sections between the face of support and a critical section located d from the face of support for nonprestressed beams or h/2 from the face of support for prestressed beams shall be permitted to be designed for Tu at that critical section unless a concentrated torsional moment occurs within this distance. In that case, the critical section shall be taken at the face of the support. V M R T T C C Beam ledge Critical section ∑Avfyt Fig. R9.4.3.2b—Location of critical section for shear in a EHDPORDGHGQHDUERWWRP Vu Vu d d d Vu Vu Vu d (c) (d) (e) (f) Fig. R9.4.3.2(c), (d), (e), (f)—Typical support conditions for locating factored shear force Vu. R9.4.4 Factored torsion R9.4.4.3 It is not uncommon for a beam to frame into one side of a girder near the support of the girder. In such a case, a concentrated shear and torsional moment are applied to the girder. American Concrete Institute – Copyrighted © Material – www.concrete.org 132 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 135. 9.4.4.4 It shall be permitted to reduce Tu in accordance with 22.7.3. 9.5—Design strength 9.5.1 General 9.5.1.1 For each applicable factored load combination, GHVLJQVWUHQJWKDWDOOVHFWLRQVVKDOOVDWLVIࢥSn•U including D WKURXJK G ,QWHUDFWLRQ EHWZHHQ ORDG H൵HFWV VKDOO EH considered. D ࢥMn•Mu E ࢥVn•Vu F ࢥTn•Tu G ࢥPn•Pu ࢥ shall be determined in accordance with 21.2. 9.5.2 0RPHQW 9.5.2.1 If Pu 0.10fcƍAg, Mn shall be calculated in accor- dance with 22.3. 9.5.2.2 If Pu•fcƍAg, Mn shall be calculated in accor- dance with 22.4. 9.5.2.3 For prestressed beams, external tendons shall EHFRQVLGHUHGDVXQERQGHGWHQGRQVLQFDOFXODWLQJÀH[XUDO VWUHQJWKXQOHVVWKHH[WHUQDOWHQGRQVDUHH൵HFWLYHOERQGHG to the concrete along the entire length. 9.5.3 Shear 9.5.3.1 Vn shall be calculated in accordance with 22.5. 9.5.3.2 For composite concrete beams, horizontal shear strength Vnh shall be calculated in accordance with 16.4. 9.5.4 Torsion 9.5.4.1 If Tu ࢥTth, where Tth is given in 22.7, it shall EHSHUPLWWHGWRQHJOHFWWRUVLRQDOH൵HFWV7KHPLQLPXPUHLQ- forcement requirements of 9.6.4 and the detailing require- PHQWVRIDQGQHHGQRWEHVDWLV¿HG 9.5.4.2 Tn shall be calculated in accordance with 22.7. R9.5—Design strength R9.5.1 General R9.5.1.1 The design conditions 9.5.1.1(a) through (d) list the typical forces and moments that need to be considered. +RZHYHUWKHJHQHUDOFRQGLWLRQࢥSn•U indicates that all forces and moments that are relevant for a given structure need to be considered. R9.5.2 0RPHQW R9.5.2.2%HDPVUHVLVWLQJVLJQL¿FDQWD[LDOIRUFHVUHTXLUH FRQVLGHUDWLRQ RI WKH FRPELQHG H൵HFWV RI D[LDO IRUFHV DQG moments. These beams are not required to satisfy the provi- sions of Chapter 10, but are required to satisfy the additional UHTXLUHPHQWV IRU WLHV RU VSLUDOV GH¿QHG LQ 7DEOH )RU VOHQGHU EHDPV ZLWK VLJQL¿FDQW D[LDO ORDGV FRQVLGHU- DWLRQVKRXOGEHJLYHQWRVOHQGHUQHVVH൵HFWVDVUHTXLUHGIRU columns in 6.2.5. R9.5.4 Torsion American Concrete Institute – Copyrighted © Material – www.concrete.org VUHVLVWLQJ H FRPELQ ams are n , but are r WLHV RU VS DPV ZLW GEHJLYHQ mns in 6.2.5 calcula sha R alculated in a - R FRQVLG ions UHTXL 2.2 UDWLR ts. T Cha PHQW PART 3: MEMBERS 133 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 136. 9.5.4.3 Longitudinal and transverse reinforcement required for torsion shall be added to that required for the Vu, Mu, and Pu that act in combination with the torsion. 9.5.4.4 For prestressed beams, the total area of longitu- dinal reinforcement, As and Aps, at each section shall be designed to resist Mu at that section, plus an additional concentric longitudinal tensile force equal to AƐ fy, based on Tu at that section. 9.5.4.5 It shall be permitted to reduce the area of longi- WXGLQDOWRUVLRQDOUHLQIRUFHPHQWLQWKHÀH[XUDOFRPSUHVVLRQ R9.5.4.3 The requirements for torsional reinforcement and shear reinforcement are added and stirrups are provided to supply at least the total amount required. Because the reinforcement area AvIRUVKHDULVGH¿QHGLQWHUPVRIDOOWKH legs of a given stirrup while the reinforcement area At for WRUVLRQLVGH¿QHGLQWHUPVRIRQHOHJRQOWKHDGGLWLRQRI transverse reinforcement area is calculated as follows: Total 2 v t v t A A A s s s + ⎛ ⎞ = + ⎜ ⎟ ⎠ (R9.5.4.3) If a stirrup group has more than two legs for shear, only the legs adjacent to the sides of the beam are included in this VXPPDWLRQEHFDXVHWKHLQQHUOHJVZRXOGEHLQH൵HFWLYHIRU resisting torsion. The longitudinal reinforcement required for torsion is added at each section to the longitudinal reinforcement required for bending moment that acts concurrently with the torsion. The longitudinal reinforcement is then chosen for this sum, but should not be less than the amount required for the maximum bending moment at that section if this exceeds the moment acting concurrently with the torsion. If the maximum bending moment occurs at one section, such as midspan, while the maximum torsional moment occurs at another, such as the face of the support, the total longitudinal reinforce- ment required may be less than that obtained by adding the PD[LPXPÀH[XUDOUHLQIRUFHPHQWSOXVWKHPD[LPXPWRUVLRQDO reinforcement. In such a case, the required longitudinal rein- forcement is evaluated at several locations. R9.5.4.4 Torsion causes an axial tensile force in the longi- tudinal reinforcement balanced by the force in the diagonal concrete compression struts. In a nonprestressed beam, the tensile force must be resisted by longitudinal reinforcement having an axial tensile strength of AƐ fy. This reinforcement LVLQDGGLWLRQWRWKHUHTXLUHGÀH[XUDOUHLQIRUFHPHQWDQGLV distributed uniformly inside and around the perimeter of the closed transverse reinforcement so that the resultant of AƐ fy acts along the axis of the member. In a prestressed beam, the same approach (providing additional reinforcing bars with strength AƐ fy) may be followed, or overstrength of the prestressed reinforcement can be used to resist some of the axial force AƐ fy. The stress in the prestressed reinforcement at nominal strength will be between fse and fps. A portion of the AƐ fy force can be resisted by a force of Aps¨fpt in the prestressed reinforce- ment. The stress required to resist the bending moment can be calculated as Mu/(ࢥ0.9dpAps). For pretensioned strands, the stress that can be developed near the free end of the strand can be calculated using the procedure illustrated in Fig. R25.4.8.3. R9.5.4.57KHORQJLWXGLQDOWHQVLRQGXHWRWRUVLRQLVR൵VHW LQSDUWEWKHFRPSUHVVLRQLQWKHÀH[XUDOFRPSUHVVLRQ]RQH American Concrete Institute – Copyrighted © Material – www.concrete.org oncurrently occurs at torsional upport, t be less t UHLQIRUFH u In such a s evaluated R9 5 require torsion. The long but should not b ending mom bend while ment r PD[L mo e m face quir XPÀ um b t acti ent nt 134 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 137. zone by an amount equal to Mu/(0.9dfy), where Mu occurs simultaneously with Tu at that section, except that the longitudinal reinforcement area shall not be less than the minimum required in 9.6.4. 9.5.4.6 For solid sections with an aspect ratio h/bt•, it shall be permitted to use an alternative design procedure, provided the adequacy of the procedure has been shown by analysis and substantial agreement with results of compre- hensive tests. The minimum reinforcement requirements of QHHGQRWEHVDWLV¿HGEXWWKHGHWDLOLQJUHTXLUHPHQWVRI 9.7.5 and 9.7.6.3 apply. 9.5.4.7 For solid precast sections with an aspect ratio h/bt •, it shall be permitted to use an alternative design proce- dure and open web reinforcement, provided the adequacy of the procedure and reinforcement have been shown by analysis and substantial agreement with results of compre- hensive tests. The minimum reinforcement requirements of 9.6.4 and detailing requirements of 9.7.5 and 9.7.6.3 need QRWEHVDWLV¿HG 9.6—Reinforcement limits 9.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG EHDPV 9.6.1.1$PLQLPXPDUHDRIÀH[XUDOUHLQIRUFHPHQWAs,min, shall be provided at every section where tension reinforce- ment is required by analysis. 9.6.1.2 As,min shall be the larger of (a) and (b), except as provided in 9.6.1.3. For a statically determinate beam with DÀDQJHLQWHQVLRQWKHYDOXHRIbw shall be the smaller of bf and 2bw. The value of fy shall be limited to a maximum of 80,000 psi. (a) 3 c w y f b d f ′ allowing a reduction in the longitudinal torsional reinforce- ment required in the compression zone. R9.5.4.6$QH[DPSOHRIDQDOWHUQDWLYHGHVLJQWKDWVDWLV¿HV this provision can be found in Zia and Hsu (2004), which has been extensively and successfully used for design of precast, prestressed concrete spandrel beams with h/bt• and closed stirrups. The seventh edition of the PCI Design Handbook (PCI MNL-120) describes the procedure of Zia and Hsu 7KLVSURFHGXUHZDVH[SHULPHQWDOOYHUL¿HGEWKH tests described in Klein (1986). R9.5.4.7 The experimental results described in Lucier et al. (2011a) demonstrate that properly designed open web UHLQIRUFHPHQWLVDVDIHDQGH൵HFWLYHDOWHUQDWLYHWRWUDGLWLRQDO closed stirrups for precast spandrels with h/bt•. Lucier et al. (2011b) SUHVHQWVDGHVLJQSURFHGXUHWKDWVDWLV¿HVWKLV provision for slender spandrels and describes the limited conditions to which the procedure applies. R9.6—Reinforcement limits R9.6.1 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHG EHDPV R9.6.1.17KLVSURYLVLRQLVLQWHQGHGWRUHVXOWLQÀH[XUDO strength exceeding the cracking strength by a margin. The objective is to produce a beam that will be able to sustain ORDGLQJ DIWHU WKH RQVHW RI ÀH[XUDO FUDFNLQJ ZLWK YLVLEOH FUDFNLQJDQGGHÀHFWLRQWKHUHEZDUQLQJRISRVVLEOHRYHU- load. Beams with less reinforcement may sustain sudden IDLOXUHZLWKWKHRQVHWRIÀH[XUDOFUDFNLQJ In practice, this provision only controls reinforcement design for beams which, for architectural or other reasons, are larger in cross section than required for strength. With a small amount of tension reinforcement required for strength, the calculated moment strength of a reinforced concrete section using cracked section analysis becomes less than that of the corresponding unreinforced concrete section calculated from its modulus of rupture. Failure in such a case FRXOGRFFXUDW¿UVWFUDFNLQJDQGZLWKRXWZDUQLQJ7RSUHYHQW such a failure, a minimum amount of tension reinforcement is required in both positive and negative moment regions. R9.6.1.2,IWKHÀDQJHRIDVHFWLRQLVLQWHQVLRQWKHDPRXQW of tension reinforcement needed to make the strength of the reinforced section equal that of the unreinforced section is approximately twice that for a rectangular section or that of DÀDQJHGVHFWLRQZLWKWKHÀDQJHLQFRPSUHVVLRQ$ODUJHU amount of minimum tension reinforcement is particularly necessary in cantilevers and other statically determinate beams where there is no possibility for redistribution of moments. American Concrete Institute – Copyrighted © Material – www.concrete.org ement lim ÀH[XUDOU SURYLVLRQ GLQJ ding the s to produc DIWHU WK FUDFNLQJ ompre requirements of 7.5 and IRU [X et al. ( provision for sl tions to which th QWLQQRQSUHVWU HLQIRUFHPHQW A i G VHG , R9. R9. R9 Rei 1 0 1.1 PART 3: MEMBERS 135 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 138. (b) 200 w y b d f 9.6.1.3 If As provided at every section is at least one-third greater than As required by analysis, 9.6.1.1 and 9.6.1.2 need QRWEHVDWLV¿HG 9.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGEHDPV 9.6.2.1 For beams with bonded prestressed reinforcement, total quantity of As and Aps shall be adequate to develop a factored load at least 1.2 times the cracking load calculated on the basis of frGH¿QHGLQ19.2.3. 9.6.2.2 )RU EHDPV ZLWK ERWK ÀH[XUDO DQG VKHDU GHVLJQ strength at least twice the required strength, 9.6.2.1 need not EHVDWLV¿HG 9.6.2.3 For beams with unbonded tendons, the minimum area of bonded deformed longitudinal reinforcement As,min shall be: AVPLQ = 0.004Act (9.6.2.3) where Act is the area of that part of the cross section between WKHÀH[XUDOWHQVLRQIDFHDQGWKHFHQWURLGRIWKHJURVVVHFWLRQ 9.6.3 0LQLPXPVKHDUUHLQIRUFHPHQW 9.6.3.1 For nonprestressed beams, minimum area of shear reinforcement, Av,min, shall be provided in all regions where Vu ࢥȜ ′ c f bwd except for the cases in Table 9.6.3.1. For these cases, at least Av,min shall be provided where Vu ࢥVc. Table 9.6.3.1—Cases where Av,min is not required if Vu ≤ ࢥVc Beam type Conditions Shallow depth h”LQ Integral with slab h”JUHDWHURItf or 0.5bw and h”LQ RQVWUXFWHGZLWKVWHHO¿EHUUHLQIRUFHG normalweight concrete conforming to 26.4.1.5.1(a), 26.4.2.2(i), and 26.12.7.1(a) and with fcƍ”SVL h”LQ and 2 u c w V f b d ≤ φ ′ One-way joist system In accordance with 9.8 R9.6.2 0LQLPXPÀH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGEHDPV R9.6.2.1 0LQLPXP ÀH[XUDO UHLQIRUFHPHQW LV UHTXLUHG for reasons similar to nonprestressed beams as discussed in R9.6.1.1. $EUXSW ÀH[XUDO IDLOXUH LPPHGLDWHO DIWHU FUDFNLQJ GRHV not occur when the prestressed reinforcement is unbonded (ACI 423.3R); therefore, this requirement does not apply to members with unbonded tendons. R9.6.2.3 Minimum bonded reinforcement is required by the Code in beams prestressed with unbonded tendons to HQVXUH ÀH[XUDO EHKDYLRU DW XOWLPDWH EHDP VWUHQJWK UDWKHU than tied arch behavior, and to limit crack width and spacing at service load when concrete tensile stresses exceed the modulus of rupture. Providing minimum bonded reinforce- ment helps to ensure acceptable behavior at all loading stages. The minimum amount of bonded reinforcement is based on research comparing the behavior of bonded and unbonded post-tensioned beams (Mattock et al. 1971). The minimum bonded reinforcement area required by Eq. (9.6.2.3) is independent of reinforcement fy. R9.6.3 0LQLPXPVKHDUUHLQIRUFHPHQW R9.6.3.1 Shear reinforcement restrains the growth of inclined cracking so that ductility of the beam is improved and a warning of failure is provided. In an unreinforced web, the formation of inclined cracking might lead directly to failure without warning. Such reinforcement is of great value if a beam is subjected to an unexpected tensile force or an overload. 7KH H[FHSWLRQ IRU EHDPV FRQVWUXFWHG XVLQJ VWHHO ¿EHU reinforced concrete is intended to provide a design alterna- WLYHWRWKHXVHRIVKHDUUHLQIRUFHPHQWDVGH¿QHGLQ22.5.8.5, IRUEHDPVZLWKORQJLWXGLQDOÀH[XUDOUHLQIRUFHPHQWLQZKLFK Vu does not exceed ࢥ ′ c f bwdKDSWHUVSHFL¿HVGHVLJQ information and compliance requirements that need to be incorporated into the construction documents when steel ¿EHUUHLQIRUFHG FRQFUHWH LV XVHG IRU WKLV SXUSRVH )LEHU reinforced concrete beams with hooked or crimped steel ¿EHUV LQ GRVDJHV DV UHTXLUHG E 26.4.2.2(i), have been shown through laboratory tests to exhibit shear strengths American Concrete Institute – Copyrighted © Material – www.concrete.org imum bond ms prestres DYLRU DW ior, and t en concr re. Provid ensure e minimum ed on researc unbond GHVLJQ 9.6.2.1 need not ded tud 00 th einforcement A (9.6 in 2.3) the HQVXU t ser modu de in ÀH[X d arc ce l s of 2.3 136 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 139. greater than 3.5 ′ c f bwd (Parra-Montesinos 2006). There DUHQRGDWDIRUWKHXVHRIVWHHO¿EHUVDVVKHDUUHLQIRUFHPHQW in concrete beams exposed to chlorides from deicing chemi- cals, salt, salt water, brackish water, seawater, or spray from WKHVHVRXUFHV:KHUHVWHHO¿EHUVDUHXVHGDVVKHDUUHLQIRUFH- ment in corrosive environments, corrosion protection should be considered. Joists are excluded from the minimum shear reinforce- ment requirement as indicated because there is a possibility of load sharing between weak and strong areas. Even when Vu is less thanࢥȜ ′ c f bwd, the use of some web reinforcement is recommended in all thin-web, post- WHQVLRQHG PHPEHUV VXFK DV MRLVWV ZD൷H VODEV EHDPV and T-beams, to reinforce against tensile forces in webs resulting from local deviations from the design tendon SUR¿OHDQGWRSURYLGHDPHDQVRIVXSSRUWLQJWKHWHQGRQVLQ WKHGHVLJQSUR¿OHGXULQJFRQVWUXFWLRQ,IVX൶FLHQWVXSSRUW is not provided, lateral wobble and local deviations from WKHVPRRWKSDUDEROLFWHQGRQSUR¿OHDVVXPHGLQGHVLJQPD result during placement of the concrete. In such cases, the deviations in the tendons tend to straighten out when the tendons are stressed. This process may impose large tensile stresses in webs, and severe cracking may develop if no web reinforcement is provided. Unintended curvature of the tendons, and the resulting tensile stresses in webs, may be minimized by securely tying tendons to stirrups that are rigidly held in place by other elements of the reinforcement cage. The recommended maximum spacing of stirrups used for this purpose is the smaller of 1.5h or 4 ft. If applicable, the shear reinforcement provisions of 9.6.3 and 9.7.6.2.2 will require closer stirrup spacings. For repeated loading of beams, the possibility of inclined diagonal tension cracks forming at stresses appreciably smaller than under static loading should be taken into account in design. In these instances, use of at least the minimum shear reinforcement expressed by 9.6.3.4 is recommended even though tests or calculations based on static loads show that shear reinforcement is not required. R9.6.3.3 When a beam is tested to demonstrate that its VKHDUDQGÀH[XUDOVWUHQJWKVDUHDGHTXDWHWKHDFWXDOEHDP dimensions and material strengths are known. Therefore, the test strengths are considered the nominal strengths Vn and Mn. Considering these strengths as nominal values ensures WKDWLIWKHDFWXDOPDWHULDOVWUHQJWKVLQWKH¿HOGZHUHOHVVWKDQ VSHFL¿HGRUWKHPHPEHUGLPHQVLRQVZHUHLQHUURUVXFKDVWR result in a reduced member strength, a satisfactory margin of VDIHWZLOOEHUHWDLQHGGXHWRWKHVWUHQJWKUHGXFWLRQIDFWRUࢥ 9.6.3.2 For prestressed beams, a minimum area of shear reinforcement, Av,min, shall be provided in all regions where Vu 0.5ࢥVc except for the cases in Table 9.6.3.1. For these cases, at least Av,min shall be provided where Vu ࢥVc. 9.6.3.3 If shown by testing that the required Mn and Vn FDQEHGHYHORSHGDQGQHHGQRWEHVDWLV¿HG 6XFKWHVWVVKDOOVLPXODWHH൵HFWVRIGL൵HUHQWLDOVHWWOHPHQW creep, shrinkage, and temperature change, based on a real- LVWLFDVVHVVPHQWRIWKHVHH൵HFWVRFFXUULQJLQVHUYLFH American Concrete Institute – Copyrighted © Material – www.concrete.org ssed. This p and sever is provi e resultin ecurely ty ace by oth mmended rpose is the shear reinfo will req is not WKHVPRRWKSDUD during placeme n the tendon stres web r be mi rigid in nfor dons miz held ns i are s t s PART 3: MEMBERS 137 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 140. R9.6.3.4 Tests (Roller and Russell 1990) have indicated the need to increase the minimum area of shear reinforce- ment as the concrete strength increases to prevent sudden shear failures when inclined cracking occurs. Therefore, expressions (a) and (c) in Table 9.6.3.4 provide for a gradual increase in the minimum area of transverse reinforcement with increasing concrete strength. Expressions (b) and (d) in Table 9.6.3.4 provide for a minimum area of transverse reinforcement independent of concrete strength and govern for concrete strengths less than 4400 psi. Tests(Olesenetal.1967)ofprestressedbeamswithminimum web reinforcement based on 9.6.3.4 indicate that the lesser of Av,minIURPH[SUHVVLRQV F DQG H LVVX൶FLHQWWRGHYHORSGXFWLOH behavior. Expression (e) is discussed in Olesen et al. (1967). R9.6.4 0LQLPXPWRUVLRQDOUHLQIRUFHPHQW R9.6.4.2 7KH GL൵HUHQFHV LQ WKH GH¿QLWLRQV RI Av and At should be noted: Av is the area of two legs of a closed stirrup, whereas At is the area of only one leg of a closed stirrup. If a stirrup group has more than two legs, only the legs adjacent to the sides of the beam are considered, as discussed in R9.5.4.3. Tests (Roller and Russell 1990) of high-strength rein- forced concrete beams have indicated the need to increase the minimum area of shear reinforcement to prevent shear failures when inclined cracking occurs. Although there are a limited number of tests of high-strength concrete beams in torsion, the equation for the minimum area of transverse closed stirrups has been made consistent with calculations required for minimum shear reinforcement. R9.6.4.3 Under combined torsion and shear, the torsional cracking moment decreases with applied shear, which leads to a reduction in torsional reinforcement required to prevent brittle failure immediately after cracking. When subjected to pure torsion, reinforced concrete beam specimens with less than 1 percent torsional reinforcement by volume have IDLOHGDW¿UVWWRUVLRQDOFUDFNLQJ MacGregor and Ghoneim 1995). Equation 9.6.4.3(a) is based on a 2:1 ratio of torsion stress to shear stress and results in a torsional reinforce- ment volumetric ratio of approximately 0.5 percent (Hsu 1968). Tests of prestressed concrete beams have shown that a similar amount of longitudinal reinforcement is required. 9.6.3.4 If shear reinforcement is required and torsional H൵HFWVFDQEHQHJOHFWHGDFFRUGLQJWRAv,min shall be in accordance with Table 9.6.3.4. Table 9.6.3.4—Required Av,min Beam type Av,min/s Nonprestressed and prestressed with Aps fse 0.4(Aps fpu + As fy) Greater of: 0.75 w c yt b f f ′ (a) 50 w yt b f (b) Prestressed with Aps fse• 0.4(Aps fpu + As fy) Lesser of: Greater of: 0.75 w c yt b f f ′ (c) 50 w yt b f (d) 80 ps pu yt w A f d f d b (e) 9.6.4 0LQLPXPWRUVLRQDOUHLQIRUFHPHQW 9.6.4.1 A minimum area of torsional reinforcement shall be provided in all regions where Tu •ࢥTth in accordance with 22.7. 9.6.4.2 If torsional reinforcement is required, minimum transverse reinforcement (Av + 2At)min/s shall be the greater of (a) and (b): (a) 0.75 w c yt b f f ′ (b) 50 w yt b f 9.6.4.3 If torsional reinforcement is required, minimum area of longitudinal reinforcement AƐPLQ shall be the lesser of (a) and (b): (a) 5 c cp yt t h y y f A f A p f s f ′ ⎛ ⎞ − ⎜ ⎟ ⎝ ⎠ (b) 5 25 c cp yt w h y yt y f A f b p f f f ⎛ ⎞ ′ − ⎜ ⎟ ⎝ ⎠ American Concrete Institute – Copyrighted © Material – www.concrete.org XPWRUVLRQ GL൵HUHQ oted: Av is v eas At is the t stirrup g yt w fy d bw (e) RUFHP tor er t reinforcement •ࢥT cord i d hall nce 4 0 138 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 141. R9.7—Reinforcement detailing R9.7.2 5HLQIRUFHPHQWVSDFLQJ R9.7.2.3 For relatively deep beams, some reinforcement should be placed near the vertical faces of the tension zone to control cracking in the web (Frantz and Breen 1980; Frosch 2002), as shown in Fig. R9.7.2.3. Without such auxil- iary reinforcement, the width of the cracks in the web may H[FHHGWKHFUDFNZLGWKVDWWKHOHYHORIWKHÀH[XUDOWHQVLRQ reinforcement. 7KH VL]H RI WKH VNLQ UHLQIRUFHPHQW LV QRW VSHFL¿HG research has indicated that the spacing rather than bar size is of primary importance (Frosch 2002). Bar sizes No. 3 to No. 5, or welded wire reinforcement with a minimum area of 0.1 in.2 per foot of depth, are typically provided. 9.7—Reinforcement detailing 9.7.1 General 9.7.1.1 Concrete cover for reinforcement shall be in accor- dance with 20.5.1. 9.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4. 9.7.1.3 Splices of deformed reinforcement shall be in accordance with 25.5. 9.7.1.4Along development and lap splice lengths of longi- tudinal bars with fy•SVL, transverse reinforcement shall be provided such that Ktr shall not be smaller than 0.5db. 9.7.1.5 Bundled bars shall be in accordance with 25.6. 9.7.2 5HLQIRUFHPHQWVSDFLQJ 9.7.2.1 Minimum spacing s shall be in accordance with 25.2. 9.7.2.2 For nonprestressed and Class C prestressed beams, spacing of bonded longitudinal reinforcement closest to the tension face shall not exceed s given in 24.3. 9.7.2.3 For nonprestressed and Class C prestressed beams with h exceeding 36 in., longitudinal skin reinforcement shall be uniformly distributed on both side faces of the beam for a distance h/2 from the tension face. Spacing of skin rein- forcement shall not exceed s given in 24.3.2, where cc is the clear cover from the skin reinforcement to the side face. It shall be permitted to include skin reinforcement in strength calculations if a strain compatibility analysis is made. American Concrete Institute – Copyrighted © Material – www.concrete.org atively de near the v cking in 2), as show reinforceme H[FHHG It R accordan Clas rei giv d tud t ment closest t 24.3. C prestressed b skin reinforce R9. shou he ams nt 2.3 be p PART 3: MEMBERS 139 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 142. h s s s s h/2 h/2 h s s s s Skin reinforcement Reinforcement in tension, positive bending Reinforcement in tension, negative bending Skin reinforcement Fig. R9.7.2.3²6NLQUHLQIRUFHPHQWIRUEHDPVDQGMRLVWVZLWK h 36 in. R9.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGEHDPV R9.7.3.2 In Codes before 2014, one of the critical sections ZDV GH¿QHG DV WKH ORFDWLRQ ZKHUH DGMDFHQW UHLQIRUFHPHQW terminates or is bent. In the 2014 Code, this critical section is UHGH¿QHGDVWKHORFDWLRQ³ZKHUHEHQWRUWHUPLQDWHGWHQVLRQ UHLQIRUFHPHQWLVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUH´ Critical sections for a typical continuous beam are indi- cated with a “c” for points of maximum stress or an “x” for points where bent or terminated tension reinforcement LVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUH )LJ5 )RU uniform loading, the positive reinforcement extending into the support is more likely governed by the requirements of 9.7.3.8.1 or 9.7.3.8.3 than by development length measured IURPDSRLQWRIPD[LPXPPRPHQWRUWKHEDUFXWR൵SRLQW. 9.7.3 )OH[XUDOUHLQIRUFHPHQWLQQRQSUHVWUHVVHGEHDPV 9.7.3.1 Calculated tensile or compressive force in rein- forcement at each section of the beam shall be developed on each side of that section. 9.7.3.2 Critical locations for development of reinforce- ment are points of maximum stress and points along the span where bent or terminated tension reinforcement is no longer UHTXLUHGWRUHVLVWÀH[XUH American Concrete Institute – Copyrighted © Material – www.concrete.org des before WKH ORF or is bent. I ¿QHGDVWKH UHLQIRUF Fig. R9 h 36 in. H[XUDO UHLQIR RQSUH co e b de sive force in hall be develope pment of reinf l R9 - on e- 3.2 3 )O UFH FH 140 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 143. R9.7.3.3 The moment diagrams customarily used in design are approximate; some shifting of the location of maximum moments may occur due to changes in loading, settlement of supports, lateral loads, or other causes. A diagonal tension FUDFNLQDÀH[XUDOPHPEHUZLWKRXWVWLUUXSVPDVKLIWWKH location of the calculated tensile stress approximately a distance d toward a point of zero moment. If stirrups are SURYLGHGWKLVH൵HFWLVOHVVVHYHUHDOWKRXJKVWLOOSUHVHQWWR some extent. To provide for shifts in the location of maximum moments, the Code requires the extension of reinforcement a distance d or 12db beyond the point at which it is calculated to be QRORQJHUUHTXLUHGWRUHVLVWÀH[XUHH[FHSWDVQRWHGXWR൵ points of bars to meet this requirement are illustrated in )LJ5,IGL൵HUHQWEDUVL]HVDUHXVHGWKHH[WHQVLRQ should be in accordance with the diameter of the bar being terminated. 9.7.3.3 Reinforcement shall extend beyond the point at ZKLFKLWLVQRORQJHUUHTXLUHGWRUHVLVWÀH[XUHIRUDGLVWDQFH equal to the greater of d and 12db, except at supports of simply-supported spans and at free ends of cantilevers. Section 25.4.2.1, or 9.7.3.8, or dc for compression when bottom bars used as compression reinforcement Bars a c x c x c x c x Bars b ≥ (d or 12db) ≥ d ≥ (d or 12db) ≥ d P.I. Diameter of bars a limited by Section 9.7.3.8.3 at point of inflection Points of inflection (P.I.) Moment strength of bars b Moment strength of bars a Face of support Embedment of bars a ≥ d ≥ d Mid-span of member ≥ (d, 12db or n /16) Moment Curve Fig. R9.7.3.2²'HYHORSPHQWRIÀH[XUDOUHLQIRUFHPHQWLQDWSLFDOFRQWLQXRXVEHDP American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 141 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 144. R9.7.3.4 Local peak stresses exist in the remaining bars ZKHUHYHUDGMDFHQWEDUVDUHFXWR൵LQWHQVLRQUHJLRQV,Q)LJ R9.7.3.2, an “x” is used to indicate the point where termi- nated tension reinforcement is no longer required to resist ÀH[XUH ,I EDUV ZHUH FXW R൵ DW WKLV ORFDWLRQ WKH UHTXLUHG FXWR൵ SRLQW LV EHRQG ORFDWLRQ ³[´ LQ DFFRUGDQFH ZLWK 9.7.3.3), peak stresses in the continuing bars would reach fy at “x”. Therefore, the continuing reinforcement is required to have a full Ɛd extension as indicated. R9.7.3.5 Reduced shear strength and loss of ductility when EDUVDUHFXWR൵LQDWHQVLRQ]RQHDVLQ)LJ5KDYH EHHQUHSRUWHG7KHRGHGRHVQRWSHUPLWÀH[XUDOUHLQIRUFH- ment to be terminated in a tension zone unless additional FRQGLWLRQVDUHVDWLV¿HG)OH[XUDOFUDFNVWHQGWRRSHQDWORZ load levels wherever any reinforcement is terminated in a tension zone. If the stress in the continuing reinforcement and the shear strength are each near their limiting values, diagonal tension cracking tends to develop prematurely IURPWKHVHÀH[XUDOFUDFNV'LDJRQDOFUDFNVDUHOHVVOLNHO WR IRUP ZKHUH VKHDU VWUHVV LV ORZ D RU ÀH[XUDO reinforcement stress is low (9.7.3.5(b)). Diagonal cracks can be restrained by closely spaced stirrups (9.7.3.5(c)). These requirements are not intended to apply to tension splices that are covered by 25.5. R9.7.3.7Abar bent to the far face of a beam and continued WKHUHPDEHFRQVLGHUHGH൵HFWLYHLQVDWLVILQJWRWKH point where the bar crosses the mid-depth of the member. R9.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW R9.7.3.8.1 Positive moment reinforcement is extended into the support to provide for some shifting of the moments due to changes in loading, settlement of supports, and lateral loads. It also enhances structural integrity. For precast beams, tolerances and reinforcement cover should be considered to avoid bearing on plain concrete where reinforcement has been discontinued. R9.7.3.8.2 Development of the positive moment reinforce- ment at the support is required for beams that are part of the primary lateral-load-resisting system to provide ductility in the event of moment reversal. R9.7.3.8.3 The diameter of the positive moment tension reinforcement is limited to ensure that the bars are devel- oped in a length short enough such that the moment capacity 9.7.3.4 RQWLQXLQJ ÀH[XUDO WHQVLRQ UHLQIRUFHPHQW VKDOO have an embedment length at least Ɛd beyond the point where bent or terminated tension reinforcement is no longer UHTXLUHGWRUHVLVWÀH[XUH 9.7.3.5 Flexural tension reinforcement shall not be termi- QDWHGLQDWHQVLRQ]RQHXQOHVV D E RU F LVVDWLV¿HG (a) Vu” ࢥVnDWWKHFXWR൵SRLQW (b) For No. 11 bars and smaller, continuing reinforcement SURYLGHVGRXEOHWKHDUHDUHTXLUHGIRUÀH[XUHDWWKHFXWR൵ point and Vu” ࢥVn (c) Stirrup or hoop area in excess of that required for shear and torsion is provided along each terminated bar or wire over a distance 3/4dIURPWKHFXWR൵SRLQW([FHVVVWLUUXS or hoop area shall be at least 60bws/fyt. Spacing s shall not exceed d ȕb) 9.7.3.6 Adequate anchorage shall be provided for tension reinforcement where reinforcement stress is not directly proportional to moment, such as in sloped, stepped, or tapered beams, or where tension reinforcement is not parallel to the compression face. 9.7.3.7 Development of tension reinforcement by bending across the web to be anchored or made continuous with rein- forcement on the opposite face of beam shall be permitted. 9.7.3.8 7HUPLQDWLRQRIUHLQIRUFHPHQW 9.7.3.8.1 At simple supports, at least one-third of the maximum positive moment reinforcement shall extend along the beam bottom into the support at least 6 in., except for precast beams where such reinforcement shall extend at least to the center of the bearing length. 9.7.3.8.2 At other supports, at least one-fourth of the maximum positive moment reinforcement shall extend along the beam bottom into the support at least 6 in. and, if the beam is part of the primary lateral-load-resisting system, shall be anchored to develop fy at the face of the support. 9.7.3.8.3$WVLPSOHVXSSRUWVDQGSRLQWVRILQÀHFWLRQdb for positive moment tension reinforcement shall be limited such that ƐdIRUWKDWUHLQIRUFHPHQWVDWLV¿HV D RU E ,IUHLQ- American Concrete Institute – Copyrighted © Material – www.concrete.org y closely sp ot intende diagon IURPWKHVHÀH[X ZKHUH VKHD nt stress is lo or wire W([FHVVVWLUUXS yt f f . Spacin ha men provided for ten ress is not dir d requ are co ion ly ment ered eme aine w ( w 142 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 145. is greater than the applied moment over the entire length of the beam. As illustrated in the moment diagram of Fig. R9.7.3.8.3(a), the slope of the moment diagram is Vu, while the slope of moment development is Mn/Ɛd, where Mn is WKHQRPLQDOÀH[XUDOVWUHQJWKRIWKHFURVVVHFWLRQ%VL]LQJ the reinforcement such that the capacity slope Mn/Ɛd equals or exceeds the demand slope Vu, proper development is provided. Therefore, Mn/Vu represents the available devel- opment length. Under favorable support conditions, a 30 percent increase for Mn/Vu is permitted when the ends of the UHLQIRUFHPHQWDUHFRQ¿QHGEDFRPSUHVVLYHUHDFWLRQ The application of this provision is illustrated in Fig. R9.7.3.8.3(b) for simple supports and in Fig. R9.7.3.8.3(c) IRUSRLQWVRILQÀHFWLRQ)RUH[DPSOHWKHEDUVL]HSURYLGHG at a simple support is satisfactory only if the corresponding bar, Ɛd, calculated in accordance with 25.4.2, does not exceed 1.3Mn/Vu + Ɛa. The ƐaWREHXVHGDWSRLQWVRILQÀHFWLRQLVOLPLWHGWRWKH H൵HFWLYHGHSWKRIWKHPHPEHUd or 12 bar diameters (12db), whichever is greater. The Ɛa limitation is provided because test data are not available to show that a long end anchorage OHQJWKZLOOEHIXOOH൵HFWLYHLQGHYHORSLQJDEDUWKDWKDV RQODVKRUWOHQJWKEHWZHHQDSRLQWRILQÀHFWLRQDQGDSRLQW of maximum stress. forcement terminates beyond the centerline of supports by a standard hook or a mechanical anchorage at least equivalent WRDVWDQGDUGKRRN D RU E QHHGQRWEHVDWLV¿HG (a) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVFRQ¿QHG by a compressive reaction (b) Ɛd” Mn/Vu + Ɛa)LIHQGRIUHLQIRUFHPHQWLVQRWFRQ¿QHG by a compressive reaction Mn is calculated assuming all reinforcement at the section is stressed to fy, and Vu is calculated at the section. At a support, Ɛa is the embedment length beyond the center of the support. $WDSRLQWRILQÀHFWLRQƐa is the embedment length beyond the SRLQWRILQÀHFWLRQOLPLWHGWRWKHJUHDWHURId and 12db. American Concrete Institute – Copyrighted © Material – www.concrete.org JWKEHWZHHQ s. H൵HFWLY whichever is gre ata are not avail EH IXOO H൵H of m mum ZLOO KRUW FWLY WL PART 3: MEMBERS 143 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 146. Vu Mn for reinforcement continuing into support Vu 1 d Max. d 1.3Mn /Vu End anchorage a Embedment length Max. d Mn /Vu Maximum effective embedment length limited to d or 12db for a Note: The 1.3 factor is applicable only if the reaction confines the ends of the reinforcement Capacity slope Mn d ( )≥ Demand slope (Vu ) d Mn Vu ≤ (a) Positive Mu Diagram (b) Maximum d at simple support (c) Maximum d for bars “a” at point of inflection Bars a P.I. Fig. R9.7.3.8.3²'HWHUPLQDWLRQ RI PD[LPXP EDU VL]H DFFRUGLQJWR 9.7.3.8.4 At least one-third of the negative moment rein- forcement at a support shall have an embedment length EHRQGWKHSRLQWRILQÀHFWLRQDWOHDVWWKHJUHDWHVWRId, 12db, and Ɛn/16. American Concrete Institute – Copyrighted © Material – www.concrete.org 144 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 147. R9.7.4 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGEHDPV R9.7.4.1 External tendons are often attached to the concrete beam at various locations between anchorages, such as midspan, quarter points, or third points, for desired ORDGEDODQFLQJH൵HFWVIRUWHQGRQDOLJQPHQWRUWRDGGUHVV tendon vibration concerns. Consideration should be given to WKHH൵HFWVFDXVHGEWKHWHQGRQSUR¿OHVKLIWLQJLQUHODWLRQ- ship to the concrete centroid as the member deforms under H൵HFWVRISRVWWHQVLRQLQJDQGDSSOLHGORDG R9.7.4.2 Nonprestressed reinforcement should be devel- oped to achieve factored load forces. The requirements of SURYLGHWKDWERQGHGUHLQIRUFHPHQWUHTXLUHGIRUÀH[- ural strength under factored loads is developed to achieve tensile or compressive forces. R9.7.4.4 7HUPLQDWLRQRIGHIRUPHGUHLQIRUFHPHQWLQEHDPV with unbonded tendons R9.7.4.4.1 The minimum lengths apply for bonded rein- forcement required by 9.6.2.3. Research (Odello and Mehta 1967) on continuous spans shows that these minimum lengths provide satisfactory behavior under service load and factored load conditions. R9.7.5 /RQJLWXGLQDOWRUVLRQDOUHLQIRUFHPHQW R9.7.5.1 Longitudinal reinforcement is needed to resist the sum of the longitudinal tensile forces due to torsion. Because the force acts along the centroidal axis of the section, the centroid of the additional longitudinal reinforcement for torsion should approximately coincide with the centroid of the section. The Code accomplishes this by requiring the longitudinal torsional reinforcement be distributed around the perimeter of the closed stirrups. Longitudinal bars or tendons are required in each corner of the stirrups to provide anchorage for the stirrup legs. Corner bars have also been IRXQGWREHH൵HFWLYHLQGHYHORSLQJWRUVLRQDOVWUHQJWKDQG controlling cracks. 9.7.4 )OH[XUDOUHLQIRUFHPHQWLQSUHVWUHVVHGEHDPV 9.7.4.1 External tendons shall be attached to the member LQDPDQQHUWKDWPDLQWDLQVWKHVSHFL¿HGHFFHQWULFLWEHWZHHQ the tendons and the concrete centroid through the full range RIDQWLFLSDWHGPHPEHUGHÀHFWLRQV 9.7.4.2 If nonprestressed reinforcement is required to VDWLVIÀH[XUDOVWUHQJWKWKHGHWDLOLQJUHTXLUHPHQWVRI VKDOOEHVDWLV¿HG 9.7.4.3 7HUPLQDWLRQRISUHVWUHVVHGUHLQIRUFHPHQW 9.7.4.3.1 Post-tensioned anchorage zones shall be designed and detailed in accordance with 25.9. 9.7.4.3.2 Post-tensioning anchorages and couplers shall be designed and detailed in accordance with 25.8. 9.7.4.4 7HUPLQDWLRQRIGHIRUPHGUHLQIRUFHPHQWLQEHDPV with unbonded tendons 9.7.4.4.1 Length of deformed reinforcement required by 9.6.2.3 shall be in accordance with (a) and (b): (a) At least Ɛn/3 in positive moment areas and be centered in those areas (b) At least Ɛn/6 on each side of the face of support in negative moment areas 9.7.5 /RQJLWXGLQDOWRUVLRQDOUHLQIRUFHPHQW 9.7.5.1 If torsional reinforcement is required, longitu- dinal torsional reinforcement shall be distributed around the perimeter of closed stirrups that satisfy 25.7.1.6 or hoops with a spacing not greater than 12 in. The longitudinal rein- forcement shall be inside the stirrup or hoop, and at least one longitudinal bar or tendon shall be placed in each corner. 9.7.5.2 Longitudinal torsional reinforcement shall have a diameter at least 0.042 times the transverse reinforcement VSDFLQJEXWQRWOHVVWKDQLQ American Concrete Institute – Copyrighted © Material – www.concrete.org WLRQRIGH dons he minim required by 7) on contin lengths ed ones shall be ith 25.9 orage anc P i 25.8. QIRUFHPHQWLQE with u DPV 4.4 bond PART 3: MEMBERS 145 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 148. R9.7.5.3 The distance (bt + d) beyond the point at which longitudinal torsional reinforcement is calculated to be no ORQJHUUHTXLUHGLVJUHDWHUWKDQWKDWXVHGIRUVKHDUDQGÀH[- ural reinforcement because torsional diagonal tension cracks develop in a helical form. The same distance is required by 9.7.6.3.2 for transverse torsional reinforcement. R9.7.5.4 Longitudinal torsional reinforcement required at a support should be adequately anchored into the support. 6X൶FLHQW HPEHGPHQW OHQJWK VKRXOG EH SURYLGHG RXWVLGH the inner face of the support to develop the needed tensile force in the bars or tendons. For bars, this may require hooks or horizontal U-shaped bars lapped with the longitudinal torsional reinforcement. R9.7.6 7UDQVYHUVHUHLQIRUFHPHQW R9.7.6.2 Shear R9.7.6.2.1 If a reinforced concrete beam is cast mono- lithically with a supporting beam and intersects one or both VLGHIDFHVRIDVXSSRUWLQJEHDPWKHVR൶WRIWKHVXSSRUWLQJ beam may be subject to premature failure unless additional transverse reinforcement, commonly referred to as hanger reinforcement, is provided (Mattock and Shen 1992). The hanger reinforcement (Fig. R9.7.6.2.1), placed in addition to other transverse reinforcement, is provided to transfer shear from the end of the supported beam. Research indicates that if the bottom of the supported beam is at or above middepth of the supporting beam or if the factored shear transferred from the supported beam is less than ′ 3 c w f b d , hanger rein- forcement is not required. 9.7.5.3 Longitudinal torsional reinforcement shall extend for a distance of at least (bt + d) beyond the point required by analysis. 9.7.5.4 Longitudinal torsional reinforcement shall be developed at the face of the support at both ends of the beam. 9.7.6 7UDQVYHUVHUHLQIRUFHPHQW 9.7.6.1 General 9.7.6.1.1 Transverse reinforcement shall be in accordance with this section. The most restrictive requirements shall apply. 9.7.6.1.2 Details of transverse reinforcement shall be in accordance with 25.7. 9.7.6.2 Shear 9.7.6.2.1 If required, shear reinforcement shall be provided using stirrups, hoops, or longitudinal bent bars. American Concrete Institute – Copyrighted © Material – www.concrete.org a reinfo with a supp IDFHVRIDVX beam m e in accordance ve require e r cement shall h ll R9. n 6.2 146 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 149. d bw Supporting beam Hanger reinforcement Other transverse reinforcement not shown Supported beam Fig. R9.7.6.2.1²+DQJHUUHLQIRUFHPHQWIRUVKHDUWUDQVIHU R9.7.6.2.2 Reduced stirrup spacing across the beam width provides a more uniform transfer of diagonal compression across the beam web, enhancing shear capacity. Laboratory tests (Leonhardt and Walther 1964; Anderson and Ramirez 1989; Lubell et al. 2009) of wide members with large spacing of legs of shear reinforcement across the member width indi- cate that the nominal shear capacity is not always achieved. The intent of this provision is to provide multiple stirrup legs across wide beams and one-way slabs that require stirrups. R9.7.6.3 Torsion R9.7.6.3.1 The stirrups are required to be closed because inclined cracking due to torsion may occur on all faces of a member. In the case of sections subjected primarily to torsion, WKHFRQFUHWHVLGHFRYHURYHUWKHVWLUUXSVVSDOOVR൵DWKLJK torsional moments (Mitchell and Collins 1976). This renders ODSVSOLFHG VWLUUXSV LQH൵HFWLYH OHDGLQJ WR D SUHPDWXUH torsional failure (Behera and Rajagopalan 1969). Therefore, 9.7.6.2.2 Maximum spacing of legs of shear reinforce- ment along the length of the member and across the width of the member shall be in accordance with Table 9.7.6.2.2. Table 9.7.6.2.2—Maximum spacing of legs of shear reinforcement Required Vs Maximum s, in. Nonprestressed beam Prestressed beam Along length Across width Along length Across width 4 c w f b d ≤ ′ Lesser of: d d 3h 3h 24 in. 4 c w f b d ′ Lesser of: d d 3h 3h 12 in. 9.7.6.2.3 Inclined stirrups and longitudinal bars bent to act as shear reinforcement shall be spaced so that every 45-degree line, extending d/2 toward the reaction from mid- depth of member to longitudinal tension reinforcement, shall be crossed by at least one line of shear reinforcement. 9.7.6.2.4 Longitudinal bars bent to act as shear reinforce- ment, if extended into a region of tension, shall be contin- uous with longitudinal reinforcement and, if extended into a region of compression, shall be anchored d/2 beyond mid- depth of member. 9.7.6.3 Torsion 9.7.6.3.1 If required, transverse torsional reinforcement shall be closed stirrups satisfying 25.7.1.6 or hoops. American Concrete Institute – Copyrighted © Material – www.concrete.org minal shear rovision i and one-w across tests (Leonhard Lubell et al. 20 ear reinforce .2. g of leg mum ed A w Prestressed be A le Acr wid 3h 3h The across ss h ent o wide of sh t the men me PART 3: MEMBERS 147 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 150. closed stirrups should not be made up of pairs of U-stirrups lapping one another. R9.7.6.3.2 The distance (bt + d) beyond the point at which transverse torsional reinforcement is calculated to be no ORQJHUUHTXLUHGLVJUHDWHUWKDQWKDWXVHGIRUVKHDUDQGÀH[- ural reinforcement because torsional diagonal tension cracks develop in a helical form. The same distance is required by 9.7.5.3 for longitudinal torsional reinforcement. R9.7.6.3.3 Spacing of the transverse torsional reinforce- ment is limited to ensure development of the torsional strength of the beam, prevent excessive loss of torsional VWL൵QHVV DIWHU FUDFNLQJ DQG FRQWURO FUDFN ZLGWKV )RU D square cross section, the ph/8 limitation requires stirrups at approximately d/2, which corresponds to 9.7.6.2. R9.7.6.3.4 The transverse torsional reinforcement in a hollow section should be located in the outer half of the wall WKLFNQHVVH൵HFWLYHIRUWRUVLRQZKHUHWKHZDOOWKLFNQHVVFDQ be taken as Aoh/ph. R9.7.6.4 /DWHUDOVXSSRUWRIFRPSUHVVLRQUHLQIRUFHPHQW R9.7.6.4.1 Compression reinforcement in beams should be enclosed by transverse reinforcement to prevent buckling. R9.7.7 6WUXFWXUDOLQWHJULWUHLQIRUFHPHQWLQFDVWLQSODFH EHDPV 9.7.6.3.2 Transverse torsional reinforcement shall extend a distance of at least (bt + d) beyond the point required by analysis. 9.7.6.3.3 Spacing of transverse torsional reinforcement shall not exceed the lesser of ph/8 and 12 in. 9.7.6.3.4 For hollow sections, the distance from the centerline of the transverse torsional reinforcement to the inside face of the wall of the hollow section shall be at least 0.5Aoh/ph. 9.7.6.4 /DWHUDOVXSSRUWRIFRPSUHVVLRQUHLQIRUFHPHQW 9.7.6.4.1 Transverse reinforcement shall be provided throughout the distance where longitudinal compression reinforcement is required. Lateral support of longitudinal compression reinforcement shall be provided by closed stir- rups or hoops in accordance with 9.7.6.4.2 through 9.7.6.4.4. 9.7.6.4.2 Size of transverse reinforcement shall be at least (a) or (b). Deformed wire or welded wire reinforcement of equivalent area shall be permitted. (a) No. 3 for longitudinal bars No. 10 and smaller (b) No. 4 for longitudinal bars No. 11 and larger and for longitudinal bundled bars 9.7.6.4.3 Spacing of transverse reinforcement shall not exceed the least of (a) through (c): (a) 16db of longitudinal reinforcement (b) 48db of transverse reinforcement (c) Least dimension of beam 9.7.6.4.4 Longitudinal compression reinforcement shall be arranged such that every corner and alternate compres- sion bar shall be enclosed by the corner of the transverse reinforcement with an included angle of not more than 135 degrees, and no bar shall be farther than 6 in. clear on each side along the transverse reinforcement from such an enclosed bar. 9.7.7 6WUXFWXUDOLQWHJULWUHLQIRUFHPHQWLQFDVWLQSODFH EHDPV American Concrete Institute – Copyrighted © Material – www.concrete.org UDOVXSSRUW ression r verse rein of holl WKLFNQHVVH൵HFW en as Aoh/p / / h. the shall be at least SUHVV rce e era be 7 shall be prov tudinal compre pport of longitu vided by closed R9. ded ion inal ir- 6.4. osed 6.4 / 148 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 151. Experience has shown that the overall integrity of a struc- ture can be substantially enhanced by minor changes in detailing of reinforcement and connections. It is the intent of this section of the Code to improve the redundancy and ductility in structures so that in the event of damage to a major supporting element or an abnormal loading event, the resulting damage may be localized and the structure will have a higher probability of maintaining overall stability. With damage to a support, top reinforcement that is FRQWLQXRXVRYHUWKHVXSSRUWEXWQRWFRQ¿QHGEVWLUUXSV will tend to tear out of the concrete and will not provide the catenary action required to bridge the damaged support. By making a portion of the bottom reinforcement continuous, catenary action can be provided. If the depth of a continuous beam changes at a support, the bottom reinforcement in the deeper member should be terminated into the support with a standard hook or headed bar and the bottom reinforcement in the shallower member should be extended into and fully developed in the deeper member. R9.7.7.1 Requiring continuous top and bottom reinforce- ment in perimeter or spandrel beams provides a continuous tie around the structure. It is not the intent to require a tension tie of continuous reinforcement of constant size around the entire perimeter of a structure, but rather to require that one- KDOIRIWKHWRSÀH[XUDOUHLQIRUFHPHQWUHTXLUHGWRH[WHQGSDVW WKHSRLQWRILQÀHFWLRQEEHIXUWKHUH[WHQGHGDQG spliced at or near midspan as required by 9.7.7.5. Similarly, the bottom reinforcement required to extend into the support in 9.7.3.8.2 should be made continuous or spliced with bottom reinforcement from the adjacent span. At noncon- tinuous supports, the longitudinal reinforcement is anchored as required by 9.7.7.4. Figure R9.7.7.1 shows an example of a two-piece stirrup WKDW VDWLV¿HV WKH UHTXLUHPHQW RI 6HFWLRQV F DQG 9.7.7.2(b). The 90-degree hook of the cap tie is located on WKHVODEVLGHVRWKDWLWLVEHWWHUFRQ¿QHG3DLUVRI8VWLUUXSV ODSSLQJRQHDQRWKHUDVGH¿QHGLQ25.7.1.7 are not permitted in perimeter or spandrel beams. In the event of damage to the side concrete cover, the top longitudinal reinforcement may tend to tear out of the concrete and will not be adequately restrained by the exposed lap splice of the stirrup. Thus, the top longitudinal reinforcement will not provide the catenary action needed to bridge over a damaged region. Further, ODSSHG 8VWLUUXSV ZLOO QRW EH H൵HFWLYH DW KLJK WRUVLRQDO moments as discussed in R9.7.6.3.1. 9.7.7.1 For beams along the perimeter of the structure, structural integrity reinforcement shall be in accordance with (a) through (c): (a) At least one-quarter of the maximum positive moment reinforcement, but not less than two bars or strands, shall be continuous (b) At least one-sixth of the negative moment reinforce- ment at the support, but not less than two bars or strands, shall be continuous (c) Longitudinal structural integrity reinforcement shall be enclosed by closed stirrups in accordance with 25.7.1.6 or hoops along the clear span of the beam American Concrete Institute – Copyrighted © Material – www.concrete.org er or spand cture. It is n inforcem structur XUDOUHLQIR FWLRQE ear midsp reinforcem 9.7.3.8.2 sho bottom be should member. Requiring co rimete nt sh e m an mum positive mo bars or strands, tie a tie of KDOIR WKHS ment hall nd th ontin erim KHW QWRI 7.1 peri ntin nti PART 3: MEMBERS 149 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 152. Cap tie U stirrup with 135- degree hooks Fig. R9.7.7.1²([DPSOHRIDWZRSLHFHVWLUUXSWKDWFRPSOLHV ZLWKWKHUHTXLUHPHQWVRI F DQG E R9.7.7.2At noncontinuous supports, the longitudinal rein- forcement is anchored as required by 9.7.7.4. R9.7.7.1 provides an example of a two-piece stirrup that VDWLV¿HV E R9.7.7.3 In the case of walls providing vertical support, the longitudinal reinforcement should pass through or be anchored in the wall. 9.7.7.2 For other than perimeter beams, structural integ- rity reinforcement shall be in accordance with (a) or (b): (a) At least one-quarter of the maximum positive moment reinforcement, but not less than two bars or strands, shall be continuous. (b) Longitudinal reinforcement shall be enclosed by closed stirrups in accordance with 25.7.1.6 or hoops along the clear span of the beam. 9.7.7.3 Longitudinal structural integrity reinforcement shall pass through the region bounded by the longitudinal reinforcement of the column. 9.7.7.4 Longitudinal structural integrity reinforcement at noncontinuous supports shall be anchored to develop fy at the face of the support. 9.7.7.5 If splices are necessary in continuous structural integrity reinforcement, the reinforcement shall be spliced in accordance with (a) and (b): (a) Positive moment reinforcement shall be spliced at or near the support (b) Negative moment reinforcement shall be spliced at or near midspan 9.7.7.6 Splices shall be mechanical or welded in accor- dance with 25.5.7 or Class B tension lap splices in accor- dance with 25.5.2. American Concrete Institute – Copyrighted © Material – www.concrete.org oncontinuo ored as req s an exam Fig. R9.7.7.1²( KHUHTXLUHPHQWV er b cor e m an with (a) or (b mum positive mo bars or strands, forc R9. ment hall ent i 7.1 7.2A 150 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY
- 153. R9.8—Nonprestressed one-way joist systems R9.8.1 General The empirical limits established for nonprestressed rein- IRUFHG FRQFUHWH MRLVW ÀRRUV DUH EDVHG RQ VXFFHVVIXO SDVW performance of joist construction using standard joist forming systems. For prestressed joist construction, this section may be used as guide. R9.8.1.4 A limit on the maximum spacing of ribs is required because of the provisions permitting higher shear strengths and less concrete cover for the reinforcement for these relatively small, repetitive members. R9.8.1.57KLVLQFUHDVHLQVKHDUVWUHQJWKLVMXVWL¿HGRQWKH basis of: 1) satisfactory performance of joist construction GHVLJQHGZLWKKLJKHUFDOFXODWHGVKHDUVWUHQJWKVVSHFL¿HGLQ previous Codes which allowed comparable shear stresses; and 2) potential for redistribution of local overloads to adja- cent joists. 9.8—Nonprestressed one-way joist systems 9.8.1 General 9.8.1.1 Nonprestressed one-way joist construction consists of a monolithic combination of regularly spaced ribs and a top slab designed to span in one direction. 9.8.1.2 Width of ribs shall be at least 4 in. at any location along the depth. 9.8.1.3 Overall depth of ribs shall not exceed 3.5 times the minimum width. 9.8.1.4 Clear spacing between ribs shall not exceed 30 in. 9.8.1.5 Vc shall be permitted to be taken as 1.1 times the value calculated in 22.5. 9.8.1.6 For structural integrity, at least one bottom bar in each joist shall be continuous and shall be anchored to develop fy at the face of supports. 9.8.1.7 Reinforcement perpendicular to the ribs shall be SURYLGHG LQ WKH VODE DV UHTXLUHG IRU ÀH[XUH FRQVLGHULQJ load concentrations, and shall be at least that required for shrinkage and temperature in accordance with 24.4. 9.8.1.8 One-way joist construction not satisfying the limi- tations of 9.8.1.1 through 9.8.1.4 shall be designed as slabs and beams. 9.8.2 -RLVWVVWHPVZLWKVWUXFWXUDO¿OOHUV 9.8.2.1,ISHUPDQHQWEXUQHGFODRUFRQFUHWHWLOH¿OOHUVRI material having a unit compressive strength at least equal to fcƍ in the joists are used, 9.8.2.1.1 and 9.8.2.1.2 shall apply. 9.8.2.1.16ODEWKLFNQHVVRYHU¿OOHUVVKDOOEHDWOHDVWWKHJUHDWHU of one-twelfth the clear distance between ribs and 1.5 in. 9.8.2.1.2 For calculation of shear and negative moment strength, it shall be permitted to include the vertical shells of ¿OOHUVLQFRQWDFWZLWKWKHULEV2WKHUSRUWLRQVRI¿OOHUVVKDOO not be included in strength calculations. 9.8.3 -RLVWVVWHPVZLWKRWKHU¿OOHUV American Concrete Institute – Copyrighted © Material – www.concrete.org for redistri or R basis of: 1) sati QHGZLWKKLJKHU des which mes the ity us east one bottom shall be anchor cent bar d to sts. s Co poten llow lo PART 3: MEMBERS 151 CODE COMMENTARY 9 Beams
- 154. 9.8.3.1,I¿OOHUVQRWFRPSOLQJZLWKRUUHPRYDEOH forms are used, slab thickness shall be at least the greater of one-twelfth the clear distance between ribs and 2 in. 9.9—Deep beams 9.9.1 General 9.9.1.1 Deep beams are members that are loaded on one face and supported on the opposite face such that strut-like compression elements can develop between the loads and supports and that satisfy (a) or (b): (a) Clear span does not exceed four times the overall member depth h (b) Concentrated loads exist within a distance 2h from the face of the support 9.9.1.2 Deep beams shall be designed taking into account nonlinear distribution of longitudinal strain over the depth of the beam. 9.9.1.3 The strut-and-tie method in accordance with Chapter 23 is deemed to satisfy 9.9.1.2. 9.9.2 'LPHQVLRQDOOLPLWV 9.9.2.1 Except as permitted by 23.4.4, deep beam dimen- sions shall be selected such that: 10 u c w V f b d ≤ φ ′ (9.9.2.1) 9.9.3 5HLQIRUFHPHQWOLPLWV 9.9.3.1 Distributed reinforcement along the side faces of deep beams shall be at least that required in (a) and (b): (a) The area of distributed reinforcement perpendicular to the longitudinal axis of the beam, Av, shall be at least 0.0025bws, where s is the spacing of the distributed trans- verse reinforcement. (b) The area of distributed reinforcement parallel to the longitudinal axis of the beam, Avh, shall be at least 0.0025bws2, where s2 is the spacing of the distributed longitudinal reinforcement. 9.9.3.27KHPLQLPXPDUHDRIÀH[XUDOWHQVLRQUHLQIRUFH- ment, As,min, shall be determined in accordance with 9.6.1. 9.9.4 5HLQIRUFHPHQWGHWDLOLQJ 9.9.4.1 Concrete cover shall be in accordance with 20.5.1. R9.9—Deep beams R9.9.1 General R9.9.1.1 The behavior of deep beams is discussed in Schlaich et al. (1987), Rogowsky and MacGregor (1986), Marti (1985), and Crist (1966). For a deep beam supporting gravity loads, this provision applies if the loads are applied on the top of the beam and the beam is supported on its bottom face. If the loads are applied through the sides or bottom of such a member, the strut-and-tie method, as GH¿QHGLQChapter 23 should be used to design reinforce- ment to internally transfer the loads to the top of the beam and distribute them to adjacent supports. R9.9.1.2 The Code does not contain detailed requirements for designing deep beams for moment, except that a nonlinear straindistributionshouldbeconsidered.Guidanceforthedesign RIGHHSEHDPVIRUÀH[XUHLVJLYHQLQChow et al. (1953), Port- land Cement Association (1946), and Park and Paulay (1975). R9.9.2 'LPHQVLRQDOOLPLWV R9.9.2.1 This limit imposes a dimensional restriction to control cracking under service loads and to guard against diagonal compression failures in deep beams. R9.9.3 5HLQIRUFHPHQWOLPLWV R9.9.3.1 The minimum reinforcement requirements of this section are to be used irrespective of the method used for design and are intended to control the width and propa- gation of inclined cracks. Tests (Rogowsky and MacGregor 1986; Marti 1985; Crist 1966) have shown that vertical shear reinforcement, perpendicular to the longitudinal axis of the PHPEHULVPRUHH൵HFWLYHIRUPHPEHUVKHDUVWUHQJWKWKDQ horizontal shear reinforcement, parallel to the longitudinal D[LVRIWKHPHPEHULQDGHHSEHDPKRZHYHUWKHVSHFL¿HG minimum reinforcement is the same in both directions to control the growth and width of diagonal cracks. R9.9.4 5HLQIRUFHPHQWGHWDLOLQJ American Concrete Institute – Copyrighted © Material – www.concrete.org ociation (19 RQDOOLPL This limit trol cracking diagona ccount n over the depth met 9 R for designing dee distributionshou PV IRU ÀH[XUH in accordance . with R9 2 ' EHDP ment LV J V 152 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 155. 9.9.4.2 Minimum spacing for longitudinal reinforcement shall be in accordance with 25.2. 9.9.4.3 Spacing of distributed reinforcement required in 9.9.3.1 shall not exceed the lesser of d/5 and 12 in. 9.9.4.4 Development of tension reinforcement shall account for distribution of stress in reinforcement that is not directly proportional to the bending moment. 9.9.4.5 At simple supports, positive moment tension rein- forcement shall be anchored to develop fy at the face of the support. If a deep beam is designed using Chapter 23, the positive moment tension reinforcement shall be anchored in accordance with 23.8.2 and 23.8.3. 9.9.4.6$WLQWHULRUVXSSRUWV D DQG E VKDOOEHVDWLV¿HG (a) Negative moment tension reinforcement shall be continuous with that of the adjacent spans. (b) Positive moment tension reinforcement shall be continuous or spliced with that of the adjacent spans. R9.9.4.4 In deep beams, the stress in the longitudinal rein- forcement is more uniform along the length than that of a beam or region that is not deep. High reinforcement stresses normally limited to the center region of a typical beam can extend to the supports in deep beams. Thus, the ends of longitudinal reinforcement may require positive anchorage in the form of standard hooks, bar heads, or other mechan- ical anchorage at supports. R9.9.4.5 The use of the strut-and-tie method for the design of deep beams illustrates that tensile forces in the bottom tie reinforcement need to be anchored at the face of the support. From this consideration, tie reinforcement should be contin- uous or developed at the face of the support (Rogowsky and MacGregor 1986). American Concrete Institute – Copyrighted © Material – www.concrete.org ored in DQG on dja on at From uous or develope regor 1986). orcement sha spans. nforcement shal e adjacent spans be be PART 3: MEMBERS 153 CODE COMMENTARY 9 Beams Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 156. American Concrete Institute – Copyrighted © Material – www.concrete.org 154 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org 154 BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE (ACI 318-19) AND COMMENTARY (ACI 318R-19) Notes Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 157. R10.1—Scope R10.1.1 Composite structural steel-concrete columns are not covered in this chapter. Composite columns include both structural steel sections encased in reinforced concrete and KROORZVWUXFWXUDOVWHHOVHFWLRQV¿OOHGZLWKFRQFUHWH'HVLJQ provisions for such composite columns are covered in AISC 360. R10.3—Design limits R10.3.1 'LPHQVLRQDOOLPLWV ([SOLFLWPLQLPXPVL]HVIRUFROXPQVDUHQRWVSHFL¿HGWR permit the use of reinforced concrete columns with small cross sections in lightly loaded structures, such as low-rise UHVLGHQWLDODQGOLJKWR൶FHEXLOGLQJV,IVPDOOFURVVVHFWLRQV are used, there is a greater need for careful workmanship, DQGVKULQNDJHVWUHVVHVKDYHLQFUHDVHGVLJQL¿FDQFH R10.3.1.2 In some cases, the gross area of a column is larger than necessary to resist the factored load. In those cases, the minimum reinforcement percentage may be calculated on the basis of the required area rather than the provided area, but the area of reinforcement cannot be less than 0.5 percent of the actual cross-sectional area. 10.1—Scope 10.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed columns, including reinforced concrete pedestals. 10.1.2 Design of plain concrete pedestals shall be in accor- dance with Chapter 14. 10.2—General 10.2.1 Materials 10.2.1.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 10.2.1.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 10.2.1.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 10.2.2 RQQHFWLRQWRRWKHUPHPEHUV 10.2.2.1 For cast-in-place construction, beam-column and slab-column joints shall satisfy Chapter 15. 10.2.2.2 For precast construction, connections shall satisfy the force transfer requirements of 16.2. 10.2.2.3 Connections of columns to foundations shall satisfy 16.3. 10.3—Design limits 10.3.1 'LPHQVLRQDOOLPLWV 10.3.1.1 For columns with a square, octagonal, or other shaped cross section, it shall be permitted to base gross area considered, required reinforcement, and design strength on a circular section with a diameter equal to the least lateral dimension of the actual shape. 10.3.1.2 For columns with cross sections larger than required by considerations of loading, it shall be permitted to base gross area considered, required reinforcement, and GHVLJQ VWUHQJWK RQ D UHGXFHG H൵HFWLYH DUHD QRW OHVV WKDQ one-half the total area. This provision shall not apply to columns in special moment frames or columns not part of the seismic-force-resisting system required to be designed in accordance with Chapter 18. 10.3.1.3 For columns built monolithically with a concrete ZDOO WKH RXWHU OLPLWV RI WKH H൵HFWLYH FURVV VHFWLRQ RI WKH American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 155 CODE COMMENTARY 10 Columns all ling requ accor HPE ns Ch c on, beam-column r 15. and CHAPTER 10—COLUMNS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 158. R10.4—Required strength R10.4.2 )DFWRUHGD[LDOIRUFHDQGPRPHQW R10.4.2.17KHFULWLFDOORDGFRPELQDWLRQVPDEHGL൶FXOW to discern without methodically checking each combina- tion. As illustrated in Fig. R10.4.2.1, considering only the factored load combinations associated with maximum axial force (LC1) and with maximum bending moment (LC2) does not necessarily provide a code-compliant design for other load combinations such as LC3. column shall not be taken greater than 1.5 in. outside the transverse reinforcement. 10.3.1.4 For columns with two or more interlocking VSLUDOVRXWHUOLPLWVRIWKHH൵HFWLYHFURVVVHFWLRQVKDOOEH taken at a distance outside the spirals equal to the minimum required concrete cover. 10.3.1.5 ,IDUHGXFHGH൵HFWLYHDUHDLVFRQVLGHUHGDFFRUGLQJ to 10.3.1.1 through 10.3.1.4, structural analysis and design of other parts of the structure that interact with the column shall be based on the actual cross section. 10.4—Required strength 10.4.1 General 10.4.1.1 Required strength shall be calculated in accor- dance with the factored load combinations in Chapter 5. 10.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. 10.4.2 )DFWRUHGD[LDOIRUFHDQGPRPHQW 10.4.2.1 Pu and Mu occurring simultaneously for each applicable factored load combination shall be considered. American Concrete Institute – Copyrighted © Material – www.concrete.org 156 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY RUHGD[LDOI LWLFDOORDG methodi in Fig. R binations nd with ecessarily load combi ulated in accor- Chapter 6 GPR ng na ultaneously for hall be consider R10 ion. A facto f ach d. 4.2.1 ern illu d loa 4.2 ) Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 159. (ɸMn , ɸPn ) LC1 LC2 LC3 Acceptable region Axial load, P Mumax Mu1 Mu3 Moment, M P0 Pumax Pu3 Pu2 (Mn, Pn) Fig. R10.4.2.1²ULWLFDOFROXPQORDGFRPELQDWLRQ R10.5—Design strength R10.5.1 General R10.5.1.1 Refer to R9.5.1.1. R10.5.4 Torsion Torsion acting on columns in buildings is typically negligible and is rarely a governing factor in the design of columns. 10.5—Design strength 10.5.1 General 10.5.1.1 For each applicable factored load combina- WLRQGHVLJQVWUHQJWKDWDOOVHFWLRQVVKDOOVDWLVIࢥSn •U, LQFOXGLQJ D WKURXJK G ,QWHUDFWLRQEHWZHHQORDGH൵HFWV shall be considered: D ࢥPn •Pu E ࢥMn •Mu F ࢥVn •Vu G ࢥTn •Tu 10.5.1.2 ࢥVKDOOEHGHWHUPLQHGLQDFFRUGDQFHZLWK 21.2. 10.5.2 $[LDOIRUFHDQGPRPHQW 10.5.2.1 Pn and Mn shall be calculated in accordance with 22.4. 10.5.3 Shear 10.5.3.1 Vn shall be calculated in accordance with 22.5. 10.5.4 Torsion 10.5.4.1 If Tu •ࢥTth, where Tth is given in 22.7, torsion shall be considered in accordance with Chapter 9. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 157 CODE COMMENTARY 10 Columns Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 160. R10.6—Reinforcement limits R10.6.10LQLPXPDQGPD[LPXPORQJLWXGLQDOUHLQIRUFHPHQW R10.6.1.1 Limits are provided for both the minimum and maximum longitudinal reinforcement ratios. 0LQLPXP UHLQIRUFHPHQW—Reinforcement is necessary to provide resistance to bending, which may exist regard- OHVVRIDQDOWLFDOUHVXOWVDQGWRUHGXFHWKHH൵HFWVRIFUHHS and shrinkage of the concrete under sustained compressive stresses. Creep and shrinkage tend to transfer load from the concrete to the reinforcement, and the resultant increase in reinforcement stress becomes greater as the reinforcement ratio decreases. Therefore, a minimum limit is placed on the reinforcement ratio to prevent reinforcement from yielding under sustained service loads (Richart 1933). 0D[LPXP UHLQIRUFHPHQW—The amount of longitudinal reinforcement is limited to ensure that concrete can be H൵HFWLYHOFRQVROLGDWHGDURXQGWKHEDUVDQGWRHQVXUHWKDW columns designed according to the Code are similar to the test specimens by which the Code was calibrated. The 0.08 limit applies at all sections, including splice regions, and can also be considered a practical maximum for longitu- dinal reinforcement in terms of economy and requirements for placing. Longitudinal reinforcement in columns should usually not exceed 4 percent if the column bars are required to be lap spliced, as the lap splice zone will have twice as much reinforcement if all lap splices occur at the same location. R10.6.2 0LQLPXPVKHDUUHLQIRUFHPHQW R10.6.2.1 The basis for the minimum shear reinforcement is the same for columns and beams. Refer to R9.6.3 for more information. R10.7—Reinforcement detailing 10.6—Reinforcement limits 10.6.1 0LQLPXPDQGPD[LPXPORQJLWXGLQDOUHLQIRUFHPHQW 10.6.1.1 For nonprestressed columns and for prestressed columns with average fpe 225 psi, area of longitudinal reinforcement shall be at least 0.01Ag but shall not exceed 0.08Ag. 10.6.2 0LQLPXPVKHDUUHLQIRUFHPHQW 10.6.2.1 A minimum area of shear reinforcement, Av,min, shall be provided in all regions where Vu 0.5ࢥVc. 10.6.2.2 If shear reinforcement is required, Av,min shall be the greater of (a) and (b): (a) 0.75 w c yt b s f f ′ (b) 50 w yt b s f 10.7—Reinforcement detailing 10.7.1 General 10.7.1.1 Concrete cover for reinforcement shall be in accordance with 20.5.1. 10.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4. American Concrete Institute – Copyrighted © Material – www.concrete.org 158 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY ment in term itudinal re 4 percent s the lap nt if all 0LQLPXPV R10 6 colum test specimens b applies at all s considered for p usuall much locat ing. not p sp einf . o be info a p a Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 161. R10.7.3 /RQJLWXGLQDOUHLQIRUFHPHQW R10.7.3.1 At least four longitudinal bars are required when bars are enclosed by rectangular or circular ties. For other tie shapes, one bar should be provided at each apex or corner and proper transverse reinforcement provided. For example, tied triangular columns require at least three longi- tudinal bars, with one at each apex of the triangular ties. For bars enclosed by spirals, at least six bars are required. If the number of bars in a circular arrangement is less than HLJKWWKHRULHQWDWLRQRIWKHEDUVPDVLJQL¿FDQWOD൵HFWWKH moment strength of eccentrically loaded columns and should be considered in design. R10.7.5 6SOLFHVRIORQJLWXGLQDOUHLQIRUFHPHQW R10.7.5.1 General R10.7.5.1.2 Frequently, the basic gravity load combina- tion will govern the design of the column itself, but a load FRPELQDWLRQLQFOXGLQJZLQGRUHDUWKTXDNHH൵HFWVPDLQGXFH greater tension in some column bars. Each bar splice should be designed for the maximum calculated bar tensile force. R10.7.5.1.3 For the purpose of calculating Ɛd for tension ODS VSOLFHV LQ FROXPQV ZLWK R൵VHW EDUV )LJ 5 illustrates the clear spacing to be used. 10.7.1.3 Along development and lap splice lengths of longitudinal bars with fy•SVL, transverse reinforce- ment shall be provided such that Ktr shall not be smaller than 0.5db. 10.7.1.4 Bundled bars shall be in accordance with 25.6. 10.7.2 5HLQIRUFHPHQWVSDFLQJ 10.7.2.1 Minimum spacing s shall be in accordance with 25.2. 10.7.3 /RQJLWXGLQDOUHLQIRUFHPHQW 10.7.3.1 For nonprestressed columns and for prestressed columns with average fpe 225 psi, the minimum number of longitudinal bars shall be (a), (b), or (c): (a) Three within triangular ties (b) Four within rectangular or circular ties (c) Six enclosed by spirals or for columns of special moment frames enclosed by circular hoops 10.7.4 2ৼVHWEHQWORQJLWXGLQDOUHLQIRUFHPHQW 10.7.4.1 7KH VORSH RI WKH LQFOLQHG SRUWLRQ RI DQ R൵VHW bent longitudinal bar relative to the longitudinal axis of the column shall not exceed 1 in 6. Portions of bar above and EHORZDQR൵VHWVKDOOEHSDUDOOHOWRD[LVRIFROXPQ 10.7.4.2 ,IWKHFROXPQIDFHLVR൵VHWLQRUPRUHORQJL- WXGLQDO EDUV VKDOO QRW EH R൵VHW EHQW DQG VHSDUDWH GRZHOV ODSVSOLFHGZLWKWKHORQJLWXGLQDOEDUVDGMDFHQWWRWKHR൵VHW column faces, shall be provided. 10.7.5 6SOLFHVRIORQJLWXGLQDOUHLQIRUFHPHQW 10.7.5.1 General 10.7.5.1.1 Lap splices, mechanical splices, butt-welded splices, and end-bearing splices shall be permitted. 10.7.5.1.2 Splices shall satisfy requirements for all factored load combinations. 10.7.5.1.3 Splices of deformed reinforcement shall be in accordance with 25.5 and, if applicable, shall satisfy the requirements of 10.7.5.2 for lap splices or 10.7.5.3 for end- bearing splices. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 159 CODE COMMENTARY 10 Columns DWLRQRIWKH f eccentric sign. examp tudinal bars, wit enclosed by spir mber of bars i mns of special hoops DOU QH RUFHP mom be con t stre ider num KHRU n a a Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 162. Clear spacing Bars in column above Offset bars from column below Fig. R10.7.5.1.3²2ৼVHWFROXPQEDUV R10.7.5.2 Lap splices In columns subject to moment and axial force, tensile stresses may occur on one face of the column for moderate and large eccentricities as shown in Fig. R10.7.5.2. If such stresses occur, 10.7.5.2.2 requires tension splices to be used. The splice requirements have been formulated on the basis that a compression lap splice has a tensile strength of at least 0.25fy. Therefore, even if columns bars are designed for compression according to 10.7.5.2.1, some tensile strength is inherently provided. All bars in compression, see 10.7.5.2.1 fs 0.5fy on tension face of member, see Table 10.7.5.2.2 (Class B splices required) M P Interaction diagram 0 ≤ fs ≤ 0.5fy on tension face of member, see Table 10.7.5.2.2 (Class A splices allowed with certain conditions) Fig. R10.7.5.2²/DSVSOLFHUHTXLUHPHQWVIRUFROXPQV R10.7.5.2.1 Reduced lap lengths are permitted if the VSOLFH LV HQFORVHG WKURXJKRXW LWV OHQJWK E VX൶FLHQW WLHV The tie leg areas perpendicular to each direction are calcu- lated separately. An example is provided in Fig. R10.7.5.2.1, ZKHUHIRXUOHJVDUHH൵HFWLYHLQRQHGLUHFWLRQDQGWZROHJVLQ the other direction. Compression lap lengths may also be reduced if the lap splice is enclosed throughout its length by spirals due to increased splitting resistance. 10.7.5.2 Lap splices 10.7.5.2.1 If the bar force due to factored loads is compres- sive, compression lap splices shall be permitted. It shall be permitted to decrease the compression lap splice length in accordance with (a) or (b), but the lap splice length shall be at least 12 in. (a) For tied columns, where ties throughout the lap splice OHQJWK KDYH DQ H൵HFWLYH DUHD QRW OHVV WKDQ 0.0015hs in both directions, lap splice length shall be permitted to be American Concrete Institute – Copyrighted © Material – www.concrete.org 160 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 163. h2 h1 Direction 1: 4Ab ≥ 0.0015h1S Direction 2: 2Ab ≥ 0.0015h2S where Ab is the area of the tie Fig. R10.7.5.2.1²([DPSOHRIDSSOLFDWLRQRI D R10.7.5.3 End-bearing splices R10.7.5.3.1 Details for end-bearing splices are provided in 25.5.6. R10.7.6 7UDQVYHUVHUHLQIRUFHPHQW R10.7.6.1 General multiplied by 0.83. Tie legs perpendicular to dimension h VKDOOEHFRQVLGHUHGLQFDOFXODWLQJH൵HFWLYHDUHD (b) For spiral columns, where spirals throughout the lap splice length satisfy 25.7.3, lap splice length shall be permitted to be multiplied by 0.75. 10.7.5.2.2 If the bar force due to factored loads is tensile, tensionlapsplicesshallbeinaccordancewithTable10.7.5.2.2. Table 10.7.5.2.2—Tension lap splice class Tensile bar stress Splice details Splice type ”fy ”EDUVVSOLFHGDWDQVHFWLRQDQGODSVSOLFHV on adjacent bars staggered by at least Ɛd Class A Other Class B 0.5fy All cases Class B 10.7.5.3 End-bearing splices 10.7.5.3.1 If the bar force due to factored loads is compres- sive, end-bearing splices shall be permitted provided the splices are staggered or additional bars are provided at splice locations. The continuing bars in each face of the column shall have a tensile strength at least 0.25fy times the area of the vertical reinforcement along that face. 10.7.6 7UDQVYHUVHUHLQIRUFHPHQW 10.7.6.1 General 10.7.6.1.1 Transverse reinforcement shall satisfy the most restrictive requirements for reinforcement spacing. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 161 CODE COMMENTARY 10 Columns Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 164. 10.7.6.1.2 Details of transverse reinforcement shall be in accordance with 25.7.2 for ties, 25.7.3 for spirals, or 25.7.4 for hoops. 10.7.6.1.3 For prestressed columns with average fpe • 225 psi, transverse ties or hoops need not satisfy the 16db spacing requirement of 25.7.2.1. 10.7.6.1.4 Longitudinal reinforcement shall be laterally supported using ties or hoops in accordance with 10.7.6.2 or spirals in accordance with 10.7.6.3, unless tests and struc- tural analyses demonstrate adequate strength and feasibility of construction. 10.7.6.1.5 If anchor bolts are placed in the top of a column or pedestal, the bolts shall be enclosed by transverse rein- forcement that also surrounds at least four longitudinal bars within the column or pedestal. The transverse reinforcement shall be distributed within 5 in. of the top of the column or pedestal and shall consist of at least two No. 4 or three No. 3 ties or hoops. 10.7.6.1.6 If mechanical couplers or extended bars for connection to a precast element are placed in the ends of columns or pedestals, the mechanical couplers or extended bars shall be enclosed by transverse reinforcement. The transverse reinforcement shall be distributed within 5 in. of the ends of the column or pedestal and shall consist of at least two No. 4 or three No. 3 ties or hoops. 10.7.6.2 Lateral support of longitudinal bars using ties or hoops 10.7.6.2.1 In any story, the bottom tie or hoop shall be located not more than one-half the tie or hoop spacing above the top of footing or slab. 10.7.6.2.2 In any story, the top tie or hoop shall be located not more than one-half the tie or hoop spacing below the lowest horizontal reinforcement in the slab, drop panel, or shear cap. If beams or brackets frame into all sides of the column, the top tie or hoop shall be located not more than 3 in. below the lowest horizontal reinforcement in the shal- lowest beam or bracket. R10.7.6.1.4 All longitudinal bars in compression should be enclosed within transverse reinforcement. Where longitu- dinal bars are arranged in a circular pattern, only one circular WLHSHUVSHFL¿HGVSDFLQJLVUHTXLUHG7KLVUHTXLUHPHQWFDQ EH VDWLV¿HG E D FRQWLQXRXV FLUFXODU WLH KHOL[ ZLWK WKH maximum pitch being equal to the required tie spacing. It is prudent to provide a set of ties at each end of lap spliced bars, above and below end-bearing splices, and at minimum spacings immediately below sloping regions of R൵VHWEHQWEDUV 3UHFDVWFROXPQVZLWKFRYHUOHVVWKDQLQSUHVWUHVVHG columns without longitudinal bars, columns of concrete with small size coarse aggregate, wall-like columns, and other unusual columns may require special designs for transverse reinforcement. R10.7.6.1.5 and R10.7.6.1.6RQ¿QHPHQWLPSURYHVORDG transfer from the anchor bolts and mechanical couplers to the column or pedestal where concrete may crack in the vicinity of the bolts and mechanical couplers. Such cracking can occur due to unanticipated forces caused by temperature, restrained shrinkage, accidental impact during construction, DQGVLPLODUH൵HFWV R10.7.6.2 Lateral support of longitudinal bars using ties or hoops R10.7.6.2.2 For rectangular columns, beams or brackets framing into all four sides at the same elevation are consid- ered to provide restraint over a joint depth equal to that of the shallowest beam or bracket. For columns with other shapes, four beams framing into the column from two orthogonal directions are considered to provide equivalent restraint. American Concrete Institute – Copyrighted © Material – www.concrete.org 162 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY R10.7.6.1 nchor bo estal wh ts and me o unantic hrinkage, PLODUH൵HFW pl en t l he th columns withou size coarse ag umns may re n the top of a co d by transverse four longitudinal verse reinforce f th mn ein- bars nt R10 he co vicin 7.6.1 fro umn of t col eme qui u Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 165. 10.7.6.3 Lateral support of longitudinal bars using spirals 10.7.6.3.1 In any story, the bottom of the spiral shall be located at the top of footing or slab. 10.7.6.3.2 In any story, the top of the spiral shall be located in accordance with Table 10.7.6.3.2. Table 10.7.6.3.2 —Spiral extension requirements at top of column Framing at column end Extension requirements Beams or brackets frame into all sides of the column Extend to the level of the lowest horizontal reinforcement in members supported above. Beams or brackets do not frame into all sides of the column Extend to the level of the lowest horizontal reinforcement in members supported above. Additional column ties shall extend above termination of spiral to bottom of slab, drop panel, or shear cap. Columns with capitals Extend to the level at which the diameter or width of capital is twice that of the column. 10.7.6.4 /DWHUDOVXSSRUWRIRৼVHWEHQWORQJLWXGLQDOEDUV 10.7.6.4.1 :KHUHORQJLWXGLQDOEDUVDUHR൵VHWKRUL]RQWDO support shall be provided by ties, hoops, spirals, or parts RIWKHÀRRUFRQVWUXFWLRQDQGVKDOOEHGHVLJQHGWRUHVLVW times the horizontal component of the calculated force in the LQFOLQHGSRUWLRQRIWKHR൵VHWEDU 10.7.6.4.2 If transverse reinforcement is provided to resist IRUFHVWKDWUHVXOWIURPR൵VHWEHQGVWLHVKRRSVRUVSLUDOV shall be placed not more than 6 in. from points of bend. 10.7.6.5 Shear 10.7.6.5.1 If required, shear reinforcement shall be provided using ties, hoops, or spirals. 10.7.6.5.2 Maximum spacing of shear reinforcement shall be in accordance with Table 10.7.6.5.2. Table 10.7.6.5.2—Maximum spacing of shear reinforcement Vs Maximum s, in. Nonprestressed column Prestressed column 4 c w f b d ≤ ′ Lesser of: d 3h 24 4 c w f b d ′ Lesser of: d 3h 12 R10.7.6.3 Lateral support of longitudinal bars using spirals R10.7.6.3.2 Refer to R10.7.6.2.2. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 163 CODE COMMENTARY 10 Columns st ch the diameter al is twice tha colum ৼVHW DO ie OO th ORQJLWXGLQDOE DUHR൵VHWKRUL] ops, spirals, or HVLJQHGWRUHVLV t d QWDO arts Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 166. 164 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 167. R11.1—Scope R11.1.1 This chapter applies generally to walls as vertical and lateral force-resisting members. Provisions for in-plane shear in ordinary structural walls, as opposed to special structural walls conforming to 18.10, are included in this chapter. R11.1.2 Special structural walls are detailed according to the provisions of 18.10. This Code uses the term “structural wall” as being synonymous with “shear wall.” While the WHUP³VKHDUZDOO´LVQRWGH¿QHGLQWKLVRGHWKHGH¿QLWLRQ of a structural wall in Chapter 2 states “a shear wall is a structural wall.” $6(6(,GH¿QHVDVWUXFWXUDOZDOODVDZDOOWKDWPHHWV WKHGH¿QLWLRQIRUDEHDULQJZDOORUDVKHDUZDOO$EHDULQJZDOO LVGH¿QHGDVDZDOOWKDWVXSSRUWVYHUWLFDOORDGEHRQGDFHUWDLQ WKUHVKROGYDOXH$VKHDUZDOOLVGH¿QHGDVDZDOOEHDULQJRU nonbearing, designed to resist lateral forces acting in the plane RIWKHZDOO$6(6(,GH¿QLWLRQVDUHZLGHODFFHSWHG R11.1.6 6SHFL¿F GHVLJQ UHFRPPHQGDWLRQV IRU FDVWLQ place walls constructed with insulating concrete forms are not provided in this Code. Guidance can be found in ACI 506R and PCA 100. R11.2—General 11.1—Scope 11.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed walls including (a) through (c): (a) Cast-in-place (b) Precast in-plant (c) Precast on-site including tilt-up 11.1.2 Design of special structural walls shall be in accor- dance with Chapter 18. 11.1.3 Design of plain concrete walls shall be in accor- dance with Chapter 14. 11.1.4 Design of cantilever retaining walls shall be in accordance with Chapter 13. 11.1.5 Design of walls as grade beams shall be in accor- dance with 13.3.5. 11.1.6 Cast-in-place walls with insulating forms shall be permitted by this Code for use in one- or two-story buildings. 11.2—General 11.2.1 Materials 11.2.1.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 11.2.1.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 11.2.1.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 11.2.2 RQQHFWLRQWRRWKHUPHPEHUV 11.2.2.1 For precast walls, connections shall be designed in accordance with 16.2. 11.2.2.2 Connections of walls to foundations shall satisfy 16.3. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 165 CODE COMMENTARY 11 Walls .1.6 6SHFL place wa s nonbe RIWKHZDOO$6 walls re de ng walls shall b ms shall be in a in or- CHAPTER 11—WALLS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 168. 11.2.3 Load distribution 11.2.3.1 Unless otherwise demonstrated by an analysis, WKH KRUL]RQWDO OHQJWK RI ZDOO FRQVLGHUHG DV H൵HFWLYH IRU resisting each concentrated load shall not exceed the lesser of the center-to-center distance between loads, and the EHDULQJ ZLGWK SOXV IRXU WLPHV WKH ZDOO WKLFNQHVV (൵HF- tive horizontal length for bearing shall not extend beyond vertical wall joints unless design provides for transfer of forces across the joints. 11.2.4 ,QWHUVHFWLQJHOHPHQWV 11.2.4.1 Walls shall be anchored to intersecting elements, VXFKDVÀRRUVDQGURRIVFROXPQVSLODVWHUVEXWWUHVVHVRU intersecting walls; and to footings. 11.2.4.2 For cast-in-place walls having Pu 0.2fcƍAg, the SRUWLRQRIWKHZDOOZLWKLQWKHWKLFNQHVVRIWKHÀRRUVVWHP VKDOOKDYHVSHFL¿HGFRPSUHVVLYHVWUHQJWKDWOHDVW0.8fcƍ of the wall. 11.3—Design limits 11.3.1 0LQLPXPZDOOWKLFNQHVV 11.3.1.1 Minimum wall thicknesses shall be in accordance with Table 11.3.1.1. Thinner walls are permitted if adequate strength and stability can be demonstrated by structural analysis. Table 11.3.1.1—Minimum wall thickness h Wall type Minimum thickness h Bearing[1] Greater of: 4 in. (a) WKHOHVVHURIXQVXSSRUWHGOHQJWK and unsupported height (b) Nonbearing Greater of: 4 in. (c) WKHOHVVHURIXQVXSSRUWHGOHQJWK and unsupported height (d) Exterior basement and foundation[1] 7.5 in. (e) [1] 2QODSSOLHVWRZDOOVGHVLJQHGLQDFFRUGDQFHZLWKWKHVLPSOL¿HGGHVLJQPHWKRGRI 11.5.3. 11.4—Required strength 11.4.1 General 11.4.1.1 Required strength shall be calculated in accor- dance with the factored load combinations in Chapter 5. 11.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. R11.2.4 ,QWHUVHFWLQJHOHPHQWV R11.2.4.1 Walls that do not depend on intersecting elements for support, do not have to be connected to those elements. It is not uncommon to separate massive retaining walls from inter- VHFWLQJZDOOVWRDFFRPPRGDWHGL൵HUHQFHVLQGHIRUPDWLRQV R11.2.4.27KHIDFWRUUHÀHFWVUHGXFHGFRQ¿QHPHQWLQ ÀRRUZDOO MRLQWV FRPSDUHG ZLWK ÀRRUFROXPQ MRLQWV XQGHU gravity loads. R11.3—Design limits R11.3.1 0LQLPXPZDOOWKLFNQHVV R11.3.1.1 The minimum thickness requirements need not be applied to bearing walls and exterior basement and foun- dation walls designed by 11.5.2 or analyzed by 11.8. R11.4—Required strength R11.4.1 General American Concrete Institute – Copyrighted © Material – www.concrete.org 166 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY imits PZDOOWKL inimum t ing walls signed by g, the WKHÀRRUVVWHP QJWKDWOH VV ne ls a m ÀRRUZDOO MRLQWV ty loads. hall be in accord ermitted if ade d b nce ate R11 R11 R11 be ap d —De 3.1 0 3.1.1 ed t Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 169. 11.4.1.36OHQGHUQHVVH൵HFWVVKDOOEHFDOFXODWHGLQDFFRU- dance with 6.6.4, 6.7, or 6.8. Alternatively, out-of-plane slenderness analysis shall be permitted using 11.8 for walls meeting the requirements of that section. 11.4.1.4 Walls shall be designed for eccentric axial loads and any lateral or other loads to which they are subjected. 11.4.2 )DFWRUHGD[LDOIRUFHDQGPRPHQW 11.4.2.1 Walls shall be designed for the maximum factored moment Mu that can accompany the factored axial force for each applicable load combination. The factored axial force Pu at given eccentricity shall not exceed ࢥPn,max, where Pn,max shall be as given in 22.4.2.1DQGVWUHQJWKUHGXFWLRQIDFWRUࢥ shall be that for compression-controlled sections in 21.2.2. The maximum factored moment MuVKDOOEHPDJQL¿HGIRU VOHQGHUQHVVH൵HFWVLQDFFRUGDQFHZLWKRU 11.4.3 Factored shear 11.4.3.1 Walls shall be designed for the maximum in-plane Vu and out-of-plane Vu. 11.5—Design strength 11.5.1 General 11.5.1.1 For each applicable factored load combination, design strength at all sections shall satisfy ࢥSn•U, including (a) through (c). Interaction between axial load and moment shall be considered. R11.4.1.3 The forces typically acting on a wall are illus- trated in Fig. R11.4.1.3. Out-of-plane shear Self-weight Axial force In-plane shear In-plane moment Out-of-plane moment Fig. R11.4.1.3—In-plane and out-of-plane forces. R11.5—Design strength American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 167 CODE COMMENTARY 11 Walls Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 170. D ࢥPn•Pu E ࢥMn•Mu F ࢥVn•Vu 11.5.1.2 ࢥVKDOOEHGHWHUPLQHGLQDFFRUGDQFHZLWK21.2. 11.5.2 $[LDOORDGDQGLQSODQHRURXWRISODQHÀH[XUH 11.5.2.1 For bearing walls, Pn and Mn (in-plane or out-of- plane) shall be calculated in accordance with 22.4. Alterna- WLYHOD[LDOORDGDQGRXWRISODQHÀH[XUHVKDOOEHSHUPLWWHG to be considered in accordance with 11.5.3. 11.5.2.2 For nonbearing walls, Mn shall be calculated in accordance with 22.3. 11.5.3 $[LDO ORDG DQG RXWRISODQH ÀH[XUH ± VLPSOL¿HG GHVLJQPHWKRG 11.5.3.1 If the resultant of all factored loads is located within the middle third of the thickness of a solid wall with a rectangular cross section, Pn shall be permitted to be calcu- lated by: 2 0.55 1 32 c n c g k P f A h ⎡ ⎤ ⎛ ⎞ = − ′ ⎢ ⎥ ⎜ ⎟ ⎝ ⎠ ⎢ ⎥ ⎣ ⎦ A (11.5.3.1) R11.5.2 $[LDOORDGDQGLQSODQHRURXWRISODQHÀH[XUH R11.5.2.21RQEHDULQJZDOOVEGH¿QLWLRQDUHQRWVXEMHFW WRDQVLJQL¿FDQWD[LDOIRUFHWKHUHIRUHÀH[XUDOVWUHQJWKLV not a function of axial force. R11.5.3 $[LDOORDGDQGRXWRISODQHÀH[XUH±VLPSOL¿HG GHVLJQPHWKRG R11.5.3.17KHVLPSOL¿HGGHVLJQPHWKRGDSSOLHVRQOWR solid rectangular cross sections; all other shapes should be designed in accordance with 11.5.2. Eccentric axial loads and moments due to out-of-plane forces are used to determine the maximum total eccentricity of the factored axial force Pu. When the resultant axial force for all applicable load combinations falls within the middle third of the wall thickness (eccentricity not greater than h/6) at all sections along the length of the undeformed wall, QRWHQVLRQLVLQGXFHGLQWKHZDOODQGWKHVLPSOL¿HGGHVLJQ method may be used. The design is then carried out consid- ering Pu as a concentric axial force. The factored axial force Pu should be less than or equal to the design axial strength ࢥPn calculated using Eq. (11.5.3.1). Equation (11.5.3.1) results in strengths comparable to those determined in accordance with 11.5.2 for members loaded at WKHPLGGOHWKLUGRIWKHWKLFNQHVVZLWKGL൵HUHQWEUDFHGDQG restrained end conditions. Refer to Fig. R11.5.3.1. American Concrete Institute – Copyrighted © Material – www.concrete.org 168 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY ordance wit loads and etermine force Pu P oad comb thicknes ons along LVLQGXFHG hod may be u ering P red load ess of ll be ⎡ 1− 1 GHVLJQ 1.5.3.17KHVLP gular cross s ⎤ 2 ⎥ ⎞ c ⎞ ⎞ c h ⎥ ⎥ ⎥ ⎟ ⎟ h h ⎦ ⎥ ⎥ ⎠ ⎟ ⎟ (11.5 3.1) E forces for all third h ntric re u actor ppli f the ctan d in ecti ct Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 171. 11.5.3.2(൵HFWLYHOHQJWKIDFWRUk for use with Eq. (11.5.3.1) shall be in accordance with Table 11.5.3.2. Table 11.5.3.2—Effective length factor k for walls Boundary conditions k Walls braced top and bottom against lateral translation and: (a) Restrained against rotation at one or both ends (top, bottom, or both) 0.8 (b) Unrestrained against rotation at both ends 1.0 Walls not braced against lateral translation 2.0 11.5.3.3 Pn from Eq. (11.5.3.1) shall be reduced by ࢥ for compression-controlled sections in 21.2.2. 11.5.3.4 Wall reinforcement shall be at least that required by 11.6. 11.5.4 In-plane shear 11.5.4.1 Vn shall be calculated in accordance with 11.5.4.2 through 11.5.4.4. Alternatively, for walls with hw/Ɛw 2, it shall be permitted to design for in-plane shear in accordance with the strut-and-tie method of Chapter 23. In all cases, rein- forcement shall satisfy the limits of 11.6, 11.7.2, and 11.7.3. 25 Pn fc ′ Ag lc h k = 0.8 C m = 0.6 C m = 0.8 k = 0.8 k = 1.0 Section 11.5.2 k = 2 . 0 20 15 10 5 0 0.6 0 0.5 0.4 0.3 0.2 0.1 Section 11.5.2 k = 2.0 C m = 1.0 fc ′ = 4000 psi eccentricity = h/6 Eq. (11.5.3.1) k = 1.0 C m = 1.0 Section 11.5.2 Fig. R11.5.3.1²6LPSOL¿HG GHVLJQ RI ZDOOV (T YHUVXV R11.5.4 In-plane shear R11.5.4.1 Shear in the plane of the wall is primarily of importance for structural walls with a small height-to-length ratio. The design of taller walls, particularly walls with uniformly distributed reinforcement, will likely be controlled EÀH[XUDOFRQVLGHUDWLRQV3RVVLEOHH[FHSWLRQVPDRFFXULQ tall structural walls subject to strong earthquake excitation. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 169 CODE COMMENTARY 11 Walls Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 172. 11.5.4.2 Vn at any horizontal section shall not exceed 8 ′ c f Acv. 11.5.4.3 Vn shall be calculated by: ( ) n c c t yt cv V f f A = α λ + ρ ′ (11.5.4.3) where: Įc = 3 for hw/Ɛw” Įc = 2 for hw/Ɛw• Įc varies linearly between 3 and 2 for 1.5 hw/Ɛw 2.0 11.5.4.4 For walls subject to a net axial tension, Įc in Eq. (11.5.4.3) shall be taken as: 2 1 0.0 500 u c g N A ⎛ ⎞ α = + ≥ ⎜ ⎟ ⎝ ⎠ (11.5.4.4) where Nu is negative for tension. 11.5.5 Out-of-plane shear 11.5.5.1 Vn shall be calculated in accordance with 22.5. 11.6—Reinforcement limits 11.6.1 If in-plane Vu”ࢥĮcȜ ′ c f AcvPLQLPXPȡƐ and PLQLPXPȡt shall be in accordance with Table 11.6.1. These OLPLWVQHHGQRWEHVDWLV¿HGLIDGHTXDWHVWUHQJWKDQGVWDELOLW can be demonstrated by structural analysis. R11.5.4.2 This limit is imposed to guard against diagonal FRPSUHVVLRQ IDLOXUH LQ VWUXFWXUDO ZDOOV7KH FRH൶FLHQW XVHG in this equation has been reduced from a value of 10 in ACI WRDYDOXHRILQ$,EHFDXVHWKHH൵HFWLYHVKHDU area has been increased to KƐw, from hd used in prior editions of the Code. R11.5.4.3To improve consistency in the Code, the nominal in-plane shear strength equation in 11.5.4.3 now has the same form as the shear strength equation used in 18.10.4.1 for structural walls resisting seismic loads. Research results reported by Orakcal et al. (2009) indicate that nominal strengths calculated using Eq. (11.5.4.3) are similar to values obtained using equations from prior editions of the Code, and thus, provide a comparable level of safety. R11.5.4.4 For structural walls where a net axial tension force is calculated for the entire wall section, the shear strength contribution attributed to the concrete is reduced and may be negligible. For these members, wall transverse reinforcement must be designed to resist most, if not all, of the factored shear force. R11.6—Reinforcement limits R11.6.1 Both horizontal and vertical shear reinforcement are required for all walls. The distributed reinforcement is LGHQWL¿HG DV EHLQJ RULHQWHG SDUDOOHO WR HLWKHU WKH ORQJLWX- dinal or transverse axis of the wall. Therefore, for vertical wall segments, the notation used to describe the horizontal GLVWULEXWHGUHLQIRUFHPHQWUDWLRLVȡt, and the notation used to describe the vertical distributed reinforcement ratio is ȡƐ. Transverse reinforcement is not required in precast, prestressed walls equal to or less than 12 ft in width because this width is less than that in which shrinkage and tempera- ture stresses can build up to a magnitude requiring trans- verse reinforcement. In addition, much of the shrinkage occurs before the members are connected into the structure. 2QFHLQWKH¿QDOVWUXFWXUHWKHPHPEHUVDUHXVXDOOQRWDV rigidly connected transversely as monolithic concrete; thus, the transverse restraint stresses due to both shrinkage and WHPSHUDWXUHFKDQJHDUHVLJQL¿FDQWOUHGXFHG The minimum area of wall reinforcement for precast walls has been used for many years and is recommended by WKH3UHFDVW3UHVWUHVVHGRQFUHWH,QVWLWXWH PCI MNL-120) and the Canadian Precast Concrete Design Standard (2016). Reduced minimum reinforcement and greater spacings in 11.7.2.2 are allowed recognizing that precast wall panels have very little restraint at their edges during early stages American Concrete Institute – Copyrighted © Material – www.concrete.org 170 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY se .6.1 nforcem Both h are requ 0.0 ⎠ n. in streng and may be neg orcement must b shear force. rdance with 22 ored Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 173. 11.6.2 If in-plane Vu”ࢥĮcȜ ′ c f Acv, (a) and (b) shall EHVDWLV¿HG (a) ȡƐ shall be at least the greater of the value calculated by Eq. (11.6.2) and 0.0025, but need not exceed ȡt required for strength by 11.5.4.3. ȡƐ• ±hwƐw ȡt± (b) ȡt shall be at least 0.0025 11.7—Reinforcement detailing 11.7.1 General 11.7.1.1 Concrete cover for reinforcement shall be in accordance with 20.5.1. 11.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4. 11.7.1.3 Splice lengths of deformed reinforcement shall be in accordance with 25.5. 11.7.2 6SDFLQJRIORQJLWXGLQDOUHLQIRUFHPHQW 11.7.2.1 Spacing s of longitudinal bars in cast-in-place walls shall not exceed the lesser of 3h and 18 in. If shear reinforcement is required for in-plane strength, spacing of longitudinal reinforcement shall not exceed Ɛw/3. 11.7.2.2 Spacing s of longitudinal bars in precast walls shall not exceed the lesser of (a) and (b): (a) 5h (b) 18 in. for exterior walls or 30 in. for interior walls If shear reinforcement is required for in-plane strength, s shall not exceed the smallest of 3h, 18 in., and Ɛw/3. of curing and develop less shrinkage stress than compa- rable cast-in-place walls. R11.6.2 For monotonically loaded walls with low height- to-length ratios, test data (Barda et al. 1977) indicate that KRUL]RQWDO VKHDU UHLQIRUFHPHQW EHFRPHV OHVV H൵HFWLYH IRU shear resistance than vertical reinforcement. This change in H൵HFWLYHQHVVRIWKHKRUL]RQWDOYHUVXVYHUWLFDOUHLQIRUFHPHQW is recognized in Eq. (11.6.2); if hw/Ɛw is less than 0.5, the amount of vertical reinforcement is equal to the amount of horizontal reinforcement. If hwȡw is greater than 2.5, only a minimum amount of vertical reinforcement is required (0.0025sh). Table 11.6.1—Minimum reinforcement for walls with in-plane Vu ≤ 0.5ࢥĮcȜ ′ c f Acv Wall type Type of nonprestressed reinforcement Bar/wire size fy, psi Minimum longitudinal[1] , ȡƐ 0LQLPXPWUDQVYHUVHȡt Cast-in-place Deformed bars ”1R • 0.0012 0.0020 60,000 0.0015 0.0025 No. 5 Any 0.0015 0.0025 Welded-wire reinforcement ”:RU' Any 0.0012 0.0020 Precast[2] Deformed bars or welded-wire reinforcement Any Any 0.0010 0.0010 [1] 3UHVWUHVVHGZDOOVZLWKDQDYHUDJHH൵HFWLYHFRPSUHVVLYHVWUHVVRIDWOHDVWSVLQHHGQRWPHHWWKHUHTXLUHPHQWIRUPLQLPXPORQJLWXGLQDOUHLQIRUFHPHQWȡƐ. [2] In one-way precast, prestressed walls not wider than 12 ft and not mechanically connected to cause restraint in the transverse direction, the minimum reinforcement requirement LQWKHGLUHFWLRQQRUPDOWRWKHÀH[XUDOUHLQIRUFHPHQWQHHGQRWEHVDWLV¿HG American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 171 CODE COMMENTARY 11 Walls n Eq. (11.6 l reinforce ement. If t of vert in he value c d not ȡ to len KRUL]RQWDO VKH resistance than VRIWKHKRUL amo horizo 0.002 of v tal r mum sh). QH gnize RQW RQ Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 174. 11.7.2.3 For walls with thickness greater than 10 in., except single story basement walls and cantilever retaining walls, distributed reinforcement in each direction shall be placed in at least two layers, one near each face. 11.7.2.4 Flexural tension reinforcement shall be well distributed and placed as close as practicable to the tension face. 11.7.3 6SDFLQJRIWUDQVYHUVHUHLQIRUFHPHQW 11.7.3.1 Spacing s of transverse reinforcement in cast-in- place walls shall not exceed the lesser of 3h and 18 in. If shear reinforcement is required for in-plane strength, s shall not exceed Ɛw/5. 11.7.3.2 Spacing s of transverse bars in precast walls shall not exceed the lesser of (a) and (b): (a) 5h (b) 18 in. for exterior walls or 30 in. for interior walls If shear reinforcement is required for in-plane strength, s shall not exceed the least of 3h, 18 in., and Ɛw/5. 11.7.4 /DWHUDOVXSSRUWRIORQJLWXGLQDOUHLQIRUFHPHQW 11.7.4.1 If longitudinal reinforcement is required for compression and if Ast exceeds 0.01Ag, longitudinal rein- forcement shall be laterally supported by transverse ties. 11.7.5 5HLQIRUFHPHQWDURXQGRSHQLQJV 11.7.5.1 In addition to the minimum reinforcement required by 11.6, at least two No. 5 bars in walls having two layers of reinforcement in both directions and one No. 5 bar in walls having a single layer of reinforcement in both direc- tions shall be provided around window, door, and similarly sized openings. Such bars shall be anchored to develop fy in tension at the corners of the openings. 11.8—Alternative method for out-of-plane slender wall analysis 11.8.1 General 11.8.1.1 It shall be permitted to analyze out-of-plane slen- GHUQHVV H൵HFWV LQ DFFRUGDQFH ZLWK WKLV VHFWLRQ IRU ZDOOV satisfying (a) through (e): (a) Cross section is constant over the height of the wall E :DOOLVWHQVLRQFRQWUROOHGIRURXWRISODQHPRPHQWH൵HFW F ࢥMn is at least Mcr, where Mcr is calculated using fr as provided in 19.2.3 (d) Pu at the midheight section does not exceed 0.06fcƍAg R11.8—Alternative method for out-of-plane slender wall analysis R11.8.1 General R11.8.1.1 This procedure is presented as an alternative to the requirements of 11.5.2.1 for the out-of-plane design of slender wall panels, where the panels are restrained against rotation at the top. Panels that have windows or other large openings are not considered to have constant cross section over the height of the panel. Such walls are to be designed taking into account WKHH൵HFWVRIRSHQLQJV Many aspects of the design of tilt-up walls and buildings are discussed in ACI 551.2R and Carter et al. (1993). American Concrete Institute – Copyrighted © Material – www.concrete.org 172 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY for interi red f 18 JL for 0 nd Ɛw/5. DOUHLQIRUFHPHQW ent is required it for Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 175. H DOFXODWHGRXWRISODQHGHÀHFWLRQGXHWRVHUYLFHORDGV ¨s, including P¨H൵HFWVGRHVQRWH[FHHGƐc/150 11.8.2 Modeling 11.8.2.1 The wall shall be analyzed as a simply supported, axially loaded member subject to an out-of-plane uniformly GLVWULEXWHGODWHUDOORDGZLWKPD[LPXPPRPHQWVDQGGHÀHF- tions occurring at midheight. 11.8.2.2 Concentrated gravity loads applied to the wall above any section shall be assumed to be distributed over a width equal to the bearing width, plus a width on each side that increases at a slope of 2 vertical to 1 horizontal, but not extending beyond (a) or (b): (a) The spacing of the concentrated loads (b) The edges of the wall panel 11.8.3 )DFWRUHGPRPHQW 11.8.3.1 MuDWPLGKHLJKWRIZDOOGXHWRFRPELQHGÀH[XUH DQGD[LDOORDGVVKDOOLQFOXGHWKHH൵HFWVRIZDOOGHÀHFWLRQLQ accordance with (a) or (b): (a) By iterative calculation using Mu = Mua + Pu¨u (11.8.3.1a) where Mua is the maximum factored moment at midheight of wall due to lateral and eccentric vertical loads, not including P¨H൵HFWV ¨u shall be calculated by: 2 5 (0.75)48 u c u c cr M E I Δ = A (11.8.3.1b) where Icr shall be calculated by: 3 2 ( ) 2 3 s u w cr s c y E P c h I A d c E f d ⎛ ⎞ = + − + ⎜ ⎟ ⎝ ⎠ A (11.8.3.1c) and the value of Es/Ec shall be at least 6. (b) By direct calculation using: 2 5 1 (0.75)48 ua u u c c cr M M P E I = ⎛ ⎞ − ⎜ ⎟ ⎝ ⎠ A (11.8.3.1d) 11.8.4 2XWRISODQHGHÀHFWLRQ±VHUYLFHORDGV R11.8.3 )DFWRUHGPRPHQW R11.8.3.1 The neutral axis depth c in Eq. (11.8.3.1c) FRUUHVSRQGVWRWKHIROORZLQJH൵HFWLYHDUHDRIORQJLWXGLQDO reinforcement. , u se w s y P h A A f d ⎛ ⎞ = + ⎜ ⎟ ⎝ ⎠ R11.8.4 2XWRISODQHGHÀHFWLRQ±VHUYLFHORDGV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 173 CODE COMMENTARY 11 Walls WKHIROORZL , se w , A A A GXHWR H൵HF sin P R11.8.3 )DF The neutra (11.8. a) rein eme .3. RQGV l a a Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 176. 11.8.4.1 Test data (Athey 1982) demonstrate that out-of- SODQH GHÀHFWLRQV LQFUHDVH UDSLGO ZKHQ WKH VHUYLFHOHYHO moment exceeds 2/3Mcr. A linear interpolation between ¨cr and ¨n is used to determine ¨s to simplify the design of slender walls if Ma 2/3Mcr. 6HUYLFHOHYHOORDGFRPELQDWLRQVDUHQRWGH¿QHGLQKDSWHU 5 of this Code, but they are discussed in Appendix C of $6(6(,$SSHQGL[HVWR$6(6(,DUHQRWFRQVLGHUHG mandatory parts of that standard. For calculating service- OHYHOODWHUDOGHÀHFWLRQVRIVWUXFWXUHV$SSHQGL[RI$6( SEI 7 recommends using the following load combination: D + 0.5L + Wa in which Wa is wind load based on serviceability wind speeds SURYLGHGLQWKHFRPPHQWDUWR$SSHQGL[RI$6(6(, ,IWKHVOHQGHUZDOOLVGHVLJQHGWRUHVLVWHDUWKTXDNHH൵HFWV E, and ELVEDVHGRQVWUHQJWKOHYHOHDUWKTXDNHH൵HFWVWKH following load combination is considered to be appropriate IRUHYDOXDWLQJWKHVHUYLFHOHYHOODWHUDOGHÀHFWLRQV D + 0.5L + 0.7E 11.8.4.12XWRISODQHGHÀHFWLRQGXHWRVHUYLFHORDGV¨s, shall be calculated in accordance with Table 11.8.4.1, where Ma is calculated by 11.8.4.2. Table 11.8.4.1—Calculation of Δs Ma ¨s ” Mcr a s cr cr M M ⎛ ⎞ Δ = Δ ⎜ ⎟ ⎝ ⎠ (a) ! Mcr a cr s cr n cr n cr M M M M − Δ = Δ + Δ − Δ − (b) 11.8.4.2 The maximum moment Ma at midheight of wall due to service lateral and eccentric vertical loads, including Ps¨sH൵HFWVVKDOOEHFDOFXODWHGE(T ZLWKLWHUD- WLRQRIGHÀHFWLRQV Ma = Msa + Ps¨s (11.8.4.2) ¨cr and ¨n shall be calculated by (a) and (b): (a) 2 5 48 cr c cr c g M E I Δ = A (11.8.4.3a) (b) 2 5 48 n c n c cr M E I Δ = l (11.8.4.3b) American Concrete Institute – Copyrighted © Material – www.concrete.org 174 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY follow IRUHYDOXDWLQJWK D ent ntri E ¨ midheight of tical loads, inclu ZLWK ll ing HUD- + 0. 0 Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 177. 12.1—Scope 12.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed diaphragms, including (a) through (d): (a) Diaphragms that are cast-in-place slabs (b) Diaphragms that comprise a cast-in-place topping slab on precast elements (c) Diaphragms that comprise precast elements with end strips formed by either a cast-in-place concrete topping slab or edge beams (d) Diaphragms of interconnected precast elements without cast-in-place concrete topping R12.1—Scope R12.1.1 Diaphragms typically are horizontal or nearly horizontal planar elements that serve to transfer lateral forces to vertical elements of the lateral-force-resisting system (Fig. R12.1.1). Diaphragms also tie the building elements together into a complete three-dimensional system and provide lateral support to those elements by connecting them to the lateral-force-resisting system. Typically, diaphragms DOVRVHUYHDVÀRRUDQGURRIVODEVRUDVSDUNLQJVWUXFWXUH ramps and, therefore, support gravity loads. A diaphragm may include chords and collectors. When subjected to lateral loads, such as the in-plane iner- tial loads acting on the roof diaphragm of Fig. R12.1.1, a diaphragm acts essentially as a beam spanning horizon- tally between vertical elements of the lateral-force-resisting system. The diaphragm thus develops in-plane bending moments, shears, and possibly other actions. Where vertical elements of the lateral-force-resisting system do not extend along the full depth of the diaphragm, collectors may be required to collect the diaphragm shear and transfer it to the vertical elements. The term “distributor” is sometimes used to describe a collector that transfers force from a vertical element of the lateral-force-resisting system into the diaphragm. This chapter describes minimum requirements for diaphragm and FROOHFWRUGHVLJQDQGGHWDLOLQJLQFOXGLQJFRQ¿JXUDWLRQDQDO- ysis models, materials, and strength. This chapter covers only the types of diaphragms listed in this provision. Other diaphragm types, such as horizontal trusses, are used successfully in buildings, but this chapter does not include prescriptive provisions for those other types. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 175 CODE COMMENTARY 12 Diaphragms ce-resisting minimum GGHWDLOLQJ ls, and st ers only Other dia d succes clude presc along required to colle al elements. Th llector that t chap FROOHF Thi in thi desc UGH dels chap prov a c atera ans n CHAPTER 12—DIAPHRAGMS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 178. R12.2—General R12.2.1 As partially illustrated in Fig. R12.1.1, diaphragms resist forces from several types of actions (Moehle et al. 2010): (a) Diaphragm in-plane forces—Lateral forces from load combinations including wind, earthquake, and hori- ]RQWDOÀXLGRUVRLOSUHVVXUHJHQHUDWHLQSODQHVKHDUD[LDO and bending actions in diaphragms as they span between, and transfer forces to, vertical elements of the lateral-force- resisting system. For wind loading, lateral force is gener- ated by wind pressure acting on building cladding that is transferred by diaphragms to the vertical elements. For earthquake loading, inertial forces are generated within the diaphragm and tributary portions of walls, columns, and other elements, and then transferred by diaphragms to the vertical elements. For buildings with subterranean levels, lateral forces are generated by soil pressure bearing against the basement walls; in a typical system, the basement walls VSDQYHUWLFDOOEHWZHHQÀRRUVDOVRVHUYLQJDVGLDSKUDJPV 12.1.2 Diaphragms in structures assigned to Seismic Design Category D, E, or F shall also satisfy requirements of 18.12. 12.2—General 12.2.1 Design shall consider forces (a) through (e): (a) Diaphragm in-plane forces due to lateral loads acting on the building (b) Diaphragm transfer forces (c) Connection forces between the diaphragm and vertical framing or nonstructural elements (d) Forces resulting from bracing vertical or sloped building elements (e) Diaphragm out-of-plane forces due to gravity and other loads applied to the diaphragm surface Below grade soil pressure In-plane inertial loads Gravity loads Out-of-plane wind pressure or inertial loads Thrust Thrust Inclined column Moment resisting frame Distributor Shear Transfer in diaphragm Transfer slab/ diaphragm Basement wall Structural (shear) wall Collector Diaphragm Collector Structural (shear) wall Fig. R12.1.1²7SLFDOGLDSKUDJPDFWLRQV American Concrete Institute – Copyrighted © Material – www.concrete.org 176 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 179. which in turn distribute the lateral soil forces to other force- resisting elements. (b) Diaphragm transfer forces—Vertical elements of the ODWHUDOIRUFHUHVLVWLQJVVWHPPDKDYHGL൵HUHQWSURSHUWLHV over their height, or their planes of resistance may change from one story to another, creating force transfers between vertical elements. A common location where planes of resis- tance change is at grade level of a building with an enlarged subterranean plan; at this location, forces may transfer from the narrower tower into the basement walls through a podium diaphragm (refer to Fig. R12.1.1). (c) Connection forces—Wind pressure acting on exposed building surfaces generates out-of-plane forces on those surfaces. Similarly, earthquake shaking can produce inertial forces in vertical framing and nonstructural elements such as cladding. These forces are transferred from the elements where the forces are developed to the diaphragm through connections. (d) Column bracing forces²$UFKLWHFWXUDO FRQ¿JXUD- tions sometimes require inclined columns, which can result in large horizontal thrusts acting within the plane of the diaphragms due to gravity and overturning actions. The WKUXVWVFDQDFWLQGL൵HUHQWGLUHFWLRQVGHSHQGLQJRQRULHQ- tation of the column and whether it is in compression or tension. Where these thrusts are not balanced locally by other elements, the forces have to be transferred into the diaphragm so they can be transmitted to other suitable elements of the lateral-force-resisting system. Such forces DUH FRPPRQ DQG PD EH VLJQL¿FDQW ZLWK HFFHQWULFDOO loaded precast concrete columns that are not monolithic with adjacent framing. The diaphragm also provides lateral support to columns not designed as part of the lateral-force- resisting system by connecting them to other elements that provide lateral stability for the structure. (e) Diaphragm out-of-plane forces—Most diaphragms DUH SDUW RI ÀRRU DQG URRI IUDPLQJ DQG WKHUHIRUH VXSSRUW gravity loads. The general building code may also require consideration of out-of-plane forces due to wind uplift pres- sure on a roof slab and vertical acceleration due to earth- TXDNHH൵HFWV R12.2.2 Refer to R7.2.1. R12.3—Design limits R12.3.1 0LQLPXPGLDSKUDJPWKLFNQHVV 12.2.27KHH൵HFWVRIVODERSHQLQJVDQGVODEYRLGVVKDOOEH considered in design. 12.2.3 Materials 12.2.3.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 12.2.3.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 12.3—Design limits 12.3.1 0LQLPXPGLDSKUDJPWKLFNQHVV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 177 CODE COMMENTARY 12 Diaphragms LQGL൵HUHQ mn and w se thrust forces h y can be ateral-for DQG PD cast concr adjacent fra support t ( ) tions sometimes rge horizontal t due to gra tatio tensio diaphr elem f th Wh eme gm s of gms FDQ vity ity Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 180. Diaphragms may be required to resist in-plane moment, shear, and axial force. For diaphragms that are entirely cast- in-place or comprise topping slabs composite with precast PHPEHUVWKLFNQHVVRIWKHHQWLUHGLDSKUDJPPXVWEHVX൶- cient to resist these actions. For noncomposite topping slabs, thickness of the cast-in-place topping alone must EHVX൶FLHQWWRUHVLVWWKHVHDFWLRQVSection 18.12 contains VSHFL¿FUHTXLUHPHQWVIRUGLDSKUDJPVLQEXLOGLQJVDVVLJQHG to Seismic Design Categories D, E, and F. In addition to requirements for in-plane force resistance, GLDSKUDJPVWKDWDUHSDUWRIÀRRURUURRIFRQVWUXFWLRQPXVW VDWLVIDSSOLFDEOHUHTXLUHPHQWVIRUVODERUÀDQJHWKLFNQHVV R12.4—Required strength Factored load combinations generally require consid- eration of out-of-plane loads that act simultaneously with diaphragm in-plane forces. For example, this is required ZKHUHDÀRRUEHDPDOVRVHUYHVDVDFROOHFWRULQZKLFKFDVH the beam is to be designed to resist axial forces acting as D FROOHFWRU DQG EHQGLQJ PRPHQWV DFWLQJ DV D ÀRRU EHDP supporting gravity loads. R12.4.2 'LDSKUDJPPRGHOLQJDQGDQDOVLV R12.4.2.1 $6(6(, includes diaphragm modeling requirements for some design conditions, such as design WRUHVLVWZLQGDQGHDUWKTXDNHORDGV:KHUH$6(6(,LV adopted as part of the general building code, those require- ments govern over provisions of this Code. R12.4.2.2 Chapter 6 contains general requirements for analysis that are applicable to diaphragms. Diaphragms are usually designed to remain elastic or nearly elastic for forces acting within their plane under factored load combinations. Therefore, analysis methods satisfying theory of elastic analysis are generally acceptable. The provisions for elastic analysis in 6.6.1 through 6.6.3 can be applied. 'LDSKUDJPLQSODQHVWL൵QHVVD൵HFWVQRWRQOWKHGLVWUL- bution of forces within the diaphragm, but also the distri- bution of displacements and forces among the vertical HOHPHQWV 7KXV WKH GLDSKUDJP VWL൵QHVV PRGHO VKRXOG EH consistent with characteristics of the building. Where the GLDSKUDJPLVYHUVWL൵FRPSDUHGWRWKHYHUWLFDOHOHPHQWV as in a low aspect ratio, cast-in-place diaphragm supported by moment frames, it is acceptable to model the diaphragm DVDFRPSOHWHOULJLGHOHPHQW:KHUHWKHGLDSKUDJPLVÀH[- ible compared with the vertical elements, as in some jointed precast systems supported by structural walls, it may be DFFHSWDEOHWRPRGHOWKHGLDSKUDJPDVDÀH[LEOHEHDPVSDQ- ning between rigid supports. In other cases, it may be advis- able to adopt a more detailed analytical model to account IRUWKHH൵HFWVRIGLDSKUDJPÀH[LELOLWRQWKHGLVWULEXWLRQ of displacements and forces. Examples include buildings 12.3.1.1 Diaphragms shall have thickness as required IRU VWDELOLW VWUHQJWK DQG VWL൵QHVV XQGHU IDFWRUHG ORDG combinations. 12.3.1.2 Floor and roof diaphragms shall have a thick- QHVVQRWOHVVWKDQWKDWUHTXLUHGIRUÀRRUDQGURRIHOHPHQWVLQ other parts of this Code. 12.4—Required strength 12.4.1 General 12.4.1.1 Required strength of diaphragms, collectors, and their connections shall be calculated in accordance with the factored load combinations in Chapter 5. 12.4.1.2 Required strength of diaphragms that are part RIÀRRURUURRIFRQVWUXFWLRQVKDOOLQFOXGHH൵HFWVRIRXWRI plane loads simultaneous with other applicable loads. 12.4.2 'LDSKUDJPPRGHOLQJDQGDQDOVLV 12.4.2.1 Diaphragm modeling and analysis requirements of the general building code shall govern where applicable. Otherwise, diaphragm modeling and analysis shall be in accordance with 12.4.2.2 through 12.4.2.4. 12.4.2.2 Modeling and analysis procedures shall satisfy requirements of Chapter 6. American Concrete Institute – Copyrighted © Material – www.concrete.org 178 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY JPPRGH (6(, some de DQGHDUWK part of the ts govern ov the be D FROOHFWRU DQG orting gravity lo hragms th QFOXG her a DQ g ll g an OVLV nalysis requirem rn where applic i R12 R12 requi ents le. 4.2 ' 4.2.1 ment Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 181. LQ ZKLFK GLDSKUDJP DQG YHUWLFDO HOHPHQW VWL൵QHVVHV KDYH approximately the same value, buildings with large force transfers, and parking structures in which ramps connect EHWZHHQÀRRUVDQGDFWHVVHQWLDOODVEUDFLQJHOHPHQWVZLWKLQ the building. For diaphragms constructed of concrete slabs, $6( SEI 7 permits the assumption of a rigid diaphragm if the diaphragm aspect ratio falls within a prescribed limit, which LVGL൵HUHQWIRUZLQGDQGHDUWKTXDNHORDGVDQGLIWKHVWUXFWXUH KDVQRKRUL]RQWDOLUUHJXODULWLHV$6(6(,SURYLVLRQVGR not prohibit the rigid diaphragm assumption for other condi- tions, provided the rigid diaphragm assumption is reasonably consistent with anticipated behavior. Cast-in-place concrete diaphragms designed with the rigid-diaphragm assumption have a long history of satisfactory performance even though WKHPDIDOORXWVLGHWKH$6(6(,LQGH[YDOXHV R12.4.2.3Forlow-aspect-ratiodiaphragmsthatareentirely cast-in-place or comprise a cast-in-place topping slab on precast elements, the diaphragm is often modeled as a rigid HOHPHQWVXSSRUWHGEÀH[LEOHYHUWLFDOHOHPHQWV+RZHYHU H൵HFWVRIGLDSKUDJPÀH[LELOLWVKRXOGEHFRQVLGHUHGZKHUH VXFKH൵HFWVZLOOPDWHULDOOD൵HFWFDOFXODWHGGHVLJQDFWLRQV 6XFKH൵HFWVVKRXOGEHFRQVLGHUHGIRUGLDSKUDJPVWKDWXVH precast elements, with or without a cast-in-place topping. Where large transfer forces occur, as outlined in R12.2.1(b), more realistic design forces can be obtained by modeling GLDSKUDJPLQSODQHVWL൵QHVV'LDSKUDJPVZLWKORQJVSDQV large cutout areas, or other irregularities may develop in-plane deformations that should be considered in design (refer to Fig. R12.4.2.3a). For a diaphragm considered rigid in its own plane, and for semi-rigid diaphragms, the diaphragm internal force distri- bution can be obtained by modeling it as a horizontal rigid EHDP VXSSRUWHG RQ VSULQJV UHSUHVHQWLQJ ODWHUDO VWL൵QHVVHV RIWKHYHUWLFDOHOHPHQWV UHIHUWR)LJ5E (൵HFWV of in-plane eccentricity between applied forces and vertical element resistances, resulting in overall building torsion, should be included in the analysis. Elements of the lateral- force-resisting system aligned in the orthogonal direction can participate in resisting diaphragm plan rotation (Moehle et al. 2010). 12.4.2.3 Any set of reasonable and consistent assumptions IRUGLDSKUDJPVWL൵QHVVVKDOOEHSHUPLWWHG American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 179 CODE COMMENTARY 12 Diaphragms OPDWHULDOO OGEHFRQV with or w r forces o gn forces QHVWL൵QHV reas, or formations r to Fig. R12 For a d cast in precast element HQWVXSSRUWHGE DSKUDJPÀH 6XFK precas more GLDSK l ൵HFW elem arge alis JP RIGL ൵HFWV [LEL E Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 182. Diaphragm span, Diaphragm depth, h Lateral force Lateral-force resisting wall at each end δmax δwall Fig. R12.4.2.3a²([DPSOHRIGLDSKUDJPWKDWPLJKWQRWEH considered rigid in its plane. Plan Diaphragm shear Diaphragm moment Diaphragm boundary Vertical element and reaction force Center of resistance Lateral load Fig. R12.4.2.3b²'LDSKUDJPLQSODQHDFWLRQVREWDLQHGE PRGHOLQJWKHGLDSKUDJPDVDKRUL]RQWDOULJLGEHDPRQÀH[- ible supports. American Concrete Institute – Copyrighted © Material – www.concrete.org 180 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 183. 12.4.2.4 Calculation of diaphragm in-plane design moments, shears, and axial forces shall be consistent with requirements of equilibrium and with design boundary conditions. It shall be permitted to calculate design moments, shears, and axial forces in accordance with one of (a) through (e): (a) A rigid diaphragm model if the diaphragm can be idealized as rigid E $ÀH[LEOHGLDSKUDJPPRGHOLIWKHGLDSKUDJPFDQEH LGHDOL]HGDVÀH[LEOH (c) A bounding analysis in which the design values are the envelope of values obtained by assuming upper bound and ORZHUERXQGLQSODQHVWL൵QHVVHVIRUWKHGLDSKUDJPLQWZR or more separate analyses G $ ¿QLWH HOHPHQW PRGHO FRQVLGHULQJ GLDSKUDJP ÀH[LELOLW (e) A strut-and-tie model in accordance with 23.2 12.5—Design strength 12.5.1 General 12.5.1.1 For each applicable factored load combination, design strengths of diaphragms and connections shall satisfy ࢥSn•U,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOOEHFRQVLGHUHG ࢥ shall be determined in accordance with 21.2. R12.4.2.4 The rigid diaphragm model is widely used for diaphragms that are entirely cast-in-place and for diaphragms that comprise a cast-in-place topping slab on precast HOHPHQWVSURYLGHGÀH[LEOHFRQGLWLRQVDUHQRWFUHDWHGED long span, by a large aspect ratio, or by diaphragm irregu- ODULW)RUPRUHÀH[LEOHGLDSKUDJPVDERXQGLQJDQDOVLVLV sometimes done in which the diaphragm is analyzed as a VWL൵RUULJLGHOHPHQWRQÀH[LEOHVXSSRUWVDQGDVDÀH[LEOH diaphragm on rigid supports, with the design values taken as the envelope of values from the two analyses. Finite element models can be suitable for any diaphragm, but are especially useful for irregularly shaped diaphragms and diaphragms UHVLVWLQJODUJHWUDQVIHUIRUFHV6WL൵QHVVVKRXOGEHDGMXVWHG to account for expected concrete cracking under design loads. For jointed precast concrete diaphragms that rely on mechanical connectors, it may be necessary to include the MRLQWVDQGFRQQHFWRUVLQWKH¿QLWHHOHPHQWPRGHO6WUXWDQG tie models may be used for diaphragm design. The strut-and- tie models should include considerations of force reversals that may occur under design load combinations. R12.5—Design strength R12.5.1 General R12.5.1.1 Design actions commonly include in-plane moment, with or without axial force; in-plane shear; and axial compression and tension in collectors and other HOHPHQWVDFWLQJDVVWUXWVRUWLHV6RPHGLDSKUDJPFRQ¿JXUD- tions may result in additional types of design actions. For example, a diaphragm vertical step can result in out-of-plane bending, torsion, or both. The diaphragm is required to be designed for such actions where they occur in elements that are part of the load path. Nominal strengths are prescribed in Chapter 22 for a diaphragm idealized as a beam or solid element resisting in-plane moment, axial force, and shear; and in Chapter 23 for a diaphragm or diaphragm segment idealized as a strut- and-tie system. Collectors and struts around openings can be designed as compression members subjected to axial force using provisions of 10.5.2 with the strength reduction factor for compression-controlled members in 21.2.2. For axial tension in such members, nominal tensile strength is As fy, and the strength reduction factor is 0.90 as required for tension-controlled members in 21.2.2. Diaphragms are designed under load combinations of 5.3. Where a diaphragm or part of a diaphragm is subjected to PXOWLSOHORDGH൵HFWVWKHLQWHUDFWLRQRIWKHORDGH൵HFWVLVWR be considered. A common example is where a collector is built within a beam or slab that also resists gravity loads, in which case the element is designed for combined moment and axial force. Another example is where a connection is subjected to simultaneous tension and shear. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 181 CODE COMMENTARY 12 Diaphragms ral n actions without ax and ten VVWUXWVRU lt in add diaphragm ding, torsion, designed e f an DG tie that may occur u sign stren d load combina nnections shall sa VVKDOOEHFRQVLG on, isfy UHG R12 axial HOHP 5.1.1 t, w omp VDF De 5.1 G gth th Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 184. 12.5.1.3 Design strengths shall be in accordance with (a), (b), (c), or (d): (a) For a diaphragm idealized as a beam whose depth is equal to the full diaphragm depth, with moment resisted by boundary reinforcement concentrated at the diaphragm edges, design strengths shall be in accordance with 12.5.2 through 12.5.4. (b) For a diaphragm or a diaphragm segment modeled as a strut-and-tie system, design strengths shall be in accor- dance with 23.3. F )RUDGLDSKUDJPLGHDOL]HGZLWKD¿QLWHHOHPHQWPRGHO design strengths shall be in accordance with Chapter 22. Nonuniform shear distributions shall be considered in design for shear. Collectors in such designs shall be provided to transfer diaphragm shears to the vertical elements of the lateral-force-resisting system. (d) For a diaphragm designed by alternative methods, such methods shall satisfy the requirements of equilibrium and shall provide design strengths at least equal to required strengths for all elements in the load path. 12.5.1.4 It shall be permitted to use precompression from prestressed reinforcement to resist diaphragm forces. 12.5.1.5 If nonprestressed, bonded prestressing reinforce- ment is designed to resist collector forces, diaphragm shear, or tension due to in-plane moment, the value of steel stress used to calculate resistance shall not exceed the lesser of the VSHFL¿HGLHOGVWUHQJWKDQGSVL 12.5.2 0RPHQWDQGD[LDOIRUFH 12.5.2.1 It shall be permitted to design a diaphragm to resist in-plane moment and axial force in accordance with 22.3 and 22.4. R12.5.1.3 'L൵HUHQW GHVLJQ VWUHQJWK UHTXLUHPHQWV DSSO depending on how the diaphragm load-path is idealized. Section 12.5.1.3(a) addresses requirements for the common case where a diaphragm is idealized as a beam spanning between supports and resisting forces within its plane, with chord reinforcement at the boundaries to resist in-plane moment and axial force. If diaphragms are designed according to this model, then it is appropriate to assume WKDW VKHDU ÀRZ LV XQLIRUP WKURXJK WKH GLDSKUDJP GHSWK Diaphragm depth refers to the dimension measured in the direction of lateral forces within the plane of the diaphragm (refer to Fig. R12.4.2.3a). If vertical elements of the lateral- force-resisting system do not extend the full depth of the diaphragm, then collectors are required to transfer shear acting along the remaining portions of the diaphragm depth to the vertical elements. Sections 12.5.2 through 12.5.4 are based on this model. This design approach is acceptable even if some of the moment is resisted by precompression as provided by 12.5.1.4. Sections 12.5.1.3(b) through (d) permit alternative methods for design of diaphragms. If diaphragms are designed to resist moment through distributed chords, or LIGLDSKUDJPVDUHGHVLJQHGDFFRUGLQJWRVWUHVV¿HOGVGHWHU- PLQHG E ¿QLWHHOHPHQW DQDOVLV WKHQ QRQXQLIRUP VKHDU ÀRZVKRXOGEHWDNHQLQWRDFFRXQW R12.5.1.4,QWKHWSLFDOFDVHRIDSUHVWUHVVHGÀRRUVODE prestressing is required, at a minimum, to resist the factored load combination 1.2D + 1.6L, where L may have been reduced as permitted by the general building code. For wind or earthquake design, however, the gravity load to be resisted by prestressing is reduced because the governing load combination is 1.2D + f1L + (W or E), where f1 is either 1.0 or 0.5 depending on the nature of L. Thus, only a portion RI WKH H൵HFWLYH SUHVWUHVV LV UHTXLUHG WR UHVLVW WKH UHGXFHG JUDYLWORDGV7KHUHPDLQGHURIWKHH൵HFWLYHSUHVWUHVVFDQ be used to resist in-plane diaphragm moments. Additional moment, if any, is resisted by added reinforcement. R12.5.1.5 Nonprestressed bonded prestressing reinforce- ment, either strand or bars, is sometimes used to resist diaphragm design forces. The imposed limit on assumed yield strength is to control crack width and joint opening. The Code does not include provisions for developing nonprestressed, bonded prestressing reinforcement. Stress limits for other provided reinforcement are prescribed in Chapter 20. R12.5.2 0RPHQWDQGD[LDOIRUFH R12.5.2.1 This section permits design for moment and axial force in accordance with the usual assumptions of 22.3 and 22.4, including the assumption that strains vary linearly through the depth of the diaphragm. In most cases, design for moment and axial force can be accomplished satisfacto- American Concrete Institute – Copyrighted © Material – www.concrete.org 182 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY UHGHVLJQHG OHPHQW DQ QLQWRDFF WSLFDOF quired, at on 1.2D permitted d or earthqua resisted m and qual to required path. to st d as pro Sections 12. ods for design resist mom precompression hragm forces. om PLQ ÀRZV R12 prest l E ¿ RXOG 5.1.4 sing d to KUDJP ent nt Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 185. 12.5.2.2Itshallbepermittedtoresisttensionduetomoment by (a), (b), (c), or (d), or those methods in combination: (a) Deformed bars conforming to 20.2.1 (b) Strands or bars conforming to 20.3.1, either prestressed or nonprestressed (c) Mechanical connectors crossing joints between precast elements (d) Precompression from prestressed reinforcement 12.5.2.3 Nonprestressed reinforcement and mechanical connectors resisting tension due to moment shall be located within h/4 of the tension edge of the diaphragm, where h is diaphragm depth measured in the plane of the diaphragm at that location. Where diaphragm depth changes along the span, it shall be permitted to develop reinforcement into adjacent diaphragm segments that are not within the h/4 limit. rily using an approximate tension-compression couple with the strength reduction factor equal to 0.90. R12.5.2.2 Bonded prestressing reinforcement used to resist in-plane moment and axial force can be either prestressed or nonprestressed. Mechanical connectors crossing joints between precast concrete elements are provided to complete a continuous load path for reinforcement embedded in those elements. The use of precompression from prestressed rein- forcement is discussed in R12.5.1.4. R12.5.2.3 Figure R12.5.2.3 illustrates permitted locations of nonprestressed reinforcement resisting tension due to moment and axial force. Where diaphragm depth changes along the span, it is permitted to develop tension reinforce- ment in adjacent sections even if the reinforcement falls outside the h/4 limit of the adjacent section. In such cases, the strut-and-tie method or elastic plane stress analysis can be used to determine bar extensions and other reinforce- ment requirements to provide continuity across the step. The restriction on location of nonprestressed reinforcement and mechanical connectors is intended to control cracking and excessive joint opening that might occur near the edges if reinforcement or mechanical connectors were distributed WKURXJKRXWWKHGLDSKUDJPGHSWK7KHFRQFHQWUDWLRQRIÀH[- ural tension reinforcement near the edge of the diaphragm DOVRUHVXOWVLQPRUHXQLIRUPVKHDUÀRZWKURXJKWKHGHSWKRI the diaphragm. There are no restrictions on placement of prestressed rein- forcement provided to resist moment through precompres- VLRQ,QH൵HFWWKHSUHFRPSUHVVLRQGHWHUPLQHVDPRPHQWWKDW the prestressed reinforcement can resist, with the remainder of the moment resisted by reinforcement or mechanical connectors placed in accordance with 12.5.2.3. The Code does not require that diaphragm boundary HOHPHQWV UHVLVWLQJ GHVLJQ ÀH[XUDO FRPSUHVVLRQ IRUFHV EH detailed as columns. However, where a boundary element resists a large compressive force compared with axial strength, or is designed as a strut adjacent to an edge or opening, detailing with transverse reinforcement similar to column hoops should be considered. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 183 CODE COMMENTARY 12 Diaphragms cation of n ctors is in ning that mechanica SKUDJPG orcement PRUHXQLI gm. here are no re forcemen jacent 4 limit. ou the strut-and-tie ed to determin ements to pro mec exces KURXJ ural ical ve jo eme RXW sion quir on o vid vid Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 186. 12.5.2.4 Mechanical connectors crossing joints between precast elements shall be designed to resist required tension under the anticipated joint opening. 12.5.3 Shear 12.5.3.1 This section shall apply to diaphragm in-plane shear strength. 12.5.3.2 ࢥVKDOOEHXQOHVVDOHVVHUYDOXHLVUHTXLUHG by 21.2.4. 12.5.3.3 For a diaphragm that is entirely cast-in-place, Vn shall be calculated by Eq. (12.5.3.3). ) (2 c n cv t y V f A f = λ + ρ ′ (12.5.3.3) Plan h2 h1 Zones for placement of reinforcement Vertical element Diaphragm boundary Lateral load 1 2 h2/4 h2/4 h1/4 h1/4 Reinforcement for span 1 placed within depth h1/4. Reinforcement can be developed outside shaded zones. Other reinforcement required for force transfer not shown. Fig. R12.5.2.3²/RFDWLRQVRIQRQSUHVWUHVVHGUHLQIRUFHPHQW UHVLVWLQJWHQVLRQGXHWRPRPHQWDQGD[LDOIRUFHDFFRUGLQJ WR R12.5.2.4 In an untopped precast diaphragm resisting in-plane forces and responding in the linear range, some joint opening (on the order of 0.1 in. or less) should be antic- ipated. A larger joint opening may occur under earthquake motions exceeding the design level. Mechanical connectors should be capable of maintaining design strength under the anticipated joint opening. R12.5.3 Shear R12.5.3.1 These provisions assume that diaphragm shear ÀRZLVDSSUR[LPDWHOXQLIRUPRYHUWKHGLDSKUDJPGHSWKDV is the case where design is in accordance with 12.5.1.3(a). Where alternative approaches are used, local variations of in-plane shear through the diaphragm depth should be considered. R12.5.3.2 A lower strength reduction factor may be required in Seismic Design Categories D, E, or F, or where special systems for earthquake resistance are used. R12.5.3.3 This provision was adapted from the earth- quake-resistant design provisions of 18.12.9. The term Acv UHIHUVWRWKHFURVVVHFWLRQDODUHDRIWKHH൵HFWLYHGHHSEHDP that forms the diaphragm. American Concrete Institute – Copyrighted © Material – www.concrete.org 184 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 187. R12.5.3.5 For diaphragms with cast-in-place topping slab RQSUHFDVWHOHPHQWVWKHH൵HFWLYHWKLFNQHVVLQ D LV reduced to the topping slab thickness if the topping slab is not composite with the precast elements. Topping slabs tend to develop cracks above and along the joints between precast elements. Thus, 12.5.3.5(b) limits the shear strength to the shear-friction strength of the topping slab above the joints between the precast elements. R12.5.3.6 This Code does not contain provisions for untopped diaphragms in buildings assigned to Seismic Design Categories D, E, and F. Diaphragm shear in untopped diaphragms can be resisted by using shear-friction reinforce- ment in grouted joints (FEMA P751). Required shear-fric- tion reinforcement is in addition to reinforcement required by design to resist other tensile forces in the diaphragm, such as those due to diaphragm moment and axial force, or due to collector tension. The intent is to reduce joint opening while simultaneously resisting shear through shear-friction. Alternatively, or additionally, mechanical connectors can be used to transfer shear across joints of precast elements. In this case, some joint opening should be anticipated. The mechanical connectors should be capable of maintaining design strength under anticipated joint opening. R12.5.3.7 In addition to having adequate shear strength within its plane, a diaphragm should be reinforced to transfer shear through shear-friction or mechanical connectors to collectorsandtoverticalelementsofthelateral-force-resisting where Acv is the gross area of concrete bounded by diaphragm web thickness and depth, reduced by void areas if present; the value of ′ c f used to calculate Vn shall not exceed 100 psi; and ȡt refers to the distributed reinforcement oriented parallel to the in-plane shear. 12.5.3.4 For a diaphragm that is entirely cast-in-place, cross-sectional dimensions shall be selected to satisfy Eq. (12.5.3.4). 8 c u cv V f A ≤ φ ′ (12.5.3.4) where the value of ′ c f used to calculate Vn shall not exceed 100 psi. 12.5.3.5 For diaphragms that are cast-in-place concrete WRSSLQJVODEVRQSUHFDVWHOHPHQWV D DQG E VKDOOEHVDWLV¿HG (a) Vn shall be calculated in accordance with Eq. (12.5.3.3), and cross-sectional dimensions shall be selected to satisfy Eq. (12.5.3.4). Acv shall be calculated using the thickness of the topping slab for noncomposite topping slab diaphragms and the combined thickness of cast-in-place and precast elements for composite topping slab diaphragms. For composite topping slab diaphragms, the value of fcƍ in Eq. (12.5.3.3) and (12.5.3.4) shall not exceed the lesser of fcƍ for the precast members and fcƍ for the topping slab. (b) Vn shall not exceed the value calculated in accordance with the shear-friction provisions of 22.9 considering the thickness of the topping slab above joints between precast elements in noncomposite and composite topping slab diaphragms and the reinforcement crossing the joints between the precast members. 12.5.3.6 For diaphragms that are interconnected precast elements without a concrete topping, and for diaphragms that are precast elements with end strips formed by either a cast-in-place concrete topping slab or edge beams, it shall be permitted to design for shear in accordance with (a), (b), or both. (a) The nominal strength of grouted joints shall not exceed 80 psi. Reinforcement shall be designed to resist shear through shear-friction in accordance with 22.9. Shear-fric- tion reinforcement shall be in addition to reinforcement designed to resist tension due to moment and axial force. (b) Mechanical connectors crossing joints between precast elements shall be designed to resist required shear under anticipated joint opening. 12.5.3.7 For any diaphragm, where shear is transferred from the diaphragm to a collector, or from the diaphragm or collector to a vertical element of the lateral-force-resisting system, (a) or (b) shall apply: American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 185 CODE COMMENTARY 12 Diaphragms cast elemen ab not co to develop crack ents. Thus, 12.5 n strength o h Eq. sions shall be cv shall b g slab the c men site 3. p c composite top ing slab diaphra d (12.5.3.4) shal t members and f d i g ms, not for ictio n the f th th Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 188. system. In diaphragms that are entirely cast-in-place, rein- forcement provided for other purposes usually is adequate to transfer force from the diaphragm into the collectors through shear-friction. However, additional reinforcement may be required to transfer diaphragm or collector shear into vertical elements of the lateral-force-resisting system through shear- friction. Figure R12.5.3.7 illustrates a common detail of dowels provided for this purpose. Dowels Structural wall Collector reinforcement distributed transversely into the diaphragm Cold joint Fig. R12.5.3.7—Typical detail showing dowels provided for shear transfer to a structural wall through shear-friction. R12.5.4 Collectors A collector is a region of a diaphragm that transfers forces between the diaphragm and a vertical element of the lateral- force-resisting system. A collector can extend transversely into the diaphragm to reduce nominal stresses and rein- forcement congestion, as shown in Fig. R12.5.3.7. Where a collector width extends into the slab, the collector width on each side of the vertical element should not exceed approxi- mately one-half the contact length between the collector and the vertical element. R12.5.4.1 The design procedure in 12.5.1.3(a) models the GLDSKUDJPDVDIXOOGHSWKEHDPZLWKXQLIRUPVKHDUÀRZ,I vertical elements of the lateral-force-resisting system do not extend the full depth of the diaphragm, then collectors are required to transfer shear acting along the remaining portions of the diaphragm depth to the vertical element, as shown in Fig. R12.5.4.1. Partial-depth collectors can also be consid- ered, but a complete force path should be designed that is capable of transmitting all forces from the diaphragm to the collector and into the vertical elements (Moehle et al. 2010). (a) Where shear is transferred through concrete, the shear- friction provisions of 22.9VKDOOEHVDWLV¿HG (b) Where shear is transferred through mechanical FRQQHFWRUVRUGRZHOVH൵HFWVRIXSOLIWDQGURWDWLRQRIWKH vertical element of the lateral-force-resisting system shall be considered. 12.5.4 Collectors 12.5.4.1 Collectors shall extend from the vertical elements of the lateral-force-resisting system across all or part of the diaphragm depth as required to transfer shear from the diaphragm to the vertical element. It shall be permitted to discontinue a collector along lengths of vertical elements of the lateral-force-resisting system where transfer of design collector forces is not required. American Concrete Institute – Copyrighted © Material – www.concrete.org 186 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 189. Compression Tension a b c d (b) Collector tension and compression forces Collector reinforcement Shear-friction reinforcement Shear Wall (a) Collector and shear- friction reinforcement Fig. R12.5.4.1—Full-depth collector and shear-friction UHLQIRUFHPHQWUHTXLUHGWRWUDQVIHUFROOHFWRUIRUFHLQWRZDOO R12.5.4.2 Tension and compression forces in a collector are determined by the diaphragm shear forces they transmit to the vertical elements of the lateral-force-resisting system (refer to Fig. R12.5.4.1). Except as required by 18.12.7.6, the Code does not require that collectors resisting design compressive forces be detailed as columns. However, in structures where collectors resist large compressive forces compared with axial strength, or are designed as struts passing adjacent to edges or openings, detailing with trans- verse reinforcement similar to column hoops should be considered. Such detailing is required by 18.12.7.6 for some diaphragms in buildings assigned to Seismic Design Catego- ries D, E, and F. R12.5.4.3 ,Q DGGLWLRQ WR KDYLQJ VX൶FLHQW GHYHORSPHQW length, the collector reinforcement should be extended as needed to fully transfer its forces into the vertical elements of the lateral-force-resisting system. A common practice is to extend some of the collector reinforcement the full length of the vertical element, such that collector forces can be transmitted uniformly through shear-friction (refer to Fig. R12.5.4.1). Figure R12.5.4.3 shows an example of collector reinforcement extended as required to transfer forces into three frame columns. 12.5.4.2 Collectors shall be designed as tension members, compression members, or both, in accordance with 22.4. 12.5.4.3 Where a collector is designed to transfer forces to a vertical element, collector reinforcement shall extend along the vertical element at least the greater of (a) and (b): (a) The length required to develop the reinforcement in tension (b) The length required to transmit the design forces to the vertical element through shear-friction in accordance with 22.9, through mechanical connectors, or through other force transfer mechanisms American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 187 CODE COMMENTARY 12 Diaphragms Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 190. Collector force Collector reinforcement Lateral-force-resisting frame ≥ d ≥ d ≥ dh Note: Collector reinforcement should extend as required to transfer forces into the vertical element and should be developed at critical sections. Fig. R12.5.4.3²6FKHPDWLFIRUFHWUDQVIHUIURPFROOHFWRULQWR YHUWLFDOHOHPHQWRIWKHODWHUDOIRUFHUHVLVWLQJVVWHP R12.7—Reinforcement detailing R12.7.1 General R12.7.1.1 For a structure assigned to Seismic Design Category D, E, or F, concrete cover may be governed by the requirements of 18.12.7.7. R12.7.2 5HLQIRUFHPHQWVSDFLQJ R12.7.2.1 For a structure assigned to Seismic Design DWHJRU'(RU)VSDFLQJRIFRQ¿QLQJUHLQIRUFHPHQWLQ collectors may be governed by the requirements of 18.12.7.6. 12.6—Reinforcement limits 12.6.1 Reinforcement to resist shrinkage and temperature stresses shall be in accordance with 24.4. 12.6.2 Except for slabs-on-ground, diaphragms that are SDUWRIÀRRURUURRIFRQVWUXFWLRQVKDOOVDWLVIUHLQIRUFHPHQW limits for one-way slabs in accordance with 7.6 or two-way slabs in accordance with 8.6, as applicable. 12.6.3 Reinforcement designed to resist diaphragm in-plane forces shall be in addition to reinforcement designed WRUHVLVWRWKHUORDGH൵HFWVH[FHSWUHLQIRUFHPHQWGHVLJQHG WR UHVLVW VKULQNDJH DQG WHPSHUDWXUH ORDG H൵HFWV VKDOO EH permitted to also resist diaphragm in-plane forces 12.7—Reinforcement detailing 12.7.1 General 12.7.1.1 Concrete cover for reinforcement shall be in accordance with 20.5.1. 12.7.1.2 Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4, unless longer lengths are required by Chapter 18. 12.7.1.3 Splices of deformed reinforcement shall be in accordance with 25.5. 12.7.1.4 Bundled bars shall be in accordance with 25.6. 12.7.2 5HLQIRUFHPHQWVSDFLQJ 12.7.2.1 Minimum spacing s of reinforcement shall be in accordance with 25.2. American Concrete Institute – Copyrighted © Material – www.concrete.org 188 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY and temperature 4. ound QVK ord s a ned o WLVIUHLQIRUFH with 7 6 or two able. resist diaph QW way m Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 191. 12.7.2.2 Maximum spacing s of deformed reinforcement VKDOOEHWKHOHVVHURI¿YHWLPHVWKHGLDSKUDJPWKLFNQHVVDQG 18 in. 12.7.3 'LDSKUDJPDQGFROOHFWRUUHLQIRUFHPHQW 12.7.3.1 Except for slabs-on-ground, diaphragms that DUHSDUWRIÀRRURUURRIFRQVWUXFWLRQVKDOOVDWLVIUHLQIRUFH- ment detailing of one-way slabs in accordance with 7.7 or two-way slabs in accordance with 8.7, as applicable. 12.7.3.2 Calculated tensile or compressive force in rein- forcement at each section of the diaphragm or collector shall be developed on each side of that section. 12.7.3.3 Reinforcement provided to resist tension shall extend beyond the point at which it is no longer required to resist tension at least Ɛd, except at diaphragm edges and at expansion joints. R12.7.3 'LDSKUDJPDQGFROOHFWRUUHLQIRUFHPHQW R12.7.3.2 Critical sections for development of reinforce- ment generally are at points of maximum stress, at points where adjacent terminated reinforcement is no longer required to resist design forces, and at other points of discon- tinuity in the diaphragm. R12.7.3.3 )RU D EHDP WKH RGH UHTXLUHV ÀH[XUDO UHLQ- forcement to extend the greater of d and 12db past points ZKHUHLWLVQRORQJHUUHTXLUHGIRUÀH[XUH7KHVHH[WHQVLRQV are important for a beam to protect against development or shear failure that could result from inaccuracies in calculated locations of tensile stress. Similar failures in diaphragms have not been reported. To simplify design and avoid exces- sively long bar extensions that could result if the beam provisions were applied to diaphragms, this provision only requires that tension reinforcement extend Ɛd beyond points where it is no longer required to resist tension. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 189 CODE COMMENTARY 12 Diaphragms nsile stress. orted. To s tensions plied to d n reinforc ger requir red to gm edges and at forcem ZKHUHLWLVQROR mportant for a b that could r have sively equir wher t be ong ons w tha t is n lur ns of sul u Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 192. 190 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 193. 13.1—Scope 13.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed foundations, including shallow foundations (a) through (f), deep foundations (g) through (i), and retaining walls (j) and (k): (a) Strip footings (b) Isolated footings (c) Combined footings (d) Mat foundations (e) Grade beams (f) Pile caps (g) Piles (h) Drilled piers (i) Caissons (j) Cantilever retaining walls (k) Counterfort and buttressed cantilever retaining walls R13.1—Scope While requirements applicable to foundations are provided in this chapter, the majority of requirements used for founda- tion design are found in other chapters of the Code. These other chapters are referenced in Chapter 13. However, the DSSOLFDELOLW RI WKH VSHFL¿F SURYLVLRQV ZLWKLQ WKHVH RWKHU FKDSWHUVPDQRWEHH[SOLFLWOGH¿QHGIRUIRXQGDWLRQV R13.1.1 Examples of foundation types covered by this chapter are illustrated in Fig. R13.1.1. Stepped and sloped footings are considered to be subsets of other footing types. The 2019 edition of the Code contains provisions for the design of deep foundations. These provisions are based in part on similar provisions that were previously included in $6(6(, and the IBC. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 191 CODE COMMENTARY 13 Foundations d ca er retaining w CHAPTER 13—FOUNDATIONS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 194. 13.1.2 Foundations excluded by 1.4.7 are excluded from this chapter. Fig. R13.1.1—Types of foundations. Strip footing Isolated footing Stepped footing Combined footing Deep foundation system with piles and pile cap Column Mat foundation Piles Pile cap Stem Heel Counterfort Counterfort/buttressed Toe Heel Key (optional) Stem Toe Key (optional) American Concrete Institute – Copyrighted © Material – www.concrete.org 192 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Pile c g Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 195. R13.2—General R13.2.3 (DUWKTXDNHHৼHFWV R13.2.3.17KHEDVHRIDVWUXFWXUHDVGH¿QHGLQDQDOVLV does not necessarily correspond to the foundation or ground OHYHORUWRWKHEDVHRIDEXLOGLQJDVGH¿QHGLQWKHJHQHUDO building code for planning (for example, for height limits or ¿UHSURWHFWLRQUHTXLUHPHQWV 'HWDLOVRIFROXPQVDQGZDOOV extending below the base of a structure to the foundation are required to be consistent with those above the base of the structure. For additional discussion of the design of founda- WLRQVIRUHDUWKTXDNHH൵HFWVVHHR18.13.1. R13.2.4 Slabs-on-ground Slabs-on-ground often act as a diaphragm to hold the EXLOGLQJWRJHWKHUDWWKHJURXQGOHYHODQGPLQLPL]HWKHH൵HFWV of out-of-phase ground motion that may occur over the foot- print of the building. In these cases, the slab-on-ground should be adequately reinforced and detailed. As required in Chapter 26, construction documents should clearly state that these slabs-on-ground are structural members so as to prohibit sawcutting of such slabs. R13.2.6 Design criteria 13.2—General 13.2.1 Materials 13.2.1.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 13.2.1.2 Design properties for steel reinforcement shall be selected to be in accordance with Chapter 20. 13.2.1.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 13.2.2 RQQHFWLRQWRRWKHUPHPEHUV 13.2.2.1 Design and detailing of cast-in-place and precast column, pedestal, and wall connections to foundations shall be in accordance with 16.3. 13.2.3 (DUWKTXDNHHৼHFWV 13.2.3.1 Structural members extending below the base of the structure that are required to transmit forces resulting IURPHDUWKTXDNHH൵HFWVWRWKHIRXQGDWLRQVKDOOEHGHVLJQHG in accordance with 18.2.2.3. 13.2.3.2 For structures assigned to Seismic Design Cate- gory (SDC) C, D, E, or F, foundations resisting earthquake- induced forces or transferring earthquake-induced forces between structure and ground shall be designed in accor- dance with 18.13. 13.2.4 Slabs-on-ground 13.2.4.1 Slabs-on-ground that transmit vertical loads or lateral forces from other parts of the structure to the ground shall be designed and detailed in accordance with applicable provisions of this Code. 13.2.4.2 Slabs-on-ground that transmit lateral forces as part of the seismic-force-resisting system shall be designed in accordance with 18.13. 13.2.5 Plain concrete 13.2.5.1 Plain concrete foundations shall be designed in accordance with Chapter 14. 13.2.6 Design criteria American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 193 CODE COMMENTARY 13 Foundations EDVHRIDE planning ( LUHPHQWV base of a sistent w itional di TXDNHH൵H e R 3.2.3.17KHEDVH essarily cor ing below transm XQGD buil ¿UHSU requir struc g cod WHFWL ng b d to e. F t nec UWR esp sp Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 196. R13.2.6.1 Permissible soil pressures or permissible deep foundation strengths are determined by principles of soil mechanics and in accordance with the general building code. The size of the base area of a footing on soil or the number and arrangement of deep foundation members are established by using allowable geotechnical strength and service-level load combinations or by using nominal geotechnical strength with resistance factor and factored load combinations. Only the calculated end moments at the base of a column or pedestal require transfer to the footing. The minimum moment requirement for slenderness considerations given in 6.6.4.5 need not be considered for transfer of forces and moments to footings. R13.2.6.3 To design a footing or pile cap for strength, the induced reactions due to factored loads applied to the foundation should be determined. For a single concentri- cally-loaded spread footing, the soil pressure due to factored loading is calculated as the factored load divided by the base area of the footing. For the case of footings or mats with eccentric loading, applied factored loads may be used to deter- mine soil pressures. For pile caps or mats supported by deep foundations, applied factored loads may be used to deter- mine member reactions. However, the resulting pressures or reactions may be incompatible with the geotechnical design resulting in unacceptable subgrade reactions or instability (Rogowsky and Wight 2010). In such cases, the design should be adjusted in coordination with the geotechnical engineer. Only the calculated end moments at the base of a column or pedestal require transfer to the footing. The minimum moment requirements for slenderness considerations given in 6.6.4.5 need not be considered for transfer of forces and moments to footings. R13.2.6.4 Foundation design is permitted to be based directly on fundamental principles of structural mechanics, provided it can be demonstrated that all strength and service- DELOLWFULWHULDDUHVDWLV¿HG'HVLJQRIWKHIRXQGDWLRQPD be achieved through the use of classic solutions based on a linearly elastic continuum, numerical solutions based on discrete elements, or yield-line analyses. In all cases, anal- yses and evaluation of the stress conditions at points of load application or pile reactions in relation to shear and torsion, DVZHOODVÀH[XUHVKRXOGEHLQFOXGHG R13.2.6.5 An example of the application of this provision is a pile cap similar to that shown in Fig. R13.1.1. Pile caps may be designed using a three-dimensional strut-and-tie 13.2.6.1 Foundations shall be proportioned for bearing H൵HFWV VWDELOLW DJDLQVW RYHUWXUQLQJ DQG VOLGLQJ DW WKH soil-foundation interface in accordance with the general building code. 13.2.6.2 For one-way shallow foundations, two-way isolated footings, or two-way combined footings and mat IRXQGDWLRQVLWLVSHUPLVVLEOHWRQHJOHFWWKHVL]HH൵HFWIDFWRU VSHFL¿HG LQ 22.5 for one-way shear strength and 22.6 for two-way shear strength. 13.2.6.3 Foundation members shall be designed to resist factored loads and corresponding induced reactions except as permitted by 13.4.2. 13.2.6.4 Foundation systems shall be permitted to be designed by any procedure satisfying equilibrium and geometric compatibility. 13.2.6.5 Foundation design in accordance with the strut- and-tie method, Chapter 23, shall be permitted. American Concrete Institute – Copyrighted © Material – www.concrete.org 194 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY uld be dete d footing, d as the fa For the pplied fac es. For pil pplied fac ber reactio ctions may b resultin .2.6.3 To desig reactions d be desig induc cally loadin eccent mine aded is c the c loa il pr uced ion ue t e Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 197. model satisfying Chapter 23 (Adebar et al. 1990) provided WKHVKHDUIRUFHOLPLWVRIDUHDOVRVDWLV¿HG Figure R13.2.6.5 illustrates the application of the shear force limits of 23.4.4 and the provisions of 13.2.7.2 for one-way shear design of a spread footing using the strut-and- tie method. Soil pressure within d from the face of the column or wall does not contribute to shear across the critical crack (Uzel et al. 2011), but the soil pressure within d contributes to the bending moment at the face of the column or wall. Shear crack Soil pressure contributing toVu d d Soil pressure Resultant of soil pressure applied to strut-and-tie model θ Fig. R13.2.6.5—One-way shear design of a spread footing XVLQJWKHVWUXWDQGWLHPHWKRG R13.2.7Criticalsectionsforshallowfoundationsandpilecaps R13.2.7.2 The shear strength of a footing is determined for the more severe condition of 8.5.3.1.1 and 8.5.3.1.2. The critical section for shear is measured from the face of the supported member (column, pedestal, or wall), except for masonry walls and members supported on steel base plates. 13.2.6.6 External moment on any section of a strip footing, isolated footing, or pile cap shall be calculated by passing a vertical plane through the member and calculating the moment of the forces acting over the entire area of member on one side of that vertical plane. 13.2.7 Critical sections for shallow foundations and pile caps 13.2.7.1 Mu at the supported member shall be permitted WREHFDOFXODWHGDWWKHFULWLFDOVHFWLRQGH¿QHGLQDFFRUGDQFH with Table 13.2.7.1. Table 13.2.7.1—Location of critical section for Mu Supported member Location of critical section Column or pedestal Face of column or pedestal Column with steel base plate Halfway between face of column and edge of steel base plate Concrete wall Face of wall Masonry wall Halfway between center and face of masonry wall 13.2.7.2 The location of critical section for factored shear in accordance with 7.4.3 and 8.4.3 for one-way shear or 8.4.4.1 for two-way shear shall be measured from the loca- tion of the critical section for Mu in 13.2.7.1. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 195 CODE COMMENTARY 13 Foundations buting toV e-way sh WLHPHWKR er il pressure f XVLQJ 3.2. HVWU So co Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 198. Calculation of shear requires that the soil reaction be obtained from factored loads, and the design strength be in accordance with Chapter 22. Where necessary, shear around individual piles may be investigated in accordance with 8.5.3.1.2. If shear perim- HWHUVRYHUODSWKHPRGL¿HGFULWLFDOSHULPHWHUbo should be taken as that portion of the smallest envelope of individual shear perimeters that will actually resist the critical shear for the group under consideration. One such situation is illus- trated in Fig. R13.2.7.2. Modified critical perimeter dpile d/2 dpile d/2 Overlap Pile Pile Cap Fig. R13.2.7.2²0RGL¿HGFULWLFDOSHULPHWHUIRUVKHDUZLWK RYHUODSSLQJFULWLFDOSHULPHWHUV 13.2.7.3 Circular or regular polygon-shaped concrete columns or pedestals shall be permitted to be treated as square members of equivalent area when locating critical sections for moment, shear, and development of reinforcement. 13.2.8 'HYHORSPHQWRIUHLQIRUFHPHQWLQVKDOORZIRXQGDWLRQV and pile caps 13.2.8.1 Development of reinforcement shall be in accor- dance with Chapter 25. 13.2.8.2 Calculated tensile or compressive force in rein- forcement at each section shall be developed on each side of that section. 13.2.8.3 Critical sections for development of reinforce- ment shall be assumed at the same locations as given in 13.2.7.1 for maximum factored moment and at all other vertical planes where changes of section or reinforcement occur. 13.2.8.4 Adequate anchorage shall be provided for tension reinforcement where reinforcement stress is not directly proportional to moment, such as in sloped, stepped, or tapered foundations; or where tension reinforcement is not parallel to the compression face. American Concrete Institute – Copyrighted © Material – www.concrete.org 196 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 199. R13.3—Shallow foundations R13.3.1 General R13.3.1.1 General discussion on the sizing of shallow foundations is provided in R13.2.6.1. R13.3.1.3 Anchorage of reinforcement in sloped, stepped, or tapered foundations is addressed in 13.2.8.4. R13.3.3 Two-way isolated footings R13.3.3.3 To minimize potential construction errors in placing bars, a common practice is to increase the amount of reinforcement in the short direction by ȕ ȕ and space it uniformly along the long dimension of the footing (CRSI Handbook 1984; Fling 1987). 13.3—Shallow foundations 13.3.1 General 13.3.1.1 Minimum base area of foundation shall be propor- tioned to not exceed the permissible bearing pressure when subjected to forces and moments applied to the foundation. Permissible bearing pressures shall be determined through principles of soil or rock mechanics in accordance with the general building code, or other requirements as determined EWKHEXLOGLQJR൶FLDO 13.3.1.2 Overall depth of foundation shall be selected such WKDWWKHH൵HFWLYHGHSWKRIERWWRPUHLQIRUFHPHQWLVDWOHDVWLQ 13.3.1.3 In sloped, stepped, or tapered foundations, depth and location of steps or angle of slope shall be such that GHVLJQUHTXLUHPHQWVDUHVDWLV¿HGDWHYHUVHFWLRQ 13.3.2 One-way shallow foundations 13.3.2.1 The design and detailing of one-way shallow foundations, including strip footings, combined footings, and grade beams, shall be in accordance with this section and the applicable provisions of Chapter 7 and Chapter 9. 13.3.2.2 Reinforcement shall be distributed uniformly across entire width of one-way footings. 13.3.3 Two-way isolated footings 13.3.3.1 The design and detailing of two-way isolated footings shall be in accordance with this section and the applicable provisions of Chapter 7 and Chapter 8. 13.3.3.2 In square two-way footings, reinforcement shall be distributed uniformly across entire width of footing in both directions. 13.3.3.3 In rectangular footings, reinforcement shall be distributed in accordance with (a) and (b): (a) Reinforcement in the long direction shall be distributed uniformly across entire width of footing. (b) For reinforcement in the short direction, a portion of the total reinforcement, ȖsAs, shall be distributed uniformly over a band width equal to the length of short side of footing, centered on centerline of column or pedestal. Remainder of reinforcement required in the short direc- tion, ±Ȗs)As, shall be distributed uniformly outside the center band width of footing, where Ȗs is calculated by: 2 ( 1) s γ = β + (13.3.3.3) where ȕ is the ratio of long to short side of footing. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 197 CODE COMMENTARY 13 Foundations -way isol he of one-w ngs, c cord f Ch ll foo 7 and Chapter distributed unifo s. mly Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 200. R13.3.4 7ZRZDFRPELQHGIRRWLQJVDQGPDWIRXQGDWLRQV R13.3.4.1 Detailed recommendations for design of combined footings and mat foundations are reported by ACI 336.2R. Also refer to Kramrisch and Rogers (1961). R13.3.4.2 The direct design method is a method used for the design of two-way slabs. Refer to R6.2.4.1. R13.3.4.3 Design methods using factored loads and VWUHQJWKUHGXFWLRQIDFWRUVࢥFDQEHDSSOLHGWRFRPELQHGIRRW- ings or mat foundations, regardless of the bearing pressure distribution. R13.3.4.4 To improve crack control due to thermal gradi- ents and to intercept potential punching shear cracks with tension reinforcement, the licensed design professional should consider specifying continuous reinforcement in each direction near both faces of mat foundations. R13.3.6 :DOOFRPSRQHQWVRIFDQWLOHYHUUHWDLQLQJZDOOV R13.3.6.2 Counterfort or buttressed cantilever retaining walls tend to behave more in two-way action than in one-way action; therefore, additional care should be given to crack control in both directions. R13.3.6.3 In general, the joint between the wall stem and the footing will be opening under lateral loads; therefore, the critical section should be at the face of the joint. If hooks are UHTXLUHGWRGHYHORSWKHZDOOÀH[XUDOUHLQIRUFHPHQWKRRNV should be located near the bottom of the footing with the free end of the bars oriented toward the opposite face of the wall (Nilsson and Losberg 1976). R13.4—Deep foundations R13.4.1 General 13.3.4 7ZRZDFRPELQHGIRRWLQJVDQGPDWIRXQGDWLRQV 13.3.4.1 The design and detailing of combined footings and mat foundations shall be in accordance with this section and the applicable provisions of Chapter 8. 13.3.4.2 The direct design method shall not be used to design combined footings and mat foundations. 13.3.4.3 Distribution of bearing pressure under combined footings and mat foundations shall be consistent with prop- erties of the soil or rock and the structure, and with estab- lished principles of soil or rock mechanics. 13.3.4.4 Minimum reinforcement in nonprestressed mat foundations shall be in accordance with 8.6.1.1. 13.3.5 :DOOVDVJUDGHEHDPV 13.3.5.1 The design of walls as grade beams shall be in accordance with the applicable provisions of Chapter 9. 13.3.5.2 If a grade beam wall is considered a deep beam in accordance with 9.9.1.1, design shall satisfy the requirements of 9.9. 13.3.5.3 Grade beam walls shall satisfy the minimum rein- forcement requirements of 11.6. 13.3.6 :DOOFRPSRQHQWVRIFDQWLOHYHUUHWDLQLQJZDOOV 13.3.6.1 The stem of a cantilever retaining wall shall be designed as a one-way slab in accordance with the appli- cable provisions of Chapter 7. 13.3.6.2 The stem of a counterfort or buttressed cantilever retaining wall shall be designed as a two-way slab in accor- dance with the applicable provisions of Chapter 8. 13.3.6.3 For walls of uniform thickness, the critical section IRUVKHDUDQGÀH[XUHVKDOOEHDWWKHLQWHUIDFHEHWZHHQWKH stem and the footing. For walls with a tapered or varied thick- ness, shear and moment shall be investigated throughout the height of the wall. 13.4—Deep foundations 13.4.1 General American Concrete Institute – Copyrighted © Material – www.concrete.org 198 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY each as gr pro is sh ns of Chapter 9 dered a deep bea tisfy the requirem m in ents Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 201. 13.4.1.1 Number and arrangement of deep foundation members shall be determined such that forces and moments applied to the foundation do not exceed the permissible deep foundation strength. Permissible deep foundation strength shall be determined through principles of soil or rock mechanics in accordance with the general building code, or RWKHUUHTXLUHPHQWVDVGHWHUPLQHGEWKHEXLOGLQJR൶FLDO 13.4.1.2 Design of deep foundation members shall be in accordance with 13.4.2 or 13.4.3. 13.4.2 $OORZDEOHD[LDOVWUHQJWK 13.4.2.1 It shall be permitted to design a deep foundation member using load combinations for allowable stress design in $6(6(, , Section 2.4, and the allowable strength VSHFL¿HGLQ7DEOHLI D DQG E DUHVDWLV¿HG (a) The deep foundation member is laterally supported for its entire height (b) The applied forces cause bending moments in the deep foundation member less than the moment due to an acci- dental eccentricity of 5 percent of the member diameter or width Table 13.4.2.1—Maximum allowable compressive strength for deep foundation members Deep foundation member type Maximum allowable compressive strength [1] Uncased cast-in-place concrete drilled or augered pile Pa = 0.3fcƍAg + 0.4fyAs (a) Cast-in-place concrete pile in rock or within a pipe, tube, or other permanent metal casing that does not satisfy 13.4.2.3 Pa = 0.33fcƍAg + 0.4fyAs [2] (b) Metal cased concrete pile FRQ¿QHGLQDFFRUGDQFHZLWK Pa = 0.4fcƍAg (c) Precast nonprestressed concrete pile Pa = 0.33fcƍAg + 0.4fyAs (d) Precast prestressed concrete pile Pa = (0.33fcƍ– 0.27fpc)Ag (e) [1] Ag applies to the gross cross-sectional area. If a temporary or permanent casing is used, the inside face of the casing shall be considered the concrete surface. [2] As does not include the steel casing, pipe, or tube. 13.4.2.2 ,I D RU E LV QRW VDWLV¿HG D deep foundation member shall be designed using strength design in accordance with 13.4.3. 13.4.2.3 Metal cased cast-in-place concrete deep foun- GDWLRQ PHPEHUV VKDOO EH FRQVLGHUHG WR EH FRQ¿QHG LI D WKURXJK I DUHVDWLV¿HG (a) Design shall not use the casing to resist any portion of the axial load imposed. (b)Casingshallhaveasealedtipandshallbemandrel-driven. R13.4.1.1 General discussion on selecting the number and arrangement of piles, drilled piers, and caissons is provided in R13.2.6.1. R13.4.2 $OORZDEOHD[LDOVWUHQJWK R13.4.2.1 Potential changes to lateral support of the deep foundation member due to liquefaction, excavation, or other causes, should be considered. The values in the Table 13.4.2.1 represent an upper bound for well understood soil conditions with quality workman- ship. A lower value for the maximum allowable compressive strength may be appropriate, depending on soil conditions and the construction and quality control procedures used. For auger-grout piles, where grout is placed through the stem of a hollow-stem auger as it is withdrawn from the soil, WKHVWUHQJWKFRH൶FLHQWRILVEDVHGRQDVWUHQJWKUHGXF- tion factor of 0.6. The designer should carefully consider the reliable grout strength, grout strength testing methods, and the minimum cross-sectional area of the pile, accounting for soil conditions and construction procedures. Additional information is provided in ACI 543R. R13.4.2.3 The basis for this allowable strength is the DGGHG VWUHQJWK SURYLGHG WR WKH FRQFUHWH E WKH FRQ¿QLQJ action of the steel casing. This strength applies only to non- axial load-bearing steel where the stress in the steel is taken in hoop tension instead of axial compression. In this Code, steel pile casing is not to be considered in the design of the pile to resist a portion of the pile axial load. Provisions for American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 199 CODE COMMENTARY 13 Foundations w-stem auge FLHQWRI he design gth, grou s-section s and con provided rted for g moment mom nt of al on M ship. A strength may be he construction rout piles, w ble compressi mbers um allowable e WKH tion fa the m for s QJWK tor o gro imu con ger-g a ho q whe he Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 202. (c) Thickness of the casing shall not be less than manufac- turer’s standard gauge No. 14 (0.068 in.). (d) Casing shall be seamless, or provided with seams of VWUHQJWKHTXDOWRWKHEDVLFPDWHULDODQGEHRIDFRQ¿JX- UDWLRQWKDWZLOOSURYLGHFRQ¿QHPHQWWRWKHFDVWLQSODFH concrete. (e) Ratio of yield strength of the steel casing to fcƍVKDOOEH at least 6, and yield strength shall be at least 30,000 psi. (f) Nominal diameter of the member shall be less than or equal to 16 in. 13.4.2.4 The use of allowable strengths greater than those VSHFL¿HGLQ7DEOHVKDOOEHSHUPLWWHGLIDFFHSWHGE WKHEXLOGLQJR൶FLDOLQDFFRUGDQFHZLWK1.10DQGMXVWL¿HGE load tests. 13.4.3 Strength design 13.4.3.1 Strength design in accordance with this section is permitted for all deep foundation members. 13.4.3.2 The strength design of deep foundation members shall be in accordance with 10.5 using the compressive strength reduction factors of Table 13.4.3.2 for axial load without moment, and the strength reduction factors of Table 21.2.1 for tension, shear, and combined axial force and moment. The provisions of 22.4.2.4 and 22.4.2.5 shall not apply to deep foundations. Table 13.4.3.2—Compressive strength reduction factors ࢥ for deep foundation members Deep foundation member type Compressive strength reduction factors ࢥ Uncased cast-in-place concrete drilled or augered pile[1] 0.55 (a) Cast-in-place concrete pile in rock or within a pipe, tube,[2] or other permanent casing that does not satisfy 13.4.2.3 0.60 (b) DVWLQSODFHFRQFUHWH¿OOHGVWHHOSLSHSLOH[3] 0.70 (c) 0HWDOFDVHGFRQFUHWHSLOHFRQ¿QHGLQ accordance with 13.4.2.3 0.65 (d) Precast-nonprestressed concrete pile 0.65 (e) Precast-prestressed concrete pile 0.65 (f) [1] The factor of 0.55 represents an upper bound for well understood soil conditions with quality workmanship. A lower value for the strength reduction factor may be appropriate, depending on soil conditions and the construction and quality control procedures used. [2] For wall thickness of the steel pipe or tube less than 0.25 in. [3] Wall thickness of the steel pipe shall be at least 0.25 in. 13.4.4 Cast-in-place deep foundations 13.4.4.1 Cast-in-place deep foundations that are subject to uplift or where Mu is greater than 0.4Mcr shall be reinforced, unless enclosed by a structural steel pipe or tube. members designed to be composite with steel pipe or casing are covered in AISC 360. Potential corrosion of the metal casing should be consid- ered; provision is based on a non-corrosive environment. R13.4.2.4 Geotechnical and load test requirements for deep foundation members can be found in the IBC. R13.4.3 Strength design R13.4.3.2 The strength design of deep foundation members is discussed in detail in ACI 543R. If cast-in-place concrete drilled or augered piles are subject WR ÀH[XUH VKHDU RU WHQVLRQ ORDGV WKH VWUHQJWK UHGXFWLRQ factors should be adjusted accordingly, considering the soil conditions, quality-control procedures that will be imple- mented, likely workmanship quality, and local experience. Guidance for adjustment factors is provided in ACI 543R. R13.4.4 Cast-in-place deep foundations American Concrete Institute – Copyrighted © Material – www.concrete.org 200 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY ussed in de oncrete dr RU WHQVLRQ djusted ac -control p orkmansh djustment ection is deep fo .5 u abl gth d c 4. The stren 4.3.2 for axial ction factors of T ned axial force nd 22.4.2.5 shal ad ble and not If WR ÀH[ condit ment t-in- XUH shou ns, lik 4.3.2 rs is gth gth Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 203. 13.4.4.2 Portions of deep foundation members in air, water, or soils not capable of providing adequate restraint throughout the member length to prevent lateral buckling shall be designed as columns in accordance with the appli- cable provisions of Chapter 10. 13.4.5 Precast concrete piles 13.4.5.1 Precast concrete piles supporting buildings assigned to SDC A or B shall satisfy the requirements of 13.4.5.2 through 13.4.5.6. 13.4.5.2 Longitudinal reinforcement shall be arranged in a symmetrical pattern. 13.4.5.3 For precast nonprestressed piles, longitudinal reinforcement shall be provided according to (a) and (b): (a) Minimum of 4 bars (b) Minimum area of 0.008Ag 13.4.5.4)RUSUHFDVWSUHVWUHVVHGSLOHVWKHH൵HFWLYHSUHVWUHVV in the pile shall provide a minimum average compressive stress in the concrete in accordance with Table 13.4.5.4. Table 13.4.5.4—Minimum compressive stress in precast prestressed piles Pile length, ft Minimum compressive stress, psi 3LOHOHQJWK” 400 3LOHOHQJWK” 550 Pile length 50 700 13.4.5.5 )RU SUHFDVW SUHVWUHVVHG SLOHV WKH H൵HFWLYH prestress in the pile shall be calculated based on an assumed total loss of 30,000 psi in the prestressed reinforcement. 13.4.5.6 The longitudinal reinforcement shall be enclosed by transverse reinforcement according to Table 13.4.5.6(a) and shall be spaced according to Table 13.4.5.6(b): Table 13.4.5.6(a)—Minimum transverse reinforcement size Least horizontal pile dimension h, in. Minimum wire size transverse reinforcement[1] h” W4, D4 16 h 20 W4.5, D5 h• W5.5, D6 [1] If bars are used, minimum of No. 3 bar applies to all values of h. R13.4.5 Precast concrete piles R13.4.5.6 The minimum transverse reinforcement UHTXLUHG LQ WKLV VHFWLRQ LV WSLFDOO VX൶FLHQW IRU GULYLQJ and handling stresses. These provisions for precast concrete piles in SDC A and B are based on information from PCI 5HFRPPHQGHG 3UDFWLFH IRU WKH 'HVLJQ 0DQXIDFWXUH DQG Installation of Prestressed Concrete Piling (1993) and the PCI Bridge Design Manual, Chapter 20 (2004). Minimum reinforcement requirements for precast concrete piles supporting buildings assigned to SDC C, D, E, and F are GH¿QHGLQ18.13.5.10. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 201 CODE COMMENTARY 13 Foundations OHVWK mum nce o mum able 13.4.5.4. ssive stress i pressive stress, p Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 204. Table 13.4.5.6(b)—Maximum transverse reinforcement spacing Reinforcement location in the pile Maximum center-to- center spacing, in. )LUVW¿YHWLHVRUVSLUDOVDWHDFKHQGRISLOH 1 24 in. from each end of pile 4 Remainder of pile 6 13.4.6 Pile caps 13.4.6.1 Overall depth of pile cap shall be selected such that WKHH൵HFWLYHGHSWKRIERWWRPUHLQIRUFHPHQWLVDWOHDVWLQ 13.4.6.2 Factored moments and shears shall be permitted to be calculated with the reaction from any pile assumed to be concentrated at the centroid of the pile section. 13.4.6.3 Except for pile caps designed in accordance with 13.2.6.5, the pile cap shall be designed such that (a) is satis- ¿HGIRURQHZDIRXQGDWLRQVDQG D DQG E DUHVDWLV¿HGIRU two-way foundations. D ࢥVn•Vu, where Vn shall be calculated in accordance with 22.5 for one-way shear, Vu shall be calculated in accordance with 13.4.2.7, and ࢥ shall be in accordance with 21.2 E ࢥvn•vu, where vn shall be calculated in accordance with 22.6 for two-way shear, vu shall be calculated in accordance with 13.4.2.7, and ࢥ shall be in accordance with 21.2 13.4.6.4 If the pile cap is designed in accordance with WKHVWUXWDQGWLHPHWKRGDVSHUPLWWHGLQWKHH൵HF- tive concrete compressive strength of the struts, fce, shall be calculated in accordance with 23.4.3, where ȕs Ȝ, and Ȝ is in accordance with 19.2.4. 13.4.6.5 Calculation of factored shear on any section through a pile cap shall be in accordance with (a) through (c): (a) Entire reaction from any pile with its center located dpile/2 or more outside the section shall be considered as producing shear on that section. (b) Reaction from any pile with its center located dpile/2 or more inside the section shall be considered as producing no shear on that section. (c) For intermediate positions of pile center, the portion of the pile reaction to be considered as producing shear on the section shall be based on a linear interpolation between full value at dpile/2 outside the section and zero value at dpile/2 inside the section. R13.4.6 Pile caps R13.4.6.4 ,W LV WSLFDOO QHFHVVDU WR WDNH WKH H൵HFWLYH concrete compressive strength from expression (d) or (f) in Table 23.4.3(a) because it is generally not practical to provide FRQ¿QLQJUHLQIRUFHPHQWVDWLVILQJ23.5 in a pile cap. R13.4.6.5 If piles are located inside the critical sections d or d/2 from face of column, for one-way or two-way shear, respectively, an upper limit on the shear strength at a section adjacent to the face of the column should be considered. The CRSI Handbook (1984)R൵HUVJXLGDQFHIRUWKLVVLWXDWLRQ American Concrete Institute – Copyrighted © Material – www.concrete.org 202 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY nce with h that (a) is satis QG E DUH be ar, nd e c ated in accord hall be calculat all be in accord lated in accord e in nce ce Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 205. R14.1—Scope R14.1.2 Structural elements, such as cast-in-place plain FRQFUHWHSLOHVDQGSLHUVLQJURXQGRURWKHUPDWHULDOVX൶- FLHQWOVWL൵WRSURYLGHDGHTXDWHODWHUDOVXSSRUWWRSUHYHQW buckling, are not covered by the Code. Such elements are covered by the general building code. R14.1.3 Because the strength and structural integrity of structural plain concrete members is based solely on the member size, concrete strength, and other concrete prop- erties, use of structural plain concrete should be limited to members: (a) That are primarily in a state of compression (b) That can tolerate random cracks without detriment to their structural integrity (c) For which ductility is not an essential feature of design The tensile strength of concrete can be used in design of structural plain concrete members. Tensile stresses due to UHVWUDLQWIURPFUHHSVKULQNDJHRUWHPSHUDWXUHH൵HFWVDUH to be considered to avoid uncontrolled cracks or structural failure. For residential construction within the scope of ACI 332, refer to 1.4.6. R14.1.5 Because plain concrete lacks the necessary ductility that columns should possess, and because a random crack in an unreinforced column will most likely endanger 14.1—Scope 14.1.1 This chapter shall apply to the design of plain concrete members, including (a) and (b): (a) Members in building structures (b) Members in non-building structures such as arches, underground utility structures, gravity walls, and shielding walls 14.1.2 This chapter shall not govern the design of cast-in- place concrete piles and piers embedded in ground. 14.1.3 Plain concrete shall be permitted only in cases (a) through (d): (a) Members that are continuously supported by soil or supported by other structural members capable of providing continuous vertical support (b) Members for which arch action provides compression under all conditions of loading (c) Walls (d) Pedestals 14.1.4 Plain concrete shall be permitted for a structure assigned to Seismic Design Category (SDC) D, E, or F, only in cases (a) and (b): (a) Footings supporting cast-in-place reinforced concrete or reinforced masonry walls, provided the footings are reinforced longitudinally with at least two continuous reinforcing bars. Bars shall be at least No. 4 and have a total area of not less than 0.002 times the gross cross- sectional area of the footing. Continuity of reinforcement shall be provided at corners and intersections. (b) Foundation elements (i) through (iii) for detached one- and two-family dwellings not exceeding three stories and constructed with stud bearing walls: (i) Footings supporting walls (ii) Isolated footings supporting columns or pedestals LLL )RXQGDWLRQRUEDVHPHQWZDOOVQRWOHVVWKDQLQ WKLFNDQGUHWDLQLQJQRPRUHWKDQIWRIXQEDODQFHG¿OO 14.1.5 Plain concrete shall not be permitted for columns and pile caps. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 203 CODE COMMENTARY 14 Plain Conc. CHAPTER 14—PLAIN CONCRETE Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 206. its structural integrity, the Code does not permit use of plain concrete for columns. It does allow its use for pedes- tals limited to a ratio of unsupported height to least lateral dimension of 3 or less (refer to 14.1.3(d) and 14.3.3). R14.2—General R14.2.2 RQQHFWLRQWRRWKHUPHPEHUV R14.2.2.2 Provisions for plain concrete walls are appli- cable only for walls laterally supported in such a manner as to prohibit relative lateral displacement at top and bottom of individual wall elements. The Code does not cover walls without horizontal support to prohibit relative displacement at top and bottom of wall elements. Such laterally unsup- ported walls are to be designed as reinforced concrete members in accordance with the Code. R14.2.3 Precast Precast structural plain concrete members are considered subject to all limitations and provisions for cast-in-place concrete contained in this chapter. The approach to contraction or isolation joints is expected WR EH VRPHZKDW GL൵HUHQW WKDQ IRU FDVWLQSODFH FRQFUHWH because the major portion of shrinkage in precast members occurs prior to erection. To ensure stability, precast members should be connected to other members. The connection should transfer no tension. R14.3—Design limits R14.3.1 Bearing walls Plain concrete walls are commonly used for basement wall construction for residential and light commercial build- ings located in areas of low seismic risk. Although the Code imposes no absolute maximum height limitation on the use of plain concrete walls, experience with use of plain concrete in relatively minor structures should not be extrapolated to using plain concrete walls in multistory construction and RWKHUPDMRUVWUXFWXUHVZKHUHGL൵HUHQWLDOVHWWOHPHQWZLQG 14.2—General 14.2.1 Materials 14.2.1.1 Design properties for concrete shall be selected to be in accordance with Chapter 19. 14.2.1.2 Steel reinforcement, if required, shall be selected to be in accordance with Chapter 20. 14.2.1.3 Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6. 14.2.2 RQQHFWLRQWRRWKHUPHPEHUV 14.2.2.1 Tension shall not be transmitted through outside edges, construction joints, contraction joints, or isolation joints of an individual plain concrete element. 14.2.2.2 Walls shall be braced against lateral translation. 14.2.3 Precast 14.2.3.1 Design of precast members shall consider all loading conditions from initial fabrication to completion of the structure, including form removal, storage, transporta- tion, and erection. 14.2.3.2 Precast members shall be connected to transfer lateral forces into a structural system capable of resisting such forces. 14.3—Design limits 14.3.1 Bearing walls 14.3.1.1 Minimum bearing wall thickness shall be in accordance with Table 14.3.1.1. American Concrete Institute – Copyrighted © Material – www.concrete.org 204 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 207. earthquake, or other unforeseen loading conditions require the walls to possess some ductility and ability to maintain integrity when cracked. For such conditions,ACI Committee 318 strongly encourages the use of walls designed in accor- dance with Chapter 11. R14.3.2 Footings R14.3.2.1 Thickness of plain concrete footings of usual SURSRUWLRQVZLOOWSLFDOOEHFRQWUROOHGEÀH[XUDOVWUHQJWK H[WUHPH¿EHUVWUHVVLQWHQVLRQQRWJUHDWHUWKDQ ࢥȜ ′ c f ) rather than shear strength (refer to R14.5.5.1). For footings cast against soil, overall thickness h used for strength calcula- WLRQVLVVSHFL¿HGLQ R14.3.3 Pedestals R14.3.3.1 The height-thickness limitation for plain concrete pedestals does not apply for portions of pedestals embedded in soil capable of providing lateral restraint. R14.3.4 Contraction and isolation joints R14.3.4.1 Joints in plain concrete construction are an important design consideration. In reinforced concrete, reinforcement is provided to resist the stresses due to UHVWUDLQW RI FUHHS VKULQNDJH DQG WHPSHUDWXUH H൵HFWV ,Q plain concrete, joints are the only means of controlling, and thereby relieving, the buildup of such tensile stresses. A plain concrete member should therefore be small enough, or divided into smaller elements by joints, to control the buildup of internal stresses. The joint may be a contraction joint or isolation joint. A minimum 25 percent reduction RIPHPEHUWKLFNQHVVLVWSLFDOOVX൶FLHQWIRUFRQWUDFWLRQ MRLQWVWREHH൵HFWLYH7KHMRLQWLQJVKRXOGEHVXFKWKDWQR D[LDOWHQVLRQRUÀH[XUDOWHQVLRQFDQEHGHYHORSHGDFURVVD joint after cracking, if applicable—a condition referred to as ÀH[XUDOGLVFRQWLQXLW:KHUHUDQGRPFUDFNLQJGXHWRFUHHS VKULQNDJHDQGWHPSHUDWXUHH൵HFWVZLOOQRWD൵HFWVWUXFWXUDO integrity and is otherwise acceptable (such as transverse cracks in a continuous wall footing), transverse contraction or isolation joints should not be necessary. Table 14.3.1.1—Minimum thickness of bearing walls Wall type Minimum thickness General Greater of: 5.5 in. WKHOHVVHURIXQVXSSRUWHG length and unsupported height Exterior basement 7.5 in. Foundation 7.5 in. 14.3.2 Footings 14.3.2.1 Footing thickness shall be at least 8 in. 14.3.2.2 Base area of footing shall be determined from unfactored forces and moments transmitted by footing to soil and permissible soil pressure selected through principles of soil mechanics. 14.3.3 Pedestals 14.3.3.1 Ratio of unsupported height to average least lateral dimension shall not exceed 3. 14.3.4 Contraction and isolation joints 14.3.4.1 Contraction or isolation joints shall be provided WRGLYLGHVWUXFWXUDOSODLQFRQFUHWHPHPEHUVLQWRÀH[XUDOO discontinuous elements. The size of each element shall be selected to limit stress caused by restraint to movements IURPFUHHSVKULQNDJHDQGWHPSHUDWXUHH൵HFWV 14.3.4.2 The number and location of contraction or isola- tion joints shall be determined considering (a) through (f): American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 205 CODE COMMENTARY 14 Plain Conc. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 208. R14.4—Required strength R14.4.1 General R14.4.1.1 Plain concrete members are proportioned for adequate strength using factored loads and forces. When the design strength is exceeded, the cross section should be LQFUHDVHG RU WKH VSHFL¿HG VWUHQJWK RI FRQFUHWH LQFUHDVHG or both, or the member designed as a reinforced concrete member in accordance with the Code. An increase in FRQFUHWHVHFWLRQPDKDYHDGHWULPHQWDOH൵HFWVWUHVVGXHWR load will decrease but stresses due to creep, shrinkage, and WHPSHUDWXUHH൵HFWVPDLQFUHDVH D ,QÀXHQFHRIFOLPDWLFFRQGLWLRQV (b) Selection and proportioning of materials (c) Mixing, placing, and curing of concrete (d) Degree of restraint to movement (e) Stresses due to loads to which an element is subjected (f) Construction techniques 14.4—Required strength 14.4.1 General 14.4.1.1 Required strength shall be calculated in accor- GDQFH ZLWK WKH IDFWRUHG ORDG FRPELQDWLRQV GH¿QHG LQ Chapter 5. 14.4.1.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. 14.4.1.3 1R ÀH[XUDO FRQWLQXLW GXH WR WHQVLRQ VKDOO EH assumed between adjacent structural plain concrete elements. 14.4.2 Walls 14.4.2.1 Walls shall be designed for an eccentricity corre- sponding to the maximum moment that can accompany the axial load but not less than 0.10h, where h is the wall thickness. 14.4.3 Footings 14.4.3.1 General 14.4.3.1.1 For footings supporting circular or regular polygon-shaped concrete columns or pedestals, it shall be permitted to assume a square section of equivalent area for determining critical sections. 14.4.3.2 )DFWRUHGPRPHQW 14.4.3.2.1 The critical section for Mu shall be located in accordance with Table 14.4.3.2.1. Table 14.4.3.2.1—Location of critical section for Mu Supported member Location of critical section Column or pedestal Face of column or pedestal Column with steel base plate Halfway between face of column and edge of steel base plate Concrete wall Face of wall Masonry wall Halfway between center and face of masonry wall American Concrete Institute – Copyrighted © Material – www.concrete.org 206 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 209. 14.4.3.3 Factored one-way shear 14.4.3.3.1 For one-way shear, critical sections shall be located h from (a) and (b), where h is the footing thickness. D /RFDWLRQGH¿QHGLQ7DEOH (b) Face of concentrated loads or reaction areas 14.4.3.3.2 Sections between (a) or (b) of 14.4.3.3.1 and the critical section for shear shall be permitted to be designed for Vu at the critical section for shear. 14.4.3.4 Factored two-way shear 14.4.3.4.1 For two-way shear, critical sections shall be located so that the perimeter bo is a minimum but need not be closer than h/2 to (a) through (c): D /RFDWLRQGH¿QHGLQ7DEOH (b) Face of concentrated loads or reaction areas (c) Changes in footing thickness 14.4.3.4.2 For square or rectangular columns, concentrated loads, or reaction areas, the critical section for two-way shear shall be permitted to be calculated assuming straight sides. 14.5—Design strength 14.5.1 General 14.5.1.1 For each applicable factored load combina- tion, design strength at all sections shall satisfy ࢥSn•U, LQFOXGLQJ D WKURXJK G ,QWHUDFWLRQEHWZHHQORDGH൵HFWV shall be considered. (a) ࢥMn • Mu (b) ࢥPn • Pu (c) ࢥVn • Vu (d) ࢥBn • Bu ࢥ shall be determined in accordance with 21.2. 14.5.1.3 Tensile strength of concrete shall be permitted to be considered in design. R14.4.3.4 Factored two-way shear R14.4.3.4.17KHFULWLFDOVHFWLRQGH¿QHGLQWKLVSURYLVLRQ LVVLPLODUWRWKDWGH¿QHGIRUUHLQIRUFHGFRQFUHWHHOHPHQWVLQ 22.6.4.1, except that for plain concrete, the critical section is based on h rather than d. R14.5—Design strength R14.5.1 General R14.5.1.1 Refer to R9.5.1.1. R14.5.1.2 The strength reduction factor ࢥ for plain concrete design is the same for all strength conditions. %HFDXVH ERWK ÀH[XUDO WHQVLOH VWUHQJWK DQG VKHDU VWUHQJWK for plain concrete depend on the tensile strength character- istics of the concrete, with no reserve strength or ductility possible due to the absence of reinforcement, equal strength reduction factors for both bending and shear are considered appropriate. R14.5.1.3 Flexural tension may be considered in design of plain concrete members to resist loads, provided the calculated stress does not exceed the permissible stress, and construction, contraction, or isolation joints are provided to relieve the resulting tensile stresses due to restraint of creep, VKULQNDJHDQGWHPSHUDWXUHH൵HFWV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 207 CODE COMMENTARY 14 Plain Conc. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 210. 14.5.1.4 Flexure and axial strength calculations shall be based on a linear stress-strain relationship in both tension and compression. Ȝ for lightweight concrete shall be in accordance with 19.2.4. 14.5.1.6Nostrengthshallbeassignedtosteelreinforcement. 14.5.1.7 :KHQ FDOFXODWLQJ PHPEHU VWUHQJWK LQ ÀH[XUH FRPELQHGÀH[XUHDQGD[LDOORDGRUVKHDUWKHHQWLUHFURVV section shall be considered in design, except for concrete cast against soil where overall thickness h shall be taken as LQOHVVWKDQWKHVSHFL¿HGWKLFNQHVV 14.5.1.8 Unless demonstrated by analysis, horizontal OHQJWKRIZDOOWREHFRQVLGHUHGH൵HFWLYHIRUUHVLVWLQJHDFK vertical concentrated load shall not exceed center-to-center distance between loads, or bearing width plus four times the wall thickness. 14.5.2 )OH[XUH 14.5.2.1 Mn shall be the lesser of Eq. (14.5.2.1a) calcu- lated at the tension face and Eq. (14.5.2.1b) calculated at the compression face: 5 Q F P M f S = λ ′ (14.5.2.1a) Mn = 0.85fcƍSP (14.5.2.1b) where Sm is the corresponding elastic section modulus. 14.5.3 $[LDOFRPSUHVVLRQ 14.5.3.1 Pn shall be calculated by: 2 0.60 1 32 c n c g P f A h ⎡ ⎤ ⎛ ⎞ = − ′ ⎢ ⎥ ⎜ ⎟ ⎝ ⎠ ⎢ ⎥ ⎣ ⎦ A (14.5.3.1) 14.5.4 )OH[XUHDQGD[LDOFRPSUHVVLRQ 14.5.4.1 Unless permitted by 14.5.4.2, member dimen- sions shall be proportioned to be in accordance with Table 14.5.4.1, where Mn is calculated in accordance with Eq. (14.5.2.1b) and Pn is calculated in accordance with Eq. (14.5.3.1). R14.5.1.7 The reduced overall thickness h for concrete cast against earth is to allow for unevenness of excavation and for some contamination of the concrete adjacent to the soil. R14.5.2 )OH[XUH R14.5.2.1 Equation (14.5.2.1b) may control for nonsym- metrical cross sections. R14.5.3 $[LDOFRPSUHVVLRQ R14.5.3.1 (TXDWLRQ LV SUHVHQWHG WR UHÀHFW the general range of braced and restrained end conditions HQFRXQWHUHGLQSODLQFRQFUHWHHOHPHQWV7KHH൵HFWLYHOHQJWK IDFWRUZDVRPLWWHGDVDPRGL¿HURIƐc, the vertical distance between supports, because this is conservative for walls with assumed pin supports that are required to be braced against lateral translation as in 14.2.2.2. R14.5.4 )OH[XUHDQGD[LDOFRPSUHVVLRQ American Concrete Institute – Copyrighted © Material – www.concrete.org 208 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 211. Table 14.5.4.1—Combined flexure and axial compression Location Interaction equation Tension face 5 u u c P J M P f S A − ≤ φ λ ′ (a) Compression face 1.0 u u n n M P M P + ≤ φ φ (b) 14.5.4.2 For walls of solid rectangular cross section where Mu”Pu(h/6), Mu need not be considered in design and Pn is calculated by: 2 0.45 1 32 c n c g P f A h ⎡ ⎤ ⎛ ⎞ = − ′ ⎢ ⎥ ⎜ ⎟ ⎝ ⎠ ⎢ ⎥ ⎣ ⎦ A (14.5.4.2) 14.5.5 Shear 14.5.5.1 Vn shall be calculated in accordance with Table 14.5.5.1. Table 14.5.5.1—Nominal shear strength Shear action Nominal shear strength Vn One-way 4 3 c w f b h λ ′ (a) Two-way Lesser of: 2 4 1 3 c o f b h ⎛ ⎞ ⎛ ⎞ + λ ′ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ β⎠ [1] (b) 4 2 3 c o f b h ⎛ ⎞ λ ′ ⎜ ⎟ ⎝ ⎠ (c) [1] ȕLVWKHUDWLRRIORQJVLGHWRVKRUWVLGHRIFRQFHQWUDWHGORDGRUUHDFWLRQDUHD 14.5.6 Bearing 14.5.6.1 Bn shall be calculated in accordance with Table 14.5.6.1. R14.5.4.2 If the resultant load falls within the middle third of the wall thickness, plain concrete walls may be designed XVLQJ WKH VLPSOL¿HG (T (FFHQWULF ORDGV DQG lateral forces are used to determine the total eccentricity of the factored axial force Pu(TXDWLRQ UHÀHFWVWKH range of braced and restrained end conditions encountered in wall design. The limitations of 14.2.2.2, 14.3.1.1, and 14.5.1.8 apply whether the wall is proportioned by 14.5.4.1 or by 14.5.4.2. R14.5.5 Shear R14.5.5.1 Proportions of plain concrete members usually are controlled by tensile strength rather than shear strength. Shear stress (as a substitute for principal tensile stress) rarely ZLOOFRQWURO+RZHYHUEHFDXVHLWLVGL൶FXOWWRIRUHVHHDOO possible conditions where shear may have to be investigated, such as shear keys, Committee 318 maintains the investiga- tion of this basic stress condition. The shear requirements for plain concrete assume an uncracked section. Shear failure in plain concrete will be a diagonal tension failure, occurring when the principal tensile stress near the centroidal axis becomes equal to the tensile strength of the concrete. Because the major portion of the principal tensile stress results from shear, the Code safe- guards against tension failure by limiting the permissible shear at the centroidal axis as calculated from the equation for a section of homogeneous material: v = VQIb where v and V are the shear stress and shear force, respec- tively, at the section considered; Q is the statical moment of the area above or below the centroid of the gross section calculated about the centroidal axis; I is the moment of inertia of the gross section; and b is the section width where shear stress is being calculated. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 3: MEMBERS 209 CODE COMMENTARY 14 Plain Conc. Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 212. Table 14.5.6.1—Nominal bearing strength Relative geometric conditions Bn Supporting surface is wider on all sides than the loaded area Lesser of: 2 1 1 c A A f A ′ (a) 2(0.85fcƍA1) (b) Other 0.85fcƍA1 (c) 14.6—Reinforcement detailing 14.6.1 At least two No. 5 bars shall be provided around window, door, and similarly sized openings. Such bars shall extend at least 24 in. beyond the corners of openings or shall be anchored to develop fy in tension at the corners of the openings. American Concrete Institute – Copyrighted © Material – www.concrete.org 210 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 213. 15.1—Scope 15.1.1 This chapter shall apply to the design and detailing of cast-in-place beam-column and slab-column joints. 15.2—General 15.2.1 Beam-column joints shall satisfy the detailing provisions of 15.3 and strength requirements of 15.4. 15.2.2 Beam-column and slab-column joints shall satisfy IRU WUDQVIHU RI FROXPQ D[LDO IRUFH WKURXJK WKH ÀRRU system. 15.2.3 If gravity load, wind, earthquake, or other lateral forces cause transfer of moment at beam-column joints, the shear resulting from moment transfer shall be considered in the design of the joint. 15.2.4$WFRUQHUMRLQWVEHWZHHQWZRPHPEHUVWKHH൵HFWV of closing and opening moments within the joint shall be considered. 15.2.5 If a beam framing into the joint and generating joint shear has depth exceeding twice the column depth, analysis and design of the joint shall be based on the strut-and-tie method in accordance with Chapter 23 and (a) and (b) shall EHVDWLV¿HG (a) Design joint shear strength determined in accordance ZLWKKDSWHUVKDOOQRWH[FHHGࢥVn calculated in accor- dance with 15.4.2. E 'HWDLOLQJSURYLVLRQVRIVKDOOEHVDWLV¿HG 15.2.6 A column extension assumed to provide continuity through a beam-column joint in the direction of joint shear considered shall satisfy (a) and (b): (a) The column extends above the joint at least one column depth, h, measured in the direction of joint shear considered. (b) Longitudinal and transverse reinforcement from the column below the joint is continued through the extension. 15.2.7 A beam extension assumed to provide continuity through a beam-column joint in the direction of joint shear considered shall satisfy (a) and (b): R15.1—Scope A joint is the portion of a structure common to intersecting members, whereas a connection is comprised of a joint and portions of adjoining members. Chapter 15 is focused on design requirements for beam-to-column and slab-to- column joints. For structures assigned to Seismic Design Categories (SDC) B through F, joints may be required to withstand several reversals of loading. Chapter 18 provides require- ments for earthquake-resistant structures that are applied in addition to the basic requirements for joints in Chapter 15. R15.2—General Tests of joints with extensions of beams with lengths at least equal to their depths have indicated similar joint shear strengths to those of joints with continuous beams. These ¿QGLQJV VXJJHVW WKDW H[WHQVLRQV RI EHDPV DQG FROXPQV when properly dimensioned and reinforced with longitu- GLQDODQGWUDQVYHUVHEDUVSURYLGHH൵HFWLYHFRQ¿QHPHQWWR the joint faces (Meinheit and Jirsa 1981). Extensions that provide beam and column continuity through a joint do not contribute to joint shear force if they do not support exter- nally applied loads. Tests (Hanson and Conner 1967) have shown that beam- column joints laterally supported on four sides by beams of approximately equal depth exhibit superior behavior FRPSDUHGWRMRLQWVZLWKRXWDOOIRXUIDFHVFRQ¿QHGEEHDPV under reversed cyclic loading. Corner joints occur where two non-colinear members transfer moment and terminate at the joint. A roof-level exterior joint is an example of a corner joint between two members, also referred to as a knee joint. Corner joints are YXOQHUDEOHWRÀH[XUDOIDLOXUHIURPHLWKHUFORVLQJRURSHQLQJ PRPHQWV HYHQ LI ÀH[XUDO VWUHQJWKV DW WKH MRLQW IDFHV DUH VX൶FLHQWRQVLGHULQJWUDQVIHURIPRPHQWDFURVVDGLDJRQDO section through a corner joint connecting to a cantilevered member is critical because the moment acting through the joint cannot be redistributed. Chapter 23 provides requirements for design and detailing of corner joints when using the strut-and-tie method. Klein (2008) provides additional guidance on design of frame corners using the strut-and-tie method. The requirements for transverse reinforcement in corner joints are given in 15.3. ACI 352R provides additional guidance on detailing of joints. )RUMRLQWVLQZKLFKWKHEHDPGHSWKLVVLJQL¿FDQWOJUHDWHU than the column depth a diagonal strut between the joint FRUQHUVPDQRWEHH൵HFWLYH7KHUHIRUHWKHRGHUHTXLUHV that joints in which the beam depth exceeds twice the column depth be designed using the strut-and-tie method of Chapter 23. Transfer of bending through joints between slabs and corner or edge columns is covered in Chapter 8. ,Q WKH RGH FODVVL¿FDWLRQ RI EHDP DQG FROXPQ PHPEHUV IUDPLQJ LQWR MRLQW IDFHV ZDV PRGL¿HG WR GLVWLQ- American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 211 CODE COMMENTARY 15 Joints CHAPTER 15—BEAM-COLUMN AND SLAB-COLUMN JOINTS Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 214. guish those members contributing to joint shear from those WKDWGRQRWFRQWULEXWHWRMRLQWVKHDUEXWPDVHUYHWRFRQ¿QH WKHMRLQW)RUDJLYHQMRLQWVKHDUGLUHFWLRQODWHUDOFRQ¿QH- ment is provided by transverse beams while the width of the beams generating joint shear is accounted for through the H൵HFWLYH MRLQW ZLGWK LQ 7KHVH FODVVL¿FDWLRQV DUH made for the purpose of establishing nominal joint shear strength in Tables 15.4.2.3 and 18.8.4.3. For beam-column joints with circular columns, the column width and depth may be taken as those of a square section of equivalent area. R15.3—Detailing of joints R15.3.1 %HDPFROXPQMRLQWWUDQVYHUVHUHLQIRUFHPHQW Tests (Hanson and Connor 1967) have shown that the joint region of a beam-to-column connection in the interior of a building does not require shear reinforcement if the joint is laterally supported on four sides by beams of approximately equal depth. However, joints that are not restrained in this manner, such as at the exterior of a building, require shear reinforcement to prevent deterioration due to shear cracking (ACI 352R). These joints may also require transverse rein- forcement to prevent buckling of longitudinal column reinforcement. (a) The beam extends at least one beam depth h beyond the joint face. (b) Longitudinal and transverse reinforcement from the beam on the opposite side of the joint is continued through the extension. 15.2.8 A beam-column joint shall be considered to be FRQ¿QHGIRUWKHGLUHFWLRQRIMRLQWVKHDUFRQVLGHUHGLIWZR transverse beams satisfying (a), (b), and (c) are provided: (a) Width of each transverse beam is at least three-quarters of the width of the column face into which the beam frames (b) Transverse beams extend at least one beam depth h beyond the joint faces (c) Transverse beams contain at least two continuous top and bottom bars satisfying 9.6.1.2 and No. 3 or larger stir- rups satisfying 9.6.3.4 and 9.7.6.2.2 15.2.9 For slab-column connections transferring moment, strength and detailing requirements shall be in accordance with applicable provisions in Chapter 8 and Sections 15.3.2 and 22.6. 15.3—Detailing of joints 15.3.1 %HDPFROXPQMRLQWWUDQVYHUVHUHLQIRUFHPHQW 15.3.1.1 Beam-column joints shall satisfy 15.3.1.2 through XQOHVV D WKURXJK F DUHVDWLV¿HG D -RLQW LV FRQVLGHUHG FRQ¿QHG E WUDQVYHUVH EHDPV LQ accordance with 15.2.8 for all shear directions considered (b) Joint is not part of a designated seismic-force-resisting system (c) Joint is not part of a structure assigned to SDC D, E, or F 15.3.1.2 Joint transverse reinforcement shall consist of ties, spirals, or hoops satisfying the requirements of 25.7.2 for ties, 25.7.3 for spirals, and 25.7.4 for hoops. 15.3.1.3 At least two layers of horizontal transverse rein- forcement shall be provided within the depth of the shal- lowest beam framing into the joint. 15.3.1.4 Spacing of joint transverse reinforcement s shall not exceed 8 in. within the depth of the deepest beam framing into the joint. 15.3.2 6ODEFROXPQMRLQWWUDQVYHUVHUHLQIRUFHPHQW 15.3.2.1 Except where laterally supported on four sides by a slab, column transverse reinforcement shall be continued through a slab-column joint, including column capital, drop panel, and shear cap, in accordance with 25.7.2 for ties, 25.7.3 for spirals, and 25.7.4 for hoops. American Concrete Institute – Copyrighted © Material – www.concrete.org 212 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 215. 15.3.3 /RQJLWXGLQDOUHLQIRUFHPHQW 15.3.3.1 Development of longitudinal reinforcement terminated in the joint or within a column or beam exten- VLRQDVGH¿QHGLQ D DQG D VKDOOEHLQDFFRU- dance with 25.4. 15.3.3.2 Longitudinal reinforcement terminated in the joint with a standard hook shall have the hook turned toward mid-depth of the beam or column. 15.4—Strength requirements for beam-column joints 15.4.1 Required shear strength 15.4.1.1 Joint shear force Vu shall be calculated on a plane DWPLGKHLJKWRIWKHMRLQWXVLQJÀH[XUDOWHQVLOHDQGFRPSUHV- sive beam forces and column shear consistent with (a) or (b): (a) The maximum moment transferred between the beam and column as determined from factored-load analysis for beam-column joints with continuous beams in the direc- tion of joint shear considered (b) Beam nominal moment strengths Mn 15.4.2 Design shear strength 15.4.2.1 Design shear strength of cast-in-place beam- column joints shall satisfy: ࢥVn•Vu 15.4.2.2 ࢥVKDOOEHLQDFFRUGDQFHZLWK21.2.1 for shear. 15.4.2.3 Vn of the joint shall be calculated in accordance with Table 15.4.2.3. R15.3.3 /RQJLWXGLQDOUHLQIRUFHPHQW R15.3.3.1 Where bars are continued through an unloaded extension at the opposite face, the bar length within the extension can be considered as part of the development length. R15.4—Strength requirements for beam-column joints Joint shear strength is evaluated separately in each prin- cipal direction of loading in accordance with 15.4. R15.4.2 Design shear strength 7KH H൵HFWLYH DUHD RI WKH MRLQW Aj, is illustrated in Fig. R15.4.2. In no case is Aj greater than the column cross- sectional area. A circular column may be considered as having a square section of equal area. The varied levels of shear strength provided by 15.4.2.3 are based on the recom- mendations of ACI 352R, although it is noted that the ACI 5 GH¿QLWLRQ RI H൵HFWLYH FURVVVHFWLRQDO MRLQW DUHD LV VRPHWLPHVGL൵HUHQWWKDQAj9DOXHVRIH൵HFWLYHMRLQWZLGWK calculated using ACI 352R and ACI 318, however, are the same or similar for many design situations. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 213 CODE COMMENTARY 15 Joints Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 216. Table 15.4.2.3—Nominal joint shear strength Vn Column Beam in direction of Vu RQ¿QHPHQWE transverse beams according to 15.2.8 Vn, lb[1] Continuous or meets 15.2.6 Continuous or meets 15.2.7 RQ¿QHG 24 c j f A λ ′ 1RWFRQ¿QHG 20 c j f A λ ′ Other RQ¿QHG 20 c j f A λ ′ 1RWFRQ¿QHG 15 c j f A λ ′ Other Continuous or meets 15.2.7 RQ¿QHG 20 c j f A λ ′ 1RWFRQ¿QHG 15 c j f A λ ′ Other RQ¿QHG 15 c j f A λ ′ 1RWFRQ¿QHG 12 c j f A λ ′ [1] ȜVKDOOEHIRUOLJKWZHLJKWFRQFUHWHDQGIRUQRUPDOZHLJKWFRQFUHWH 15.4.2.4(൵HFWLYHFURVVVHFWLRQDODUHDZLWKLQDMRLQWAj, VKDOOEHFDOFXODWHGDVWKHSURGXFWRIMRLQWGHSWKDQGH൵HF- tive joint width. Joint depth shall be the overall depth of the column, hLQWKHGLUHFWLRQRIMRLQWVKHDUFRQVLGHUHG(൵HF- tive joint width shall be the overall width of the column where the beam is wider than the column. Where the column LVZLGHUWKDQWKHEHDPH൵HFWLYHMRLQWZLGWKVKDOOQRWH[FHHG the lesser of (a) and (b): (a) Beam width plus joint depth (b) Twice the perpendicular distance from longitudinal axis of beam to nearest side face of the column 15.5—Transfer of column axial force through the floor system 15.5.1 If fcƍRIDÀRRUVVWHPLVOHVVWKDQ0.7fcƍ of a column, WUDQVPLVVLRQRID[LDOIRUFHWKURXJKWKHÀRRUVVWHPVKDOOEH in accordance with (a), (b), or (c): D RQFUHWH RI FRPSUHVVLYH VWUHQJWK VSHFL¿HG IRU WKH FROXPQVKDOOEHSODFHGLQWKHÀRRUVVWHPDWWKHFROXPQ location. Column concrete shall extend outward at least IWLQWRWKHÀRRUVVWHPIURPIDFHRIFROXPQIRUWKHIXOO GHSWK RI WKH ÀRRU VVWHP DQG EH LQWHJUDWHG ZLWK ÀRRU concrete. E 'HVLJQVWUHQJWKRIDFROXPQWKURXJKDÀRRUVVWHP shall be calculated using the lower value of concrete strength with vertical dowels and transverse reinforce- ment as required to achieve design strength. (c) For beam-column joints laterally supported on four sides by beams of approximately equal depth that satisfy h = Joint depth in plane parallel to reinforcement generating shear b Effective joint width = lesser of (b + h) and (b + 2x) x Reinforcement generating shear Effective joint area, Aj Note: Effective area of joint for forces in each direction of framing is to be considered separately. Plan x Column Fig. R15.4.2²(ৼHFWLYHMRLQWDUHD R15.5—Transfer of column axial force through the floor system 7KH UHTXLUHPHQWV RI WKLV VHFWLRQ FRQVLGHU WKH H൵HFW RI ÀRRU VVWHP FRQFUHWH VWUHQJWK RQ FROXPQ D[LDO VWUHQJWK (Bianchini et al. 1960 ,IÀRRUVVWHPFRQFUHWHVWUHQJWKLV less than 70 percent of column concrete strength, methods in 15.5.1(a) or 15.5.1(b) may be applied to corner or edge columns. Methods in 15.5.1(a), (b), or (c) may be applied to interior columns. Application of the concrete placement procedure GHVFULEHGLQ D UHTXLUHVWKHSODFLQJRIWZRGL൵HUHQW FRQFUHWH PL[WXUHV LQ WKH ÀRRU VVWHP7KH RGH UHTXLUHV that column concrete be placed through the thickness of the ÀRRUVVWHPDQGWKDWPL[WXUHVEHSODFHGDQGUHPDLQSODVWLF such that the two can be vibrated so they are well integrated. Additional inspection may be required for this process. As required in Chapter 26, it is the responsibility of the licensed design professional to indicate on the construction docu- American Concrete Institute – Copyrighted © Material – www.concrete.org 214 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 217. 15.2.7 and 15.2.8(a) and for slab-column joints supported on four sides by the slab, it shall be permitted to calcu- late the design strength of the column using an assumed concrete strength in the column joint equal to 75 percent RI FROXPQ FRQFUHWH VWUHQJWK SOXV SHUFHQW RI ÀRRU system concrete strength, where the value of column FRQFUHWH VWUHQJWK VKDOO QRW H[FHHG WLPHV WKH ÀRRU system concrete strength. ments where the higher- and lower-strength concretes are to be placed. Research (Ospina and Alexander 1998) has shown that KHDYLOORDGHGVODEVGRQRWSURYLGHDVPXFKFRQ¿QHPHQWDV lightly loaded slabs when ratios of column concrete strength to slab concrete strength exceed approximately 2.5. Conse- quently, a limit is given in 15.5.1(c) on the ratio of concrete strengths assumed in design. As an alternative to 15.5.1(a) or 15.5.1(c), 15.5.1(b) permits WKH XVH RI GRZHO EDUV DQG FRQ¿QHPHQW UHLQIRUFHPHQW WR LQFUHDVHWKHH൵HFWLYHFRPSUHVVLYHVWUHQJWKRIFRQFUHWHLQWKH column core (Paultre and Légeron 2008; Richart et al. 1929). American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 215 CODE COMMENTARY 15 Joints Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 218. 216 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY American Concrete Institute – Copyrighted © Material – www.concrete.org Notes CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 219. 16.1—Scope 16.1.1 This chapter shall apply to the design of joints and connections at the intersection of concrete members and for load transfer between concrete surfaces, including (a) through (d): (a) Connections of precast members (b) Connections between foundations and either cast-in- place or precast members F +RUL]RQWDOVKHDUVWUHQJWKRIFRPSRVLWHFRQFUHWHÀH[- ural members (d) Brackets and corbels 16.2—Connections of precast members 16.2.1 General 16.2.1.1 Transfer of forces by means of grouted joints, shear keys, bearing, anchors, mechanical connectors, steel reinforcement, reinforced topping, or a combination of these, shall be permitted. 16.2.1.2 $GHTXDF RI FRQQHFWLRQV VKDOO EH YHUL¿HG E analysis or test. 16.2.1.3 Connection details that rely solely on friction caused by gravity loads shall not be permitted. 16.2.1.4 Connections, and regions of members adjacent to connections, shall be designed to resist forces and accom- PRGDWHGHIRUPDWLRQVGXHWRDOOORDGH൵HFWVLQWKHSUHFDVW structural system. 16.2.1.5 Design of connections shall consider structural H൵HFWV RI UHVWUDLQW RI YROXPH FKDQJH LQ DFFRUGDQFH ZLWK 5.3.6. 16.2.1.6'HVLJQRIFRQQHFWLRQVVKDOOFRQVLGHUWKHH൵HFWV RIWROHUDQFHVVSHFL¿HGIRUIDEULFDWLRQDQGHUHFWLRQRISUHFDVW members. R16.2—Connections of precast members R16.2.1 General Connection details should be arranged to minimize the potential for cracking due to restrained creep, shrinkage, and WHPSHUDWXUHPRYHPHQWV7KH3UHFDVW3UHVWUHVVHGRQFUHWH Institute (MNL 123) provides information on recommended connection details for precast concrete structures. R16.2.1.1 If two or more connection methods are used to satisfy the requirements for force transfer, their individual load-deformation characteristics should be considered to FRQ¿UPWKDWWKHPHFKDQLVPVZRUNWRJHWKHUDVLQWHQGHG R16.2.1.4 The structural behavior of precast members may GL൵HU VXEVWDQWLDOO IURP WKDW RI VLPLODU PHPEHUV WKDW DUH cast-in-place. Design of connections to minimize or transmit forces due to shrinkage, creep, temperature change, elastic GHIRUPDWLRQ GL൵HUHQWLDO VHWWOHPHQW ZLQG DQG HDUWKTXDNH require particular consideration in precast construction. R16.2.1.5 Connections should be designed to either permit WKHGLVSODFHPHQWVRUUHVLVWWKHIRUFHVLQGXFHGEODFNRI¿W volume changes caused by shrinkage, creep, thermal, and RWKHUHQYLURQPHQWDOH൵HFWVRQQHFWLRQVLQWHQGHGWRUHVLVW the forces should do so without loss of strength. Restraint assumptions should be consistent in all interconnected members. There are also cases in which the intended force PDEHLQRQHGLUHFWLRQEXWLWPDD൵HFWWKHVWUHQJWKRI the connection in another. For example, shrinkage-induced ORQJLWXGLQDOWHQVLRQLQDSUHFDVWEHDPPDD൵HFWWKHYHUWLFDO shear strength on the corbel supporting it. R16.2.1.6 Refer to R26.9.1(a). CHAPTER 16—CONNECTIONS BETWEEN MEMBERS American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 217 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 220. R16.2.1.8 Appendix B of the PCI Design Handbook (PCI MNL 120) provides a review of structural integrity and minimum integrity ties for precast concrete bearing wall structures. R16.2.2 Required strength R16.2.2.3 Bearing connections subjected to sustained loads will experience volume change restraint forces due WRWKHH൵HFWVRIFUHHSVKULQNDJHDQGWHPSHUDWXUHFKDQJH Sustained loads are dead loads and any other permanent loads such as soil loads or equipment loads that may be included with live loads. Section 5.3.6 prescribes the general FRQVLGHUDWLRQIRUUHVWUDLQWRIYROXPHFKDQJHDQGGL൵HUHQ- tial settlement in combination with other loading but does QRWGH¿QHDVSHFL¿FORDGIDFWRUIRUSUHFDVWFRQFUHWHEHDULQJ conditions. Load factors are provided with these provisions. Nuc,max provides a capacity-design limit. For mechanical connections, steel-to-steel contact, or other high-friction bearings, the horizontal force is usually due to volume change restraint. Such bearing connec- tions will experience volume change restraint forces due WRWKHH൵HFWVRIFUHHSVKULQNDJHDQGWHPSHUDWXUHFKDQJH Because the magnitude of volume change restraint forces acting on bearing connections cannot usually be determined with a high degree of accuracy, it is required to treat the restraint force Nuc as a live load in 16.2.2.3(a) when using the factored load combinations of 5.3.6 and multiplied by 1.6 in 16.2.2.3(b). Common precast concrete bearing connections use elasto- meric pads or other structural bearing media that limit trans- ferred forces by pad deformation or slip. The limiting load of such connections can be taken as 20 percent of the sustained unfactored reaction, as recognized by 16.2.2.3(b). R16.2.2.4 Bearings explicitly designed for low friction, VXFKDVSROWHWUDÀXRURHWKOHQH 37)( IDFHGVOLGLQJEHDU- ings, may reduce volume change restraint forces. If the fric- WLRQFRH൶FLHQWKDVEHHQUHOLDEOGHWHUPLQHGIRUDEHDULQJ material considering service conditions such as temperature, aging, and exposure, that information can be used to calcu- late the maximum restraint force. 16.2.1.7 Design of a connection with multiple compo- QHQWVVKDOOFRQVLGHUWKHGL൵HUHQFHVLQVWL൵QHVVVWUHQJWKDQG ductility of the components. 16.2.1.8 Integrity ties shall be provided in the vertical, longitudinal, and transverse directions and around the perimeter of a structure in accordance with 16.2.4 or 16.2.5. 16.2.2 Required strength 16.2.2.1 Required strength of connections and adjacent regions shall be calculated in accordance with the factored load combinations in Chapter 5. 16.2.2.2 Required strength of connections and adjacent regions shall be calculated in accordance with the analysis procedures in Chapter 6. 16.2.2.3 For bearing connections, Nuc shall be (a) or (b), but need not exceed Nuc,max, where Nuc,max is the maximum restraint force that can be transmitted through the load path of a bearing connection multiplied by the load factor used for OLYHORDGVLQFRPELQDWLRQVZLWKRWKHUIDFWRUHGORDGH൵HFWV (a) For connections not on bearing pads, Nuc shall be calculated simultaneously with Vu using factored load combinations in accordance with 5.3.6. The restraint force shall be treated as a live load. (b) For connections on bearing pads, Nuc shall be 20 percent of the sustained unfactored vertical reaction multi- plied by a load factor of 1.6. 16.2.2.4,IWKHIULFWLRQFRH൶FLHQWIRUDEHDULQJPDWHULDO has been determined by results of tests, Nuc,max shall be permitted to be determined by multiplying the sustained XQIDFWRUHGYHUWLFDOUHDFWLRQEWKHIULFWLRQFRH൶FLHQWDQGD load factor of 1.6. American Concrete Institute – Copyrighted © Material – www.concrete.org 218 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 221. R16.2.4 0LQLPXP FRQQHFWLRQ VWUHQJWK DQG LQWHJULW WLH UHTXLUHPHQWV R16.2.4.1 It is not intended that these minimum require- ments supersede other applicable provisions of the Code for design of precast concrete structures. The overall integrity of a structure can be substantially enhanced by minor changes in the amount, location, and detailing of member reinforcement and in the detailing of connection hardware. The integrity ties should constitute a complete load path, and load transfers along that load path should be as direct as possible. Eccentricity of the load path, especially within any connection, should be minimized. R16.2.4.2 The connection between the diaphragm and the member laterally supported by the diaphragm may be direct or indirect. For example, a column may be connected directly to the diaphragm, or it may be connected to a span- drel beam, which is connected to the diaphragm. R16.2.4.3 Base connections and connections at hori- zontal joints in precast columns and wall panels, including structural walls, are designed to transfer all design forces and moments. The minimum integrity tie requirements of this provision are not additive to these design require- ments. Common practice is to place the wall integrity ties symmetrically about the vertical centerline of the wall panel and within the outer quarters of the panel width, wherever possible. 16.2.3 Design strength 16.2.3.1 For each applicable load combination, design strengths of precast member connections shall satisfy ࢥSn•U (16.2.3.1) ࢥ shall be determined in accordance with 21.2. 16.2.3.3 At the contact surface between supported and supporting members, or between a supported or supporting member and an intermediate bearing element, nominal bearing strength for concrete surfaces, Bn, shall be calculated in accordance with 22.8. Bn shall be the lesser of the nominal concrete bearing strengths for the supported or supporting member surface, and shall not exceed the strength of inter- mediate bearing elements, if present. 16.2.3.4 If shear is the primary result of imposed loading and shear transfer occurs across a given plane, it shall be permitted to calculate Vn in accordance with the shear fric- tion provisions in 22.9. 16.2.4 0LQLPXP FRQQHFWLRQ VWUHQJWK DQG LQWHJULW WLH UHTXLUHPHQWV 16.2.4.1 Except where the provisions of 16.2.5 govern, longitudinal and transverse integrity ties shall connect precast members to a lateral-force-resisting system, and vertical integrity ties shall be provided in accordance with WRFRQQHFWDGMDFHQWÀRRUDQGURRIOHYHOV 16.2.4.2 :KHUH SUHFDVW PHPEHUV IRUP ÀRRU RU URRI diaphragms, the connections between the diaphragm and those members being laterally supported by the diaphragm shall have a nominal tensile strength of not less than 300 lb per linear ft. 16.2.4.3 Vertical integrity ties shall be provided at hori- zontal joints between all vertical precast structural members, except cladding, and shall satisfy (a) or (b): (a) Connections between precast columns shall have vertical integrity ties, with a nominal tensile strength of at least 200Ag lb, where Ag is the gross area of the column. For columns with a larger cross section than required by FRQVLGHUDWLRQRIORDGLQJDUHGXFHGH൵HFWLYHDUHDEDVHGRQ the cross section required shall be permitted. The reduced H൵HFWLYHDUHDVKDOOEHDWOHDVWRQHKDOIWKHJURVVDUHDRI the column. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 219 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 222. R16.2.5 ,QWHJULW WLH UHTXLUHPHQWV IRU SUHFDVW FRQFUHWH EHDULQJZDOOVWUXFWXUHVWKUHHVWRULHVRUPRUHLQKHLJKW Section 16.2.4 gives requirements for integrity ties that DSSOWRDOOSUHFDVWFRQFUHWHVWUXFWXUHV7KHVSHFL¿FUHTXLUH- ments in this section apply only to precast concrete bearing wall structures with three or more stories, often called large SDQHOVWUXFWXUHV,IWKHUHTXLUHPHQWVRIWKLVVHFWLRQFRQÀLFW with the requirements of 16.2.4, the requirements in this section control. These minimum provisions for structural integrity ties in large panel bearing wall structures are intended to provide an alternate load path in case of loss of a bearing wall support (Portland Cement Association 1980). Tie require- PHQWVFDOFXODWHGIRUVSHFL¿FORDGH൵HFWVPDH[FHHGWKHVH minimum provisions. The minimum integrity tie require- ments are illustrated in Fig. R16.2.5, and are based on PCI’s recommendations for design of precast concrete bearing wall buildings (PCI Committee on Precast Concrete Bearing Wall Buildings 1976). Integrity tie strength is based on yield strength. Appendix B of the PCI Design Handbook (PCI MNL 120) provides a review of structural integrity and minimum integrity ties for precast concrete bearing wall structures. (b) Connections between precast wall panels shall have at least two vertical integrity ties, with a nominal tensile strength of at least 10,000 lb per tie. 16.2.5 ,QWHJULW WLH UHTXLUHPHQWV IRU SUHFDVW FRQFUHWH EHDULQJZDOOVWUXFWXUHVWKUHHVWRULHVRUPRUHLQKHLJKW American Concrete Institute – Copyrighted © Material – www.concrete.org 220 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 223. R16.2.5.1(a) Longitudinal integrity ties may project from slabs and be lap spliced, welded, mechanically connected, or HPEHGGHGLQJURXWMRLQWVZLWKVX൶FLHQWOHQJWKDQGFRYHUWR develop the required force. Bond length for non-tensioned SUHVWUHVVLQJUHLQIRUFHPHQWLIXVHGVKRXOGEHVX൶FLHQWWR develop the yield strength (Salmons and McCrate 1977; PCA 1980). R16.2.5.1(c) It is not uncommon to have integrity ties positioned in the walls reasonably close to the plane of the ÀRRURUURRIVVWHP R16.2.5.1(e) Transverse integrity ties may be uniformly spaced and either encased in the panels or in a topping, or they may be concentrated at the transverse bearing walls. R16.2.5.1(f) The perimeter integrity tie requirements need not be additive with the longitudinal and transverse integrity tie requirements. 16.2.5.1 ,QWHJULW WLHV LQ ÀRRU DQG URRI VVWHPV VKDOO satisfy (a) through (f): (a) Longitudinal and transverse integrity ties shall be provided in floor and roof systems to provide a nominal tensile strength of at least 1500 lb per foot of width or length. (b) Longitudinal and transverse integrity ties shall be SURYLGHGRYHULQWHULRUZDOOVXSSRUWVDQGEHWZHHQWKHÀRRU or roof system and exterior walls. (c) Longitudinal and transverse integrity ties shall be posi- WLRQHGLQRUZLWKLQIWRIWKHSODQHRIWKHÀRRURUURRI system. (d) Longitudinal integrity ties shall be oriented parallel to ÀRRURUURRIVODEVSDQVDQGVKDOOEHVSDFHGQRWJUHDWHU than 10 ft on center. Provisions shall be made to transfer forces around openings. (e) Transverse integrity ties shall be oriented perpendic- XODUWRÀRRURUURRIVODEVSDQVDQGVKDOOEHVSDFHGQRW greater than the bearing wall spacing. I ,QWHJULWWLHVDWWKHSHULPHWHURIHDFKÀRRUDQGURRI within 4 ft of the edge, shall provide a nominal tensile strength of at least 16,000 lb. T = Transverse L = Longitudinal V = Vertical P = Perimeter L L L L L L L L L L L L L L T T Fig. R16.2.5²7SLFDODUUDQJHPHQWRILQWHJULWWLHVLQODUJHSDQHOVWUXFWXUHV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 221 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 224. 16.2.5.2 Vertical integrity ties shall satisfy (a) through (c): (a) Integrity ties shall be provided in all wall panels and shall be continuous over the height of the building. (b) Integrity ties shall provide a nominal tensile strength of at least 3000 lb per horizontal foot of wall. (c) At least two integrity ties shall be provided in each wall panel. 16.2.6 0LQLPXPGLPHQVLRQVDWEHDULQJFRQQHFWLRQV 16.2.6.1 Dimensions of bearing connections shall satisfy 16.2.6.2 or 16.2.6.3 unless shown by analysis or test that lesser dimensions will not impair performance. 16.2.6.2 For precast slabs, beams, or stemmed members, minimum design dimensions from the face of support to end of precast member in the direction of the span, consid- HULQJVSHFL¿HGWROHUDQFHVVKDOOEHLQDFFRUGDQFHZLWK7DEOH 16.2.6.2. Table 16.2.6.2—Minimum design dimensions from face of support to end of precast member Member type Minimum distance, in. Solid or hollow-core slab Greater of: Ɛn 2 Beam or stemmed member Greater of: Ɛn 3 16.2.6.3 Bearing pads adjacent to unarmored faces shall be set back from the face of the support and the end of the supported member a distance not less than 0.5 in. or the chamfer dimension at a chamfered face. 16.3—Connections to foundations 16.3.1 General 16.3.1.1 Factored forces and moments at base of columns, walls, or pedestals shall be transferred to supporting founda- tions by bearing on concrete and by reinforcement, dowels, anchor bolts, or mechanical connectors. 16.3.1.2 Reinforcement, dowels, or mechanical connec- tors between a supported member and foundation shall be designed to transfer (a) and (b): R16.2.6 0LQLPXPGLPHQVLRQVDWEHDULQJFRQQHFWLRQV 7KLV VHFWLRQ GL൵HUHQWLDWHV EHWZHHQ EHDULQJ OHQJWK DQG length of the end of a precast member over the support (refer to Fig. R16.2.6). Bearing pads distribute concentrated loads and reactions over the bearing area, and allow limited horizontal and rota- tional movements for stress relief. To prevent spalling under heavily loaded bearing areas, bearing pads should not extend to the edge of the support unless the edge is armored. Edges can be armored with anchored steel plates or angles. Section 16.5 gives requirements for bearing on brackets or corbels. Unarmored edge Support Precast Member Bearing length 1/2 in. minimum and not less than the size of the chamfer n /180 ≥ 2 in. (slabs) n /180 ≥ 3 in. (beams) Fig. R16.2.6—Bearing length on support. R16.3—Connections to foundations The requirements of 16.3.1 through 16.3.3 apply to both cast-in-place and precast construction. Additional require- ments for cast-in-place construction are given in 16.3.4 and 16.3.5, while additional requirements for precast construc- tion are given in 16.3.6. American Concrete Institute – Copyrighted © Material – www.concrete.org 222 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 225. (a) Compressive forces that exceed the lesser of the concrete bearing strengths of either the supported member or the foundation, calculated in accordance with 22.8 (b) Any calculated tensile force across the interface 16.3.1.3 At the base of a composite column with a struc- WXUDOVWHHOFRUH D RU E VKDOOEHVDWLV¿HG (a) Base of structural steel section shall be designed to transfer the total factored forces from the entire composite member to the foundation. (b) Base of structural steel section shall be designed to transfer the factored forces from the steel core only, and the remainder of the total factored forces shall be trans- ferred to the foundation by compression in the concrete and by reinforcement. 16.3.2 Required strength 16.3.2.1 Factored forces and moments transferred to foun- dations shall be calculated in accordance with the factored load combinations in Chapter 5 and analysis procedures in Chapter 6. 16.3.3 Design strength 16.3.3.1 Design strengths of connections between columns, walls, or pedestals and foundations shall satisfy Eq. (16.3.3.1) for each applicable load combination. For connections between precast members and foundations, requirements for YHUWLFDOLQWHJULWWLHVLQRUVKDOOEHVDWLV¿HG ࢥSn•U (16.3.3.1) where SnLVWKHQRPLQDOÀH[XUDOVKHDUD[LDOWRUVLRQDORU bearing strength of the connection. ࢥ shall be determined in accordance with 21.2. 16.3.3.3 Combined moment and axial strength of connec- tions shall be calculated in accordance with 22.4. 16.3.3.4 At the contact surface between a supported member and foundation, or between a supported member or foundation and an intermediate bearing element, nominal bearing strength Bn shall be calculated in accordance with 22.8 for concrete surfaces. Bn shall be the lesser of the nominal concrete bearing strengths for the supported member or foundation surface, and shall not exceed the strength of intermediate bearing elements, if present. 16.3.3.5At the contact surface between supported member and foundation, Vn shall be calculated in accordance with the shear-friction provisions in 22.9 or by other appropriate means. R16.3.3 Design strength R16.3.3.4 In the common case of a column bearing on a footing, where the area of the footing is larger than the area of the column, the bearing strength should be checked at the base of the column and the top of the footing. In the absence of dowels or column reinforcement that continue into the foundation, the strength of the lower part of the column should be checked using the strength of the concrete alone. R16.3.3.5 Shear-friction may be used to check for transfer of lateral forces to the supporting pedestal or footing. As an alternative to using shear-friction across a shear plane, shear keys may be used, provided that the reinforcement crossing American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 223 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 226. 16.3.3.6 At the base of a precast column, pedestal, or wall, anchor bolts and anchors for mechanical connections shall be designed in accordance with Chapter 17. Forces devel- oped during erection shall be considered. 16.3.3.7 At the base of a precast column, pedestal, or wall, mechanical connectors shall be designed to reach their design strength before anchorage failure or failure of surrounding concrete. 16.3.4 0LQLPXP UHLQIRUFHPHQW IRU FRQQHFWLRQV EHWZHHQ FDVWLQSODFHPHPEHUVDQGIRXQGDWLRQ 16.3.4.1 For connections between a cast-in-place column or pedestal and foundation, As crossing the interface shall be at least 0.005Ag, where Ag is the gross area of the supported member. 16.3.4.2 For connections between a cast-in-place wall and foundation, area of vertical reinforcement crossing the inter- face shall satisfy 11.6.1. 16.3.5 Details for connections between cast-in-place PHPEHUVDQGIRXQGDWLRQ 16.3.5.1 At the base of a cast-in-place column, pedestal, or wall, reinforcement required to satisfy 16.3.3 and 16.3.4 shall be provided either by extending longitudinal bars into supporting foundation or by dowels. 16.3.5.2 Where continuity is required, splices and mechan- ical connectors for the longitudinal reinforcement or dowels shall satisfy 10.7.5 and, if applicable, 18.13.2.2. 16.3.5.3 If a pinned or rocker connection is used at the base of a cast-in-place column or pedestal, the connection to foundation shall satisfy 16.3.3. 16.3.5.4 At footings, compression lap splices of No. 14 and No. 18 bars that are in compression for all factored load combinations shall be permitted in accordance with 25.5.5.3. 16.3.6 'HWDLOVIRUFRQQHFWLRQVEHWZHHQSUHFDVWPHPEHUV and foundation WKHMRLQWVDWLV¿HVIRUFDVWLQSODFHFRQVWUXFWLRQRU 16.3.6.1 for precast construction. In precast construction, resistance to lateral forces may be provided by mechanical or welded connections. R16.3.3.6 Chapter 17 covers anchor design, including seismic design requirements. In precast concrete construc- tion, erection considerations may control base connection design and need to be considered. R16.3.4 0LQLPXPUHLQIRUFHPHQWIRUFRQQHFWLRQVEHWZHHQ FDVWLQSODFHPHPEHUVDQGIRXQGDWLRQ The Code requires a minimum amount of reinforcement between all supported and supporting members to ensure ductile behavior. This reinforcement is required to provide a degree of structural integrity during the construction stage and during the life of the structure. R16.3.4.1 The minimum area of reinforcement at the base of a column may be provided by extending the longitudinal bars and anchoring them into the footing or by providing properly anchored dowels. R16.3.5 Details for connections between cast-in-place PHPEHUVDQGIRXQGDWLRQ R16.3.5.4 Satisfying 16.3.3.1 might require that each No. 14 or 18 bar be spliced in compression to more than one No. 11 or smaller dowel bar. American Concrete Institute – Copyrighted © Material – www.concrete.org 224 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 227. 16.3.6.1 At the base of a precast column, pedestal, or wall, the connection to the foundation shall satisfy 16.2.4.3 or 16.2.5.2. 16.3.6.2Iftheapplicableloadcombinationsof16.3.3result in no tension at the base of precast walls, vertical integrity ties required by 16.2.4.3(b) shall be permitted to be devel- oped into an adequately reinforced concrete slab-on-ground. 16.4—Horizontal shear transfer in composite concrete flexural members 16.4.1 General 16.4.1.1 ,Q D FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHU IXOO transfer of horizontal shear forces shall be provided at contact surfaces of interconnected elements. 16.4.1.2 Where tension exists across any contact surface between interconnected concrete elements, horizontal shear transfer by contact shall be permitted only where transverse reinforcement is provided in accordance with 16.4.6 and 16.4.7. 16.4.1.3 Surface preparation assumed for design shall be VSHFL¿HGLQWKHFRQVWUXFWLRQGRFXPHQWV 16.4.2 Required strength 16.4.2.1 Factored forces transferred along the contact VXUIDFH LQ FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHUV VKDOO EH calculated in accordance with the factored load combina- tions in Chapter 5. 16.4.2.2 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6. 16.4.3 Design strength 16.4.3.1 Design strength for horizontal shear transfer shall satisfy Eq. (16.4.3.1) at all locations along the contact VXUIDFH LQ D FRPSRVLWH FRQFUHWH ÀH[XUDO PHPEHU XQOHVV LVVDWLV¿HG ࢥVnh•Vu (16.4.3.1) where nominal horizontal shear strength Vnh is calculated in accordance with 16.4.4. ࢥ shall be determined in accordance with 21.2. 16.4.4 1RPLQDOKRUL]RQWDOVKHDUVWUHQJWK R16.4—Horizontal shear transfer in composite concrete flexural members R16.4.1 General R16.4.1.1 Full transfer of horizontal shear forces between segments of composite members can be provided by hori- zontal shear strength at contact surfaces through interface shear, properly anchored ties, or both. R16.4.1.3 Section 26.5.6 requires the licensed design professional to specify the surface preparation in the construction documents. R16.4.4 1RPLQDOKRUL]RQWDOVKHDUVWUHQJWK American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 225 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 228. 16.4.4.1 If Vu ࢥ(500bvd), Vnh shall be taken as Vn calcu- lated in accordance with 22.9, where bv is the width of the contact surface, and d is in accordance with 16.4.4.3. 16.4.4.2 If Vu ” ࢥ(500bvd), Vnh shall be calculated in accordance with Table 16.4.4.2, where Av,min is in accor- dance with 16.4.6, bv is the width of the contact surface, and d is in accordance with 16.4.4.3. 16.4.4.3 In Table 16.4.4.2, d shall be the distance from H[WUHPHFRPSUHVVLRQ¿EHUIRUWKHHQWLUHFRPSRVLWHVHFWLRQ to the centroid of prestressed and nonprestressed longitu- dinal tension reinforcement, if any, but need not be taken less than 0.80h for prestressed concrete members. 16.4.4.4 Transverse reinforcement in the previously cast concrete that extends into the cast-in-place concrete and is anchored on both sides of the interface shall be permitted to be included as ties for calculation of Vnh. 16.4.5 $OWHUQDWLYH PHWKRG IRU FDOFXODWLQJ GHVLJQ KRUL- zontal shear strength 16.4.5.1 As an alternative to 16.4.3.1, factored horizontal shear Vuh VKDOO EH FDOFXODWHG IURP WKH FKDQJH LQ ÀH[XUDO compressive or tensile force in any segment of the composite FRQFUHWHPHPEHUDQG(T VKDOOEHVDWLV¿HGDWDOO locations along the contact surface: ࢥVnh•Vuh (16.4.5.1) Nominal horizontal shear strength Vnh shall be calcu- lated in accordance with 16.4.4.1 or 16.4.4.2, where area of contact surface shall be substituted for bvd and Vuh shall be substituted for Vu. Provisions shall be made to transfer the change in compressive or tensile force as horizontal shear force across the interface. 16.4.5.2 Where shear transfer reinforcement is designed to resist horizontal shear to satisfy Eq. (16.4.5.1), the tie area to tie spacing ratio along the member shall approxi- R16.4.4.2 The permitted horizontal shear strengths and the UHTXLUHPHQWRILQDPSOLWXGHIRULQWHQWLRQDOURXJKQHVV are based on tests discussed in Kaar et al. (1960), Saemann and Washa (1964), and Hanson (1960). R16.4.4.3 In composite prestressed concrete members, the depth of the tension reinforcement may vary along the PHPEHU7KHGH¿QLWLRQRId used in Chapter 22 for deter- mining the vertical shear strength is also appropriate for determining the horizontal shear strength. R16.4.5 $OWHUQDWLYHPHWKRGIRUFDOFXODWLQJGHVLJQKRUL- zontal shear strength R16.4.5.2 The distribution of horizontal shear stresses DORQJWKHFRQWDFWVXUIDFHLQDFRPSRVLWHPHPEHUZLOOUHÀHFW the distribution of shear along the member. Horizontal Table 16.4.4.2—Nominal horizontal shear strength Shear transfer reinforcement Contact surface preparation[1] Vnh, lb Av•AYPLQ Concrete placed against hardened concrete intentionally roughened to a full DPSOLWXGHRIDSSUR[LPDWHOLQ Lesser of: 260 0.6 v yt v v A f b d b s ⎛ ⎞ λ + ⎜ ⎟ ⎝ ⎠ (a) 500bvd (b) Concrete placed against hardened concrete not intentionally roughened 80bvd (c) Other cases Concrete placed against hardened concrete intentionally roughened 80bvd (d) [1] Concrete contact surface shall be clean and free of laitance. American Concrete Institute – Copyrighted © Material – www.concrete.org 226 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 229. shear failure will initiate where the horizontal shear stress is a maximum and will spread to regions of lower stress. Because the slip at peak horizontal shear resistance is small for a concrete-to-concrete contact surface, longitudinal redistribution of horizontal shear resistance is very limited. Therefore, the spacing of ties along the contact surface should provide horizontal shear resistance distributed approximately the same as the distribution of shear stress along the contact surface. R16.4.6 0LQLPXPUHLQIRUFHPHQWIRUKRUL]RQWDOVKHDUWUDQVIHU R16.4.6.1 The requirements for minimum area of shear transfer reinforcement are based on test data given in Kaar et al. (1960), Saemann and Washa (1964), Hanson (1960), *URVV¿HOGDQG%LUQVWLHO DQG0DVW R16.4.75HLQIRUFHPHQWGHWDLOLQJIRUKRUL]RQWDOVKHDUWUDQVIHU R16.4.7.3 Proper anchorage of ties extending across the interface is required to maintain contact along the interface. R16.5—Brackets and corbels R16.5.1 General Brackets and corbels are short cantilevers that tend to act as simple trusses or deep beams, rather than beams, which are designed for shear according to 22.5. The corbel shown in Fig. R16.5.1a and Fig. 16.5.1b may fail by shearing along the interface between the column and the corbel, yielding of the tension tie, crushing or splitting of the compression strut, or localized bearing or shearing failure under the loading plate. These failure modes are illustrated and discussed in Elzanaty et al. (1986). PDWHOUHÀHFWWKHGLVWULEXWLRQRILQWHUIDFHVKHDUIRUFHVLQWKH FRPSRVLWHFRQFUHWHÀH[XUDOPHPEHU 16.4.5.3 Transverse reinforcement in a previously cast section that extends into the cast-in-place section and is anchored on both sides of the interface shall be permitted to be included as ties for calculation of Vnh. 16.4.6 0LQLPXPUHLQIRUFHPHQWIRUKRUL]RQWDOVKHDUWUDQVIHU 16.4.6.1 Where shear transfer reinforcement is designed to resist horizontal shear, Av,min shall be the greater of (a) and (b): (a) 0.75 w c y b s f f ′ (b) 50 w y b s f 16.4.7 5HLQIRUFHPHQWGHWDLOLQJIRUKRUL]RQWDOVKHDUWUDQVIHU 16.4.7.1 Shear transfer reinforcement shall consist of single bars or wire, multiple leg stirrups, or vertical legs of welded wire reinforcement. 16.4.7.2 Where shear transfer reinforcement is designed to resist horizontal shear, longitudinal spacing of shear transfer reinforcement shall not exceed the lesser of 24 in. and four times the least dimension of the supported element. 16.4.7.3 Shear transfer reinforcement shall be developed in interconnected elements in accordance with 25.7.1. 16.5—Brackets and corbels 16.5.1 General American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 227 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 230. The method of design addressed in this section has only been validated experimentally for av/d”. In addition, an upper limit is provided for Nuc because this method of design has only been validated experimentally for Nuc”Vu. Shear plane Compression strut Vu Nuc ϕAscfy h ≥ 0.5d av d Fig. R16.5.1a—Structural action of a corbel. Vu Nuc h d d 2 3 av Bearing plate Framing bar to anchor stirrups or ties Anchor bar Ah (closed stirrups or ties) Asc (primary reinforcement) Fig. R16.5.1b²1RWDWLRQXVHGLQ6HFWLRQ R16.5.1.1 Design of brackets and corbels in accordance with Chapter 23 is permitted, regardless of shear span. 16.5.1.1 Brackets and corbels with shear span-to-depth ratio av/d” and with factored restraint force Nuc”Vu shall be permitted to be designed in accordance with 16.5. American Concrete Institute – Copyrighted © Material – www.concrete.org 228 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 231. R16.5.2 'LPHQVLRQDOOLPLWV R16.5.2.2 A minimum depth, as shown in Fig. R16.5.1a and R16.5.1b, is required at the outside edge of the bearing area so that a premature failure will not occur due to a major crack propagating from below the bearing area to the sloping face of the corbel or bracket. Failures of this type have been observed (Kriz and Raths 1965) in corbels having depths at the outside edge of the bearing area less than required in 16.5.2.2. R16.5.2.3 The restriction on the location of the bearing DUHDLVQHFHVVDUWRHQVXUHGHYHORSPHQWRIWKHVSHFL¿HGLHOG strength of the primary tension reinforcement near the load. If the corbel is designed to resist restraint force Nuc, a bearing plate should be provided and fully anchored to the primary tension reinforcement (Fig. R16.5.1b). R16.5.2.4 These limits impose dimensional restrictions on brackets and corbels necessary to comply with the maximum shear friction strength allowed on the critical section at the face of support. R16.5.2.5 Tests (Mattock et al. 1976a) have shown that the maximum shear friction strength of lightweight concrete brackets and corbels is a function of both fcƍ and av/d. R16.5.3 Required strength R16.5.3.1 Figure R16.5.1b shows the forces applied to the corbel. Mu can be calculated as [Vuav + Nuc(h – d)]. R16.5.3.2 In editions of the Code prior to ACI 318-19, VSHFL¿F SURYLVLRQV IRU UHVWUDLQW IRUFHV DW EHDULQJ FRQQHF- tions were included only for corbels and brackets. In 2019, 16.2.2.3 and 16.2.2.4 were added to include consideration of restraint forces at all bearing connections. Consequently the provisions applicable only to brackets or corbels were removed and a reference made to 16.2.2.3 or 16.2.2.4. 16.5.2 'LPHQVLRQDOOLPLWV 16.5.2.1(൵HFWLYHGHSWKd for a bracket or corbel shall be calculated at the face of the support. 16.5.2.2 Overall depth of bracket or corbel at the outside edge of the bearing area shall be at least 0.5d. 16.5.2.3 No part of the bearing area on a bracket or corbel shall project farther from the face of support than (a) or (b): (a) End of the straight portion of the primary tension reinforcement (b) Interior face of the transverse anchor bar, if one is provided 16.5.2.4 For normalweight concrete, the bracket or corbel dimensions shall be selected such that Vu/ࢥVKDOOQRWH[FHHG the least of (a) through (c): (a) 0.2fcƍbwd (b) (480 + 0.08fcƍ bwd (c) 1600bwd 16.5.2.5 For lightweight concrete, the bracket or corbel dimensions shall be selected such that Vuࢥ shall not exceed the lesser of (a) and (b): (a) 0.2 0.07 v c w a f b d d ⎛ ⎞ − ′ ⎜ ⎟ ⎝ ⎠ (b) 800 280 v w a b d d ⎛ ⎞ − ⎜ ⎟ ⎝ ⎠ 16.5.3 Required strength 16.5.3.1 The section at the face of the support shall be designed to resist simultaneously the factored shear Vu, the factored restraint force Nuc, and the factored moment Mu. 16.5.3.2 Factored restraint force, Nuc, and shear, Vu, shall be the maximum values calculated in accordance with the factored load combinations in Chapter 5. It shall be permitted to calculate Nuc in accordance with 16.2.2.3 or 16.2.2.4, as appropriate. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 229 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 232. R16.5.5 5HLQIRUFHPHQWOLPLWV R16.5.5.1 Test results (Mattock et al. 1976a) indicate that the total amount of primary tension reinforcement, Asc, required to cross the face of the support should be the greatest of: (a) The sum of the amount of reinforcement needed to UHVLVWGHPDQGVIURPÀH[XUHAf, plus the amount of rein- forcement needed to resist the axial force, An, as deter- mined by 16.5.4.3. (b) The sum of two-thirds of the total required shear friction reinforcement, Avf, as determined by 16.5.4.4, plus the amount of reinforcement needed to resist the axial force, An, deter- mined by 16.5.4.3. The remaining Avf/3 should be provided as closed stirrups parallel to Asc as required by 16.5.5.2. (c)Aminimum amount of reinforcement, multiplied by the ratio of concrete strength to steel strength. This amount is required to prevent the possibility of sudden failure should WKHEUDFNHWRUFRUEHOFUDFNXQGHUWKHDFWLRQRIÀH[XUHDQG outward tensile force. R16.5.5.2 Closed stirrups parallel to the primary tension reinforcement are necessary to prevent a premature diagonal tension failure of the corbel or bracket. Distribution of Ah is required to be in accordance with 16.5.6.6. The total amount 16.5.3.3 Required strength shall be calculated in accor- dance with the analysis procedures in Chapter 6, and the requirements in this section. 16.5.4 Design strength 16.5.4.1'HVLJQVWUHQJWKDWDOOVHFWLRQVVKDOOVDWLVIࢥSn• ULQFOXGLQJ D WKURXJK F ,QWHUDFWLRQEHWZHHQORDGH൵HFWV shall be considered. D ࢥNn•Nuc E ࢥVn•Vu F ࢥMn•Mu 16.5.4.2 ࢥVKDOOEHGHWHUPLQHGLQDFFRUGDQFHZLWK21.2. 16.5.4.3 Nominal tensile strength Nn provided by An shall be calculated by Nn = An fy (16.5.4.3) 16.5.4.4 Nominal shear strength Vn provided by Avf shall be calculated in accordance with provisions for shear-friction in 22.9, where Avf is the area of reinforcement that crosses the assumed shear plane. 16.5.4.5 1RPLQDO ÀH[XUDO VWUHQJWK Mn provided by Af shall be calculated in accordance with the design assump- tions in 22.2. 16.5.5 5HLQIRUFHPHQWOLPLWV 16.5.5.1 Area of primary tension reinforcement, Asc, shall be at least the greatest of (a) through (c): (a) Af + An (b) (2/3)Avf + An (c) 0.04(fcƍfy)(bwd) 16.5.5.2 Total area of closed stirrups or ties parallel to primary tension reinforcement, Ah, shall be at least: Ah = 0.5(Asc±An) (16.5.5.2) American Concrete Institute – Copyrighted © Material – www.concrete.org 230 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 233. of reinforcement required to cross the face of the support, as shown in Fig. R16.5.1b, is the sum of Asc and Ah. R16.5.6 5HLQIRUFHPHQWGHWDLOLQJ R16.5.6.3 For brackets and corbels of variable depth (refer to Fig. R16.5.1a), the stress at ultimate in the rein- forcement is almost constant at approximately fy from the face of support to the load point. This is because the hori- zontal component of the inclined concrete compression strut is transferred to the primary tension reinforcement at the location of the vertical load. Therefore, reinforcement should be fully anchored at its outer end (refer to 16.5.6.3) and in the supporting column (refer to 16.5.6.4), so as to be able to GHYHORSLWVVSHFL¿HGLHOGVWUHQJWKIURPWKHIDFHRIVXSSRUW to the vertical load (refer to Fig. R16.5.6.3a). Satisfactory anchorage at the outer end can be obtained by bending the primary tension reinforcement bars in a horizontal loop as VSHFL¿HGLQERUEZHOGLQJDEDURIHTXDOGLDPHWHU or a suitably sized angle across the ends of the primary tension reinforcement bars. The weld detail used successfully in the corbel tests reported in Mattock et al. (1976a) is shown in Fig. R16.5.6.3b. Refer to ACI Committee 408 (1966). An end hook in the vertical plane, with the minimum GLDPHWHU EHQG LV QRW WRWDOO H൵HFWLYH EHFDXVH D ]RQH RI unreinforced concrete beneath the point of loading will exist for loads applied close to the end of the bracket or corbel. )RUZLGHEUDFNHWV SHUSHQGLFXODUWRWKHSODQHRIWKH¿JXUH and loads not applied close to the end, U-shaped bars in a KRUL]RQWDOSODQHSURYLGHH൵HFWLYHHQGKRRNV dh See Fig. R16.5.6.3b Standard 90- or 180-degree hook (see Table 25.3.1) P Fig. R16.5.6.3a²0HPEHUODUJHOGHSHQGHQWRQVXSSRUWDQG end anchorages. 16.5.6 5HLQIRUFHPHQWGHWDLOLQJ 16.5.6.1 Concrete cover shall be in accordance with 20.5.1.3. 16.5.6.2 Minimum spacing for deformed reinforcement shall be in accordance with 25.2. 16.5.6.3 At the front face of a bracket or corbel, primary tension reinforcement shall be anchored by (a), (b), or (c): (a) A weld to a transverse bar of at least equal size that is designed to develop fy of primary tension reinforcement (b) Bending the primary tension reinforcement back to form a horizontal loop (c) Other means of anchorage that develops fy American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 231 CODE COMMENTARY 16 Connections Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 234. db tweld = db 2 weld = db 4 3 tweld = db 2 weld = db 4 3 db Anchor bar Primary reinforcement Fig. R16.5.6.3b—Weld details used in tests of Mattock et al. D R16.5.6.5 Calculated stress in reinforcement at service loads, fs, does not decrease linearly in proportion to a decreasing moment in brackets, corbels, and members of variable depth. Additional consideration is required for SURSHUGHYHORSPHQWRIWKHÀH[XUDOUHLQIRUFHPHQW R16.5.6.6 Refer to R16.5.5.2. 16.5.6.4 Primary tension reinforcement shall be devel- oped at the face of the support. 16.5.6.5 Development of tension reinforcement shall account for distribution of stress in reinforcement that is not directly proportional to the bending moment. 16.5.6.6 Closed stirrups or ties shall be spaced such that Ah is uniformly distributed within (2/3)d measured from the primary tension reinforcement. American Concrete Institute – Copyrighted © Material – www.concrete.org 232 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 235. 17.1—Scope 17.1.1 This chapter shall apply to the design of anchors in concrete used to transmit loads by means of tension, shear, or a combination of tension and shear between: (a) connected structural elements; or (b) safety-related attachments and VWUXFWXUDOHOHPHQWV6DIHWOHYHOVVSHFL¿HGDUHLQWHQGHGIRU in-service conditions rather than for short-term handling and construction conditions. 17.1.2 Provisions of this chapter shall apply to the following anchor types (a) through (g): (a) Headed studs and headed bolts having a geometry that has been demonstrated to result in a pullout strength in uncracked concrete equal to or exceeding 1.4Np, where Np is given in Eq. (17.6.3.2.2a). (b) Hooked bolts having a geometry that has been demon- VWUDWHGWRUHVXOWLQDSXOORXWVWUHQJWKZLWKRXWWKHEHQH¿W of friction in uncracked concrete equal to or exceeding 1.4Np, where Np is given in Eq. (17.6.3.2.2b) (c) Post-installed expansion (torque-controlled and displacement-controlled) anchors that meet the assess- ment criteria of ACI 355.2. (d) Post-installed undercut anchors that meet the assess- ment criteria of ACI 355.2. (e) Post-installed adhesive anchors that meet the assess- ment criteria of ACI 355.4. (f) Post-installed screw anchors that meet the assessment criteria of ACI 355.2. (g) Attachments with shear lugs. 17.1.3 The removal and resetting of post-installed mechan- ical anchors is prohibited. 17.1.4 This chapter does not apply for load applications that are predominantly high-cycle fatigue or due to impact. R17.1—Scope R17.1.1 This chapter is restricted in scope to structural anchors that transmit loads related to strength, stability, or life safety. Two types of applications are envisioned. The ¿UVWLVFRQQHFWLRQVEHWZHHQVWUXFWXUDOHOHPHQWVZKHUHWKH failure of an anchor or anchor group could result in loss of equilibrium or stability of any portion of the structure. The second is where safety-related attachments that are not part of the structure (such as sprinkler systems, heavy suspended pipes, or barrier rails) are attached to structural elements. 7KHOHYHOVRIVDIHWGH¿QHGEWKHIDFWRUHGORDGFRPELQD- WLRQV DQG ࢥIDFWRUV DUH DSSURSULDWH IRU VWUXFWXUDO DSSOLFD- tions. Other standards may require more stringent safety levels during temporary handling. The format for this chapter was revised in 2019 to be more consistent with the other chapters of this Code. R17.1.2 Typical cast-in headed studs and headed bolts with head geometries consistent with ASME B1.1, B18.2.1, and B18.2.6 have been tested and proven to behave predict- ably; therefore, calculated pullout strengths are acceptable. Post-installed expansion, screw, and undercut anchors do not have predictable pullout strengths, and therefore quali- ¿FDWLRQWHVWVWRHVWDEOLVKWKHSXOORXWVWUHQJWKVDFFRUGLQJWR ACI 355.2 are required. For post-installed expansion, screw, and undercut anchors to be used in conjunction with the requirements of this chapter, the results of the ACI 355.2 tests have to indicate that pullout failures exhibit acceptable load-displacement characteristics or that pullout failures are precluded by another failure mode. For adhesive anchors, the characteristic bond stress and suitability for structural applications are established by testing in accordance with ACI 355.4. Adhesive anchors are particularly sensitive to a number of factors including instal- lation direction and load type. If adhesive anchors are used to resist sustained tension, the provisions include testing requirements for horizontal or upwardly inclined installa- WLRQVLQGHVLJQUHTXLUHPHQWVLQFHUWL¿FDWLRQ requirements in 26.7, and inspection requirements in 26.13. $GKHVLYHDQFKRUVTXDOL¿HGLQDFFRUGDQFHZLWK$, are tested in concrete with compressive strengths within two ranges: 2500 to 4000 psi and 6500 to 8500 psi. Bond strength is, in general, not highly sensitive to concrete compressive strength. R17.1.3 ACI 355.2 prohibits reuse of post-installed mechanical anchors. R17.1.4 The exclusion of load applications producing high-cycle fatigue or extremely short duration impact (such as blast or shock wave) from the scope of this chapter is not meant to exclude earthquake loads. Section 17.10 presents additional requirements for design when earthquake loads are included. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 233 17 Anchoring CODE COMMENTARY CHAPTER 17—ANCHORING TO CONCRETE Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 236. R17.1.57KHZLGHYDULHWRIVKDSHVDQGFRQ¿JXUDWLRQVRI specialty inserts precludes prescription of generalized tests and design equations. R17.1.6 Concrete breakout strength in tension and shear should be considered for reinforcing bars in a group used as anchorage. Concrete breakout behavior can occur even if reinforcement is fully developed in accordance with Chapter 25. Breakout behavior of straight reinforcement as a group is analogous to tension and shear breakout behavior of adhesive anchors whereby hef is taken as equal to or less than the embedded bar length. Similarly, breakout behavior of hooked and headed reinforcement groups is similar to tension and shear breakout behavior of headed anchors. Consideration should be given to extending bars beyond the development length. As an alternative to explicit determination of the concrete breakout strength of a group, anchor reinforcement provided in accordance with 17.5.2.1 may be used, or the reinforce- ment should be extended. R17.2—General R17.2.1 If the strength of an anchor group is governed by concrete breakout, the behavior is brittle, and there is limited redistribution of forces between the highly stressed and less stressed anchors. In this case, the theory of elasticity is required to be used, assuming the attachment that distrib- XWHVORDGVWRWKHDQFKRUVLVVX൶FLHQWOVWL൵7KHIRUFHVLQWKH anchors are considered to be proportional to the external load and its distance from the neutral axis of the anchor group. If anchor strength is governed by ductile yielding of the DQFKRUVWHHOVLJQL¿FDQWUHGLVWULEXWLRQRIDQFKRUIRUFHVFDQ occur. In this case, an analysis based on the theory of elas- ticity will be conservative. Cook and Klingner (1992a,b) and Lotze et al. (2001) discuss nonlinear analysis, using theory of plasticity, for the determination of the strengths of ductile anchor groups. R17.2.2 The design performance of adhesive anchors cannot be ensured by establishing a minimum concrete compressive strength at the time of installation in early-age concrete. Therefore, a concrete age of at least 21 days at the time of adhesive anchor installation was adopted. R17.2.3 ACI 355.4LQFOXGHVRSWLRQDOWHVWVWRFRQ¿UPWKH suitability of adhesive anchors for horizontal or upwardly inclined installations. R17.2.4 /LJKWZHLJKWFRQFUHWHPRGL¿FDWLRQIDFWRU Ȝa R17.2.4.1 The number of tests available to establish the strength of anchors in lightweight concrete is limited. Tests of headed studs cast in lightweight concrete indicate that the 17.1.5 This chapter does not apply to specialty inserts, through-bolts, multiple anchors connected to a single steel plate at the embedded end of the anchors, grouted anchors, or power driven anchors such as powder or pneumatic actu- ated fasteners. 17.1.6 Reinforcement used as part of an embedment shall have development length established in accordance with other parts of this Code. If reinforcement is used as anchorage, concrete breakout failure shall be considered. Alternatively, anchor reinforcement in accordance with 17.5.2.1 shall be provided. 17.2—General 17.2.1 Anchors and anchor groups shall be designed IRU FULWLFDO H൵HFWV RI IDFWRUHG ORDGV FDOFXODWHG E HODVWLF analysis. If nominal strength is controlled by ductile steel elements, plastic analysis is permitted provided that defor- mation compatibility is taken into account. 17.2.1.1$QFKRUJURXSH൵HFWVVKDOOEHFRQVLGHUHGLIWZR or more anchors loaded by a common structural element are spaced closer than the spacing required for unreduced breakout strength. If adjacent anchors are not loaded by a FRPPRQ VWUXFWXUDO HOHPHQW JURXS H൵HFWV VKDOO FRQVLGHU simultaneous maximum loading of adjacent anchors. 17.2.2 Adhesive anchors shall be installed in concrete having a minimum age of 21 days at time of anchor installation. 17.2.3 Adhesive anchors installed horizontally or XSZDUGOLQFOLQHGVKDOOEHTXDOL¿HGLQDFFRUGDQFHZLWKACI 355.4 requirements for sensitivity to installation direction. 17.2.4 /LJKWZHLJKWFRQFUHWHPRGL¿FDWLRQIDFWRU Ȝa 17.2.4.1 0RGL¿FDWLRQ IDFWRU Ȝa for lightweight concrete shall be in accordance with Table 17.2.4.1. It shall be American Concrete Institute – Copyrighted © Material – www.concrete.org 234 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 237. present reduction factor ȜDGHTXDWHOUHSUHVHQWVWKHLQÀX- ence of lightweight concrete (Shaikh and Yi 1985; Anderson and Meinheit 2005). Anchor manufacturer data developed for evaluation reports on post-installed expansion, screw, undercut, and adhesive anchors indicate that a reduced Ȝ is needed to provide the necessary safety factor for the respec- tive design strength. ACI 355.2 and ACI 355.4 provide SURFHGXUHVZKHUHEDVSHFL¿FYDOXHRIȜa can be used based on testing, assuming the lightweight concrete is similar to the reference test material. R17.3—Design limits R17.3.1 A limited number of tests of cast-in and post- installed anchors in high-strength concrete (Primavera et al. 1997) indicate that the design procedures contained in this chapter become unconservative with increasing concrete strength, particularly for cast-in anchors in concrete with compressive strengths in the range of 11,000 to 12,000 psi. Until further tests are available, an upper limit on fcƍ of 10,000 psi has been imposed for the design of cast-in anchors. This limitation is consistent with those for shear strength, torsion strength, and reinforcement development length in this Code (22.5.3.1, 22.6.3.1, 22.7.2.1, 25.4.1.4). For some post-installed anchors, the capacity may be nega- WLYHOD൵HFWHGEYHUKLJKVWUHQJWKFRQFUHWH7KHVHH൵HFWV DUHDVVRFLDWHGZLWKGL൶FXOWLQIXOOH[SDQGLQJH[SDQVLRQ anchors, cutting grooves in the sidewall of the predrilled hole by the screw anchor’s threads, and reduced bond strength of adhesive anchors. The 8000 psi limit for post- LQVWDOOHGDQFKRUVUHÀHFWVWKHFXUUHQWFRQFUHWHVWUHQJWKUDQJH IRUWHVWLQJVSHFL¿HGLQ$,DQG$,7KH SVLOLPLWPDEHH[FHHGHGLIYHUL¿HGZLWKWHVWV R17.3.2 The limitation on anchor diameter is based on the current range of test data. In the 2002 through 2008 editions of the Code, there were limitations on the diameter and embedment of anchors to calculate the concrete breakout strength. These limitations were necessitated by the lack of test results on anchors with diameters larger than 2 in. and embedment lengths longer than 24 in. In 2011, limitations on anchor diameter and embedment length were revised to limit the diameter to 4 in. based on the results of tension and shear tests on large-diameter anchors with deep embed- ments (Lee et al. 2007, 2010). These tests included 4.25 in. diameter anchors, embedded 45 in., tested in tension and 3 in. diameter anchors tested in shear. The 4 in. diameter limit was selected to maintain consistency with the largest diam- eter anchor permitted in ASTM F1554. Other ASTM speci- ¿FDWLRQVSHUPLWXSWRLQGLDPHWHUDQFKRUVKRZHYHUWKH have not been tested to ensure applicability of the 17.6.2 and 17.7.2 concrete breakout provisions. permitted to use an alternate value of Ȝa if tests are performed and evaluated in accordance with ACI 355.2 or ACI 355.4. Table 17.2.4.1—Modification factor Ȝa for lightweight concrete Case Ȝa [1] Cast-in and undercut anchor concrete failure Ȝ Expansion, screw, and adhesive anchor concrete failure Ȝ Adhesive anchor bond failure per Eq. (17.6.5.2.1) Ȝ [1] ȜVKDOOEHLQDFFRUGDQFHZLWK 17.2.5 Anchors shall be installed and inspected in accor- dance with the requirements of 26.7 and 26.13. 17.3—Design Limits 17.3.1 The value of fcƍ used for calculation purposes in this chapter shall not exceed 10,000 psi for cast-in anchors and 8000 psi for post-installed anchors. Post-installed anchors shall not be used in concrete with a strength greater than 8000 psi without testing to verify acceptable performance. 17.3.2 For anchors with diameters da ” LQ, concrete EUHDNRXWVWUHQJWKUHTXLUHPHQWVVKDOOEHFRQVLGHUHGVDWLV¿HG by the design procedures of 17.6.2 and 17.7.2. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 235 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 238. R17.3.3 ACI 355.4 limits the embedment depth of adhe- sive anchors to 4da”hef”da, which represents the theo- retical limits of the bond model (Eligehausen et al. 2006a). R17.3.4 Screw anchor research by Olsen et al. (2012) is based on the nominal screw anchor diameter corresponding WR WKH QRPLQDO GULOO ELW VL]H IRU H[DPSOH D LQ VFUHZ DQFKRULQVWDOOVLQDKROHGULOOHGEDLQ$16,GULOOELW 7KLV GH¿QLWLRQ RI VFUHZ DQFKRU VL]H LV DSSUR[LPDWHO WKH diameter of the core or shank of the screw rather than the size RIWKHODUJHUH[WHUQDOGLDPHWHURIWKHWKUHDG7KLVGH¿QLWLRQ GL൵HUVIURPWKHGLDPHWHURIVWDQGDUGDQFKRUVZLWKASME B1.1 threads that have a reduced shaft area and smaller H൵HFWLYHDUHD7KHH൵HFWLYHDUHDRIWKHVFUHZDQFKRUDVZLWK other post-installed mechanical anchors, is provided by the manufacturer. The Olsen et al. (2012) empirical design model was derived from a database of tests in cracked and uncracked concrete on metric-sized screw anchors tested in Europe and inch-sized anchors tested by independent laboratories in accordance with ICC-ES AC193. )RU FRQFUHWH VFUHZ DQFKRUV WKH H൵HFWLYH HPEHGPHQW depth, hef, is determined as a reduction from the nominal embedment based on geometric characteristics of the screw. 7KHH൵HFWLYHHPEHGPHQWLVYHUL¿HGGXULQJWKHTXDOL¿FDWLRQ testing under ACI 355.2 and provided by the manufacturer IRUXVHLQGHVLJQ8VLQJWKHUHGXFHGH൵HFWLYHHPEHGPHQW depth with the concrete capacity design (CCD) method is shown to adequately represent the behavior of concrete screws in the current concrete screw database and also vali- GDWHVWKHH൵HFWVDQGOLPLWDWLRQVRIFHUWDLQUHOHYDQWSDUDP- HWHUVVXFKDVWKHH൵HFWLYHHPEHGPHQWGHSWKDQGVSDFLQJRI anchors (17.9). R17.5—Design strength 17.3.3 For adhesive anchors with embedment depths 4da ”hef”da, bond strength requirements shall be considered VDWLV¿HGEWKHGHVLJQSURFHGXUHRI 17.3.4 For screw anchors with embedment depths 5da”hef ”da, and hef•LQ, concrete breakout strength require- PHQWVVKDOOEHFRQVLGHUHGVDWLV¿HGEWKHGHVLJQSURFHGXUHV of 17.6.2 and 17.7.2. 17.3.5 Anchors shall satisfy the edge distances, spacings, and thicknesses in 17.9 unless supplementary reinforcement is provided to control splitting failure. 17.4—Required strength 17.4.1 Required strength shall be calculated in accordance with the factored load combinations in Chapter 5. 17.4.2 For anchors in structures assigned to SDC C, D, E, and F, the additional requirements of 17.10 shall apply. 17.5—Design strength 17.5.1 For each applicable factored load combination, design strength of individual anchors and anchor groups VKDOOVDWLVIࢥSn•U,QWHUDFWLRQEHWZHHQORDGH൵HFWVVKDOO be considered in accordance with 17.8.1. 17.5.1.1 Strength reduction factor, ࢥ, shall be determined in accordance with 17.5.3. American Concrete Institute – Copyrighted © Material – www.concrete.org 236 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 239. R17.5.1.2 This section provides requirements for estab- lishing the strength of anchors in concrete. The various types of steel and concrete failure modes for anchors are shown in Fig. R17.5.1.2(a) and R17.5.1.2(b). Comprehensive discus- sions of anchor failure modes are included in CEB (1997), Fuchs et al. (1995), Eligehausen and Balogh (1995), and Cook et al. (1998). Tension failure modes related to concrete include concrete breakout failure (applicable to all anchor types), pullout failure (applicable to cast-in anchors, post- installed expansion, screw, and undercut anchors), side- face blowout failure (applicable to headed anchors), and bond failure (applicable to adhesive anchors). Shear failure modes related to concrete include concrete breakout failure and concrete pryout (applicable to all anchor types). These failure modes are described in the deemed-to-comply provi- sions of 17.6.2, 17.6.3, 17.6.4, 17.6.5, 17.7.2, and 17.7.3. Any model that complies with the requirements of 17.5.1.2 and 17.5.2.3 can be used to establish the concrete-related strengths. Additionally, anchor tensile and shear strengths are limited by the minimum spacings and edge distances of 17.9 to preclude splitting. The design of post-installed anchors recognizes that the strength of anchors is sensi- tive to appropriate installation; installation requirements are included in Chapter 26. Some post-installed anchors are less sensitive to installation errors and tolerances. This is UHÀHFWHGLQYDULRXVࢥIDFWRUVJLYHQLQDQGEDVHGRQ the assessment criteria of ACI 355.2 and ACI 355.4. The breakout strength of an unreinforced connection can EH WDNHQ DV DQ LQGLFDWLRQRI WKH ORDG DW ZKLFK VLJQL¿FDQW cracking will occur. Such cracking can represent a service- ability problem if not controlled (refer to R17.7.2.1). 17.5.1.2 Nominal strength for an anchor or anchor groups shall be based on design models that result in predictions of strength in substantial agreement with results of comprehen- sive tests. The materials used in the tests shall be compat- ible with the materials used in the structure. The nominal strength shall be based on the 5 percent fractile of the basic individual anchor strength. For nominal strengths related to FRQFUHWHVWUHQJWKPRGL¿FDWLRQVIRUVL]HH൵HFWVQXPEHURI DQFKRUVH൵HFWVRIFORVHVSDFLQJRIDQFKRUVSUR[LPLWWR edges, depth of the concrete member, eccentric loadings of DQFKRUJURXSVDQGLQÀXHQFHRIFUDFNLQJVKDOOEHWDNHQLQWR account. Limits on edge distance and anchor spacing in the design models shall be consistent with the tests that veri- ¿HGWKHPRGHO6WUHQJWKRIDQFKRUVVKDOOEHEDVHGRQGHVLJQ models that satisfy 17.5.1.2 for the following: (a) Steel strength of anchor in tension (b) Concrete breakout strength of anchor in tension (c) Pullout strength of a single cast-in anchor and single post-installed expansion, screw, and undercut anchor in tension (d) Concrete side-face blowout strength of headed anchor in tension (e) Bond strength of adhesive anchor in tension (f) Steel strength of anchor in shear (g) Concrete breakout strength of anchor in shear (h) Concrete pryout strength of anchor in shear American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 237 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 240. 17.5.1.3 Strength of anchors shall be permitted to be deter- mined in accordance with 17.6 for 17.5.1.2(a) through (e), and 17.7 for 17.5.1.2(f) through (h). For adhesive anchors that resist sustained tension, the requirements of 17.5.2.2 shall apply. R17.5.1.3 The method for concrete breakout design deemed to comply with the requirements of 17.5.1.2 was developed from the concrete capacity design (CCD) Method (Fuchs et al. (1995); Eligehausen and Balogh (1995), which was an adaptation of the Kappa Method (Eligehausen and Fuchs 1988; Eligehausen et al. 2006a) with a breakout failure surface angle of approximately 35 degrees (Fig. Fig. R17.5.1.2²)DLOXUHPRGHVIRUDQFKRUV N N N N N N N N N N N N V V V V V V V V V (i) Steel failure (ii) Pullout (iii) Concrete breakout (iv) Concrete splitting (v) Side-face blowout (vi) Bond failure Single Group (a) Tensile loading (b) Shear loading (i) Steel failure preceded by concrete spall (ii) Concrete pryout for anchors far from a free edge (iii) Concrete breakout American Concrete Institute – Copyrighted © Material – www.concrete.org 238 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 241. 17.5.1.3.1$QFKRUJURXSH൵HFWVVKDOOEHFRQVLGHUHGZKHU- ever two or more anchors have spacing less than the crit- ical spacing in Table 17.5.1.3.1, where only those anchors susceptible to the particular failure mode under investigation shall be included in the group. Table 17.5.1.3.1—Critical spacing Failure mode under investigation Critical spacing Concrete breakout in tension 3hef Bond strength in tension 2cNa Concrete breakout in shear 3ca1 17.5.1.4 Strength of anchors shall be permitted to be based on test evaluation using the 5 percent fractile of applicable test results for 17.5.1.2 (a) through (h). DDQGE ,WLVFRQVLGHUHGWREHVX൶FLHQWODFFXUDWH relatively easy to apply, and capable of extension to irreg- ular layouts. The CCD Method predicts the strength of an anchor or anchor group by using a basic equation for tension in cracked concrete, which is multiplied by factors that account for the number of anchors, edge distance, spacing, eccentricity, and absence of cracking. For shear, a similar approach is used. Experimental and numerical investigations have demonstrated the applicability of the CCD Method to adhesive anchors as well (Eligehausen et al. 2006a). hef ≈ 35 degrees N 1.5hef 1.5hef Elevation Fig. R17.5.1.3a—Breakout cone for tension. 1.5ca1 1.5ca1 ca1 ≈ 35 degrees V Anchor Plan Edge of concrete Fig. R17.5.1.3b—Breakout cone for shear. R17.5.1.4 Sections 17.5.1.2 and 17.5.2.3 establish the performance factors for which anchor design models are UHTXLUHG WR EH YHUL¿HG 0DQ SRVVLEOH GHVLJQ DSSURDFKHV exist, and the user is always permitted to “design by test” XVLQJ DV ORQJ DV VX൶FLHQW GDWD DUH DYDLODEOH WR verify the model. Test procedures can be used to determine the single-anchor breakout strength in tension and in shear. The test results, however, are required to be evaluated on a basis statistically equivalent to that used to select the values for the concrete breakout method considered to satisfy provisions of 17.5.1.2. The basic strength cannot be taken American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 239 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 242. 17.5.2 For each applicable factored load combination, design strength of anchors shall satisfy the criteria in Table 17.5.2. Table 17.5.2—Design strength requirements of anchors Failure mode Single anchor Anchor group[1] Individual anchor in a group Anchors as a group Steel strength in tension (17.6.1)[2] ࢥNsa•Nua ࢥNsa•Nua,i Concrete breakout strength in tension[3] (17.6.2) ࢥNcb•Nua ࢥNcbg•Nua,g Pullout strength in tension (17.6.3) ࢥNpn•Nua ࢥNpn•Nua,i Concrete side-face blowout strength in tension (17.6.4) ࢥNsb•Nua ࢥNsbg•Nua,g Bond strength of adhesive anchor in tension (17.6.5) ࢥNa•Nua ࢥNag•Nua,g Steel strength in shear (17.7.1) ࢥVsa•Vua ࢥVsa•Vua,i Concrete breakout strength in shear[3] (17.7.2) ࢥVcb•Vua ࢥVcbg•Vua,g Concrete pryout strength in shear (17.7.3) ࢥVcp•Vua ࢥVcpg•Vua,g [1] Design strengths for steel and pullout failure modes shall be calculated for the most highly stressed anchor in the group. [2] Sections referenced in parentheses are pointers to models that are permitted to be used to evaluate the nominal strengths. [3] If anchor reinforcement is provided in accordance with 17.5.2.1, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength 17.5.2.1 The design strength of anchor reinforcement shall be permitted to be used instead of the concrete breakout VWUHQJWKLI D RU E LVVDWLV¿HG (a) For tension, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface (b) For shear, if anchor reinforcement is developed in accordance with Chapter 25 on both sides of the concrete breakout surface, or encloses and contacts the anchor and is developed beyond the breakout surface. 17.5.2.1.1 Strength reduction factor ࢥ for anchor rein- forcement shall be in accordance with 17.5.3. greater than the 5 percent fractile. The number of tests has to EHVX൶FLHQWIRUVWDWLVWLFDOYDOLGLWDQGVKRXOGEHFRQVLGHUHG in the determination of the 5 percent fractile. R17.5.2 Under combined tension and bending, indi- YLGXDODQFKRUVLQDJURXSPDEHUHTXLUHGWRUHVLVWGL൵HUHQW magnitudes of tensile force. Similarly, under combined shear and torsion, individual anchors in a group may be required WRUHVLVWGL൵HUHQWPDJQLWXGHVRIVKHDU7DEOHLQFOXGHV requirements to design single anchors and individual anchors in a group to safeguard against all potential failure modes. For steel and pullout failure modes, the most highly stressed DQFKRULQWKHJURXSVKRXOGEHFKHFNHGWRHQVXUHLWKDVVX൶- cient strength to resist its required load. For concrete breakout, the anchors should be checked as a group. Elastic analysis or plastic analysis of ductile anchors as described in 17.2.1 may be used to determine the loads resisted by each anchor. The addition of reinforcement in the direction of the load to restrain concrete breakout can enhance the strength and deformation capacity of the anchor connection. Such enhancement is practical with cast-in anchors such as those used in precast sections. Klingner et al. (1982), ¿E (2011), ACI 349, and Eligehausen et al. (2006b) provide informa- WLRQUHJDUGLQJWKHH൵HFWRIUHLQIRUFHPHQWRQWKHEHKDYLRURI DQFKRUV7KHH൵HFWRIUHLQIRUFHPHQWLVQRWLQFOXGHGLQWKH ACI 355.2 and ACI 355.4 anchor acceptance tests or in the concrete breakout calculation method of 17.6.2 and 17.7.2. Anchor reinforcement may be provided in accordance with 17.5.2.1 and developed according to Chapter 25 instead of calculating breakout strength. R17.5.2.1 For conditions where the factored tensile or shear force exceeds the concrete breakout strength of the anchor(s) or if the breakout strength is not evaluated, the nominal strength can be based on properly developed anchor reinforcement as illustrated in Fig. R17.5.2.1a for tension and Fig. R17.5.2.1b(i) and Fig. R17.5.2.1b(ii) for shear. Because anchor reinforcement is placed below where the shear is applied (refer to Fig. R17.5.2.1b), the force in the anchor reinforcement will be larger than the shear force. Anchor reinforcement is distinguished from supplementary reinforcement in that it is designed exclusively for the anchor loads and is intended to preclude concrete breakout. Strut- and-tie models may be used to design anchor reinforcement. American Concrete Institute – Copyrighted © Material – www.concrete.org 240 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 243. For practical reasons, anchor reinforcement is only used for cast-in anchor applications. (a) Care needs to be taken in the selection and positioning of anchor reinforcement for tension. Ideally tension anchor reinforcement should consist of stirrups, ties, or hairpins SODFHGDVFORVHDVSUDFWLFDEOHWRWKHDQFKRU,WLVEHQH¿FLDO for the anchor reinforcement to enclose the surface rein- forcement where applicable. Anchor reinforcement spaced less than 0.5hef from the anchor centerline may be consid- HUHGDVH൵HFWLYH7KHUHVHDUFK Eligehausen et al. 2006b) on which these provisions are based was limited to anchor reinforcement with maximum diameter equivalent to a No. 5 bar. (b) To ensure development of anchor reinforcement for shear, the enclosing anchor reinforcement shown in Fig. R17.5.2.1(b)(i) should be in contact with the anchor and placed as close as practicable to the concrete surface. The research (Eligehausen et al. 2006b) on which the provi- sions for enclosing reinforcement are based was limited to anchor reinforcement with maximum diameter equivalent to a No. 5 bar. The larger bend radii associated with larger bar GLDPHWHUVPDVLJQL¿FDQWOUHGXFHWKHH൵HFWLYHQHVVRIWKH anchor reinforcement for shear; therefore, anchor reinforce- ment larger than a No. 6 bar is not recommended. Because development for full fy is required, the use of excess rein- forcement to reduce development length is not permitted for anchor reinforcement. The anchor reinforcement for shear may also consist of stirrups, ties, hoops, or hairpins enclosing the edge reinforcement embedded in the breakout volume and placed as close to the anchors as practicable (refer to Fig. R17.5.2.1b(ii)). Generally, reinforcement spaced less than the smaller of 0.5ca1 and 0.3ca2 from the anchor centerline should be included as anchor reinforcement. In this case, the anchor reinforcement must be developed on both sides of the breakout surface. For equilibrium, edge reinforcement is required. The research on which these provisions are based was limited to anchor reinforcement with maximum diam- eter equivalent to a No. 6 bar. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 241 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 244. ≈ 35° ≈ 35° 1.5hef 1.5hef ≤ 0.5hef ≤ 0.5hef hef dh Elevation ≥ d Section A-A N N A A hef Anchor reinforcement Anchor reinforcement placed symmetrically Fig. R17.5.2.1a²$QFKRUUHLQIRUFHPHQWIRUWHQVLRQ American Concrete Institute – Copyrighted © Material – www.concrete.org 242 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 245. Anchor group Anchor reinforcement ≈ 35° ≥ d ≥ d Plan A A Anchor reinforcement Anchor group ≈ 35° V V V ≈ 35° Anchor reinforcement Anchor group Plan As small as possible observing cover requirements Section A-A V ≥ d Anchor group V A similar A similar Fig. R17.5.2.1b(i)²+DLUSLQDQFKRUUHLQIRUFHPHQWIRUVKHDU American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 243 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 246. 17.5.2.2 Design of adhesive anchors to resist sustained tension shall satisfy Eq. (17.5.2.2) ࢥNba•Nua,s (17.5.2.2) where Nba is basic bond strength in tension of a single adhe- sive anchor and Nua,s is the factored sustained tensile load. B B V ca2 ≥ dh ≥ d Bars effective as anchor reinforcement ≤ the lesser of 0.5ca1 and 0.3ca2 ca1 ≈35° Plan ≈35° V Anchor reinforcement Anchor group Edge reinforcement Section B-B Fig. R17.5.2.1b(ii)²(GJHUHLQIRUFHPHQWDQGDQFKRUUHLQ- IRUFHPHQWIRUVKHDU R17.5.2.2 For adhesive anchors that resist sustained tensile load, an additional calculation for the sustained portion of the factored load for a reduced bond resistance is required to account for possible bond strength reductions under sustained tension. The resistance of adhesive anchors to sustained tension is particularly dependent on correct installation, including hole cleaning, adhesive metering and mixing, and prevention of voids in the adhesive bond line (annular gap). In addition, care should be taken in the selection of the correct adhesive and bond strength for the expected on-site conditions such as the concrete condition during installation (dry or saturated, cold or hot), the drilling method used (rotary impact drill, rock drill, or core drill), and anticipated in-service temperature variations in the concrete. American Concrete Institute – Copyrighted © Material – www.concrete.org 244 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 247. 17.5.2.2.1 For groups of adhesive anchors subject to VXVWDLQHG WHQVLRQ (T VKDOO EH VDWLV¿HG IRU WKH anchor that resists the highest sustained tension. 17.5.2.3 If both Nua and VuaDUHSUHVHQWLQWHUDFWLRQH൵HFWV shall be considered using an interaction expression that results in calculated strengths in substantial agreement with results of comprehensive tests. This requirement shall be FRQVLGHUHGVDWLV¿HGE 17.5.2.4 Anchors shall satisfy the edge distances, spac- ings, and thicknesses in 17.9 to preclude splitting failure. 17.5.2.5 Anchors in structures assigned to Seismic Design Category C, D, E, or F shall satisfy the additional require- ments of 17.10. 17.5.2.6 Attachments with shear lugs used to transfer structural loads shall satisfy the requirements of 17.11. 17.5.3 Strength reduction factor ࢥ for anchors in concrete shall be in accordance with Tables 17.5.3(a), 17.5.3(b), and 17.5.3(c). Strength reduction factor ࢥ for anchor reinforce- ment shall be 0.75. The 0.55 factor used for the additional calculation for sustained tension is correlated with ACI 355.4 test require- ments and provides satisfactory performance of adhesive anchors under sustained tensile loads in accordance with ACI 355.4. Product evaluation according to ACI 355.4 is based on sustained tensile loads being present for 50 years at a standard temperature of 70°F and 10 years at a temper- ature of 110°F. For longer life spans (for example, greater than 50 years) or higher temperatures, lower factors should be considered. Additional information on use of adhesive anchors for such conditions can be found by consulting with the adhesive manufacturer. Adhesive anchors are particularly sensitive to installation direction and load type.Adhesive anchors installed overhead that resist sustained tension are of concern because previous applications of this type have led to failures (National Trans- portation Safety Board 2007). Other anchor types may be more appropriate for such cases. For adhesive anchors that resist sustained tension in horizontal or upwardly inclined orientations, it is essential to meet test requirements of ACI IRU VHQVLWLYLW WR LQVWDOODWLRQ GLUHFWLRQ XVH FHUWL¿HG installers, and require special inspection. Inspection and installation requirements are provided in Chapter 26. R17.5.2.2.1 The check for anchor groups is limited to the highest loaded anchor in the group, analogous to the design for pullout. R17.5.3 The ࢥ-factors for the anchor steel strength in Table 17.5.3(a) are based on using futa to determine the nominal strength of the anchor (refer to 17.6.1 and 17.7.1) rather than fya, as used in the design of reinforced concrete members. Although the ࢥ-factors for use with futa appear low, they result in a level of safety consistent with the use of higher ࢥ-factors applied to fya. The ࢥ-factors for shear, which are VPDOOHUWKDQIRUWHQVLRQGRQRWUHÀHFWEDVLFPDWHULDOGL൵HU- ences but rather account for the possibility of a non-uniform distribution of shear in connections with multiple anchors. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 245 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 248. Table 17.5.3(a)—Anchor strength governed by steel Type of steel element Strength reduction factor ࢥ Tension (steel) Shear (steel) Ductile 0.75 0.65 Brittle 0.65 0.60 Table 17.5.3(b)—Anchor strength governed by concrete breakout, bond, and side-face blowout Supplementary reinforcement Type of anchor installation Anchor Category[1] from ACI 355.2 or ACI 355.4 Strength reduction factor ࢥ Tension (concrete breakout, bond, or side-face blowout) Shear (concrete breakout) Supplementary reinforcement present Cast-in anchors Not applicable 0.75 0.75 Post- installed anchors 1 0.75 2 0.65 3 0.55 Supplementary reinforcement not present Cast-in Anchors Not applicable 0.70 0.70 Post- installed anchors 1 0.65 2 0.55 3 0.45 [1] Anchor Category 1 indicates low sensitivity to installation and high reliability; Anchor Category 2 indicates medium sensitivity and medium reliability; Anchor Cate- gory 3 indicates high sensitivity and lower reliability. Table 17.5.3(c)—Anchor strength governed by concrete pullout, or pryout strength Type of anchor installation Anchor Category[1] from ACI 355.2 or ACI 355.4 Strength reduction factor ࢥ Tension (concrete pullout) Shear (concrete pryout) Cast-in anchors Not applicable 0.70 0.70 Post-installed anchors 1 0.65 2 0.55 3 0.45 [1] Anchor Category 1 indicates low sensitivity to installation and high reliability; Anchor Category 2 indicates medium sensitivity and medium reliability; and Anchor Category 3 indicates high sensitivity and lower reliability. 17.6—Tensile strength 17.6.1 Steel strength of anchors in tension, Nsa 17.6.1.1 Nominal steel strength of anchors in tension as governed by the steel, Nsa, shall be evaluated based on the 7KHࢥIDFWRUVIRUDQFKRUVWUHQJWKJRYHUQHGEFRQFUHWH breakout, bond, and side-face blowout in Table 17.5.3(b) are separated into two groups based on the presence or absence of supplementary reinforcement. The supplementary rein- IRUFHPHQWFODVVL¿FDWLRQVRIWKLVWDEOHUHSODFHWKH³RQGL- tion A” and “Condition B” designations in previous Codes. Applications with supplementary reinforcement provide more deformation capacity, permitting the ࢥ-factors to be increased. An explicit design of supplementary reinforce- ment for anchor-related forces is not required; however, the arrangement of supplementary reinforcement should gener- ally conform to that of the anchor reinforcement shown in Fig. R17.5.2.1(a) and R17.5.2.1(b)(i) and (ii). Unlike anchor rein- forcement, full development of supplementary reinforcement beyond the assumed breakout failure plane is not required. For concrete breakout in shear for all anchor types and for brittle concrete failure modes for cast-in anchors, the basic strength reduction factor for brittle concrete failures (ࢥ 0.70) was chosen based on results of probabilistic studies. While this factor is greater than the strength reduction factor of structural plain concrete (ࢥ ), the nominal resistance expressions used in this chapter and in the test requirements are based on the 5 percent fractiles; therefore, ࢥ would be overly conservative. Comparison with other design procedures and probabilistic studies (Farrow and Klingner 1995) indicated that the choice of ࢥ LVMXVWL¿HG)RU the same cases with supplementary reinforcement, the value of ࢥ is compatible with the level of safety for shear failures in concrete beams, and has been recommended in the PCI Design Handbook (MNL 120) and by ACI 349. Tests included in ACI 355.2 and ACI 355.4 to assess sensitivity to installation procedures determine the Anchor Categories as given in Table 17.5.3(b) for proprietary post- installed expansion, screw, undercut, and adhesive anchors. $,WHVWVIRULQVWDOODWLRQVHQVLWLYLWPHDVXUHH൵HFWVRI variability in anchor torque during installation, tolerance on drilled hole size, and energy level used in setting anchors; for expansion, screw, and undercut anchors intended for use in cracked concrete, increased crack widths are considered. $,WHVWVIRULQVWDOODWLRQVHQVLWLYLWDVVHVVWKHLQÀX- HQFHRIDGKHVLYHPL[LQJDQGWKHLQÀXHQFHRIKROHFOHDQLQJ LQGUVDWXUDWHGDQGZDWHU¿OOHGXQGHUZDWHUERUHKROHV R17.6—Tensile strength R17.6.1 Steel strength of anchors in tension, Nsa American Concrete Institute – Copyrighted © Material – www.concrete.org 246 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 249. properties of the anchor material and the physical dimen- sions of the anchors. 17.6.1.2 Nominal steel strength of an anchor in tension, Nsa, shall be calculated by: Nsa = Ase,N futa (17.6.1.2) where Ase,NLVWKHH൵HFWLYHFURVVVHFWLRQDODUHDRIDQDQFKRU in tension, in.2 , and futa used for calculations shall not exceed either 1.9fya or 125,000 psi. 17.6.2 Concrete breakout strength of anchors in tension, Ncb 17.6.2.1 Nominal concrete breakout strength in tension, Ncb of a single anchor or Ncbg of an anchor group satisfying 17.5.1.3.1, shall be calculated by (a) or (b), respectively: (a) For a single anchor , , , Nc cb ed N c N cp N b Nco A N N A = ψ ψ ψ (17.6.2.1a) (b) For an anchor group , , , , Nc cbg ec N ed N c N cp N b Nco A N N A = ψ ψ ψ ψ (17.6.2.1b) where ȥec,N, ȥed,N, ȥc,N, and ȥcp,N are given in 17.6.2.3, 17.6.2.4, 17.6.2.5, and 17.6.2.6, respectively. R17.6.1.2 The nominal strength of anchors in tension is best represented as a function of futa rather than fya because the large majority of anchor materials do not exhibit a well- GH¿QHG LHOG SRLQW $,6 KDV EDVHG WHQVLRQ VWUHQJWK RI anchors on Ase,N futa since the 1986 edition of their speci- ¿FDWLRQV 7KH XVH RI (T ZLWK WKH ORDG IDFWRUV provided in 5.3 and the ࢥ-factors provided in 17.5.3 result in design strengths consistent with AISC 360. The limitation of 1.9fya on futa is to ensure that, under service load conditions, the anchor does not exceed fya. Although not a concern for standard structural steel anchors (maximum value of futa/fya is 1.6 for ASTM A307), the limi- tation is applicable to some stainless steels. The limit on futa of 1.9fya was determined by converting the LRFD provi- sions to corresponding service level conditions. From 5.3, the average load factor of 1.4 (from 1.2D + 1.6L) divided by the highest ࢥ-factor (0.75 for tension) results in a limit of futa/fyaRI For post-installed anchors having a reduced cross-sectional area anywhere along the anchor length, such as wedge-type DQFKRUV WKH H൵HFWLYH FURVVVHFWLRQDO DUHD RI WKH DQFKRU should be provided by the manufacturer. For threaded rods and headed bolts, ASME B1.1GH¿QHVAse,N as 2 , 0.9743 4 se N a t A d n ⎛ ⎞ π = − ⎜ ⎟ ⎝ ⎠ where nt is the number of threads per inch. R17.6.2 Concrete breakout strength of anchors in tension, Ncb R17.6.2.1 7KH H൵HFWV RI PXOWLSOH DQFKRUV VSDFLQJ RI anchors, and edge distance on the nominal concrete breakout VWUHQJWKLQWHQVLRQDUHLQFOXGHGEDSSOLQJWKHPRGL¿FDWLRQ factors ANc /ANco and ȥed,N in Eq. (17.6.2.1a) and (17.6.2.1b). Figure R17.6.2.1(a) shows ANco and the development of Eq. (17.6.2.1.4). ANco is the maximum projected area for a single anchor. Figure R17.6.2.1(b) shows examples of the projected areas for various single-anchor and multiple- anchor arrangements. Because ANc is the total projected area for an anchor group, and ANco is the area for a single anchor, there is no need to include n, the number of anchors, in Eq. (17.6.2.1b). If anchor groups are positioned in such a way that their projected areas overlap, the value of ANc is required to be reduced accordingly. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 247 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 250. hef ≈ 35 degrees N 1.5hef 1.5hef Section through failure cone The critical edge distance for headed studs, headed bolts, expansion anchors, screw anchors, and undercut anchors is 1.5hef 1.5hef 1.5hef 1.5hef 1.5hef ANco Plan ANco = (2 x 1.5hef) x (2 x 1.5hef) = 9hef 2 (a) 1.5hef s2 ca2 1.5hef ca1 s1 ANc If ca1 and ca2 1.5hef and s1 and s2 3hef ANc = (ca1 + s1 + 1.5hef) x (ca2 + s2 + 1.5hef) 1.5hef ca1 s1 1.5hef 1.5hef If ca1 1.5hef and s1 3hef ANc = (ca1 + s1 + 1.5hef) x (2 x 1.5hef) ANc 1.5hef 1.5hef 1.5hef ca1 If ca1 1.5hef ANc = (ca1 + 1.5hef) x (2 x 1.5hef) ANc (b) Fig. R17.6.2.1² D DOFXODWLRQRIANcoDQG E FDOFXODWLRQRIANc for single anchors and anchor groups. American Concrete Institute – Copyrighted © Material – www.concrete.org 248 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 251. 17.6.2.1.1 ANc is the projected concrete failure area of a single anchor or of an anchor group that is approximated as the base of the rectilinear geometrical shape that results from projecting the failure surface outward 1.5hef from the centerlines of the anchor, or in the case of an anchor group, from a line through a row of adjacent anchors. ANc shall not exceed nANco, where n is the number of anchors in the group that resist tension. 17.6.2.1.2 If anchors are located less than 1.5hef from three or more edges, the value of hef used to calculate ANc in accordance with 17.6.2.1.1, as well as for the equations in 17.6.2.1 through 17.6.2.4, shall be the greater of (a) and (b): (a) ca,max/1.5 (b) s/3, where s is the maximum spacing between anchors within the group. R17.6.2.1.2 For anchors located less than 1.5hef from three or more edges, the CCD Method (refer to R17.5.1.3), which is the basis for the equations in 17.6.2.1 through 17.6.2.4, gives overly conservative results for the tensile breakout strength (Lutz 1995 7KLV RFFXUV EHFDXVH WKH RUGLQDU GH¿QLWLRQV of ANc/ANco GR QRW FRUUHFWO UHÀHFW WKH HGJH H൵HFWV7KLV problem is corrected by limiting the value of hef used in the equations in 17.6.2.1 through 17.6.2.4 to (ca,max)/1.5, where ca,maxLVWKHJUHDWHVWRIWKHLQÀXHQFLQJHGJHGLVWDQFHVWKDWGR not exceed the actual 1.5hef. In no case should (ca,max)/1.5 be taken less than one-third of the maximum spacing between anchors within the group. The limit on hef of at least one- third of the maximum spacing between anchors within the group prevents the use of a calculated strength based on LQGLYLGXDOEUHDNRXWYROXPHVIRUDQDQFKRUJURXSFRQ¿JXUD- tion. This approach is illustrated in Fig. R17.6.2.1.2. In this example, the proposed limit on the value of hef to be used in calculations where hef = (ca,max)/1.5, results in hef = hƍef = 4 in. For this example, this would be the proper value to be used for hef in calculating the resistance even if the actual embedment depth is greater. The requirement of 17.6.2.1.2 may be visualized by moving the actual concrete breakout surface, which origi- nates at the actual hef, toward the surface of the concrete parallel to the applied tensile load. The value of hef used in 17.6.2.1 through 17.6.2.4 is determined when (a) the outer ERXQGDULHVRIWKHIDLOXUHVXUIDFH¿UVWLQWHUVHFWDIUHHHGJHRU (b) the intersection of the breakout surface between anchors ZLWKLQWKHJURXS¿UVWLQWHUVHFWVWKHVXUIDFHRIWKHFRQFUHWH For the example shown in Fig. R17.6.2.1.2, point “A” shows the intersection of the assumed failure surface for limiting hef with the concrete surface. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 249 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 252. 17.6.2.1.3 If an additional plate or washer is added at the head of the anchor, it shall be permitted to calculate the projected area of the failure surface by projecting the failure surface outward 1.5hefIURPWKHH൵HFWLYHSHULPHWHURIWKHSODWHRUZDVKHU7KH H൵HFWLYH SHULPHWHU VKDOO QRW H[FHHG WKH YDOXH DW D VHFWLRQ projected outward more than the thickness of the washer or plate from the outer edge of the head of the anchor. 17.6.2.1.4 ANco is the projected concrete failure area of a single anchor with an edge distance of at least 1.5hef and shall be calculated by Eq. (17.6.2.1.4). ANco = 9hef 2 (17.6.2.1.4) 17.6.2.2 Basic single anchor breakout strength, Nb 17.6.2.2.1 Basic concrete breakout strength of a single anchor in tension in cracked concrete, Nb, shall be calculated by Eq. (17.6.2.2.1), except as permitted in 17.6.2.2.3 Nb = kcȜa c f ′ hef 1.5 (17.6.2.2.1) R17.6.2.2 Basic single anchor breakout strength, Nb R17.6.2.2.1 The equation for the basic concrete breakout strength was derived assuming concrete breakout with an angle of approximately 35 degrees, considering fracture mechanics concepts (Fuchs et al. 1995; Eligehausen and Balogh 1995; Eligehausen and Fuchs 1988; ¿E 2011). ≈ 35° ≈ 35° 6 in. 4 in. 5 in. 9 in. 1.5h’ef N 5.5 in. h’ef N 1.5h’ef Actual failure surface Assumed failure surface for limiting hef Actual failure surface Assumed failure surface for limiting hef Point A 5.5 in. h’ef Side section Plan Actual failure surface Assumed failure surface for limiting hef A’Nc Elevation The actual hef = 5.5 in. but three edges are ≤ 1.5hef therefore the limiting value of hef (shown as h’ef in the figure) is the larger of ca,max /1.5 and one-third of the maximum spacing for an anchor group: h’ef = max (6/1.5, 9/3) = 4 in. Therefore, use hef = 4 in. for the value of hef in equations 17.6.2.1 through 17.6.2.5 including the calculation of A’Nc: A’Nc = (6 + 4)(5 + 9 + [1.5 x 4]) = 200 in.2 Point A shows the intersection of the assumed failure surface for limiting hef with the concrete surface. Fig. R17.6.2.1.2²([DPSOHRIWHQVLRQZKHUHDQFKRUVDUHORFDWHGLQQDUURZPHPEHUV American Concrete Institute – Copyrighted © Material – www.concrete.org 250 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 253. where kc = 24 for cast-in anchors and 17 for post-installed anchors. 17.6.2.2.2 kc for post-installed anchors shall be permitted to be increased based on ACI 355.2 or ACI 355.4 product- VSHFL¿FWHVWVEXWVKDOOQRWH[FHHG 17.6.2.2.3 For single cast-in headed studs and headed bolts with LQ”hef”LQ, Nb shall be calculated by: Nb Ȝa c f ′ hef (17.6.2.2.3) 17.6.2.3 Breakout eccentricity factor, ȥec,N 17.6.2.3.10RGL¿FDWLRQIDFWRUIRUDQFKRUJURXSVORDGHG HFFHQWULFDOO LQ WHQVLRQ ȥec,N, shall be calculated by Eq. (17.6.2.3.1). , 1 1.0 1 1.5 ec N N ef e h ψ = ≤ ⎛ ⎞ ′ + ⎜ ⎟ ⎝ ⎠ (17.6.2.3.1) The values of kc in Eq. (17.6.2.2.1) were determined from a large database of test results in uncracked concrete at the 5 percent fractile (Fuchs et al. 1995). The values were adjusted to corresponding kc values for cracked concrete (Elige- hausen and Balogh 1995; Goto 1971). Tests have shown that the values of kc applicable to adhesive anchors are approxi- mately equal to those derived for expansion anchors (Elige- hausen et al. 2006a; Zhang et al. 2001). R17.6.2.2.3 For anchors with a deeper embedment (hef 11 in.), test evidence indicates the use of hef 1.5 can be overly conservative for some cases. An alternative expression (Eq. (17.6.2.2.3)) is provided using hef 5/3 for evaluation of cast-in headed studs and headed bolts with LQ”hef”LQ This expression can also be appropriate for some undercut post- installed anchors. However, for such anchors, the use of Eq. VKRXOGEHMXVWL¿HGEWHVWUHVXOWVLQDFFRUGDQFH with 17.5.1.4. Experimental and numerical investigations indicate that Eq. (17.6.2.2.3) may be unconservative for hef 25 in. if bearing pressure on the anchor head is at or near the limit permitted by Eq. (17.6.3.2.2a) (2åEROWHWDO). R17.6.2.3 Breakout eccentricity factor, ȥec,N R17.6.2.3.1 Figure 17.6.2.3.1(a) shows an anchor group where all anchors are in tension but the resultant force is eccentric with respect to the centroid of the anchor group. Anchors can also be loaded in such a way that only some of the anchors are in tension (Fig. 17.6.2.3.1(b)). In this case, only the anchors in tension are to be considered for the calculation of eƍ N. The eccentricity eƍ N of the resultant tensile force is determined with respect to the center of gravity of the anchors in tension. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 251 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 254. R17.6.2.4 %UHDNRXWHGJHHৼHFWIDFWRU ȥed,N R17.6.2.4.1 If anchors are located close to an edge such WKDW WKHUH LV LQVX൶FLHQW VSDFH IRU D FRPSOHWH EUHDNRXW volume to develop, the strength of the anchor is further UHGXFHGEHRQGWKDWUHÀHFWHGLQANc /ANco. If the smallest side cover distance is at least 1.5hef, the design model assumes a complete breakout volume can form, and there is no reduction (ȥed,N = 1). If the side cover is less than 1.5hef, the factor ȥed,N LVUHTXLUHGWRDGMXVWIRUWKHHGJHH൵HFW Fuchs et al. 1995). R17.6.2.5 Breakout cracking factor, ȥc,N R17.6.2.5.1 Post-installed anchors that do not meet the requirements for use in cracked concrete according to ACI 355.2 or ACI 355.4 should be used only in regions that will remain uncracked. The analysis for the determination RIFUDFNIRUPDWLRQVKRXOGLQFOXGHWKHH൵HFWVRIUHVWUDLQHG shrinkage (refer to 24.4.2 7KH DQFKRU TXDOL¿FDWLRQ WHVWV of ACI 355.2 or ACI 355.4 require that anchors in cracked 17.6.2.3.2 If the loading on an anchor group is such that only some of the anchors in the group are in tension, only those anchors that are in tension shall be considered for determining eccentricity eƍN in Eq. (17.6.2.3.1) and for the calculation of Ncbg according to Eq. (17.6.2.1b). 17.6.2.3.3 If the loading is eccentric with respect to two orthogonal axes, ȥec,N shall be calculated for each axis indi- vidually, and the product of these factors shall be used as ȥec,N in Eq. (17.6.2.1b). 17.6.2.4 %UHDNRXWHGJHHৼHFWIDFWRU ȥed,N 17.6.2.4.10RGL¿FDWLRQIDFWRUIRUHGJHH൵HFWVIRUVLQJOH anchors or anchor groups loaded in tension, ȥed,N, shall be determined by (a) or (b). (a) If cDPLQ•hefWKHQȥed,N = 1.0 (17.6.2.4.1a) (b) If cDPLQ 1.5hefWKHQȥed,N = 0.7 + 0.3 1.5 DPLQ ef c h (17.6.2.4.1b) 17.6.2.5 Breakout cracking factor, ȥc,N 17.6.2.5.10RGL¿FDWLRQIDFWRUIRUWKHLQÀXHQFHRIFUDFNLQJ in anchor regions at service load levels, ȥc,N, shall be deter- mined by (a) or (b): (a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ȥc,N shall be permitted to be: T1 T2 T3 T1 T2 C Elevation e’N e’N Resultant tensile force = T1 + T2 + T3 Resultant tensile force = T1 + T2 Centroid of anchors loaded in tension Centroid of anchors loaded in tension Only anchors that are in tension are considered in determining e’N Elevation (a) Where all anchors in a group are in tension (b) Where only some anchors are in tension N M Fig. R17.6.2.3.1²'H¿QLWLRQRIeNƍ for an anchor group. American Concrete Institute – Copyrighted © Material – www.concrete.org 252 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 255. ȥc,N = 1.25 for cast-in anchors ȥc,N = 1.4 for post-installed anchors, if the value of kc used in Eq. (17.6.2.2.1) is 17. If the value of kc used in Eq. (17.6.2.2.1) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors: (i) ȥc,N shall be based on the ACI 355.2 or ACI 355.4 SURGXFWHYDOXDWLRQUHSRUWIRUDQFKRUVTXDOL¿HGIRUXVH in both cracked and uncracked concrete (ii) ȥc,NVKDOOEHWDNHQDVIRUDQFKRUVTXDOL¿HGIRU use in uncracked concrete. (b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ȥc,N shall be taken as 1.0 for both cast-in anchors and post- LQVWDOOHGDQFKRUVDQGVKDOOEHVDWLV¿HG 17.6.2.5.23RVWLQVWDOOHGDQFKRUVVKDOOEHTXDOL¿HGIRUXVHLQ cracked concrete in accordance with ACI 355.2 or ACI 355.4. UDFNLQJLQWKHFRQFUHWHVKDOOEHFRQWUROOHGEÀH[XUDOUHLQ- forcement distributed in accordance with 24.3.2, or equivalent FUDFNFRQWUROVKDOOEHSURYLGHGEFRQ¿QLQJUHLQIRUFHPHQW 17.6.2.6 Breakout splitting factor, ȥcp,N 17.6.2.6.10RGL¿FDWLRQIDFWRUIRUSRVWLQVWDOOHGDQFKRUV designed for uncracked concrete in accordance with 17.6.2.5 without supplementary reinforcement to control splitting, ȥcp,N, shall be determined by (a) or (b) using the critical distance cacDVGH¿QHGLQ (a) If cDPLQ•cacWKHQȥcp,N = 1.0 (17.6.2.6.1a) (b) If cDPLQ cacWKHQȥcp,N = , 1.5 D PLQ a e c c f a c h c c ≥ (17.6.2.6.1b) 17.6.2.6.2 For all other cases, including cast-in anchors, ȥcp,N shall be taken as 1.0. 17.6.3 Pullout strength of a single cast-in anchor or a VLQJOHSRVWLQVWDOOHGH[SDQVLRQVFUHZRUXQGHUFXWDQFKRU in tension, Npn 17.6.3.1 Nominal pullout strength of a single cast-in anchor or a single-post-installed expansion, screw, or undercut anchor in tension, Npn, shall be calculated by: Npn ȥc,PNp (17.6.3.1) concrete zones perform well in a crack that is 0.012-in. wide. If wider cracks are expected, reinforcement to control the crack width to approximately 0.012 in. should be provided. Refer to ACI 224R for more information. The concrete breakout strengths given by Eq. (17.6.2.2.1) and (17.6.2.2.3) assume cracked concrete (ȥc,N = 1.0) with ȥc,Nkc = 24 for cast-in anchors and 17 for post-installed anchors. If the uncracked concrete ȥc,N factors are applied (1.25 for cast-in and 1.4 for post-installed), ȥc,Nkc factors become 30 for cast-in anchors and 24 for post-installed DQFKRUV 7KLV DJUHHV ZLWK ¿HOG REVHUYDWLRQV DQG WHVWV demonstrating cast-in anchor strength exceeds that of post- installed for both cracked and uncracked concrete. R17.6.2.6 Breakout splitting factor, ȥcp,N R17.6.2.6.1 The design provisions in 17.6 are based on the assumption that the basic concrete breakout strength can be achieved if the minimum edge distance ca,min equals 1.5hef. Test results (Asmus 1999), however, indicate that many torque-controlled and displacement-controlled expansion anchors and some undercut anchors require edge distances exceeding 1.5hef to achieve the basic concrete breakout strength if tested in uncracked concrete without supplemen- tary reinforcement to control splitting. When a tensile load is applied, the resulting tensile stresses at the embedded end of the anchor are added to the tensile stresses induced due to anchor installation, and splitting failure may occur before reaching the concrete breakout strength given in 17.6.2.1. To account for this potential splitting mode of failure, the basic concrete breakout strength is reduced by a factor ȥcp,N if ca,min is less than the critical edge distance cac. R17.6.2.6.2 If supplementary reinforcement to control splitting is present or if the anchors are located in a region where analysis indicates cracking of the concrete at service loads, the reduction factor ȥcp,N is taken as 1.0. R17.6.3 Pullout strength of a single cast-in anchor or a VLQJOHSRVWLQVWDOOHGH[SDQVLRQVFUHZRUXQGHUFXWDQFKRU in tension, Npn R17.6.3.1 The design requirements for pullout are appli- cable to cast-in anchors and post-installed expansion, screw, and undercut anchors. They are not applicable to adhesive anchors, which are instead evaluated for bond failure in accordance with 17.6.5. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 253 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 256. where ȥc,P is given in 17.6.3.3. 17.6.3.2 Basic single anchor pullout strength, Np 17.6.3.2.1 For post-installed expansion, screw, and undercut anchors, the values of Np shall be based on the 5 percent fractile of results of tests performed and evaluated according to ACI 355.2. It is not permissible to calculate the pullout strength in tension for such anchors. 17.6.3.2.2 For single anchors, it shall be permitted to evaluate the pullout strength in tension, Np, for use in Eq. (17.6.3.1) in accordance with (a) or (b).Alternatively, it shall be permitted to use values of Np based on the 5 percent frac- tile of tests performed and evaluated in the same manner as WKH$,SURFHGXUHVEXWZLWKRXWWKHEHQH¿WRIIULFWLRQ (a) For cast-in headed studs and headed bolts, Np shall be calculated by: Np = 8Abrg fcƍ D (b) For J- or L-bolts, Np shall be calculated by: Np = 0.9fcƍehda (17.6.3.2.2b) where 3da”eh”da. 17.6.3.3 Pullout cracking factor, ȥc,P 17.6.3.3.10RGL¿FDWLRQIDFWRUWRDFFRXQWIRUWKHLQÀXHQFH of cracking in anchor regions at service load levels, ȥc,P, shall be determined by (a) or (b): (a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ȥc,P shall be permitted to be 1.4. (b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ȥc,P, shall be taken as 1.0. R17.6.3.2 Basic single anchor pullout strength, Np R17.6.3.2.2 The pullout strength equations given in 17.6.3.2.2(a) and 17.6.3.2.2(b) are only applicable to cast-in headed and hooked anchors (Kuhn and Shaikh 1996; ¿E 2011); they are not applicable to post-installed expansion, screw, and undercut anchors that use various mechanisms for end anchorage unless the validity of the pullout strength HTXDWLRQVLVYHUL¿HGEWHVWV The value calculated from Eq. (17.6.3.2.2a) corresponds to the force at which crushing of the concrete occurs due to bearing of the anchor head (¿E 2011; ACI 349). It is not the force required to pull the anchor completely out of the concrete; therefore, the equation does not contain a term relating to embedment depth. Local crushing of the concrete JUHDWOUHGXFHVWKHVWL൵QHVVRIWKHFRQQHFWLRQ, and gener- ally will be the beginning of a pullout failure. The pullout strength in tension of headed studs or headed bolts can be increased by providing reinforcement, such as closely spaced spirals, throughout the head region. This increase can be demonstrated by tests, as required by the Licensed Design 3URIHVVLRQDOIRUWKHVSHFL¿FDSSOLFDWLRQ Equation (17.6.3.2.2b) for hooked bolts was developed by Lutz based on the results of Kuhn and Shaikh (1996). Reli- ance is placed on the bearing component only, neglecting any frictional component, because crushing inside the hook ZLOOJUHDWOUHGXFHWKHVWL൵QHVVRIWKHFRQQHFWLRQDQGJHQHU- ally will be the beginning of a pullout failure. The limits on eh are based on the range of variables used in the three test programs reported in Kuhn and Shaikh (1996). American Concrete Institute – Copyrighted © Material – www.concrete.org 254 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 257. 17.6.4 Concrete side-face blowout strength of headed anchors in tension, Nsb 17.6.4.1 For a single headed anchor with deep embedment close to an edge (hef 2.5ca1), the nominal side-face blowout strength, Nsb, shall be calculated by: 1 160 sb a brg a c N c A f = λ ′ (17.6.4.1) 17.6.4.1.1 If ca2 for the single headed anchor is less than 3ca1, the value of Nsb shall be multiplied by the factor (1 + ca2/ca1)/4, where ”ca2/ca1”. 17.6.4.2 For multiple headed anchors with deep embed- ment close to an edge (hef 2.5ca1) and anchor spacing less than 6ca1, the nominal strength of those anchors susceptible to a side-face blowout failure, Nsbg, shall be calculated by: Nsbg = 1 1 6 a s c ⎛ ⎞ + ⎜ ⎟ ⎝ ⎠ Nsb (17.6.4.2) where s is the distance between the outer anchors along the edge, and Nsb is obtained from Eq. (17.6.4.1) without modi- ¿FDWLRQIRUDSHUSHQGLFXODUHGJHGLVWDQFH 17.6.5 Bond strength of adhesive anchors in tension, Na or Nag 17.6.5.1 Nominal bond strength in tension, Na of a single adhesive anchor or Nag of an adhesive anchor group satis- fying 17.5.1.3.1, shall be calculated by (a) or (b), respectively. (a) For a single adhesive anchor: , , Na a ed Na cp Na ba Nao A N N A = ψ ψ (17.6.5.1a) (b) For an adhesive anchor group: , , , Na ag ec Na ed Na cp Na ba Nao A N N A = ψ ψ ψ (17.6.5.1b) where ȥec,Na, ȥed,Na, and ȥcp,Na are given in 17.6.5.3, 17.6.5.4, and 17.6.5.5, respectively. 17.6.5.1.1 ANaLVWKHSURMHFWHGLQÀXHQFHDUHDRIDVLQJOH adhesive anchor or an adhesive anchor group that is approxi- mated as a rectilinear area that projects outward a distance cNa from the centerline of the adhesive anchor, or in the case of an adhesive anchor group, from a line through a row of adjacent adhesive anchors. ANa shall not exceed nANao, where n is the number of adhesive anchors in the group that resist tension. R17.6.4 Concrete side-face blowout strength of headed anchors in tension, Nsb R17.6.4.1 The design requirements for side-face blowout are based on the recommendations of Furche and Elige- hausen (1991) and are applicable to headed anchors that usually are cast-in. Splitting during installation rather than side-face blowout generally governs post-installed anchors and is evaluated by ACI 355.2 requirements. R17.6.4.2 To calculate nominal side-face blowout strength for multiple headed anchors, only those anchors close to an edge (ca1 0.4hef) that are loaded in tension should be considered. Their strength is compared to the portion of the tensile load applied to those anchors. R17.6.5 Bond strength of adhesive anchors in tension, Na or Nag R17.6.5.1 Evaluation of bond strength applies only to adhe- sive anchors. Single anchors with small embedment loaded to failure in tension may exhibit concrete breakout failures, while deeper embedments produce bond failures. Adhesive anchors that exhibit bond failures when loaded individually may exhibit concrete failures in a group or in a near-edge condition. In all cases, the strength in tension of adhesive anchors is limited by concrete breakout strength as given by Eq. (17.6.2.1a) and (17.6.2.1b) (Eligehausen et al. 2006a). 7KHLQÀXHQFHRIDQFKRUVSDFLQJDQGHGJHGLVWDQFHRQERWK bond strength and concrete breakout strength must be evalu- DWHGIRUDGKHVLYHDQFKRUV7KHLQÀXHQFHRIDQFKRUVSDFLQJ and edge distance on the nominal bond strength of adhesive DQFKRUVLQWHQVLRQDUHLQFOXGHGLQWKHPRGL¿FDWLRQIDFWRUV ANa/ANao and ȥed,Na in Eq. (17.6.5.1a) and (17.6.5.1b). 7KH LQÀXHQFH RI QHDUE HGJHV DQG DGMDFHQW ORDGHG anchors on bond strength is dependent on the volume of concrete mobilized by a single adhesive anchor. In contrast to the projected concrete failure area concept used in Eq. (17.6.2.1a) and (17.6.2.1b) to calculate the breakout strength RIDQDGKHVLYHDQFKRUWKHLQÀXHQFHDUHDDVVRFLDWHGZLWKWKH bond strength of an adhesive anchor used in Eq. (17.6.5.1a) and (17.6.5.1b) is not a function of the embedment depth, but rather a function of the anchor diameter and characteristic bond stress. The critical distance cNa is assumed the same whether the concrete is cracked or uncracked. For simplicity, American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 255 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 258. 17.6.5.1.2 ANaoLVWKHSURMHFWHGLQÀXHQFHDUHDRIDVLQJOH adhesive anchor with an edge distance of at least cNa: ANao = (2cNa)2 (17.6.5.1.2a) where cNa = 10da 1100 uncr τ (17.6.5.1.2b) the relationship for cNaLQ(T E XVHVIJuncr, the characteristic bond stress in uncracked concrete. This has EHHQYHUL¿HGEH[SHULPHQWDODQGQXPHULFDOVWXGLHV Elige- hausen et al. 2006a). Figure R17.6.5.1(a) shows ANao and the development of Eq. (17.6.5.1.2a). ANaoLVWKHSURMHFWHGLQÀX- ence area for the bond strength of a single adhesive anchor. Figure R17.6.5.1(b) shows an example of the projected LQÀXHQFHDUHDIRUDQDQFKRUJURXS%HFDXVHLQWKLVFDVH ANa LV WKH SURMHFWHG LQÀXHQFH DUHD IRU DQ DQFKRU JURXS and ANaoLVWKHSURMHFWHGLQÀXHQFHDUHDIRUDVLQJOHDQFKRU there is no need to include n, the number of anchors, in Eq. (17.6.5.1b). If individual anchors in a group (anchors loaded by a common base plate or attachment) are positioned in VXFKDZDWKDWWKHSURMHFWHGLQÀXHQFHDUHDVRIWKHLQGL- vidual anchors overlap, the value of ANa is less than nANao. The tensile strength of closely spaced adhesive anchors ZLWKORZERQGVWUHQJWKPDVLJQL¿FDQWOH[FHHGWKHYDOXH given by Eq. (17.6.5.1b). A correction factor is given in the literature (Eligehausen et al. 2006a) to address this issue, but for simplicity, this factor is not included in the Code. American Concrete Institute – Copyrighted © Material – www.concrete.org 256 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 259. Fig. R17.6.5.1²DOFXODWLRQRILQÀXHQFHDUHDVANao and ANa. N Plan view cNa ca1 s1 cNa s2 ca2 ANa ANa = (cNa + s1 + ca1)(cNa + s2 + ca2) if ca1 and ca2 cNa s1 and s2 2cNa Section through anchor group showing principal stress trajectories (b) Group of four adhesive anchors located near a corner N Plan view cNa cNa cNa cNa ANao ANao = (2cNa)2 Section through anchor showing principal stress trajectories (a) Single adhesive anchor away from edges and other anchors Change in stress pattern with increasing embedment American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 257 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 260. 17.6.5.2 Basic single anchor bond strength, Nba 17.6.5.2.1 Basic bond strength of a single adhesive anchor in tension in cracked concrete, Nba, shall be calculated by Eq. (17.6.5.2.1) Nba ȜaIJcrʌdahef (17.6.5.2.1) 17.6.5.2.2 Characteristic bond stress, IJcr, shall be taken as the 5 percent fractile of results of tests performed and evalu- ated in accordance with ACI 355.4. 17.6.5.2.3 If analysis indicates cracking at service load OHYHOVDGKHVLYHDQFKRUVVKDOOEHTXDOL¿HGIRUXVHLQFUDFNHG concrete in accordance with ACI 355.4. 17.6.5.2.4 For adhesive anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, IJuncr shall be permitted to be used in place of IJcr in Eq. (17.6.5.2.1) and shall be taken as the 5 percent fractile of results of tests performed and evaluated according to ACI 355.4. 17.6.5.2.5 It shall be permitted to use the minimum char- acteristic bond stress values in Table 17.6.5.2.5, provided (a) WKURXJK H DUHVDWLV¿HG (a) Anchors shall meet the requirements of ACI 355.4 (b) Anchors shall be installed in holes drilled with a rotary impact drill or rock drill (c) Concrete compressive strength at time of anchor instal- lation shall be at least 2500 psi (d) Concrete age at time of anchor installation shall be at least 21 days (e) Concrete temperature at time of anchor installation shall be at least 50°F R17.6.5.2 Basic single anchor bond strength, Nba R17.6.5.2.1 The equation for basic bond strength of adhesive anchors as given in Eq. (17.6.5.2.1) represents a uniform bond stress model that has been shown to provide the best prediction of adhesive anchor bond strength based RQQXPHULFDOVWXGLHVDQGFRPSDULVRQVRIGL൵HUHQWPRGHOVWR an international database of experimental results (Cook et al. 1998). The basic bond strength is valid for bond failures that occur between the concrete and the adhesive as well as between the anchor and the adhesive. R17.6.5.2.2 Characteristic bond stresses should be based on tests performed in accordance with ACI 355.4 and should UHÀHFWWKHSDUWLFXODUFRPELQDWLRQRILQVWDOODWLRQDQGXVHFRQGL- tions anticipated during construction and during anchor service OLIH,ISURGXFWVSHFL¿FLQIRUPDWLRQLVXQDYDLODEOHDWWKHWLPHRI design, Table 17.6.5.2.5 provides lower-bound default values. R17.6.5.2.5 The characteristic bond stresses in Table 17.6.5.2.5 are the minimum values permitted for adhesive DQFKRUVVWHPVTXDOL¿HGLQDFFRUGDQFHZLWK$,IRU the tabulated installation and use conditions. Use of these YDOXHVLVUHVWULFWHGWRWKHFRPELQDWLRQVRIVSHFL¿FFRQGLWLRQV listed; values for other combinations of installation and use conditions should not be inferred. If both sustained tension and earthquake-induced forces are required to be resisted by the anchors, the applicable factors given in the footnotes of Table 17.6.5.2.5 should be multiplied together. The table assumes a concrete age of at least 21 days and a concrete compressive strength of at least 2500 psi. The terms “indoor” and “outdoor” as used in Table 17.6.5.2.5 UHIHUWRDVSHFL¿FVHWRILQVWDOODWLRQDQGVHUYLFHHQYLURQPHQWV Indoor conditions represent anchors installed in dry concrete with a rotary impact drill or rock drill and subjected to limited concrete temperature variations over the service life of the anchor. Outdoor conditions are assumed to occur if, at the time of installation, the concrete is exposed to weather that might leave the concrete wet. Anchors installed in outdoor conditions are also assumed to be subject to greater concrete tempera- ture variations such as might be associated with freezing and thawing or elevated temperatures resulting from direct sun H[SRVXUH:KLOHWKHLQGRRURXWGRRUFKDUDFWHUL]DWLRQLVXVHIXO for many applications, there may be situations in which a literal American Concrete Institute – Copyrighted © Material – www.concrete.org 258 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 261. Table 17.6.5.2.5—Minimum characteristic bond stresses[1][2] Installation and service environment Moisture content of concrete at time of anchor installation Peak in-service temperature of concrete, °F IJcr, psi IJuncr, psi Outdoor Dry to fully saturated 175 200 650 Indoor Dry 110 300 1000 [1] ,IDQFKRUGHVLJQLQFOXGHVVXVWDLQHGWHQVLRQPXOWLSOYDOXHVRIIJcrDQGIJuncr by 0.4. [2] If anchor design includes earthquake-induced forces for structures assigned to SDC '(RU)PXOWLSOYDOXHVRIIJcrEDQGIJuncr by 0.4. interpretation of the terms “indoor” and “outdoor” do not apply. For example, anchors installed before the building envelope is completed may involve drilling in saturated concrete. As such, the minimum characteristic bond stress associated with the outdoor condition in Table 17.6.5.2.5 applies, regardless of whether the service environment is “indoor” or “outdoor.” Rotary impact drills and rock drills produce non-uniform hole geometries that are generally favorable for bond. Instal- lation of adhesive anchors in core-drilled holes may result in substantially lower characteristic bond stresses. Because this H൵HFWLVKLJKOSURGXFWGHSHQGHQWGHVLJQRIDQFKRUVWREH installed in core-drilled holes should adhere to the product- VSHFL¿F FKDUDFWHULVWLF ERQG VWUHVVHV HVWDEOLVKHG WKURXJK testing in accordance with ACI 355.4. 7KH FKDUDFWHULVWLF ERQG VWUHVVHV DVVRFLDWHG ZLWK VSHFL¿F adhesive anchor systems are dependent on a number of param- eters. Consequently, care should be taken to include all param- eters relevant to the value of characteristic bond stress used in the design. These parameters include but are not limited to: (a) Type and duration of loading—bond strength is reduced for sustained tension (b) Concrete cracking—bond strength is higher in uncracked concrete (c) Anchor size—bond strength is generally inversely proportional to anchor diameter (d) Drilling method—bond strength may be lower for anchors installed in core-drilled holes (e) Degree of concrete saturation at time of hole drilling and anchor installation—bond strength may be reduced due to concrete saturation (f) Concrete temperature at time of installation—installa- tion of anchors in cold conditions may result in retarded adhesive cure and reduced bond strength (g) Concrete age at time of installation—installation in early-age concrete may result in reduced bond strength (refer to R17.2.2) (h) Peak concrete temperatures during anchor service OLIH²XQGHU VSHFL¿F FRQGLWLRQV IRU H[DPSOH DQFKRUV LQ thin concrete members exposed to direct sunlight), elevated concrete temperatures can result in reduced bond strength (i) Chemical exposure—anchors used in industrial envi- ronments may be exposed to increased levels of contami- nants that can reduce bond strength over time Anchors tested and assessed underACI 355.4 may in some FDVHVQRWEHTXDOL¿HGIRUDOORIWKHLQVWDOODWLRQDQGVHUYLFH environments represented in Table 17.6.5.2.5. Therefore, where the minimum values given in Table 17.6.5.2.5 are used for design, the relevant installation and service envi- URQPHQWVVKRXOGEHVSHFL¿HGLQDFFRUGDQFHZLWK L M N DQG O DQGRQODQFKRUVWKDWKDYHEHHQTXDOL¿HG under ACI 355.4 for the installation and service environ- ments corresponding to the characteristic bond stress taken IURP7DEOHVKRXOGEHVSHFL¿HG American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 259 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 262. 17.6.5.3 Bond eccentricity factor, ȥec,Na 17.6.5.3.10RGL¿FDWLRQIDFWRUIRUDGKHVLYHDQFKRUJURXSV ORDGHGHFFHQWULFDOOLQWHQVLRQȥec,Na, shall be calculated by Eq (17.6.5.3.1). ȥec,Na = 1 1 N Na e c ⎛ ⎞ ′ + ⎜ ⎟ ⎝ ⎠ ” 17.6.5.3.2 If the loading on an adhesive anchor group is such that only some of the adhesive anchors are in tension, only those adhesive anchors that are in tension shall be considered for determining eccentricity eƍN in Eq. (17.6.5.3.1) and for the calculation of Nag according to Eq. (17.6.5.1b). 17.6.5.3.3 If a load is eccentric about two orthogonal axes, ȥec,Na shall be calculated for each axis individually, and the product of these factors shall be used as ȥec,Na in Eq. (17.6.5.1b). 17.6.5.4 %RQGHGJHHৼHFWIDFWRU, ȥed,Na 17.6.5.4.10RGL¿FDWLRQIDFWRUIRUHGJHH൵HFWVIRUVLQJOH adhesive anchors or adhesive anchor groups in tension, ȥed,Na, shall be determined by (a) or (b) using the critical distance cNaDVGH¿QHGLQ(T E (a) If cDPLQ•cNaWKHQȥed,Na = 1.0 (17.6.5.4.1a) (b) If cDPLQ cNaWKHQȥed,Na = 0.7 + 0.3 DPLQ Na c c (17.6.5.4.1b) 17.6.5.5 Bond splitting factor, ȥcp,Na 17.6.5.5.10RGL¿FDWLRQIDFWRUIRUDGKHVLYHDQFKRUVGHVLJQHG for uncracked concrete in accordance with 17.6.5.1 without supplementary reinforcement to control splitting,ȥcp,Na, shall be determined by (a) or (b) where cacLVGH¿QHGLQ (a) If cDPLQ•cacWKHQȥcp,Na = 1.0 (17.6.5.5.1a) (b) If cDPLQ cacWKHQȥcp,Na = c DPLQ ac Na a c c c c ≥ (17.6.5.5.1b) KDUDFWHULVWLF ERQG VWUHVVHV DVVRFLDWHG ZLWK TXDOL¿HG DGKHVLYH DQFKRU VVWHPV IRU D VSHFL¿F VHW RI LQVWDOODWLRQ and use conditions may substantially exceed the minimum YDOXHV SURYLGHG LQ 7DEOH )RU H[DPSOH LQ WRLQGLDPHWHUDQFKRUVLQVWDOOHGLQLPSDFWGULOOHGKROHV in dry concrete where use is limited to indoor conditions in uncracked concrete as described above may exhibit charac- teristic bond stresses IJuncr in the range of 2000 to 2500 psi. R17.6.5.3 Bond eccentricity factor, ȥec,Na R17.6.5.3.1 Refer to R17.6.2.3.1. R17.6.5.4 %RQGHGJHHৼHFWIDFWRU, ȥed,Na R17.6.5.4.1 If anchors are located close to an edge, their VWUHQJWKLVIXUWKHUUHGXFHGEHRQGWKDWUHÀHFWHGLQANa/ANao. 7KHIDFWRUȥed,NaDFFRXQWVIRUWKHHGJHH൵HFW Fuchs et al. 1995; Eligehausen et al. 2006a). American Concrete Institute – Copyrighted © Material – www.concrete.org 260 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 263. 17.6.5.5.2 For all other cases, ȥcp,Na shall be taken as 1.0. 17.7—Shear strength 17.7.1 Steel strength of anchors in shear, Vsa 17.7.1.1 Nominal steel strength of anchors in shear as governed by the steel, Vsa, shall be evaluated based on the properties of the anchor material and the physical dimen- sions of the anchors. If concrete breakout is a potential failure mode, the required steel shear strength shall be consistent with the assumed breakout surface. 17.7.1.2 Nominal strength of an anchor in shear, Vsa, shall not exceed (a) through (c): (a) For cast-in headed stud anchor Vsa = Ase,V futa (17.7.1.2a) where Ase,V LV WKH H൵HFWLYH FURVVVHFWLRQDO DUHD RI DQ anchor in shear, in.2 , and futa used for calculations shall not exceed either 1.9fya or 125,000 psi. (b) For cast-in headed bolt and hooked bolt anchors and for post-installed anchors where sleeves do not extend through the shear plane Vsa = 0.6Ase,V futa (17.7.1.2b) where Ase,V LV WKH H൵HFWLYH FURVVVHFWLRQDO DUHD RI DQ anchor in shear, in.2 , and the value of futa shall not exceed either 1.9fya or 125,000 psi. (c) For post-installed anchors where sleeves extend through the shear plane, Vsa shall be based on the 5 percent fractile of results of tests performed and evaluated in accordance with ACI 355.2. Alternatively, Eq. (17.7.1.2b) shall be permitted to be used. 17.7.1.2.1 If anchors are used with built-up grout pads, nominal strength Vsa calculated in accordance with 17.7.1.2 shall be multiplied by 0.80. 17.7.2 Concrete breakout strength of anchors in shear, Vcb 17.7.2.1 Nominal concrete breakout strength in shear, Vcb of a single anchor or Vcbg of an anchor group satisfying 17.5.1.3.1, shall be calculated in accordance with (a) through (d): (a) For shear perpendicular to the edge on a single anchor , , , Vc cb ed V c V h V b Vco A V V A = ψ ψ ψ (17.7.2.1a) (b) For shear perpendicular to the edge on an anchor group , , , , Vc cbg ec V ed V c V h V b Vco A V V A = ψ ψ ψ ψ (17.7.2.1b) R17.7—Shear strength R17.7.1 Steel strength of anchors in shear, Vsa R17.7.1.1 The shear applied to each anchor in an anchor group may vary depending on assumptions for the concrete breakout surface and load redistribution (refer to R17.7.2.1). R17.7.1.2 The nominal shear strength of anchors is best represented as a function of futa rather than fya because the large majority of anchor materials do not exhibit a well- GH¿QHG LHOG SRLQW :HOGHG VWXGV GHYHORS D KLJKHU VWHHO VKHDUVWUHQJWKWKDQKHDGHGDQFKRUVGXHWRWKH¿[LWSURYLGHG by the weld between the studs and the base plate. The use of Eq. (17.7.1.2a) and (17.7.1.2b) with the load factors of 5.3 and the ࢥ-factors of 17.5.3 result in design strengths consis- tent with AISC 360. The limitation of 1.9fya on futa is to ensure that, under service load conditions, the anchor stress does not exceed fya. The limit on futa of 1.9fya was determined by converting the LRFD provisions to corresponding service-level condi- tions, as discussed in R17.6.1.2. For post-installed anchors having a reduced cross- VHFWLRQDODUHDDQZKHUHDORQJWKHDQFKRUOHQJWKWKHH൵HF- tive cross-sectional area of the anchor should be provided by the manufacturer. For threaded rods and headed bolts, ASME B1.1GH¿QHVAse,V as 2 , 0.9743 4 se V a t A d n ⎛ ⎞ π = − ⎜ ⎟ ⎝ ⎠ where nt is the number of threads per inch. R17.7.2 Concrete breakout strength of anchors in shear, Vcb R17.7.2.1 The shear strength equations were developed from the CCD Method (refer to R17.5.1.3). They assume a breakout angle of approximately 35 degrees (refer to Fig. R17.5.1.3b) and consider fracture mechanics theory. 7KHH൵HFWVRIPXOWLSOHDQFKRUVVSDFLQJRIDQFKRUVHGJH distance, and thickness of the concrete member on nominal concrete breakout strength in shear are included by applying the reduction factor of AVc/AVco in Eq. (17.7.2.1a) and (17.7.2.1b), and ȥec,V in Eq. (17.7.2.1b). For anchors far from the edge, 17.7.2 usually will not govern. For these cases, 17.7.1 and 17.7.3 often govern. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 261 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 264. Figure R17.7.2.1a shows AVco and the development of Eq. (17.7.2.1.3). AVco is the maximum projected area for a single anchor that approximates the surface area of the full breakout YROXPHIRUDQDQFKRUXQD൵HFWHGEHGJHGLVWDQFHVSDFLQJ or depth of member. Figure R17.7.2.1b shows examples of the projected areas for various single-anchor and multiple- anchor arrangements. AVc approximates the full surface area of the breakout for the particular arrangement of anchors. Because AVc is the total projected area for an anchor group, and AVco is the area for a single anchor, there is no need to include the number of anchors in the equation. As shown in the examples in Fig. R17.7.2.1b of two-anchor groups loaded in shear, when using Eq. (17.7.2.1b) for cases where the anchor spacing s is greater than the edge distance to the near-edge anchor ca1,1, both assumptions for load distribution illustrated in Cases 1 and 2 should be consid- ered. This is because the anchors nearest to the free edge FRXOGIDLO¿UVWRUWKHHQWLUHJURXSFRXOGIDLODVDXQLWZLWK the failure surface originating from the anchors farthest from the edge. For Case 1, the steel shear strength is provided by both anchors. For Case 2, the steel shear strength is provided entirely by the anchor farthest from the edge; no contribu- tion of the anchor near the edge is considered. In addition, checking the near-edge anchor for concrete breakout under service loads is advisable to preclude undesirable cracking at service conditions. If the anchor spacing s is less than the edge distance to the near-edge anchor, the failure surfaces may merge (Eligehausen et al. 2006b) and Case 3 of Fig. R17.7.2.1b may be taken as a conservative approach. If the anchors are welded to a common plate (regardless of anchor spacing s), when the anchor nearest the front edge begins to form a breakout failure, shear is transferred to the VWL൵HUDQGVWURQJHUUHDUDQFKRU)RUWKLVUHDVRQRQODVH need be considered, which is consistent with Section 6.5.5 of the PCI Design Handbook (PCI MNL 120). For determi- nation of steel shear strength, it is conservative to consider only the anchor farthest from the edge. However, for anchors having a ratio of s/ca1,1 less than 0.6, both the front and rear anchors may be assumed to resist the shear (Anderson and Meinheit 2007). For ratios of s/ca1,1 greater than 1, it is advis- able to check concrete breakout of the near-edge anchor to preclude undesirable cracking at service conditions. Further discussion of design for multiple anchors is given in Primavera et al. (1997). For anchors near a corner required to resist a shear force with components normal to each edge, a satisfactory solu- tion is to check the connection independently for each component of the shear force. Other specialized cases, such as the shear resistance of anchor groups where all anchors do not have the same edge distance, are treated in Eligehausen et al. (2006a). The detailed provisions of 17.7.2.1(a) apply to the case of shear directed toward an edge. If the shear is directed away from the edge, the strength will usually be governed by 17.7.1 or 17.7.3. The case of shear parallel to an edge (c) For shear parallel to an edge, Vcb or Vcbg shall be permitted to be twice the value of the shear calculated by Eq. (17.7.2.1a) or (17.7.2.1b), respectively, with the shear DVVXPHGWRDFWSHUSHQGLFXODUWRWKHHGJHDQGȥed,V taken equal to 1.0. (d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be calculated for each edge, and the lesser value shall be used. where ȥec,V, ȥed,V, ȥc,V, and ȥh,V are given in 17.7.2.3, 17.7.2.4, 17.7.2.5, and 17.7.2.6, respectively. 17.7.2.1.1 AVc is the projected area of the failure surface on the side of the concrete member at its edge for a single anchor or an anchor group. It shall be permitted to evaluate AVc as the base of a truncated half-pyramid projected on the side face of the member where the top of the half-pyramid is given by the axis of the anchor row selected as critical. The value of ca1 shall be taken as the distance from the edge to this axis. AVc shall not exceed nAVco, where n is the number of anchors in the group. American Concrete Institute – Copyrighted © Material – www.concrete.org 262 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 265. is shown in Fig. R17.7.2.1c. The maximum shear that can be applied parallel to the edge, V||, as governed by concrete breakout, is twice the maximum shear that can be applied perpendicular to the edge, Vŏ. For a single anchor required to resist shear near a corner (refer to Fig. R17.7.2.1d), the provisions for shear applied perpendicular to the edge should be checked in addition to the provisions for shear applied parallel to the edge. The critical edge distance for headed studs, headed bolts, expansion anchors, screw anchors, and undercut anchors is 1.5ca1 1.5ca1 ca1 1.5ca1 1.5ca1 ≈ 35° hef V V 1.5ca1 1.5ca1 ca1 Plan Side section Elevation AVco = 2(1.5ca1) x (1.5ca1) = 4.5ca1 2 Edge of concrete ≈ 35° Fig. R17.7.2.1a—Calculation of AVco. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 263 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 266. ca1 V ha 1.5ca1 1.5ca1 Avc Avc = 2(1.5ca1)ha If ha 1.5ca1 1.5ca1 ca1 V 1.5ca1 ca2 Avc Avc = 1.5ca1(1.5ca1 + ca2) If ca2 1.5ca1 ca1 V ha 1.5ca1 1.5ca1 s1 Avc Avc = [2(1.5ca1) + s1]ha If ha 1.5ca1 and s1 3ca1 0.5V 0.5V ca1,1 ca1,2 s ≥ ca1,1 ha 1.5ca1,1 1.5ca1,1 Avc If ha 1.5ca1 Avc = 2(1.5ca1,1)ha Case 1: One assumption of the distribution of forces indicates that half of the shear force would be critical on the front anchor and the projected area. For the calculation of concrete breakout, ca1 is taken as ca1,1. If ha 1.5ca1 Avc = 2(1.5ca1,2)ha ca1,1 Avc 1.5ca1,2 1.5ca1,2 ca1,2 ha s ≥ ca1,1 V Note: For s ≥ ca1,1, both Case 1 and Case 2 should be evaluated to determine which controls for design except as noted for anchors welded to a common plate V ca1,1 ha ca1,2 s ca1,1 1.5ca1,1 1.5ca1,1 If ha 1.5ca1 Avc = 2(1.5ca1,1)ha Case 3: Where s ca1,1, apply the entire shear load V to the front anchor. This case does not apply for anchors welded to a common plate. For the calculation of concrete breakout, ca1 is taken as ca1,1. Case 2: Another assumption of the distribution of forces indicates that the total shear force would be critical on the rear anchor and its projected area. Only this assumption needs to be considered when anchors are welded to a common plate independent of s. For the calculation of concrete breakout, ca1 is taken as ca1,2. Avc Fig. R17.7.2.1b—Calculation of Avc for single anchors and anchor groups. American Concrete Institute – Copyrighted © Material – www.concrete.org 264 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 267. V ca1 V = 2V Edge Fig. R17.7.2.1c—Shear force parallel to an edge. Anchor A Anchor A V ca1 ca2 ca2 ca1 V Fig. R17.7.2.1d—Shear near a corner. R17.7.2.1.2 For anchors located in narrow sections of limited thickness where the edge distances perpendicular to the direction of load and the member thickness are less than 1.5ca1, the shear breakout strength calculated by the CCD Method (refer to R17.5.1.3) is overly conservative. These cases were studied for the Kappa Method (Eligehausen and Fuchs 1988), and the problem was pointed out by Lutz (1995). Similar to the approach used for concrete breakout strength in tension in 17.6.2.1.2, the concrete breakout strength in shear for this case is more accurately evaluated if the value of ca1 used in 17.7.2.1 through 17.7.2.6 and in the calculation of AVc is limited to the maximum of two- thirds of the greater of the two edge distances perpendicular to the direction of shear, two-thirds of the member thick- ness, and one-third of the maximum spacing between indi- vidual anchors within the group, measured perpendicular to the direction of shear. The limit on ca1 of at least one-third of the maximum spacing between anchors within the group 17.7.2.1.2 If anchors are located in narrow sections of limited thickness such that both edge distances ca2 and thick- ness ha are less than 1.5ca1, the value of ca1 used to calculate AVc in accordance with 17.7.2.1.1 as well as for the equations in 17.7.2.1 through 17.7.2.6 shall not exceed the greatest of (a) through (c). (a) ca2 /1.5, where ca2 is the greatest edge distance (b) ha/1.5 (c) s/3, where s is the maximum spacing perpendicular to direction of shear, between anchors within a group American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 265 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 268. prevents the use of a calculated strength based on individual EUHDNRXWYROXPHVIRUDQDQFKRUJURXSFRQ¿JXUDWLRQ This approach is illustrated in Fig. R17.7.2.1.2. In this example, the limiting value of ca1 is denoted as cƍa1 and is used to calculate AVc, AVco, ȥed,V, and ȥh,V as well as Vb (not shown). The requirement of 17.7.2.1.2 may be visual- ized by moving the actual concrete breakout surface origi- nating at the actual ca1 toward the surface of the concrete in the direction of the applied shear. The value of ca1 used to calculate AVc and to be used in 17.7.2.1 through 17.7.2.6 is determined when (a) an outer boundary of the failure surface ¿UVWLQWHUVHFWVWKHFRQFUHWHVXUIDFH;, or (b) the intersection of the breakout surface between individual anchors within the JURXS¿UVWLQWHUVHFWVWKHFRQFUHWHVXUIDFH)RUWKHH[DPSOH shown in Fig. R17.7.2.1.2, point “A” shows the intersec- tion of the assumed failure surface for limiting ca1 with the concrete surface. 1 1.5 1 1.5 The actual ca1 = 12 in. The two edge distances ca2 as well as ha are all less than 1.5ca1. The limiting value of ca1 (shown as c’a1 in the figure) to be used to calculate AVc and to be used in 17.7.2.1 through 17.7.2.6 is the largest of the following: (ca2,max)/1.5 = (7)/1.5 = 4.67 in. (ha)/1.5 = (8)/1.5 = 5.33 in. (controls) s/3 = 9/3 = 3 in. For this case, AVc, AVco, ψed,V, and ψh,V are: AVc = (5 + 9 + 7)(1.5 x 5.33) = 168 in.2 AVco = 4.5(5.33)2 = 128 in.2 ψed,V = 0.7 + 0.3(5)/5.33 = 0.98 ψh,V = 1.0 because ca1 =(ha)/1.5. Point A shows the intersection of the assumed failure surface with the concrete surface that establishes the limiting value of ca1. ca2,2 = 5 in. ca2,1 = 7 in. s = 9 in. c’a1 ca1 = 12 in. V V c’a1 ha = 8 in. Point A Plan Side section Assumed failure surface for limiting ca1 Actual failure surface Assumed failure surface for limiting ca1 Actual failure surface 1. 2. 3. 4. Fig. R17.7.2.1.2²([DPSOHRIVKHDUZKHUHDQFKRUVDUHORFDWHGLQQDUURZPHPEHUVRIOLPLWHGWKLFNQHVV American Concrete Institute – Copyrighted © Material – www.concrete.org 266 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 269. 17.7.2.1.3 AVco is the projected area for a single anchor in a deep member with a distance from edges of at least 1.5ca1 in the direction perpendicular to the shear. It shall be permitted to calculate AVco by Eq. (17.7.2.1.3), which gives the area of the base of a half-pyramid with a side length parallel to the edge of 3ca1 and a depth of 1.5ca1. AVco = 4.5(ca1)2 (17.7.2.1.3) 17.7.2.1.4 If anchors are located at varying distances from the edge and the anchors are welded to the attachment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to base the value of ca1 on the distance from the edge to the axis of the farthest anchor row that is selected as critical, and all of the shear shall be assumed to be resisted by this critical anchor row alone. 17.7.2.2 Basic single anchor breakout strength, Vb 17.7.2.2.1 Basic concrete breakout strength of a single anchor in shear in cracked concrete, Vb, shall not exceed the lesser of (a) and (b): (a) ( ) 0.2 1.5 1 7 e b a a c a a V d f c d ⎛ ⎞ ⎛ ⎞ = λ ′ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ A (17.7.2.2.1a) where Ɛe is the load-bearing length of the anchor for shear: Ɛe = hefIRUDQFKRUVZLWKDFRQVWDQWVWL൵QHVVRYHUWKHIXOO length of embedded section, such as headed studs and post- installed anchors with one tubular shell over full length of the embedment depth; Ɛe = 2da for torque-controlled expansion anchors with a distance sleeve separated from expansion sleeve; Ɛe”da in all cases. (b) Vb Ȝa c f ′ (ca1)1.5 (17.7.2.2.1b) 17.7.2.2.2 For cast-in headed studs, headed bolts, or hooked bolts that are continuously welded to steel attach- ments, basic concrete breakout strength of a single anchor in shear in cracked concrete, Vb, shall be the lesser of Eq. (17.7.2.2.1b) and Eq. (17.7.2.2.2) provided that (a) through G DUHVDWLV¿HG ( ) 0.2 1.5 1 8 e b a a c a a V d f c d ⎛ ⎞ ⎛ ⎞ = λ ′ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ A (17.7.2.2.2) where ƐeLVGH¿QHGLQ (a) Steel attachment thickness is the greater of 0.5daDQGLQ R17.7.2.2 Basic single anchor breakout strength, Vb R17.7.2.2.1 Like the concrete breakout tensile strength, the concrete breakout shear strength does not increase with the failure surface, which is proportional to (ca1)2 . Instead, the strength increases proportionally to (ca1)1.5 due to the VL]H H൵HFW 7KH FRQVWDQW LQ WKH VKHDU VWUHQJWK HTXD- tion (17.7.2.2.1a) was determined from test data reported in Fuchs et al. (1995) at the 5 percent fractile adjusted for cracking. 7KH VWUHQJWK LV DOVR LQÀXHQFHG E WKH DQFKRU VWL൵QHVV and the anchor diameter (Fuchs et al. 1995; Eligehausen and Balogh 1995; Eligehausen et al. 1987, 2006b; Elige- hausen and Fuchs 1988 7KHLQÀXHQFHRIDQFKRUVWL൵QHVV and diameter is not apparent in large-diameter anchors (Lee et al. 2010), resulting in a limitation on the shear breakout strength provided by Eq. (17.7.2.2.1b). R17.7.2.2.2 For cast-in headed bolts continuously welded to an attachment, test data (Shaikh and Yi 1985) show that somewhat higher shear strength exists, possibly due to the VWL൵ZHOGHGFRQQHFWLRQFODPSLQJWKHEROWPRUHH൵HFWLYHO than an attachment with an anchor gap. Because of this, the basic shear breakout strength for such anchors is increased, but the upper limit of Eq. (17.7.2.2.1b) is imposed because tests on large-diameter anchors welded to steel attach- ments are not available to justify a higher value than Eq. (17.7.2.2.1b). The design of supplementary reinforcement is discussed in ¿E (2011), Eligehausen et al. (1987, 2006b), and Eligehausen and Fuchs (1988). American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 267 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 270. (b) Anchor spacing s is at least 2.5 in. (c) Reinforcement is provided at the corners if ca2”hef (d) For anchor groups, the strength is calculated based on the strength of the row of anchors farthest from the edge. 17.7.2.3 Breakout eccentricity factor, ȥec,V 17.7.2.3.10RGL¿FDWLRQIDFWRUIRUDQFKRUJURXSVORDGHG eccentrically in shear, ȥec,V, shall be calculated by Eq. (17.7.2.3.1). . 1 1 1.0 1 1.5 ec V V a e c ψ = ≤ ⎛ ⎞ + ⎜ ⎟ ⎠ ′ ⎝ (17.7.2.3.1) 17.7.2.3.2 If the loading on an anchor group is such that only some of the anchors in the group are in shear, only those anchors that are in shear in the same direction shall be considered for determining the eccentricity eƍV in Eq. (17.7.2.3.1) and for the calculation of Vcbg according to Eq. (17.7.2.1b). 17.7.2.4 %UHDNRXWHGJHHৼHFWIDFWRU, ȥed,V 17.7.2.4.10RGL¿FDWLRQIDFWRUIRUHGJHH൵HFWVIRUVLQJOH anchors or anchor groups loaded in shear, ȥed,V, shall be determined by (a) or (b) using the lesser value of ca2. (a) If ca2•ca1WKHQȥed,V = 1.0 (17.7.2.4.1a) R17.7.2.3 Breakout eccentricity factor, ȥec,V R17.7.2.3.17KLVVHFWLRQSURYLGHVDPRGL¿FDWLRQIDFWRUIRU an eccentric shear toward an edge on an anchor group. If the shear originates above the plane of the concrete surface, the VKHDUVKRXOG¿UVWEHUHVROYHGDVDVKHDULQWKHSODQHRIWKH concrete surface, acting in combination with a moment that may or may not also cause tension in the anchors, depending RQWKHQRUPDOIRUFH)LJXUH5GH¿QHVWKHWHUPeƍV for calculating the ȥec,VPRGL¿FDWLRQIDFWRUWKDWDFFRXQWVIRU the fact that more shear is applied to one anchor than others, tending to split the concrete near an edge. e’v s/2 s/2 Edge of concrete Plan V Fig. R17.7.2.3.1²'H¿QLWLRQRIeƍV for an anchor group. American Concrete Institute – Copyrighted © Material – www.concrete.org 268 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 271. (b) If ca2 1.5ca1WKHQȥed,V = 0.7 + 0.3 2 1 1.5 a a c c (17.7.2.4.1b) 17.7.2.5 Breakout cracking factor, ȥc,V 17.7.2.5.1 0RGL¿FDWLRQ IDFWRU IRU WKH LQÀXHQFH RI cracking in anchor regions at service load levels and pres- ence or absence of supplementary reinforcement, ȥc,V, shall be determined as follows: (a) For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, ȥc,V shall be permitted to be 1.4. (b) For anchors located in a region of a concrete member where analysis indicates cracking at service load levels, ȥc,V shall be in accordance with Table 17.7.2.5.1. Table 17.7.2.5.1—Modification factor where analysis indicates cracking at service load levels, ȥc,V Condition ȥc,V Anchors without supplementary reinforcement or with edge reinforcement smaller than a No. 4 bar 1.0 Anchors with reinforcement of at least a No. 4 bar or greater between the anchor and the edge 1.2 Anchors with reinforcement of at least a No. 4 bar or greater between the anchor and the edge, and with the reinforcement enclosed within stirrups spaced at not more than 4 in. 1.4 17.7.2.6 Breakout thickness factor, ȥh,V 17.7.2.6.1 0RGL¿FDWLRQ IDFWRU IRU DQFKRUV ORFDWHG LQ D concrete member where ha 1.5ca1ȥh,V shall be calculated by Eq. (17.7.2.6.1) 1 , 1.5 1.0 a h V a c h ψ = ≥ (17.7.2.6.1) 17.7.3 Concrete pryout strength of anchors in shear, Vcp or Vcpg 17.7.3.1 Nominal pryout strength, Vcp of a single anchor or Vcpg of an anchor group satisfying 17.5.1.3.1, shall not exceed (a) or (b), respectively. (a) For a single anchor Vcp = kcpNcp (17.7.3.1a) (b) For an anchor group Vcpg = kcpNcpg (17.7.3.1b) where R17.7.2.6 Breakout thickness factor, ȥh,V R17.7.2.6.1 For anchors located in a concrete member where ha 1.5ca1, tests (¿E 2011; Eligehausen et al. 2006b) have shown that the concrete breakout strength in shear is not directly proportional to the member thickness ha. The IDFWRUȥh,VDFFRXQWVIRUWKLVH൵HFW R17.7.3 Concrete pryout strength of anchors in shear, Vcp or Vcpg R17.7.3.1 Fuchs et al. (1995) indicates that the pryout shear resistance can be approximated as one to two times the anchor tensile resistance with the lower value appropriate for hef less than 2.5 in. Because it is possible that the bond strength of adhesive anchors could be less than the concrete breakout strength, it is necessary to consider both 17.6.2.1 and 17.6.5.1 to calculate pryout strength. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 269 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 272. R17.8—Tension and shear interaction The tension-shear interaction expression has traditionally been expressed as 1.0 ua ua n n N V N V ς ς ⎛ ⎞ ⎛ ⎞ + ≤ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ where Ȣ varies from 1 to 2. The current trilinear recom- PHQGDWLRQLVDVLPSOL¿FDWLRQRIWKHH[SUHVVLRQZKHUHȢ 5/3 (Fig. R17.8). The limits were chosen to eliminate the UHTXLUHPHQWIRUFDOFXODWLRQRILQWHUDFWLRQH൵HFWVZKHUHYHU small values of the second force are present. Any other inter- DFWLRQH[SUHVVLRQWKDWLVYHUL¿HGEWHVWGDWDKRZHYHUFDQ be used to satisfy 17.5.2.3. Trilinear interaction approach + = 1 5 /3 5 /3 I 0.2 Nn I 0.2 Vn I Vn INn Nn INn Vn IVn Nua Vua Fig. R17.8—Shear and tensile load interaction equation. R17.9—Edge distances, spacings, and thicknesses to preclude splitting failure R17.9.1 Minimum spacings, edge distances, and thick- nesses are dependent on the anchor characteristics. Installa- tion forces and torques in post-installed anchors can cause splitting of the surrounding concrete. Such splitting also can kcp = 1.0 for hef 2.5 in. kcp = 2.0 for hef•LQ 17.7.3.1.1 For cast-in anchors and post-installed expan- sion, screw, and undercut anchors, Ncp shall be taken as Ncb calculated by Eq. (17.6.2.1a), and for adhesive anchors, Ncp shall be the lesser of Na calculated by Eq. (17.6.5.1a) and Ncb calculated by Eq. (17.6.2.1a). 17.7.3.1.2 For cast-in anchors and post-installed expan- sion, screw, and undercut anchors, Ncpg shall be taken as Ncbg calculated by Eq. (17.6.2.1b), and for adhesive anchors, Ncpg shall be the lesser of Nag calculated by Eq. (17.6.5.1b) and Ncbg calculated by Eq. (17.6.2.1b). 17.8—Tension and shear interaction 17.8.1 8QOHVV WHQVLRQ DQG VKHDU LQWHUDFWLRQ H൵HFWV DUH considered in accordance with 17.5.2.3, anchors or anchor groups that resist both tension and shear shall satisfy 17.8.2 DQG7KHYDOXHVRIࢥNnDQGࢥVn shall be in accor- dance with 17.5.2 or 17.10. 17.8.2 It shall be permitted to neglect the interaction EHWZHHQWHQVLRQDQGVKHDULI D RU E LVVDWLV¿HG (a) Nua/(ࢥNn ” (17.8.2a) (b) Vua/(ࢥVn ” (17.8.2b) 17.8.3 If Nua /(ࢥNn) 0.2 for the governing strength in tension and Vua/(ࢥVn) 0.2 for the governing strength in VKHDUWKHQ(T VKDOOEHVDWLV¿HG 1.2 ua ua n n N V N V + ≤ φ φ (17.8.3) 17.9—Edge distances, spacings, and thicknesses to preclude splitting failure 17.9.1 Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to this section, unless supplementary reinforcement is provided to FRQWUROVSOLWWLQJ/HVVHUYDOXHVIURPSURGXFWVSHFL¿FWHVWV American Concrete Institute – Copyrighted © Material – www.concrete.org 270 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 273. performed in accordance with ACI 355.2 or ACI 355.4 shall be permitted. 17.9.2 Unless determined in accordance with 17.9.3, minimumspacingparametersshallconformtoTable17.9.2(a). Table 17.9.2(a)—Minimum spacing and edge distance requirements Spacing parameter Anchor type Cast-in anchors Post-installed expansion and undercut anchors Post- installed screw anchors Not torqued Torqued Minimum anchor spacing 4da 6da 6da Greater of 0.6hef and 6da Minimum edge distance 6SHFL¿HG cover requirements for reinforcement according to 20.5.1.3 6da Greatest of (a), (b), and (c): D 6SHFL¿HGFRYHU requirements for reinforcement according to 20.5.1.3 (b) Twice the maximum aggregate size (c) Minimum edge distance requirements according to ACI 355.2 or 355.4, or Table 17.9.2(b) when product information is absent Table 17.9.2(b)—Minimum edge distance in absence of product-specific ACI 355.2 or ACI 355.4 test information Post-installed anchor type Minimum edge distance Torque-controlled 8da Displacement-controlled 10da Screw 6da Undercut 6da Adhesive 6da 17.9.3 For anchors where installation does not produce a splitting force and that will not be torqued, if the edge distance or spacing is less than those given in 17.9.2, calcu- lations shall be performed by substituting for da a lesser value daƍ that meets the requirements of 17.9.2. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of daƍ. 17.9.4 Value of hef for a post-installed expansion, screw, or undercut post-installed anchor shall not exceed the greater be produced in subsequent torquing during connection of attachments to anchors including cast-in anchors. The primary source of values for minimum spacings, edge distances, and thicknesses of post-installed anchors should be the product- VSHFL¿FWHVWVRIACI 355.2 and ACI 355.4. In some cases, KRZHYHUVSHFL¿FSURGXFWVDUHQRWNQRZQLQWKHGHVLJQVWDJH Approximate values are provided for use in design. R17.9.2 Edge cover for anchors with deep embedments FDQKDYHDVLJQL¿FDQWH൵HFWRQWKHVLGHIDFHEORZRXWVWUHQJWK provided in 17.6.4. It is therefore advantageous to increase edge cover beyond that required in 20.5.1.3 to increase side- face blowout strength. Drilling holes for post-installed anchors can cause micro- cracking. The requirement for edge distance to be at least WZLFHWKHPD[LPXPDJJUHJDWHVL]HLVWRUHGXFHH൵HFWVRI such microcracking. R17.9.3 In some cases, it may be desirable to use a larger- diameter anchor than the requirements of 17.9.2 permit. In these cases, it is permissible to use a larger-diameter anchor, provided the design strength of the anchor is based on a smaller assumed anchor diameter daƍ. R17.9.4 Splitting failures are caused by load transfer between the bolt and the concrete. The limitations on the American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 271 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 274. value of hef do not apply to cast-in and adhesive anchors because the splitting forces associated with these anchor types are less than for expansion, screw, and undercut anchors. For all post-installed anchors, the embedment depth for a given member thickness should be limited to avoid back- face blowout on the opposite side of the concrete member during hole drilling and anchor setting. This depth limit is dependent on many variables, including anchor type, drilling method, drilling technique, type and size of drilling equip- ment, presence of reinforcement, and strength and condition of the concrete. R17.9.5 The critical edge distance cac is required for design of post-installed anchors for use in uncracked concrete where no supplemental reinforcement is available to restrain split- ting cracks. To permit the design of these types of anchors LISURGXFWVSHFL¿FLQIRUPDWLRQLVQRWDYDLODEOHFRQVHUYDWLYH default values for cac are provided. Alternately, product- VSHFL¿FYDOXHVRIcac may be determined in accordance with ACI 355.2 or ACI 355.4. Corner-test requirements in the DIRUHPHQWLRQHGTXDOL¿FDWLRQVWDQGDUGVPDQRWEHVDWLV¿HG with ca,min = 1.5hef for many expansion, screw, undercut, and DGKHVLYHDQFKRUVGXHWRWHQVLOHDQGÀH[XUDOVWUHVVHVDVVRFL- ated with anchor installation and loading, which may result in a premature splitting failure. R17.10—Earthquake-resistant anchor design requirements R17.10.1 Unless 17.10.5.1 or 17.10.6.1 apply, all anchors in structures assigned to Seismic Design Categories (SDC) C, D, E, or F are required to satisfy the additional require- ments of 17.10.2 through 17.10.7, regardless of whether earthquake-induced forces are included in the controlling load combination for the anchor design. In addition, all post-installed anchors in structures assigned to SDC C, D, E, or F must meet the requirements of ACI 355.2 or ACI IRUSUHTXDOL¿FDWLRQRIDQFKRUVWRUHVLVWHDUWKTXDNH induced forces. Ideally, for tension, anchor strength should be governed by yielding of the ductile steel element of the DQFKRU ,I WKH DQFKRU FDQQRW PHHW WKH VSHFL¿HG GXFWLOLW requirements of 17.10.5.3(a), then the attachment should be designed to yield if it is structural or light gauge steel, or designed to crush if it is wood. If ductility requirements RI D DUH VDWLV¿HG WKHQ DQ DWWDFKPHQWV WR WKH anchor should be designed not to yield. In designing attach- ments using yield mechanisms to provide adequate ductility, as permitted by 17.10.5.3(b) and 17.10.6.3(a), the ratio of VSHFL¿HGLHOGVWUHQJWKWRH[SHFWHGVWUHQJWKIRUWKHPDWHULDO of the attachment should be considered in determining the design force. The value used for the expected strength should consider both material overstrength and strain hardening H൵HFWV)RUH[DPSOHWKHPDWHULDOLQDFRQQHFWLRQHOHPHQW could yield and, due to an increase in its strength with strain hardening, cause a secondary failure of a sub-element or place extra force or deformation demands on the anchors. RIRIWKHPHPEHUWKLFNQHVVha, and the member thick- ness minus 4 in., unless determined from tests in accordance with ACI 355.2. 17.9.5 Critical edge distance cac shall be in accordance with Table 17.9.5 unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4. Table 17.9.5—Critical edge distance Post-installed anchor type Critical edge distance cac Torque-controlled 4hef Displacement-controlled 4hef Screw 4hef Undercut 2.5hef Adhesive 2hef 17.10—Earthquake-resistant anchor design requirements 17.10.1 Anchors in structures assigned to Seismic Design Category (SDC) C, D, E, or F shall satisfy the additional requirements of this section. American Concrete Institute – Copyrighted © Material – www.concrete.org 272 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 275. 17.10.2 Provisions of this chapter shall not apply to the design of anchors in plastic hinge zones of concrete struc- tures resisting earthquake-induced forces. 17.10.33RVWLQVWDOOHGDQFKRUVVKDOOEHTXDOL¿HGIRUHDUWK- quake-induced forces in accordance with ACI 355.2 or ACI 355.4.The pullout strength, Np, and steel strength in shear, Vsa, of post-installed expansion, screw, and undercut anchors shall be based on the results of the ACI 355.2 Simulated Seismic Tests. For adhesive anchors, the steel strength in shear, Vsa, and the characteristic bond stresses, IJuncr and IJcr, shall be based on results of the ACI 355.4 Simulated Seismic Tests. 17.10.4 Anchor reinforcement used in structures assigned to SDC C, D, E, or F shall be deformed reinforcement and shall be in accordance with the anchor reinforcement requirements of 20.2.2. 17.10.5 7HQVLOHORDGLQJGHVLJQUHTXLUHPHQWV 17.10.5.1 If the tensile component of the strength-level earthquake-induced force applied to a single anchor or anchor group does not exceed 20 percent of the total factored anchor tensile force associated with the same load combina- tion, it shall be permitted to design a single anchor or anchor group in accordance with 17.6 and the tensile strength requirements of Table 17.5.2. 17.10.5.2 If the tensile component of the strength-level earthquake-induced force applied to anchors exceeds 20 percent of the total factored anchor tensile force associated with the same load combination, anchors and their attach- ments shall be designed in accordance with 17.10.5.3. The )RUDVWUXFWXUDOVWHHODWWDFKPHQWLIRQOWKHVSHFL¿HGLHOG strength of the steel is known, the expected strength should EH WDNHQ DV DSSUR[LPDWHO WLPHV WKH VSHFL¿HG LHOG strength. If the actual yield strength of the steel is known, the expected strength should be taken as approximately 1.25 times the actual yield strength. Under earthquake conditions, the direction of shear may not be predictable. The full shear should be assumed in any direction for a safe design. R17.10.2 The possible higher levels of cracking and spalling in plastic hinge zones are beyond the conditions for which the nominal concrete-governed strength values in this chapter are applicable. Plastic hinge zones are considered to extend a distance equal to twice the member depth from any column or beam face, and also include any other sections in walls, frames, and slabs where yielding of reinforcement is likely to occur as a result of lateral displacements. If anchors must be located in plastic hinge regions, they should be detailed so that the anchor forces are transferred directly to anchor reinforcement that is designed to transmit the anchor forces into the body of the member beyond the DQFKRUDJH UHJLRQ RQ¿JXUDWLRQV WKDW UHO RQ FRQFUHWH tensile strength should not be used. R17.10.3 Anchors that are not suitable for use in cracked concrete should not be used to resist earthquake-induced IRUFHV 4XDOL¿FDWLRQ RI SRVWLQVWDOOHG DQFKRUV IRU XVH LQ FUDFNHGFRQFUHWHLVDQLQWHJUDOSDUWRIWKHTXDOL¿FDWLRQIRU resisting earthquake-induced forces in ACI 355.2 and ACI 355.4. The design values obtained from the Simulated Seismic Tests of ACI 355.2 and ACI 355.4 are expected to be less than those for static load applications. R17.10.5 7HQVLOHORDGLQJGHVLJQUHTXLUHPHQWV R17.10.5.1 The requirements of 17.10.5.3 need not apply if the applied earthquake-induced tensile force is a small fraction of the total factored tensile force. R17.10.5.2 If the ductile steel element is ASTM A36 or ASTM A307 steel, the futa/fya value is typically approxi- mately 1.5, and the anchor can stretch considerably before rupturing at the threads. For other steels, calculations may need to be made to ensure that similar behavior can occur. Section R17.6.1.2 provides additional information on the American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 273 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 276. anchor design tensile strength shall be determined in accor- dance with 17.10.5.4. 17.10.5.3 Anchors and their attachments shall satisfy (a), (b), (c), or (d). (a) For single anchors, the concrete-governed strength shall be greater than the steel strength of the anchor. For anchor groups, the ratio of the tensile load on the most highly stressed anchor to the steel strength of that anchor shall be equal to or greater than the ratio of the tensile load on anchors loaded in tension to the concrete-governed strength of those anchors. In each case: (i) The steel strength shall be taken as 1.2 times the nominal steel strength of the anchor. (ii) The concrete-governed strength shall be taken as the nominal strength considering pullout, side-face blowout, concrete breakout, and bond strength as appli- cable. For consideration of pullout in groups, the ratio shall be calculated for the most highly stressed anchor. ,QDGGLWLRQWKHIROORZLQJVKDOOEHVDWLV¿HG (iii) Anchors shall transmit tensile loads via a ductile steel element with a stretch length of at least 8da unless otherwise determined by analysis. (iv) Anchors that resist load reversals shall be protected against buckling. (v) If connections are threaded and the ductile steel elements are not threaded over their entire length, the ratio of futa/fya shall be at least 1.3 unless the threaded portions are upset. The upset portions shall not be included in the stretch length. (vi) Deformed reinforcing bars used as ductile steel elements to resist earthquake-induced forces shall be in accordance with the anchor reinforcement requirements of 20.2.2. (b) Anchor or anchor groups shall be designed for the maximum tension that can be transmitted to the anchor or group of anchors based on the development of a ductile LHOG PHFKDQLVP LQ WKH DWWDFKPHQW LQ WHQVLRQ ÀH[XUH shear, or bearing, or a combination of those conditions, considering both material overstrength and strain-hard- HQLQJH൵HFWVIRUWKHDWWDFKPHQW7KHDQFKRUGHVLJQWHQVLOH strength shall be calculated in accordance with 17.10.5.4. (c) Anchor or anchor groups shall be designed for the maximum tension that can be transmitted to the anchors by a non-yielding attachment. The anchor design tensile strength shall be calculated in accordance with 17.10.5.4. (d) Anchor or anchor groups shall be designed for the maximum tension obtained from factored load combina- tions that include E, with Eh increased by ȍo. The anchor design tensile strength shall be calculated in accordance with 17.10.5.4. steel properties of anchors. Use of upset threaded ends, whereby the threaded end of the anchor is enlarged to compensate for the area reduction associated with threading, can ensure that yielding occurs over the stretch length regardless of the tensile to yield strength ratio. R17.10.5.3 Four options are provided for determining the required anchor or attachment strength to protect against nonductile tensile failure: In option (a), anchor ductility requirements are imposed, and the required anchor strength is that determined using strength-level earthquake-induced forces acting on the struc- ture. Research (Hoehler and Eligehausen 2008; Vintzileou and Eligehausen 1992) has shown that if the steel of the anchor yields before the concrete anchorage fails, no reduc- WLRQLQWKHDQFKRUWHQVLOHVWUHQJWKLVQHHGHGIRUHDUWKTXDNH± LQGXFHGIRUFHV'XFWLOHVWHHODQFKRUVVKRXOGVDWLVIWKHGH¿- nition for steel element, ductile in Chapter 2. To facilitate comparison between steel strength, which is based on the most highly-stressed anchor, and concrete strength based on group behavior, the design is performed on the basis of the ratio of applied load to strength for the steel and concrete, respectively. For some structures, anchors provide the best locations for energy dissipation in the nonlinear range of response. The stretch length of the anchor, shown in Fig. R17.10.5.3, D൵HFWV WKH ODWHUDO GLVSODFHPHQW FDSDFLW RI WKH VWUXFWXUH WKHUHIRUH WKDW OHQJWK QHHGV WR EH VX൶FLHQW VXFK WKDW WKH displacement associated with the design-basis earthquake can be achieved (FEMA P750). Observations from earth- quakes indicate that the provision of a stretch length of 8da results in good structural performance. If the required stretch OHQJWKLVFDOFXODWHGWKHUHODWLYHVWL൵QHVVRIWKHFRQQHFWHG elements needs to be considered. When an anchor is subject to load reversals, and its yielding length outside the concrete exceeds 6da, buckling of the anchor in compression is likely. Buckling can be restrained by placing the anchor in a tube. However, care must be taken that the tube does not share in resisting the tensile load assumed to act on the anchor. For anchor bolts that are not threaded over their length, it is important to ensure that yielding occurs over the unthreaded portion of the bolt within the stretch length before failure in WKHWKUHDGV7KLVLVDFFRPSOLVKHGEPDLQWDLQLQJVX൶FLHQW PDUJLQEHWZHHQWKHVSHFL¿HGLHOGDQGWHQVLOHVWUHQJWKVRI the bolt. It should be noted that the available stretch length PDEHDGYHUVHOLQÀXHQFHGEFRQVWUXFWLRQWHFKQLTXHV IRU example, the addition of leveling nuts to the examples illus- trated in Fig. R17.10.5.3). In option (b), the anchor is designed for the tensile force associated with the expected strength of the attachment. Care must be taken in design to consider the consequences RISRWHQWLDOGL൵HUHQFHVEHWZHHQWKHVSHFL¿HGLHOGVWUHQJWK and the expected strength of the attachment. An example is the design of connections of intermediate precast walls where a connection not designed to yield should develop at American Concrete Institute – Copyrighted © Material – www.concrete.org 274 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 277. least 1.5Sy, where Sy is the nominal strength of the yielding HOHPHQW EDVHG RQ LWV VSHFL¿HG LHOG VWUHQJWK UHIHU WR 18.5.2.2). Similarly, steel design manuals require structural steel connections that are designated nonyielding and part of the seismic load path to have design strengths that exceed a multiple of the nominal strength. That multiple depends on DIDFWRUUHODWLQJWKHOLNHODFWXDOWRVSHFL¿HGLHOGVWUHQJWK of the material and an additional factor exceeding unity to account for material strain hardening. For attachments of cold-formed steel or wood, similar principles should be used to determine the expected strength of the attachment in order to determine the required strength of the anchors. Additional guidance on the use of options (a) through (d) is provided in the 2009 edition of the NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (FEMA P750). The design of anchors in accordance with option (a) should be used only if the anchor yield behavior LVZHOOGH¿QHGDQGLIWKHLQWHUDFWLRQRIWKHLHOGLQJDQFKRU with other elements in the load path has been adequately addressed. For the design of anchors in accordance with option (b), the force associated with yield of a steel attach- ment, such as an angle, baseplate, or web tab, should be the H[SHFWHGVWUHQJWKUDWKHUWKDQWKHVSHFL¿HGLHOGVWUHQJWKRI the steel. Option (c) may apply to cases, such as the design of sill bolts where crushing of the wood limits the force that can be transferred to the bolt, or where the provisions of the $PHULFDQ 1DWLRQDO 6WDQGDUGV ,QVWLWXWH$PHULFDQ ,QVWLWXWH of Steel Construction (AISC) Code Seismic Provisions for Structural Steel Buildings (AISC 341) specify design loads based on member strengths. Nut and washer Stretch length Anchor chair Grout pad Base plate Stretch length Nut and washer Grout pad Base plate Sleeve (a) Anchor chair (b) Sleeve Fig. R17.10.5.3—Illustrations of stretch length. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 275 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 278. R17.10.5.4 The reduced anchor nominal tensile strengths associated with concrete failure modes is to account for increased cracking and spalling in the concrete resulting IURPHDUWKTXDNHH൵HFWV%HFDXVHHDUWKTXDNHUHVLVWDQWGHVLJQ generally assumes that all or portions of the structure are loaded beyond yield, it is likely that the concrete is cracked throughout for the purpose of calculating anchor strength. In locations where it can be demonstrated that the concrete does not crack, uncracked concrete may be assumed in calculating anchor strength as governed by concrete failure modes. R17.10.5.5 If anchor reinforcement conforming to 17.5.2.1a LV XVHG ZLWK WKH SURSHUWLHV DV GH¿QHG LQ 20.2.2.5, separa- tion of the potential breakout from the substrate is unlikely to occur provided the anchor reinforcement is designed for a force exceeding the concrete breakout strength. R17.10.6 6KHDUGHVLJQUHTXLUHPHQWV R17.10.6.1 The requirements of 17.10.6.3 need not apply if the applied earthquake-induced shear is a small fraction of the total factored shear. R17.10.6.2 If the shear component of the earthquake- induced force applied to the anchor exceeds 20 percent of the total anchor shear force, three options are recognized to determine the required shear strength to protect the anchor or anchor group against premature shear failure. R17.10.6.3 Option (a) of 17.10.5.3 is not permitted for shear because the cross section of the steel element of the DQFKRU FDQQRW EH FRQ¿JXUHG VR WKDW VWHHO IDLOXUH LQ VKHDU provides any meaningful degree of ductility. Design of the anchor or anchor group for the strength associated with force-limiting mechanisms under option (b), such as the bearing strength at holes in a steel attachment or the combined crushing and bearing strength for wood members, may be particularly relevant. Tests on typical anchor bolt connections for wood-framed structural walls (Fennel et al. 2009) demonstrated that wood components attached to concrete with minimum edge distances exhib- LWHGGXFWLOHEHKDYLRU:RRG³LHOG´ FUXVKLQJ ZDVWKH¿UVW limiting state and resulted in nail slippage in shear. Nail 17.10.5.4 The anchor design tensile strength shall be calculated from (a) through (e) for the failure modes given in Table 17.5.2 assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked. (a) ࢥNsa for a single anchor, or for the most highly stressed individual anchor in an anchor group (b) ࢥNcb or ࢥNcbg, except that Ncb or Ncbg need not be calculated if anchor reinforcement satisfying 17.5.2.1(a) is provided (c) ࢥNpn for a single anchor or for the most highly stressed individual anchor in an anchor group (d) ࢥNsb or ࢥNsbg (e) ࢥNa or ࢥNag ZKHUHࢥLVLQDFFRUGDQFHZLWK 17.10.5.5 If anchor reinforcement is provided in accor- dance with 17.5.2.1(a), no reduction in design tensile strength beyond that given in 17.5.2.1 shall be required. 17.10.6 6KHDUGHVLJQUHTXLUHPHQWV 17.10.6.1 If the shear component of the strength-level earthquake-induced force applied to a single anchor or anchor group does not exceed 20 percent of the total factored anchor shear associated with the same load combination, it shall be permitted to design a single anchor or anchor group in accordance with 17.7 and the shear strength requirements of 17.5.2. 17.10.6.2 If the shear component of the strength-level earthquake-induced force applied to anchors exceeds 20 percent of the total factored anchor shear associated with the same load combination, anchors and their attachments shall be designed in accordance with 17.10.6.3. The anchor design shear strength for resisting earthquake-induced forces shall be determined in accordance with 17.7. 17.10.6.3 Anchors and their attachments shall satisfy (a), (b) or (c). (a) Anchor or anchor groups shall be designed for the maximum shear that can be transmitted to the anchor or anchor groups based on the development of a ductile yield PHFKDQLVPLQWKHDWWDFKPHQWLQWHQVLRQÀH[XUHVKHDURU bearing, or a combination of those conditions, and consid- ering both material overstrength and strain-hardening H൵HFWVLQWKHDWWDFKPHQW (b) Anchor or anchor groups shall be designed for the maximum shear that can be transmitted to the anchors by a non-yielding attachment. American Concrete Institute – Copyrighted © Material – www.concrete.org 276 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 279. slippage combined with bolt bending provided the required ductility and toughness for the structural walls and limited WKHORDGVDFWLQJRQWKHEROWV3URFHGXUHVIRUGH¿QLQJEHDULQJ and shear limit states for connections to cold-formed steel are described in AISI S100, and examples of strength calculations are provided in the AISI manual (AISI D100). In such cases, exceeding the bearing strength may lead to tearing and an unacceptable loss of connectivity. If anchors are located far from edges, it may not be possible to design such that anchor reinforcement controls the anchor strength. In such cases, anchors should be designed for overstrength in accordance with option (c). R17.10.6.4 If anchor reinforcement conforming to ELVXVHGZLWKWKHSURSHUWLHVDVGH¿QHGLQ20.2.2.5, separation of the potential breakout from the substrate is unlikely to occur provided the anchor reinforcement is designed for a force exceeding the concrete breakout strength. R17.11—Attachments with shear lugs R17.11.1 General R17.11.1.1 The provisions of 17.11 cover concrete failure modes of attachments with shear lugs. These provisions do not cover the steel or welding design of the attachment base plate or shear lugs. Attachments with shear lugs may be embedded in cast- in-place or precast concrete, or post-installed by using a blockout in the concrete that receives the shear lug and is WKHQ¿OOHGZLWKDÀXLGQRQVKULQNJURXWDVVKRZQLQ)LJ R17.11.1.1a. Base plates with anchors provide moment resistance, which prevents pryout action on the shear lugs. Attachments with embedded shapes and without base plates and anchors, which must resist moment by pryout action on the embedment, are not covered in this section. Bearing strength in shear refers to the strength prior to concrete fracture in front of the shear lug. Bearing failure occurs at small displacements (Cook and Michler 2017). )ROORZLQJEHDULQJIDLOXUHWKHUHLVDVLJQL¿FDQWGHFUHDVHLQ strength and increase in lateral displacement leading even- tually to steel failure of the anchors (Fig. R17.11.1.1b) at lateral displacements at least an order of magnitude greater than that corresponding to bearing failure. Typesofattachmentswithshearlugsthatsatisfy17.11.1.1.1 through 17.11.1.1.9 are shown in Fig. R17.11.1.1a. Shear OXJV WKDW DUH GL൵HUHQW WKDQ WKRVH FRYHUHG LQ through 17.11.1.1.9, such as shear lugs composed of steel (c) Anchor or anchor groups shall be designed for the maximum shear obtained from factored load combina- tions that include E, with Eh increased by ȍo. 17.10.6.4 If anchor reinforcement is provided in accor- dance with 17.5.2.1(b), no reduction in design shear strength beyond that given in 17.5.2.1 shall be required. 17.10.7 Tension and shear interaction 17.10.7.1 Single anchors or anchor groups that resist both tensile and shear forces shall be designed in accordance with 17.8, and the anchor design tensile strength calculated in accordance with 17.10.5.4. 17.11—Attachments with shear lugs 17.11.1 General 17.11.1.1 It is permitted to design attachments with shear lugs in accordance with 17.11.1.1.1 through 17.11.1.1.9. Alternatively, it is permitted to design using alterna- tive methods if adequate strength and load transfer can be demonstrated by analysis or tests. 17.11.1.1.1 Shear lugs shall be constructed of rectangular plates, or steel shapes composed of plate-like elements, welded to an attachment base plate. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 277 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 280. pipe or attachments with shear lugs where the top of plate is located below the concrete surface, can be used provided adequate strength and load transfer can be demonstrated by analysis or tests. Elevation (a) Cast-in-place (b) Post-installed Elevation Plan Plan Inspection/vent holes hef hsl Csl Csl Shear lugs Grout Fig. R17.11.1.1a²([DPSOHVRIDWWDFKPHQWVZLWKVKHDUOXJV American Concrete Institute – Copyrighted © Material – www.concrete.org 278 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 281. Fracture progression just prior to bearing failure (a) Just prior to bearing failure (b) Just prior to anchor steel failure Fig. R17.11.1.1b—Bearing failure and subsequent anchor VWHHOIDLOXUHIRUHPEHGGHGSODWHZLWKVKHDUOXJ LIFRQFUHWH EUHDNRXWLVQRWDSSOLFDEOH R17.11.1.1.3 Although neglected in the bearing strength evaluation in 17.11.2, welded anchors resist a portion of the shear load because they displace the same as the shear lug. The portion of the applied shear, Vu, that each anchor carries, Vua,i, is given by , ua i u , V V ua i u ⎛ ⎞ 2 2 a da ⎜ ⎟ 2 a ⎛ ⎞ ⎛ ⎞ a ⎝ ⎠ ef sl a , A n d 2 ef sl a ef sl 2 ⎜ ⎟ ⎜ ⎟ 2 A n d 2 7KHH൵HFWLYHEHDULQJDUHDRIDQDQFKRULVDVVXPHGWREH WKHGLDPHWHURIWKHDQFKRUPXOWLSOLHGEDQH൵HFWLYHEHDULQJ depth of twice its diameter (Cook and Michler 2017). The bearing reaction on the anchor is not large enough to fail the anchor in shear alone but does need to be considered in tension and shear interaction for steel failure (refer to 17.8). 17.11.1.1.2 A minimum of four anchors shall be provided that satisfy the requirements of Chapter 17 with the excep- tion of the requirements of 17.5.1.2(f), (g), and (h) and the corresponding requirements of Table 17.5.2 for steel strength of anchors in shear, concrete breakout strength of anchors in shear, and concrete pryout strength of anchors in shear. 17.11.1.1.3 For anchors welded to the attachment base plate, tension and shear interaction requirements of 17.8 shall include a portion of the total shear on the anchor. 17.11.1.1.4%HDULQJVWUHQJWKLQVKHDUVKDOOVDWLVIࢥVbrg,sl •Vu with ࢥ . 17.11.1.1.5 Nominal bearing strength in shear, Vbrg,sl, shall be determined by 17.11.2. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 279 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 282. R17.11.1.1.8 The lower bound limitations on the ratios of anchor embedment depth to shear lug embedment depth and anchor embedment depth to the distance between the centerline of the anchors in tension and the centerline of the shear lug in the direction of shear are based on available test data. The required lower limits reduce potential interaction between concrete breakout of the anchors in tension and bearing failure in shear of the shear lug. R17.11.1.1.9 The bearing reaction on shear lugs occurs further below the surface of the concrete than the bearing reaction on anchors and embedded plates. As a result, the couple caused by the bearing reaction and the shear load needs to be considered when determining anchor tension. R17.11.1.2 Base plate holes are necessary to verify proper concrete or grout consolidation around the shear lug and to avoid trapping air immediately below a horizontal plate. Holes in the base plate should be placed close to each face of the shear lug. For a single shear lug, place at least one inspection hole near the center of each long side of the shear lug. For a cruciform-shaped shear lug, four inspection holes DUH UHFRPPHQGHG RQH SHU TXDGUDQW )RU RWKHU FRQ¿JXUD- tions or long shear lug lengths, the licensed design profes- sional should specify inspection hole locations that will permit adequate observation and allow trapped air to escape. R17.11.2 %HDULQJVWUHQJWKLQVKHDURIDWWDFKPHQWVZLWK shear lugs, Vbrg,sl R17.11.2.1 The nominal bearing strength in shear of a shear lug, Vbrg,sl, given by Eq. (17.11.2.1) is based on a uniform bearing stress of 1.7fcƍDFWLQJRYHUWKHH൵HFWLYHDUHD of the shear lug as discussed in Cook and Michler (2017). Although the bearing strength in shear of attachments with shear lugs is a function of bearing on the shear lug, embedded plate (if present), and welded anchors (if present), the method presented in 17.11.2 only includes the contribu- tion of shear lugs. Cook and Michler (2017) discuss devel- opment of the method and a less conservative procedure to include bearing on the embedded plate and welded anchors. 17.11.1.1.6 Concrete breakout strength of the shear lug shall satisfy ࢥVcb,sl•Vu with ࢥ . 17.11.1.1.7 Nominal concrete breakout strength, Vcb,sl, shall be determined by 17.11.3. 17.11.1.1.8 For attachments with anchors in tension, both D DQG E VKDOOEHVDWLV¿HG (a) hef /hsl• (b) hef /csl• 17.11.1.1.9 The moment from the couple developed by the bearing reaction on the shear lug and the shear shall be considered in the design of the anchors for tension. 17.11.1.2 Horizontally installed steel base plates with shear lugs shall have a minimum 1 in. diameter hole along each of the long sides of the shear lug. 17.11.2 %HDULQJ VWUHQJWK LQ VKHDU RI DWWDFKPHQWV ZLWK shear lugs, Vbrg,sl 17.11.2.1 Nominal bearing strength in shear of a shear lug, Vbrg,sl, shall be calculated as: Vbrg,sl = 1.7fcƍAef,slȥbrg,sl (17.11.2.1) where ȥbrg,sl is given in 17.11.2.2. American Concrete Institute – Copyrighted © Material – www.concrete.org 280 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 283. 17.11.2.1.17KHH൵HFWLYHEHDULQJDUHDAef,sl, shall be below the surface of the concrete, perpendicular to the applied shear, and composed of areas according to (a) through (d): (a) Bearing area of shear lugs located within 2tsl of the bottom surface of the base plate if the top or bottom VXUIDFHRIWKHEDVHSODWHLVÀXVKZLWKWKHVXUIDFHRIWKH concrete (b) Bearing area of shear lugs located within 2tsl of the surface of the concrete if the base plate is above the surface of the concrete (c) Bearing area of shear lugs located within 2tsl of the LQWHUIDFHZLWKVWL൵HQHUV G %HDULQJDUHDRQWKHOHDGLQJHGJHRIVWL൵HQHUVEHORZ the surface of the concrete R17.11.2.1.1 Figure R17.11.2.1.1 shows examples of H൵HFWLYHEHDULQJDUHDV7KHH൵HFWLYHEHDULQJDUHDIRUVWL൵- ened shear lugs is applicable to both welded plates and steel shapes composed of plate-like elements in which case WKH ZHE ZRXOG EH WKH VWL൵HQLQJ HOHPHQW7KH OLPLW RI D distance of 2tslLQGHWHUPLQLQJWKHH൵HFWLYHEHDULQJDUHDLV described in Cook and Michler (2017). Fig. R17.11.2.1.1²([DPSOHVRIHৼHFWLYHEHDULQJDUHDVIRUDWWDFKPHQWVZLWKVKHDUOXJV Direction of shear load tsl ≥0.5hsl Aef,sl Aef,sl 2tsl 2tsl 2tsl tsl Plan Plan Note: Anchors and inspection holes not shown for clarity. Elevation parallel to load Elevation perpendicular to load Elevation perpendicular to load (a) Shear lug without stiffeners (b) Post-installed shear lug with stiffeners Elevation parallel to load Grout Grout Stiffeners Stiffener ~ ~ ~ ~ 2tsl hsl American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 281 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 284. 17.11.2.2 Bearing factor, ȥbrg,sl 17.11.2.2.10RGL¿FDWLRQIDFWRUȥbrg,slIRUWKHH൵HFWVRI axial load, Pu, on bearing strength in shear, shall be deter- mined by (a), (b), or (c): (a) For applied axial tension: , 1 1.0 u brg sl sa P n N ψ = + ≤ (17.11.2.2.1a) where Pu is negative for tension and n is the number of anchors in tension. (b) For no applied axial load: ȥbrg,sl = 1 (17.11.2.2.1b) (c) For applied axial compression: , 1 4 2.0 u brg sl bp c P A f ψ = + ≤ ′ (17.11.2.2.1c) where Pu is positive for compression. 17.11.2.3,IXVHGWKHOHQJWKRIVKHDUOXJVWL൵HQHUVLQWKH direction of the shear load shall not be less than 0.5hsl. 17.11.2.4 For attachments with multiple shear lugs arranged perpendicular to the direction of applied shear, the bearing strength of the individual shear lugs may be consid- ered to be additive provided the shear stress on a shear plane in the concrete at the bottom of the shear lugs, and extending between the shear lugs, does not exceed 0.2fcƍ. The nominal bearing strength of each individual lug shall be determined E(T XVLQJWKHH൵HFWLYHDUHDRIWKHOXJ 17.11.3 Concrete breakout strength of shear lug, Vcb,sl 17.11.3.1 Nominal concrete breakout strength of a shear lug for shear perpendicular to the edge, Vcb,sl, shall be deter- mined from 17.7.2 using Eq. (17.7.2.1a), where Vb is calcu- lated using Eq. (17.7.2.2.1b) with ca1 taken as the distance from the bearing surface of the shear lug to the free edge and where Avc is the projected area of the failure surface on the side of the concrete member. 17.11.3.1.1 Avc is the projected concrete failure area on the side face of the concrete that is approximated as the rect- angular shape resulting from projecting horizontally 1.5ca1 from the edge of the shear lug and projecting vertically 1.5ca1IURPWKHHGJHRIWKHH൵HFWLYHGHSWKRIWKHVKHDUOXJ hef,sl7KHH൵HFWLYHDUHDRIWKHVKHDUOXJAef,sl, shall not be LQFOXGHG7KHH൵HFWLYHHPEHGPHQWGHSWKRIWKHVKHDUOXJ hef,sl, shall be taken as the distance from the concrete surface WRWKHERWWRPRIWKHH൵HFWLYHEHDULQJDUHDAef,sl. R17.11.2.4 The limitation for considering multiple shear OXJVWREHH൵HFWLYHLVEDVHGRQWKHPD[LPXPOLPLWVIRUVKHDU friction in Table 22.9.4.4 and two tests reported in Rotz and Reifschneider (1984). The area of the shear plane is the clear distance between adjacent shear lugs measured in the direc- tion of the applied shear multiplied by the width of the shear lugs perpendicular to the applied shear. R17.11.3 Concrete breakout strength of shear lug, Vcb,sl R17.11.3.1 The method for evaluating concrete breakout strength where shear is perpendicular to an edge is similar WRWKDWXVHGLQIRUDQFKRUV7KHGL൵HUHQFHLVLQWKH determination of AVc, which is illustrated in Fig. R17.11.3.1. 7KHPHWKRGKDVEHHQFRQ¿UPHGEWHVWVZKHUHWKHVKHDUOXJ is concentrically loaded in shear (Gomez et al. 2009; Cook and Michler 2017). With shear transferred by the shear lug, embedded plate (if present), and welded anchors (if present), the bearing surfaces all displace the same amount with any incremental change in applied shear. This behavior is similar to connections with anchors welded to steel attach- ments where concrete edge failure originates from the row of anchors farthest from the edge. In anchorages with shear OXJVWKHH൵HFWLYHFRQWULEXWLRQVWRFRQFUHWHEUHDNRXWVWUHQJWK from the bearing areas of the shear lug and embedded plate LISUHVHQW GRPLQDWHRYHUWKHFRQWULEXWLRQIURPWKHH൵HFWLYH bearing area of anchors farther from the edge than the shear lug. As a result, concrete breakout strength for the anchorage American Concrete Institute – Copyrighted © Material – www.concrete.org 282 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 285. should be determined based on the concrete breakout surface originating at the shear lug (Fig. R17.11.3.1). The nominal concrete breakout strength of a shear lug is based on Eq. (17.7.2.2.1b) for Vb that applies to concrete edge failure in shear for large diameter anchors. Elevation Section ca1 ca1 1.5ca1 1.5ca1 V V Aef,sl hef,sl bsl Plan 1.5ca1 AVc ~ ~ Fig. R17.11.3.1²([DPSOHRIAVc for a shear lug near an edge. R17.11.3.2 The concrete breakout strength for shear lugs loaded parallel to the edge is based on 17.7.2.1(c) for concrete failure with load applied parallel to the free edge, assuming shear lug breakout behavior is similar to that of a single anchor. R17.11.3.3 The concrete breakout strength for shear lugs located near a corner is based on 17.7.2.1(d) for anchors. R17.11.3.4 The concrete breakout strength for multiple shear lugs is based on R17.7.2.1 and shown in Fig. R17.7.2.1b Case 1 and Case 2. 17.11.3.2 Nominal concrete breakout strength of a shear lug for shear parallel to the edge shall be permitted to be determined in accordance with 17.7.2.1(c) using Eq. (17.7.2.1(a)) with ca1 taken as the distance from the edge to the center of the shear lug and with ȥec,V taken as 1.0. 17.11.3.3 For shear lugs located at a corner, the limiting concrete breakout strength shall be determined for each edge, and the minimum value shall be used. 17.11.3.4 For cases with multiple shear lugs, the concrete breakout strength shall be determined for each potential breakout surface. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 4: JOINTS/CONNECTIONS/ANCHORS 283 17 Anchoring CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 286. 284 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE American Concrete Institute – Copyrighted © Material – www.concrete.org Notes Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 287. 18.1—Scope 18.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed concrete structures assigned to Seismic Design Categories (SDC) B through F, including, where applicable: (a) Structural systems designated as part of the seismic- force-resisting system, including diaphragms, moment frames, structural walls, and foundations (b) Members not designated as part of the seismic-force- resisting system but required to support other loads while undergoing deformations associated with earthquake H൵HFWV 18.1.2 Structures designed according to the provisions of this chapter are intended to resist earthquake motions through ductile inelastic response of selected members. 18.2—General 18.2.1 6WUXFWXUDOVVWHPV 18.2.1.1All structures shall be assigned to a SDC in accor- dance with 4.4.6.1. R18.1—Scope Chapter 18 does not apply to structures assigned to Seismic Design Category (SDC) A. For structures assigned to SDC B and C, Chapter 18 applies to structural systems designated as part of the seismic-force-resisting system. For structures assigned to SDC D through F, Chapter 18 applies to both structural systems designated as part of the seismic- force-resisting system and structural systems not designated as part of the seismic-force-resisting system. Chapter 18 contains provisions considered to be the minimum requirements for a cast-in-place or precast concrete structure capable of sustaining a series of oscil- lations into the inelastic range of response without critical deterioration in strength. The integrity of the structure in the inelastic range of response should be maintained because WKHGHVLJQHDUWKTXDNHIRUFHVGH¿QHGLQGRFXPHQWVVXFKDV $6(6(, , the 2018 IBC, the UBC (ICBO 1997), and the NEHRP (FEMA P749) provisions are considered less than those corresponding to linear response at the antici- pated earthquake intensity (FEMA P749; Blume et al. 1961; Clough 1960; Gulkan and Sozen 1974). The design philosophy in Chapter 18 is for cast-in-place concrete structures to respond in the nonlinear range when subjected to design-level ground motions, with decreased VWL൵QHVVDQGLQFUHDVHGHQHUJGLVVLSDWLRQEXWZLWKRXWFULW- ical strength decay. Precast concrete structures designed in accordance with Chapter 18 are intended to emulate cast- in-place construction, except 18.5, 18.9.2.3, and 18.11.2.2, which permit precast construction with alternative yielding PHFKDQLVPV 7KH FRPELQDWLRQ RI UHGXFHG VWL൵QHVV DQG increased energy dissipation tends to reduce the response accelerations and lateral inertia forces relative to values that would occur were the structure to remain linearly elastic and lightly damped (Gulkan and Sozen 1974). Thus, the use of GHVLJQIRUFHVUHSUHVHQWLQJHDUWKTXDNHH൵HFWVVXFKDVWKRVH LQ $6(6(, UHTXLUHV WKDW WKH VHLVPLFIRUFHUHVLVWLQJ system retain a substantial portion of its strength into the inelastic range under displacement reversals. The provisions of Chapter 18 relate detailing require- ments to type of structural framing and SDC. Seismic design FDWHJRULHVDUHDGRSWHGGLUHFWOIURP$6(6(,DQGUHODWH to considerations of seismic hazard level, soil type, occu- pancy, and use. Before the 2008 Code, low, intermediate, and high seismic risk designations were used to delineate detailing requirements. For a qualitative comparison of seismic design categories and seismic risk designations, refer to Table R5.2.2. The assignment of a structure to a SDC is regulated by the general building code (refer to 4.4.6.1). R18.2—General Structures assigned to SDC A need not satisfy require- ments of Chapter 18 but must satisfy all other applicable requirements of this Code. Structures assigned to Seismic Design Categories B through F must satisfy requirements of American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 285 CODE COMMENTARY 18 Seismic CHAPTER 18—EARTHQUAKE-RESISTANT STRUCTURES Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 288. Chapter 18 in addition to all other applicable requirements of this Code. Sections 18.2.1.3 through 18.2.1.5 identify those parts of Chapter 18 that apply to the building based on its assigned SDC, regardless of the vertical elements of the seismic- force-resisting system. $6(6(,GH¿QHVWKHSHUPLVVLEOH vertical elements of the seismic-force-resisting system and applies where adopted. The remaining commentary of R18.2 summarizes the intent of ACI 318 regarding which vertical elements should be permissible in a building considering LWV6'6HFWLRQGH¿QHVWKHUHTXLUHPHQWVIRUWKH vertical elements of the seismic-force-resisting system. The design and detailing requirements should be compat- ible with the level of inelastic response assumed in the calcu- lation of the design earthquake forces. The terms “ordinary,” “intermediate,” and “special” are used to facilitate this compatibility. For any given structural element or system, the terms “ordinary,” “intermediate,” and “special,” refer to increasing requirements for detailing and proportioning, with expectations of increased deformation capacity. Struc- tures assigned to SDC B are not expected to be subjected to strong ground motion, but instead are expected to expe- rience low levels of ground motion at long time intervals. This Code provides some requirements for beam-column ordinary moment frames to improve deformation capacity. Structures assigned to SDC C may be subjected to moder- ately strong ground motion. The designated seismic-force- resisting system typically comprises some combination of ordinary cast-in-place structural walls, intermediate precast structural walls, and intermediate moment frames. The general building code also may contain provisions for use of other seismic-force-resisting systems in SDC C. Provi- VLRQGH¿QHVUHTXLUHPHQWVIRUZKDWHYHUVVWHPLV selected. Structures assigned to SDC D, E, or F may be subjected to strong ground motion. It is the intent of ACI Committee 318 that the seismic-force-resisting system of structural concrete buildings assigned to SDC D, E, or F be provided by special moment frames, special structural walls, or a combination of the two. In addition to 18.2.2 through 18.2.8, these struc- tures also are required to satisfy requirements for continuous inspection (26.13.1.3), diaphragms and trusses (18.12), foun- dations (18.13), and gravity-load-resisting elements that are not designated as part of the seismic-force-resisting system (18.14). These provisions have been developed to provide the structure with adequate deformation capacity for the high demands expected for these seismic design categories. The general building code may also permit the use of inter- mediate moment frames as part of dual systems for some buildings assigned to SDC D, E, or F. It is not the intent of ACI Committee 318 to recommend the use of interme- diate moment frames as part of moment-resisting frame or dual systems in SDC D, E, or F. The general building code may also permit substantiated alternative or nonprescriptive designs or, with various supplementary provisions, the use 18.2.1.2 All members shall satisfy Chapters 1 to 17 and 19 to 26. Structures assigned to SDC B, C, D, E, or F also shall satisfy 18.2.1.3 through 18.2.1.7, as applicable. Where KDSWHU FRQÀLFWV ZLWK RWKHU FKDSWHUV RI WKLV RGH Chapter 18 shall govern. 18.2.1.3 Structures assigned to SDC B shall satisfy 18.2.2. 18.2.1.4 Structures assigned to SDC C shall satisfy 18.2.2, 18.2.3, and 18.13. 18.2.1.5 Structures assigned to SDC D, E, or F shall satisfy 18.2.2 through 18.2.8 and 18.12 through 18.14. 18.2.1.6 Structural systems designated as part of the seismic-force-resisting system shall be restricted to those designated by the general building code, or determined by other authority having jurisdiction in areas without a legally adopted building code. Except for SDCA, for which Chapter GRHVQRWDSSO D WKURXJK K VKDOOEHVDWLV¿HGIRUHDFK structural system designated as part of the seismic-force- resisting system, in addition to 18.2.1.3 through 18.2.1.5: (a) Ordinary moment frames shall satisfy 18.3 (b) Ordinary reinforced concrete structural walls need not satisfy any detailing provisions in Chapter 18, unless required by 18.2.1.3 or 18.2.1.4 (c) Intermediate moment frames shall satisfy 18.4 (d) Intermediate precast walls shall satisfy 18.5 (e) Special moment frames shall satisfy 18.2.3 through 18.2.8 and 18.6 through 18.8 (f) Special moment frames constructed using precast concrete shall satisfy 18.2.3 through 18.2.8 and 18.9 (g) Special structural walls shall satisfy 18.2.3 through 18.2.8 and 18.10 (h) Special structural walls constructed using precast concrete shall satisfy 18.2.3 through 18.2.8 and 18.11 18.2.1.7 A reinforced concrete structural system not satis- fying this chapter shall be permitted if it is demonstrated by experimental evidence and analysis that the proposed system will have strength and toughness equal to or exceeding those provided by a comparable reinforced concrete structure satisfying this chapter. American Concrete Institute – Copyrighted © Material – www.concrete.org 286 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 289. of ordinary or intermediate systems for nonbuilding struc- tures in the higher seismic design categories. These are not the typical applications that were considered in the writing of this chapter, but wherever the term “ordinary or inter- mediate moment frame” is used in reference to reinforced concrete, 18.3 or 18.4 apply. Table R18.2 summarizes the applicability of the provi- sions of Chapter 18 as they are typically applied when using the minimum requirements in the various seismic design categories. Where special systems are used for structures in SDC B or C, it is not required to satisfy the requirements RIDOWKRXJKLWVKRXOGEHYHUL¿HGWKDWPHPEHUVQRW designated as part of the seismic-force-resisting system will be stable under design displacements. Table R18.2—Sections of Chapter 18 to be satisfied in typical applications[1] Component resisting HDUWKTXDNHH൵HFW unless otherwise noted SDC A (None) B (18.2.1.3) C (18.2.1.4) D, E, F (18.2.1.5) Analysis and design requirements None 18.2.2 18.2.2 18.2.2, 18.2.4 Materials None None 18.2.5 through 18.2.8 Frame members 18.3 18.4 18.6 through 18.9 Structural walls and coupling beams None None 18.10 Precast structural walls None 18.5 18.5[2] , 18.11 Diaphragms and trusses None 18.12 18.12 Foundations None 18.13 18.13 Frame members not designated as part of the seismic-force- resisting system None None 18.14 Anchors None 18.2.3 18.2.3 [1] In addition to requirements of Chapters 1 through 17, 19 through 26, and ACI 318.2, H[FHSWDVPRGL¿HGEKDSWHU6HFWLRQDOVRDSSOLHVLQ6''(DQG) [2] As permitted by the general building code. The proportioning and detailing requirements in Chapter DUHEDVHGSUHGRPLQDQWORQ¿HOGDQGODERUDWRUH[SH- rience with monolithic reinforced concrete building struc- tures and precast concrete building structures designed and detailed to behave like monolithic building structures. Extrapolation of these requirements to other types of cast-in- place or precast concrete structures should be based on evidence SURYLGHGE¿HOGH[SHULHQFHWHVWVRUDQDOVLV7KHDFFHSWDQFH criteria for moment frames given in ACI 374.1 can be used in conjunction with Chapter 18 to demonstrate that the strength, American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 287 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 290. energy dissipation capacity, and deformation capacity of a proposed frame system equals or exceeds that provided by a comparable monolithic concrete system.ACI ITG-5.1 provides similar information for precast wall systems. The toughness requirement in 18.2.1.7 refers to the requirement to maintain structural integrity of the entire seismic-force-resisting system at lateral displacements anticipated for the maximum considered earthquake motion. Depending on the energy-dissipation characteristics of the structural system used, such displacements may be larger than for a monolithic reinforced concrete structure satisfying the prescriptive provisions of other parts of this Code. R18.2.2 $QDOVLVDQGSURSRUWLRQLQJRIVWUXFWXUDOPHPEHUV It is assumed that the distribution of required strength to the various components of a seismic-force-resisting system will be determined from the analysis of a linearly elastic model of the system acted upon by the factored forces, as required by the general building code. If nonlinear response history anal- yses are to be used, base motions should be selected after a detailed study of the site conditions and local seismic history. Because the basis for earthquake-resistant design admits nonlinear response, it is necessary to investigate the stability of the seismic-force-resisting system, as well as its interaction with other structural and nonstructural members, under expected lateral displacements corresponding to maximum considered earthquake ground motion. For lateral displacement calcula- tions, assuming all the structural members to be fully cracked is likely to lead to better estimates of the possible drift than using XQFUDFNHGVWL൵QHVVIRUDOOPHPEHUV7KHDQDOVLVDVVXPSWLRQV described in 6.6.3.1PDEHXVHGWRHVWLPDWHODWHUDOGHÀHFWLRQV of reinforced concrete building systems. The main objective of Chapter 18 is the safety of the struc- ture. The intent of 18.2.2.1 and 18.2.2.2 is to draw atten- WLRQWRWKHLQÀXHQFHRIQRQVWUXFWXUDOPHPEHUVRQVWUXFWXUDO response and to hazards from falling objects. Section 18.2.2.3 serves as an alert that the base of structure as GH¿QHGLQDQDOVLVPDQRWQHFHVVDULOFRUUHVSRQGWRWKHIRXQ- dation or ground level. Details of columns and walls extending below the base of structure to the foundation are required to be consistent with those above the base of structure. In selecting member sizes for earthquake-resistant struc- tures, it is important to consider constructibility problems related to congestion of reinforcement. The design should be such that all reinforcement can be assembled and placed in the proper location and that concrete can be cast and consolidated properly. Using the upper limits of permitted reinforcement ratios may lead to construction problems. 18.2.2 $QDOVLVDQGSURSRUWLRQLQJRIVWUXFWXUDOPHPEHUV 18.2.2.1 The interaction of all structural and nonstructural PHPEHUVWKDWD൵HFWWKHOLQHDUDQGQRQOLQHDUUHVSRQVHRIWKH structure to earthquake motions shall be considered in the analysis. 18.2.2.2 Rigid members assumed not to be a part of the seismic-force-resisting system shall be permitted provided WKHLUH൵HFWRQWKHUHVSRQVHRIWKHVVWHPLVFRQVLGHUHGLQ the structural design. Consequences of failure of structural and nonstructural members that are not a part of the seismic- force-resisting system shall be considered. 18.2.2.3 Structural members extending below the base of structure that are required to transmit forces resulting from HDUWKTXDNHH൵HFWVWRWKHIRXQGDWLRQVKDOOFRPSOZLWKWKH requirements of Chapter 18 that are consistent with the seismic-force-resisting system above the base of structure. 18.2.3 Anchoring to concrete 18.2.3.1 Anchors resisting earthquake-induced forces in structures assigned to SDC C, D, E, or F shall be in accor- dance with 17.10. American Concrete Institute – Copyrighted © Material – www.concrete.org 288 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 291. R18.2.4 Strength reduction factors R18.2.4.1 Chapter 21 contains strength reduction factors for all members, joints, and connections of earthquake-resis- WDQW VWUXFWXUHV LQFOXGLQJ VSHFL¿F SURYLVLRQV LQ 21.2.4 for buildings that use special moment frames, special structural walls, and intermediate precast walls. R18.2.5 RQFUHWHLQVSHFLDOPRPHQWIUDPHVDQGVSHFLDO structural walls Requirements of this section refer to concrete quality in frames and walls that resist earthquake-induced forces. 7KH PD[LPXP VSHFL¿HG FRPSUHVVLYH VWUHQJWK RI OLJKW- weight concrete to be used in structural design calcula- tions is limited to 5000 psi, primarily because of paucity RIH[SHULPHQWDODQG¿HOGGDWDRQWKHEHKDYLRURIPHPEHUV made with lightweight concrete subjected to displacement reversals in the nonlinear range. If convincing evidence is GHYHORSHGIRUDVSHFL¿FDSSOLFDWLRQWKHOLPLWRQPD[LPXP VSHFL¿HGFRPSUHVVLYHVWUHQJWKRIOLJKWZHLJKWFRQFUHWHPD EHLQFUHDVHGWRDOHYHOMXVWL¿HGEWKHHYLGHQFH R18.2.6 5HLQIRUFHPHQW LQ VSHFLDO PRPHQW IUDPHV DQG special structural walls R18.2.6.1 Nonprestressed reinforcement for seismic systems is required to meet 20.2.2.4 and 20.2.2.5. Starting with ACI 318-19, ASTM A706 Grades 80 and 100 reinforce- ment is permitted to resist moments, axial, and shear forces in special structural walls and all components of special structural walls, including coupling beams and wall piers. ASTM A706 Grade 80 reinforcement is also permitted in special moment frames. Results of tests and analytical studies presented in NIST (2014) and Sokoli and Ghannoum (2016) indicate that properly detailed beams and columns of special moment frames with ASTM A706 Grade 80 reinforcement exhibit strength and deformation capacities similar to those of members reinforced with Grade 60 reinforcement. The use of Grade 100 reinforcement is not allowed in special PRPHQWIUDPHVEHFDXVHWKHUHLVLQVX൶FLHQWGDWDWRGHPRQ- strate satisfactory seismic performance. To allow the use of ASTM A706 Grade 80 and 100 rein- forcement, the 2019 Code includes limits for spacing of transverse reinforcement to provide adequate longitudinal bar support to control longitudinal bar buckling. In special moment frames, the use of Grade 80 reinforcement requires increased joint depths to prevent excessive slip of beam bars passing through beam-column joints (18.8.2.3). The requirement for a tensile strength greater than the yield strength of the reinforcement (20.2.2.5, Table 20.2.1.3(b)) is based on the assumption that the capability of a structural member to develop inelastic rotation capacity is a func- tion of the length of the yield region along the axis of the member. In interpreting experimental results, the length of 18.2.4 Strength reduction factors 18.2.4.1 Strength reduction factors shall be in accordance with Chapter 21. 18.2.5 RQFUHWH LQ VSHFLDO PRPHQW IUDPHV DQG VSHFLDO structural walls 18.2.5.1 6SHFL¿HG FRPSUHVVLYH VWUHQJWK RI FRQFUHWH LQ special moment frames and special structural walls shall be in accordance with the special seismic systems requirements of Table 19.2.1.1. 18.2.6 5HLQIRUFHPHQW LQ VSHFLDO PRPHQW IUDPHV DQG special structural walls 18.2.6.1 Reinforcement in special moment frames and special structural walls shall be in accordance with the special seismic systems requirements of 20.2.2. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 289 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 292. 18.2.7 0HFKDQLFDOVSOLFHVLQVSHFLDOPRPHQWIUDPHVDQG special structural walls the yield region has been related to the relative magnitudes of nominal and yield moments (ACI 352R). According to this interpretation, the greater the ratio of nominal to yield moment, the longer the yield region. Chapter 20 requires that the ratio of actual tensile strength to actual yield strength be at least 1.25 for ASTM A615 Grade 60. The restrictions on the value of fyt apply to all types of transverse reinforcement, including spirals, circular hoops, rectilinear hoops, and crossties. Research results (Budek et al. 2002; Muguruma and Watanabe 1990; Sugano et al. 1990) indicate that higher yield strengths can be used H൵HFWLYHO DV FRQ¿QHPHQW UHLQIRUFHPHQW DV VSHFL¿HG LQ 18.7.5.4. The increases to 80,000 psi and 100,000 psi for shear design of some special seismic system members is based on research indicating the design shear strength can be developed (Wallace 1998; Aoyama 2001; Budek et al. 2002; Sokoli and Ghannoum 2016; Cheng et al. 2016; Huq et al. 2018; Weber-Kamin et al. 2019). The 60,000 psi restriction on the value of fyt for deformed bar in 20.2.2.4 for calcu- lating nominal shear strength is intended to limit the width of shear cracks at service-level loads. Service-level cracking is not a concern in members of the seismic-force-resisting system subjected to design-level earthquake forces. R18.2.7 0HFKDQLFDOVSOLFHVLQVSHFLDOPRPHQWIUDPHVDQG special structural walls In a structure undergoing inelastic deformations during an earthquake, the tensile stresses in reinforcement may approach the tensile strength of the reinforcement. The requirements for Type 2 mechanical splices are intended to avoid a splice failure when the reinforcement is subjected to expected stress levels in yielding regions. Type 1 mechanical splices on any grade of reinforcement and Type 2 mechan- ical splices on Grade 80 and Grade 100 reinforcement may not be capable of resisting the stress levels expected in yielding regions. The locations of these mechanical splices are restricted because tensile stresses in reinforcement in yielding regions can exceed the strength requirements of 18.2.7.1. The restriction on all Type 1 mechanical splices and on Type 2 mechanical splices on Grade 80 and Grade 100 reinforcement applies to all reinforcement resisting HDUWKTXDNHH൵HFWVLQFOXGLQJWUDQVYHUVHUHLQIRUFHPHQW Recommended detailing practice would preclude the use of splices in regions of potential yielding in members UHVLVWLQJHDUWKTXDNHH൵HFWV,IXVHRIPHFKDQLFDOVSOLFHVLQ regions of potential yielding cannot be avoided, there should be documentation on the actual strength characteristics of the bars to be spliced, on the force-deformation characteristics of the spliced bar, and on the ability of the mechanical splice WREHXVHGWRPHHWWKHVSHFL¿HGSHUIRUPDQFHUHTXLUHPHQWV $OWKRXJKPHFKDQLFDOVSOLFHVDVGH¿QHGEQHHGQRW be staggered, staggering is encouraged and may be necessary for constructibility or provide enough space around the splice for installation or to meet the clear spacing requirements. American Concrete Institute – Copyrighted © Material – www.concrete.org 290 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 293. 18.2.7.10HFKDQLFDOVSOLFHVVKDOOEHFODVVL¿HGDV D RU E D 7SH±0HFKDQLFDOVSOLFHFRQIRUPLQJWR25.5.7 E 7SH±0HFKDQLFDOVSOLFHFRQIRUPLQJWRDQG FDSDEOHRIGHYHORSLQJWKHVSHFL¿HGWHQVLOHVWUHQJWKRIWKH spliced bars 18.2.7.2 Except for Type 2 mechanical splices on Grade 60 reinforcement, mechanical splices shall not be located within a distance equal to twice the member depth from the column or beam face for special moment frames or from critical sections where yielding of the reinforcement is likely to occur as a result of lateral displacements beyond the linear range of behavior. Type 2 mechanical splices on Grade 60 reinforcement shall be permitted at any location, except as noted in 18.9.2.1(c). 18.2.8 :HOGHG VSOLFHV LQ VSHFLDO PRPHQW IUDPHV DQG special structural walls 18.2.8.1 Welded splices in reinforcement resisting earth- quake-induced forces shall conform to 25.5.7 and shall not be located within a distance equal to twice the member depth from the column or beam face for special moment frames or from critical sections where yielding of the reinforcement is likely to occur as a result of lateral displacements beyond the linear range of behavior. 18.2.8.2 Welding of stirrups, ties, inserts, or other similar elements to longitudinal reinforcement required by design shall not be permitted. 18.3—Ordinary moment frames 18.3.1 Scope 18.3.1.1 This section shall apply to ordinary moment frames forming part of the seismic-force-resisting system. 18.3.2 Beams shall have at least two continuous bars at both top and bottom faces. Continuous bottom bars shall have area not less than one-fourth the maximum area of bottom bars along the span. These bars shall be anchored to develop fy in tension at the face of support. 18.3.3 Columns having unsupported length Ɛu”c1 shall have ࢥVn at least the lesser of (a) and (b): (a) The shear associated with development of nominal moment strengths of the column at each restrained end of the unsupported length due to reverse curvature bending. ROXPQÀH[XUDOVWUHQJWKVKDOOEHFDOFXODWHGIRUWKHIDFWRUHG R18.2.8 :HOGHG VSOLFHV LQ VSHFLDO PRPHQW IUDPHV DQG special structural walls R18.2.8.1 Welding of reinforcement should be in accor- dance with AWS D1.4 as required in Chapter 26. The loca- tions of welded splices are restricted because reinforcement tension stresses in yielding regions can exceed the strength requirements of 25.5.7. The restriction on welded splices DSSOLHV WR DOO UHLQIRUFHPHQW UHVLVWLQJ HDUWKTXDNH H൵HFWV including transverse reinforcement. R18.2.8.2 Welding of crossing reinforcing bars can lead to local embrittlement of the steel. If welding of crossing bars is used to facilitate fabrication or placement of rein- forcement, it should be done only on bars added for such purposes. The prohibition of welding crossing reinforcing bars does not apply to bars that are welded with welding operations under continuous, competent control, as in the manufacture of welded-wire reinforcement. R18.3—Ordinary moment frames This section applies only to ordinary moment frames assigned to SDC B. The provisions for beam reinforcement are intended to improve continuity in the framing members and thereby improve lateral force resistance and structural integrity; these provisions do not apply to slab-column moment frames. The provisions for columns are intended to provide additional capacity to resist shear for columns with proportions that would otherwise make them more suscep- tible to shear failure under earthquake loading. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 291 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 294. axial force, consistent with the direction of the lateral forces FRQVLGHUHGUHVXOWLQJLQWKHKLJKHVWÀH[XUDOVWUHQJWK (b) The maximum shear obtained from design load combi- nations that include E, with ȍoE substituted for E. 18.3.4 Beam-column joints shall satisfy Chapter 15 with joint shear Vu calculated on a plane at mid-height of the joint using tensile and compressive beam forces and column shear consistent with beam nominal moment strengths Mn. 18.4—Intermediate moment frames 18.4.1 Scope 18.4.1.1 This section shall apply to intermediate moment frames including two-way slabs without beams forming part of the seismic-force-resisting system. 18.4.2 %HDPV 18.4.2.1 Beams shall have at least two continuous bars at both top and bottom faces. Continuous bottom bars shall have area not less than one-fourth the maximum area of bottom bars along the span. These bars shall be anchored to develop fy in tension at the face of support. 18.4.2.2 The positive moment strength at the face of the joint shall be at least one-third the negative moment strength provided at that face of the joint. Neither the negative nor the positive moment strength at any section along the length of WKHEHDPVKDOOEHOHVVWKDQRQH¿IWKWKHPD[LPXPPRPHQW strength provided at the face of either joint. ࢥVn shall be at least the lesser of (a) and (b): (a) The sum of the shear associated with development of nominal moment strengths of the beam at each restrained end of the clear span due to reverse curvature bending and the shear calculated for factored gravity and vertical earth- quake loads (b) The maximum shear obtained from design load combinations that include E, with E taken as twice that prescribed by the general building code 18.4.2.4At both ends of the beam, hoops shall be provided over a length of at least 2h measured from the face of the VXSSRUWLQJPHPEHUWRZDUGPLGVSDQ7KH¿UVWKRRSVKDOOEH located not more than 2 in. from the face of the supporting member. Spacing of hoops shall not exceed the smallest of (a) through (d): (a) d/4 (b) Eight times the diameter of the smallest longitudinal bar enclosed (c) 24 times the diameter of the hoop bar R18.4—Intermediate moment frames The objective of the requirements in 18.4.2.3 and 18.4.3.1 is to reduce the risk of failure in shear in beams and columns during an earthquake. Two options are provided to deter- mine the factored shear force. R18.4.2 %HDPV According to 18.4.2.3(a), the factored shear force is determined from a free-body diagram obtained by cutting through the beam ends, with end moments assumed equal to the nominal moment strengths acting in reverse curva- ture bending, both clockwise and counterclockwise. Figure R18.4.2 demonstrates only one of the two options that are to be considered for every beam. To determine the maximum beam shear, it is assumed that its nominal moment strengths (ࢥ for moment) are developed simultaneously at both ends of its clear span. As indicated in Fig. R18.4.2, the shear associated with this condition [(MQƐ + Mnr)/Ɛn] is added algebraically to the shear due to the factored gravity loads DQGYHUWLFDOHDUWKTXDNHH൵HFWVWRREWDLQWKHGHVLJQVKHDUIRU the beam. For the example shown, dead load, live load, and snow load have been assumed to be uniformly distributed. 7KH¿JXUHDOVRVKRZVWKDWYHUWLFDOHDUWKTXDNHH൵HFWVDUHWR be included, as is typically required by the general building code. For example,$6(6(, requires vertical earthquake H൵HFWV0.2SDS, to be included. Provision 18.4.2.3(b) bases Vu on the load combination LQFOXGLQJWKHHDUWKTXDNHH൵HFWE, which should be doubled. )RUH[DPSOHWKHORDGFRPELQDWLRQGH¿QHGE(T H would be U = 1.2D + 2.0E + 1.0L + 0.2S where ELVWKHYDOXHVSHFL¿HGEWKHJHQHUDOEXLOGLQJFRGH The factor of 1.0 applied to L is allowed to be reduced to 0.5 in accordance with 5.3.3. Transverse reinforcement at the ends of the beam is required to be hoops. In most cases, transverse reinforce- ment required by 18.4.2.3 for the design shear force will be more than those required by 18.4.2.4. Beams may be subjected to axial compressive force due to prestressing or applied loads. The additional requirements American Concrete Institute – Copyrighted © Material – www.concrete.org 292 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 295. (d) 12 in. 18.4.2.5 Transverse reinforcement spacing shall not exceed d/2 throughout the length of the beam. 18.4.2.6 In beams having factored axial compressive force exceeding Ag fcƍ, transverse reinforcement required by 18.4.2.5 shall conform to 25.7.2.2 and either 25.7.2.3 or 25.7.2.4. 18.4.3 ROXPQV 18.4.3.1 ࢥVn shall be at least the lesser of (a) and (b): (a) The shear associated with development of nominal moment strengths of the column at each restrained end of in 18.4.2.6 are intended to provide lateral support for beam longitudinal reinforcement. n n u u Beam Column wu = (1.2 + 0.2SDS)D + 1.0L + 0.2S Pu Pu Mnt Mnb Vu Vu Mnl Mnr Vul Vur Beam shear Column shear Vu = Mnl + Mnr n + wu n 2 Vu = Mnt + Mnb u Fig. R18.4.2²'HVLJQ VKHDUV IRU LQWHUPHGLDWH PRPHQW IUDPHV R18.4.3 ROXPQV According to 18.4.3.1(a), the factored shear force is determined from a free-body diagram obtained by cutting through the column ends, with end moments assumed equal to the nominal moment strengths acting in reverse curva- American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 293 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 296. the unsupported length due to reverse curvature bending. ROXPQ ÀH[XUDO VWUHQJWK VKDOO EH FDOFXODWHG IRU WKH factored axial force, consistent with the direction of the ODWHUDOIRUFHVFRQVLGHUHGUHVXOWLQJLQWKHKLJKHVWÀH[XUDO strength (b) The maximum shear obtained from factored load combinations that include E, with ȍoE substituted for E 18.4.3.2 Columns shall be spirally reinforced in accor- dance with Chapter 10 or shall be in accordance with 18.4.3.3 through 18.4.3.5. Provision 18.4.3.6 shall apply to DOOFROXPQVVXSSRUWLQJGLVFRQWLQXRXVVWL൵PHPEHUV 18.4.3.3At both ends of the column, hoops shall be provided at spacing so over a length Ɛo measured from the joint face. Spacing so shall not exceed the least of (a) through (c): (a) For Grade 60, the smaller of 8db of the smallest longi- tudinal bar enclosed and 8 in. (b) For Grade 80, the smaller of 6db of the smallest longi- tudinal bar enclosed and 6 in. (c) One-half of the smallest cross-sectional dimension of the column Length Ɛo shall not be less than the longest of (d), (e), and (f): (d) One-sixth of the clear span of the column (e) Maximum cross-sectional dimension of the column (f) 18 in. 18.4.3.47KH¿UVWKRRSVKDOOEHORFDWHGQRWPRUHWKDQso/2 from the joint face. 18.4.3.5 Outside of length Ɛo, spacing of transverse rein- forcement shall be in accordance with 10.7.6.5.2. 18.4.3.6 Columns supporting reactions from discontin- XRXVVWL൵PHPEHUVVXFKDVZDOOVVKDOOEHSURYLGHGZLWK transverse reinforcement at the spacing so in accordance with 18.4.3.3 over the full height beneath the level at which the discontinuity occurs if the portion of factored axial compres- VLYH IRUFH LQ WKHVH PHPEHUV UHODWHG WR HDUWKTXDNH H൵HFWV exceeds Ag fcƍ,IGHVLJQIRUFHVKDYHEHHQPDJQL¿HGWR account for the overstrength of the vertical elements of the seismic-force-resisting system, the limit of Ag fcƍ shall be increased to Ag fcƍ. Transverse reinforcement shall extend above and below the column in accordance with 18.7.5.6(b). 18.4.4 Joints 18.4.4.1Beam-columnjointsshallsatisfythedetailingrequire- ments of 15.3.1.2, 15.3.1.3, and 18.4.4.2 through 18.4.4.5. 18.4.4.2 If a beam framing into the joint and generating joint shear has depth exceeding twice the column depth, ture bending, both clockwise and counterclockwise. Figure R18.4.2 demonstrates only one of the two options that are to be considered for every column. The factored axial force Pu should be chosen to develop the largest moment strength of the column within the range of design axial forces. Provision 18.4.3.1(b) for columns is similar to 18.4.2.3(b) for beams except it bases Vu on load combinations including the earth- TXDNHH൵HFWE, with E increased by the overstrength factor ȍo rather than the factor 2.0. In $6(6(,, ȍo = 3.0 for intermediate moment frames. The higher factor for columns relative to beams is because of greater concerns about shear failures in columns. Transverse reinforcement at the ends of columns is required to be spirals or hoops. The amount of transverse reinforcement at the ends must satisfy both 18.4.3.1 and 18.4.3.2. Note that hoops require seismic hooks at both ends. The maximum spacing allowed for hoops is intended to inhibit or delay buckling of longitudinal reinforcement. 'LVFRQWLQXRXV VWUXFWXUDO ZDOOV DQG RWKHU VWL൵ PHPEHUV can impose large axial forces on supporting columns during earthquakes. The required transverse reinforcement in 18.4.3.6 is to improve column toughness under anticipated demands. The factored axial compressive force related to HDUWKTXDNHH൵HFWVKRXOGLQFOXGHWKHIDFWRUȍo if required by the general building code. R18.4.4 Joints R18.4.4.2)RUMRLQWVLQZKLFKWKHEHDPGHSWKLVVLJQL¿- cantly greater than the column depth, a diagonal strut between American Concrete Institute – Copyrighted © Material – www.concrete.org 294 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 297. WKHMRLQWFRUQHUVPDQRWEHH൵HFWLYH7KHUHIRUHWKHRGH requires that joints in which the beam depth exceeds twice the column depth be designed using the strut-and-tie method of Chapter 23. R18.4.4.3 Refer to R18.8.2.2. R18.4.4.4 The maximum spacing of transverse reinforce- ment within a joint is consistent with the spacing limits for reinforcement in columns of intermediate moment frames. R18.4.4.5 This provision refers to a knee joint in which beam reinforcement terminates with headed deformed bars. 6XFK MRLQWV UHTXLUH FRQ¿QHPHQW RI WKH KHDGHG EHDP EDUV DORQJ WKH WRS IDFH RI WKH MRLQW 7KLV FRQ¿QHPHQW FDQ EH provided by either (a) a column that extends above the top of the joint or (b) vertical reinforcement hooked around the beam top reinforcing bars and extending downward into the joint in addition to the column longitudinal reinforcement. Detailing guidance and design recommendations for vertical joint reinforcement may be found in ACI 352R. 18.4.4.7 6KHDU VWUHQJWK UHTXLUHPHQWV IRU EHDPFROXPQ joints R18.4.4.7.2 Factored joint shear force is determined assuming that beams framing into the joint develop end moments equal to their nominal moment strengths. Conse- TXHQWOMRLQWVKHDUIRUFHJHQHUDWHGEWKHÀH[XUDOUHLQIRUFH- ment is calculated for a stress of fy in the reinforcement. This is consistent with 18.4.2 and 18.4.3 for determination of minimum design shear strength in beams and columns of intermediate moment frames. analysis and design of the joint shall be based on the strut- and-tie method in accordance with Chapter 23 and (a) and E VKDOOEHVDWLV¿HG (a) Design joint shear strength determined in accordance with Chapter 23VKDOOQRWH[FHHGࢥVn calculated in accor- dance with 15.4.2. (b) Detailing requirements of 18.4.4.3 through 18.4.4.5 VKDOOEHVDWLV¿HG 18.4.4.3 Longitudinal reinforcement terminated in a joint shall extend to the far face of the joint core and shall be developed in tension in accordance with 18.8.5 and in compression in accordance with 25.4.9. 18.4.4.4 Spacing of joint transverse reinforcement s shall not exceed the lesser of 18.4.3.3(a) through (c) within the height of the deepest beam framing into the joint. 18.4.4.5 Where the top beam longitudinal reinforcement consists of headed deformed bars that terminate in the joint, the column shall extend above the top of the joint a distance at least the depth h of the joint. Alternatively, the beam rein- forcement shall be enclosed by additional vertical joint rein- IRUFHPHQWSURYLGLQJHTXLYDOHQWFRQ¿QHPHQWWRWKHWRSIDFH of the joint. 18.4.4.6 Slab-column joints shall satisfy transverse rein- forcement requirements of 15.3.2. Where slab-column joint transverse reinforcement is required, at least one layer of joint transverse reinforcement shall be placed between the top and bottom slab reinforcement. 18.4.4.7 6KHDU VWUHQJWK UHTXLUHPHQWV IRU EHDPFROXPQ joints 18.4.4.7.1 Design shear strength of cast-in-place beam- column joints shall satisfy: ࢥVn•Vu 18.4.4.7.2 Vu of the joint shall be determined in accor- dance with 18.3.4. 18.4.4.7.3 ࢥ shall be in accordance with 21.2.1 for shear. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 295 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 298. R18.4.5 7ZRZDVODEVZLWKRXWEHDPV Section 18.4.5 applies to two-way slabs without beams, VXFKDVÀDWSODWHV Using load combinations of Eq. (5.3.1e) and (5.3.1g) may result in moments requiring top and bottom reinforcement at the supports. The moment Msc refers, for a given design load combi- nation with E acting in one horizontal direction, to that portion of the factored slab moment that is balanced by the supporting members at a joint. It is not necessarily equal to the total design moment at the support for a load combination LQFOXGLQJ HDUWKTXDNH H൵HFW ,Q DFFRUGDQFH ZLWK 8.4.2.2.3, only a fraction of the moment Msc is assigned to the slab H൵HFWLYHZLGWK)RUHGJHDQGFRUQHUFRQQHFWLRQVÀH[XUDO reinforcement perpendicular to the edge is not considered IXOOH൵HFWLYHXQOHVVLWLVSODFHGZLWKLQWKHH൵HFWLYHVODE width (ACI 352.1R; Pan and Moehle 1989). Refer to Fig. R18.4.5.1. Application of the provisions of 18.4.5 is illustrated in Fig. R18.4.5.2 and R18.4.5.3. 18.4.4.7.4 Vn of the joint shall be in accordance with 18.8.4.3. 18.4.5 7ZRZDVODEVZLWKRXWEHDPV 18.4.5.1 Factored slab moment at the support including HDUWKTXDNHH൵HFWVE, shall be calculated for load combina- tions given in Eq. (5.3.1e) and (5.3.1g). Reinforcement to resist MscVKDOOEHSODFHGZLWKLQWKHFROXPQVWULSGH¿QHGLQ 8.4.1.5. 18.4.5.25HLQIRUFHPHQWSODFHGZLWKLQWKHH൵HFWLYHZLGWK given in 8.4.2.2.3 shall be designed to resist Ȗf Msc(൵HF- tive slab width for exterior and corner connections shall not extend beyond the column face a distance greater than ct measured perpendicular to the slab span. 18.4.5.3 At least one-half of the reinforcement in the FROXPQVWULSDWWKHVXSSRUWVKDOOEHSODFHGZLWKLQWKHH൵HF- tive slab width given in 8.4.2.2.3. 18.4.5.4 At least one-fourth of the top reinforcement at the support in the column strip shall be continuous throughout the span. 18.4.5.5 Continuous bottom reinforcement in the column strip shall be at least one-third of the top reinforcement at the support in the column strip. 18.4.5.6 At least one-half of all bottom middle strip rein- forcement and all bottom column strip reinforcement at midspan shall be continuous and shall develop fy at the face of columns, capitals, brackets, or walls. 18.4.5.7 At discontinuous edges of the slab, all top and bottom reinforcement at the support shall be developed at the face of columns, capitals, brackets, or walls. American Concrete Institute – Copyrighted © Material – www.concrete.org 296 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 299. c2 c2 Effective width Effective width c1 ct 1.5h ≤ ct c1 ct 1.5h ≤ ct 1.5h ≤ ct Edge Edge Edge Slab, thickness = h Slab, thickness = h ≤ 45° ≤ 45° Direction of moment (a) Edge connection Direction of moment (b) Corner connection Yield line Yield line Column Column Fig. R18.4.5.1²(ৼHFWLYH ZLGWK IRU UHLQIRUFHPHQW SODFH- PHQWLQHGJHDQGFRUQHUFRQQHFWLRQV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 297 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 300. Column c2a c2a + 3h Column strip All reinforcement to resist Msc to be placed in column strip (18.4.5.1) Reinforcement to resist γfMsc (18.4.5.2), but not less than half of reinforcement in column strip (18.4.5.3) Note: Applies to both top and bottom reinforcement Fig. R18.4.5.2²/RFDWLRQRIUHLQIRUFHPHQWLQVODEV Not less than one-fourth of top reinforcement at support (18.4.5.4) Top and bottom reinforcement to be developed (18.4.5.6 and 18.4.5.7) Top and bottom reinforcement to be developed Column strip Middle strip Not less than half bottom reinforcement at mid-span (18.4.5.6) Not less than one-third of top reinforcement at support Fig. R18.4.5.3²$UUDQJHPHQWRIUHLQIRUFHPHQWLQVODEV R18.4.5.8 The requirements apply to two-way slabs that are designated part of the seismic-force-resisting system. Nonprestressed slab-column connections in laboratory tests (Pan and Moehle 1989) exhibited reduced lateral displace- ment ductility when the shear stress at the column connection exceeded the recommended limit of ࢥvc. Based on labo- ratory test data (Kang and Wallace 2006; Kang et al. 2007), a higher maximum factored gravity shear stress of 0.5ࢥvc is allowed for unbonded post-tensioned slab-column connec- tions with fpc in each direction meeting the requirements of 8.6.2.1. Post-tensioned slab-column connections with fpc in each direction not meeting the requirements of 8.6.2.1 can be designed as nonprestressed slab-column connections in accordance with 8.2.3. Slab-column connections also must 18.4.5.8$W WKH FULWLFDO VHFWLRQV IRU FROXPQV GH¿QHG LQ 22.6.4.1, two-way shear stress caused by factored gravity loads without moment transfer shall not exceed ࢥvc for nonprestressed slab-column connections and ࢥvc for unbonded post-tensioned slab-column connections with fpc in each direction meeting the requirements of 8.6.2.1, where vc shall be calculated in accordance with 22.6.5. This UHTXLUHPHQWQHHGQRWEHVDWLV¿HGLIWKHVODEFROXPQFRQQHF- WLRQVDWLV¿HV American Concrete Institute – Copyrighted © Material – www.concrete.org 298 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 301. satisfy shear and moment strength requirements of Chapter 8 XQGHUORDGFRPELQDWLRQVLQFOXGLQJHDUWKTXDNHH൵HFW R18.5—Intermediate precast structural walls Connections between precast wall panels or between wall panels and the foundation are required to resist forces induced by earthquake motions and to provide for yielding in the vicinity of connections. If mechanical splices are used to directly connect primary reinforcement, the probable strength of the splice should be at least 1.5 times the speci- ¿HGLHOGVWUHQJWKRIWKHUHLQIRUFHPHQW R18.6—Beams of special moment frames R18.6.1 Scope This section applies to beams of special moment frames resisting lateral loads induced by earthquake motions. In previous Codes, any frame member subjected to a factored axial compressive force exceeding (Ag fcƍ) under any load combination was to be proportioned and detailed as described in 18.7. In the 2014 Code, all requirements for beams are contained in 18.6 regardless of the magnitude of axial compressive force. This Code is written with the assumption that special moment frames comprise horizontal beams and vertical columns interconnected by beam-column joints. It is accept- able for beams and columns to be inclined provided the resulting system behaves as a frame—that is, lateral resis- tance is provided primarily by moment transfer between beams and columns rather than by strut or brace action. In special moment frames, it is acceptable to design beams to resist combined moment and axial force as occurs in beams that act both as moment frame members and as chords or collectors of a diaphragm. It is acceptable for beams of special moment frames to cantilever beyond columns, but such cantilevers are not part of the special moment frame that forms part of the seismic-force-resisting system. It is acceptable for beams of a special moment frame to connect into a wall boundary if the boundary is reinforced as a special moment frame column in accordance with 18.7. A concrete braced frame, in which lateral resistance is provided primarily by axial forces in beams and columns, is not a recognized seismic-force-resisting system. 18.5—Intermediate precast structural walls 18.5.1 Scope 18.5.1.1This section shall apply to intermediate precast struc- tural walls forming part of the seismic-force-resisting system. 18.5.2 General 18.5.2.1 In connections between wall panels, or between wall panels and the foundation, yielding shall be restricted to steel elements or reinforcement. 18.5.2.2 For elements of the connection that are not designed to yield, the required strength shall be based on 1.5Sy of the yielding portion of the connection. 18.5.2.3 In structures assigned to SDC D, E, or F, wall piers shall be designed in accordance with 18.10.8 or 18.14. 18.6—Beams of special moment frames 18.6.1 Scope 18.6.1.1 This section shall apply to beams of special moment frames that form part of the seismic-force-resisting system and DUHSURSRUWLRQHGSULPDULOWRUHVLVWÀH[XUHDQGVKHDU 18.6.1.2 Beams of special moment frames shall frame into columns of special moment frames satisfying 18.7. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 299 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 302. R18.6.2 'LPHQVLRQDOOLPLWV Experimental evidence (Hirosawa 1977) indicates that, under reversals of displacement into the nonlinear range, behavior of continuous members having length-to-depth UDWLRVRIOHVVWKDQLVVLJQL¿FDQWOGL൵HUHQWIURPWKHEHKDYLRU of relatively slender members. Design rules derived from experience with relatively slender members do not apply directly to members with length-to-depth ratios less than 4, especially with respect to shear strength. Geometric constraints indicated in 18.6.2.1(b) and (c) were derived from practice and research (ACI 352R) on reinforced concrete frames resisting earthquake-induced forces. The limits LQ F GH¿QHWKHPD[LPXPEHDPZLGWKWKDWFDQH൵HF- tively transfer forces into the beam-column joint. An example RIPD[LPXPH൵HFWLYHEHDPZLGWKLVVKRZQLQ)LJ5 A A c1 c2 Not greater than the smaller of c2 and 0.75c1 bw Plan Section A-A Transverse reinforcement through the column to confine beam longitudinal reinforcement passing outside the column core Direction of analysis Fig. R18.6.2²0D[LPXPHৼHFWLYHZLGWKRIZLGHEHDPDQG UHTXLUHGWUDQVYHUVHUHLQIRUFHPHQW 18.6.2 'LPHQVLRQDOOLPLWV 18.6.2.1 Beams shall satisfy (a) through (c): (a) Clear span Ɛn shall be at least 4d (b) Width bw shall be at least the lesser of 0.3h and 10 in. (c) Projection of the beam width beyond the width of the supporting column on each side shall not exceed the lesser of c2 and 0.75c1. American Concrete Institute – Copyrighted © Material – www.concrete.org 300 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 303. R18.6.3 /RQJLWXGLQDOUHLQIRUFHPHQW R18.6.3.1 The limiting reinforcement ratios of 0.025 and 0.02 are based primarily on considerations of providing adequate deformation capacity, avoiding reinforcement congestion, and, indirectly, on limiting shear stresses in beams of typical proportions. R18.6.3.3 Lap splices of reinforcement are prohibited DORQJOHQJWKVZKHUHÀH[XUDOLHOGLQJLVDQWLFLSDWHGEHFDXVH such splices are not reliable under conditions of cyclic loading into the inelastic range. Transverse reinforcement for lap splices at any location is mandatory because of the SRWHQWLDORIFRQFUHWHFRYHUVSDOOLQJDQGWKHQHHGWRFRQ¿QH the splice. R18.6.3.5 These provisions were developed, in part, based on observations of building performance in earthquakes (ACI 423.3R). For calculating the average prestress, the least cross-sectional dimension in a beam normally is the web GLPHQVLRQDQGLVQRWLQWHQGHGWRUHIHUWRWKHÀDQJHWKLFN- ness. In a potential plastic hinge region, the limitation on strain and the requirement for unbonded tendons are intended to prevent fracture of tendons under inelastic earthquake deformation. Calculation of strain in the prestressed rein- forcement is required considering the anticipated inelastic mechanism of the structure. For prestressed reinforcement unbonded along the full beam span, strains generally will EHZHOOEHORZWKHVSHFL¿HGOLPLW)RUSUHVWUHVVHGUHLQIRUFH- ment with short unbonded length through or adjacent to the joint, the additional strain due to earthquake deformation is calculated as the product of the depth to the neutral axis and the sum of plastic hinge rotations at the joint, divided by the unbonded length. 7KHUHVWULFWLRQVRQWKHÀH[XUDOVWUHQJWKSURYLGHGEWKH tendons are based on the results of analytical and experi- mental studies (Ishizuka and Hawkins 1987; Park and 18.6.3 /RQJLWXGLQDOUHLQIRUFHPHQW 18.6.3.1 Beams shall have at least two continuous bars at both top and bottom faces. At any section, for top as well as for bottom reinforcement, the amount of reinforcement shall be at least that required by 9.6.1.2, and the reinforcement ratio ȡ shall not exceed 0.025 for Grade 60 reinforcement and 0.02 for Grade 80 reinforcement. 18.6.3.2 Positive moment strength at joint face shall be at least one-half the negative moment strength provided at that face of the joint. Both the negative and the positive moment strength at any section along member length shall be at least one-fourth the maximum moment strength provided at face of either joint. 18.6.3.3 Lap splices of deformed longitudinal reinforce- ment shall be permitted if hoop or spiral reinforcement is provided over the lap length. Spacing of the transverse rein- forcement enclosing the lap-spliced bars shall not exceed the lesser of d/4 and 4 in. Lap splices shall not be used in loca- tions (a) through (c): (a) Within the joints (b) Within a distance of twice the beam depth from the face of the joint (c) Within a distance of twice the beam depth from crit- LFDOVHFWLRQVZKHUHÀH[XUDOLHOGLQJLVOLNHOWRRFFXUDV a result of lateral displacements beyond the elastic range of behavior 18.6.3.4 Mechanical splices shall conform to 18.2.7 and welded splices shall conform to 18.2.8. 18.6.3.5 Unless used in a special moment frame as permitted by 18.9.2.3, prestressing shall satisfy (a) through (d): (a) The average prestress fpc calculated for an area equal to the least cross-sectional dimension of the beam multiplied by the perpendicular cross-sectional dimension shall not exceed the lesser of 500 psi and fcƍ. (b) Prestressed reinforcement shall be unbonded in poten- tial plastic hinge regions, and the calculated strains in prestressed reinforcement under the design displacement shall be less than 0.01. (c) Prestressed reinforcement shall not contribute more WKDQRQHIRXUWKRIWKHSRVLWLYHRUQHJDWLYHÀH[XUDOVWUHQJWK at the critical section in a plastic hinge region and shall be anchored at or beyond the exterior face of the joint. (d) Anchorages of post-tensioning tendons resisting earth- quake-induced forces shall be capable of allowing tendons to withstand 50 cycles of loading, with prestressed rein- forcement forces bounded by 40 and 85 percent of the VSHFL¿HGWHQVLOHVWUHQJWKRIWKHSUHVWUHVVLQJUHLQIRUFHPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 301 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 304. Thompson 1977). Although satisfactory seismic perfor- mance can be obtained with greater amounts of prestressed reinforcement, this restriction is needed to allow the use of WKHVDPHUHVSRQVHPRGL¿FDWLRQDQGGHÀHFWLRQDPSOL¿FDWLRQ IDFWRUVDVWKRVHVSHFL¿HGLQPRGHOFRGHVIRUVSHFLDOPRPHQW frames without prestressed reinforcement. Prestressed special moment frames will generally contain continuous prestressed reinforcement that is anchored with adequate cover at or beyond the exterior face of each beam-column connection located at the ends of the moment frame. Fatigue testing for 50 cycles of loading between 40 and SHUFHQWRIWKHVSHFL¿HGWHQVLOHVWUHQJWKRIWKHSUHVWUHVVHG reinforcement has been a long-standing industry prac- tice (ACI 423.3R; ACI 423.7). The 80 percent limit was increased to 85 percent to correspond to the 1 percent limit on the strain in prestressed reinforcement. Testing over this range of stress is intended to conservatively simulate the H൵HFWRIDVHYHUHHDUWKTXDNH$GGLWLRQDOGHWDLOVRQWHVWLQJ procedures are provided in ACI 423.7. R18.6.4 7UDQVYHUVHUHLQIRUFHPHQW 7UDQVYHUVHUHLQIRUFHPHQWLVUHTXLUHGSULPDULOWRFRQ¿QH the concrete and maintain lateral support for the reinforcing bars in regions where yielding is expected. Examples of hoops suitable for beams are shown in Fig. R18.6.4. In earlier Code editions, the upper limit on hoop spacing was the least of d/4, eight longitudinal bar diameters, 24 tie bar diameters, and 12 in. The upper limits were changed in the 2011 edition because of concerns about adequacy of longitu- GLQDOEDUEXFNOLQJUHVWUDLQWDQGFRQ¿QHPHQWLQODUJHEHDPV In the case of members with varying strength along the span or members for which the permanent load represents a large proportion of the total design load, concentrations of inelastic rotation may occur within the span. If such a condi- tion is anticipated, transverse reinforcement is also required in regions where yielding is expected. Because spalling of the concrete shell might occur, especially at and near regions RIÀH[XUDOLHOGLQJDOOZHEUHLQIRUFHPHQWLVUHTXLUHGWREH provided in the form of closed hoops. 18.6.4 7UDQVYHUVHUHLQIRUFHPHQW 18.6.4.1 Hoops shall be provided in the following regions of a beam: (a) Over a length equal to twice the beam depth measured from the face of the supporting column toward midspan, at both ends of the beam (b) Over lengths equal to twice the beam depth on both VLGHVRIDVHFWLRQZKHUHÀH[XUDOLHOGLQJLVOLNHOWRRFFXU as a result of lateral displacements beyond the elastic range of behavior. 18.6.4.2 Where hoops are required, primary longitudinal reinforcing bars closest to the tension and compression faces shall have lateral support in accordance with 25.7.2.3 and 25.7.2.4 7KH VSDFLQJ RI WUDQVYHUVHO VXSSRUWHG ÀH[XUDO reinforcing bars shall not exceed 14 in. Skin reinforcement required by 9.7.2.3 need not be laterally supported. 18.6.4.3 Hoops in beams shall be permitted to be made up of two pieces of reinforcement: a stirrup having seismic hooks at both ends and closed by a crosstie. Consecutive crossties engaging the same longitudinal bar shall have their GHJUHHKRRNVDWRSSRVLWHVLGHVRIWKHÀH[XUDOPHPEHU If the longitudinal reinforcing bars secured by the crossties DUHFRQ¿QHGEDVODERQRQORQHVLGHRIWKHEHDPWKH 90-degree hooks of the crossties shall be placed on that side. 18.6.4.47KH¿UVWKRRSVKDOOEHORFDWHGQRWPRUHWKDQLQ from the face of a supporting column. Spacing of the hoops shall not exceed the least of (a) through (d): (a) d/4 (b) 6 in. American Concrete Institute – Copyrighted © Material – www.concrete.org 302 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 305. Maximum spacing between bars restrained by legs of crossties or hoops = 14 in. Detail A Detail C Detail B A B C Consecutive crossties engaging the same longitudinal bars have their 90-degree hooks on opposite sides 6db ≥ 3 in. extension Crosstie as defined in 25.3.5 6db extension C A Fig. R18.6.4²([DPSOHVRIRYHUODSSLQJKRRSVDQGLOOXVWUD- WLRQRIOLPLWRQPD[LPXPKRUL]RQWDOVSDFLQJRIVXSSRUWHG longitudinal bars. R18.6.5 Shear strength Unless a beam possesses a moment strength that is on the order of 3 or 4 times the design moment, it should be DVVXPHGWKDWLWZLOOLHOGLQÀH[XUHLQWKHHYHQWRIDPDMRU earthquake. The design shear force should be selected so as to be a good approximation of the maximum shear that may develop in a member. Therefore, required shear strength IRU IUDPH PHPEHUV LV UHODWHG WR ÀH[XUDO VWUHQJWKV RI WKH designed member rather than to factored shear forces indi- cated by lateral load analysis. The conditions described by DUHLOOXVWUDWHGLQ)LJ57KH¿JXUHDOVRVKRZV WKDWYHUWLFDOHDUWKTXDNHH൵HFWVDUHWREHLQFOXGHGDVLVWSL- cally required by the general building code. For example, $6(6(,UHTXLUHVYHUWLFDOHDUWKTXDNHH൵HFWV0.2SDS, to be included. Because the actual yield strength of the longitudinal UHLQIRUFHPHQWPDH[FHHGWKHVSHFL¿HGLHOGVWUHQJWKDQG because strain hardening of the reinforcement is likely to (c) For Grade 60, 6db RI WKH VPDOOHVW SULPDU ÀH[XUDO reinforcing bar excluding longitudinal skin reinforcement required by 9.7.2.3 (d) For Grade 80, 5db RI WKH VPDOOHVW SULPDU ÀH[XUDO reinforcing bar excluding longitudinal skin reinforcement required by 9.7.2.3 18.6.4.5 Where hoops are required, they shall be designed to resist shear according to 18.6.5. 18.6.4.6 Where hoops are not required, stirrups with seismic hooks at both ends shall be spaced at a distance not more than d/2 throughout the length of the beam. 18.6.4.7 In beams having factored axial compressive force exceeding Ag fcƍ, hoops satisfying 18.7.5.2 through 18.7.5.4 shall be provided along lengths given in 18.6.4.1. Along the remaining length, hoops satisfying 18.7.5.2 shall have spacing s not exceeding the least of 6 in., 6db of the smallest Grade 60 enclosed longitudinal beam bar, and 5db of the smallest Grade 80 enclosed longitudinal beam bar. Where concrete cover over transverse reinforcement exceeds 4 in., additional transverse reinforcement having cover not exceeding 4 in. and spacing not exceeding 12 in. shall be provided. 18.6.5 Shear strength 18.6.5.1 Design forces The design shear force Ve shall be calculated from consid- eration of the forces on the portion of the beam between faces of the joints. It shall be assumed that moments of opposite VLJQFRUUHVSRQGLQJWRSUREDEOHÀH[XUDOVWUHQJWKMpr, act at the joint faces and that the beam is loaded with the factored gravity and vertical earthquake loads along its span. 18.6.5.2 7UDQVYHUVHUHLQIRUFHPHQW 7UDQVYHUVH UHLQIRUFHPHQW RYHU WKH OHQJWKV LGHQWL¿HG LQ 18.6.4.1 shall be designed to resist shear assuming Vc = 0 when both (a) and (b) occur: American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 303 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 306. take place at a joint subjected to large rotations, required shear strengths are determined using a stress of at least 1.25fy in the longitudinal reinforcement. Experimental studies (Popov et al. 1972) of reinforced concrete members subjected to cyclic loading have demon- strated that more shear reinforcement is required to ensure DÀH[XUDOIDLOXUHLIWKHPHPEHULVVXEMHFWHGWRDOWHUQDWLQJ nonlinear displacements than if the member is loaded in only one direction: the necessary increase of shear reinforcement being higher in the case of no axial load. This observation LV UHÀHFWHG LQ WKH RGH UHIHU WR E HOLPLQDWLQJ the term representing the contribution of concrete to shear strength. The added conservatism on shear is deemed neces- VDULQORFDWLRQVZKHUHSRWHQWLDOÀH[XUDOKLQJLQJPDRFFXU However, this stratagem, chosen for its relative simplicity, should not be interpreted to mean that no concrete is required to resist shear. On the contrary, it may be argued that the concrete core resists all the shear with the shear WUDQVYHUVH UHLQIRUFHPHQWFRQ¿QLQJDQGVWUHQJWKHQLQJWKH FRQFUHWH 7KH FRQ¿QHG FRQFUHWH FRUH SODV DQ LPSRUWDQW role in the behavior of the beam and should not be reduced to a minimum just because the design expression does not explicitly recognize it. (a) The earthquake-induced shear force calculated in accordance with 18.6.5.1 represents at least one-half of the maximum required shear strength within those lengths. (b) The factored axial compressive force Pu including HDUWKTXDNHH൵HFWVLVOHVVWKDQAg fcƍ. American Concrete Institute – Copyrighted © Material – www.concrete.org 304 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 307. R18.7—Columns of special moment frames R18.7.1 Scope This section applies to columns of special moment frames regardless of the magnitude of axial force. Before 2014, the Code permitted columns with low levels of axial stress to be detailed as beams. R18.7.2 'LPHQVLRQDOOLPLWV The geometric constraints in this provision follow from previous practice (Seismology Committee of SEAOC 1996). R18.7.3 0LQLPXPÀH[XUDOVWUHQJWKRIFROXPQV The intent of 18.7.3.2 is to reduce the likelihood of yielding in columns that are considered as part of the seismic-force- resisting system. If columns are not stronger than beams framing into a joint, there is increased likelihood of inelastic 18.7—Columns of special moment frames 18.7.1 Scope 18.7.1.1 This section shall apply to columns of special moment frames that form part of the seismic-force-resisting VVWHP DQG DUH SURSRUWLRQHG SULPDULO WR UHVLVW ÀH[XUH shear, and axial forces. 18.7.2 'LPHQVLRQDOOLPLWV 18.7.2.1 Columns shall satisfy (a) and (b): (a) The shortest cross-sectional dimension, measured on a straight line passing through the geometric centroid, shall be at least 12 in. (b) The ratio of the shortest cross-sectional dimension to the perpendicular dimension shall be at least 0.4. 18.7.3 0LQLPXPÀH[XUDOVWUHQJWKRIFROXPQV 18.7.3.1 Columns shall satisfy 18.7.3.2 or 18.7.3.3, except at connections where the column is discontinuous above the connection and the column factored axial compressive force Notes on Fig. R18.6.5: Direction of shear force Ve depends on relative magnitudes of gravity loads and shear generated by end moments. End moments Mpr based on steel tensile stress of 1.25fy, where fy is specified yield strength. (Both end moments should be considered in both directions, clockwise and counter-clockwise). End moment Mpr for columns need not be greater than moments generated by the Mpr of the beams framing into the beam-column joints. Ve should not be less than that required by analysis of the structure. 1. 2. 3. n n u u Beam Column Pu Pu Mpr3 Mpr4 Ve4 Ve3 Mpr1 Mpr2 Ve1 Ve2 Beam shear Column shear Ve = Mpr1 + Mpr2 n ± wu n 2 Ve3,4 = Mpr3 + Mpr4 u wu = (1.2 + 0.2SDS)D + 1.0L + 0.2S Fig. R18.6.5²'HVLJQVKHDUVIRUEHDPVDQGFROXPQV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 305 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 308. DFWLRQ,QWKHZRUVWFDVHRIZHDNFROXPQVÀH[XUDOLHOGLQJ can occur at both ends of all columns in a given story, resulting in a column failure mechanism that can lead to collapse. Connections with discontinuous columns above the connection, such as roof-level connections, are exempted if the column axial load is low, because special moment frame columns with low axial stress are inherently ductile and column yielding at such levels is unlikely to create a column failure mechanism that can lead to collapse. In 18.7.3.2, the nominal strengths of the beams and columns are calculated at the joint faces, and those strengths are compared directly using Eq. (18.7.3.2). The 1995 and earlier Codes required design strengths to be compared at the center of the joint, which typically produced similar UHVXOWVEXWZLWKDGGHGFDOFXODWLRQH൵RUW In determining the nominal moment strength of a beam section in negative bending (top in tension), longitudinal UHLQIRUFHPHQWFRQWDLQHGZLWKLQDQH൵HFWLYHÀDQJHZLGWKRID top slab that acts monolithically with the beam increases the beam strength. French and Moehle (1991), on beam-column subassemblies under lateral loading, indicates that using the H൵HFWLYH ÀDQJH ZLGWKV GH¿QHG LQ 6.3.2 gives reasonable estimates of beam negative moment strengths of interior connections at story displacements approaching 2 percent of VWRUKHLJKW7KLVH൵HFWLYHZLGWKLVFRQVHUYDWLYHZKHUHWKH slab terminates in a weak spandrel. ,IFDQQRWEHVDWLV¿HGDWDMRLQWUHTXLUHV that any positive contribution of the column or columns LQYROYHGWRWKHODWHUDOVWUHQJWKDQGVWL൵QHVVRIWKHVWUXFWXUH is to be ignored. Negative contributions of the column or columns should not be ignored. For example, ignoring the VWL൵QHVVRIWKHFROXPQVRXJKWQRWWREHXVHGDVDMXVWL¿FD- tion for reducing the design base shear. If inclusion of those columns in the analytical model of the building results in an LQFUHDVHLQWRUVLRQDOH൵HFWVWKHLQFUHDVHVKRXOGEHFRQVLG- ered as required by the general building code. Furthermore, the column must be provided with transverse reinforcement to increase its resistance to shear and axial forces. R18.7.4 /RQJLWXGLQDOUHLQIRUFHPHQW The lower limit of the area of longitudinal reinforcement is to control time-dependent deformations and to have the yield moment exceed the cracking moment. The upper limit RI WKH DUHD UHÀHFWV FRQFHUQ IRU UHLQIRUFHPHQW FRQJHVWLRQ ORDGWUDQVIHUIURPÀRRUHOHPHQWVWRFROXPQ HVSHFLDOOLQ low-rise construction) and the development of high shear stresses. Spalling of the shell concrete, which is likely to occur QHDUWKHHQGVRIWKHFROXPQLQIUDPHVRIWSLFDOFRQ¿JXUD- tion, makes lap splices in these locations vulnerable. If lap splices are to be used at all, they should be located near the midheight where stress reversal is likely to be limited to a smaller stress range than at locations near the joints. Trans- verse reinforcement is required along the lap-splice length PuXQGHUORDGFRPELQDWLRQVLQFOXGLQJHDUWKTXDNHH൵HFWE, are less than Ag fcƍ. 18.7.3.27KHÀH[XUDOVWUHQJWKVRIWKHFROXPQVVKDOOVDWLVI ™Mnc• ™Mnb (18.7.3.2) where ™Mnc LV VXP RI QRPLQDO ÀH[XUDO VWUHQJWKV RI FROXPQV framing into the joint, evaluated at the faces of the joint. ROXPQÀH[XUDOVWUHQJWKVKDOOEHFDOFXODWHGIRUWKHIDFWRUHG axial force, consistent with the direction of the lateral forces FRQVLGHUHGUHVXOWLQJLQWKHORZHVWÀH[XUDOVWUHQJWK ™Mnb LV VXP RI QRPLQDO ÀH[XUDO VWUHQJWKV RI WKH EHDPV framing into the joint, evaluated at the faces of the joint. In T-beam construction, where the slab is in tension under moments at the face of the joint, slab reinforcement within DQH൵HFWLYHVODEZLGWKGH¿QHGLQDFFRUGDQFHZLWK6.3.2 shall be assumed to contribute to Mnb if the slab reinforcement is GHYHORSHGDWWKHFULWLFDOVHFWLRQIRUÀH[XUH Flexural strengths shall be summed such that the column moments oppose the beam moments. Equation (18.7.3.2) VKDOOEHVDWLV¿HGIRUEHDPPRPHQWVDFWLQJLQERWKGLUHFWLRQV in the vertical plane of the frame considered. 18.7.3.3,ILVQRWVDWLV¿HGDWDMRLQWWKHODWHUDO VWUHQJWKDQGVWL൵QHVVRIWKHFROXPQVIUDPLQJLQWRWKDWMRLQW VKDOOEHLJQRUHGZKHQFDOFXODWLQJVWUHQJWKDQGVWL൵QHVVRI the structure. These columns shall conform to 18.14. 18.7.4 /RQJLWXGLQDOUHLQIRUFHPHQW 18.7.4.1 Area of longitudinal reinforcement, Ast, shall be at least 0.01Ag and shall not exceed 0.06Ag. 18.7.4.2 In columns with circular hoops, there shall be at least six longitudinal bars. American Concrete Institute – Copyrighted © Material – www.concrete.org 306 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 309. because of the uncertainty in moment distributions along the KHLJKWDQGWKHQHHGIRUFRQ¿QHPHQWRIODSVSOLFHVVXEMHFWHG to stress reversals (Sivakumar et al. 1983). R18.7.4.3 Bond splitting failure along longitudinal bars within the clear column height may occur under earthquake demands (Ichinose 1995; Sokoli and Ghannoum 2016). Splitting can be controlled by restricting longitudinal bar size, increasing the amount of transverse reinforcement, or increasing concrete strength, all of which reduce the devel- opment length of longitudinal bars (Ɛd) over column clear height (Ɛu). Increasing the ratio of column-to-beam moment strength at joints can reduce the inelastic demands on longi- tudinal bars in columns under earthquake demands. R18.7.5 7UDQVYHUVHUHLQIRUFHPHQW 7KLVVHFWLRQLVFRQFHUQHGZLWKFRQ¿QLQJWKHFRQFUHWHDQG providing lateral support to the longitudinal reinforcement. R18.7.5.1 This section stipulates a minimum length over which to provide closely-spaced transverse reinforcement at WKHFROXPQHQGVZKHUHÀH[XUDOLHOGLQJQRUPDOORFFXUV Research results indicate that the length should be increased by 50 percent or more in locations, such as the base of a EXLOGLQJZKHUHD[LDOORDGVDQGÀH[XUDOGHPDQGVPDEH especially high (Watson et al. 1994). R18.7.5.2 Sections 18.7.5.2 and 18.7.5.3 provide require- PHQWV IRU FRQ¿JXUDWLRQ RI WUDQVYHUVH UHLQIRUFHPHQW IRU columns and joints of special moment frames. Figure R18.7.5.2 shows an example of transverse reinforcement provided by one hoop and three crossties. Crossties with D GHJUHH KRRN DUH QRW DV H൵HFWLYH DV HLWKHU FURVVWLHV ZLWKGHJUHHKRRNVRUKRRSVLQSURYLGLQJFRQ¿QHPHQW For lower values of Pu/Ag fcƍ and lower concrete compres- sive strengths, crossties with 90-degree hooks are adequate if the ends are alternated along the length and around the perimeter of the column. For higher values of Pu/Ag fcƍ, for which compression-controlled behavior is expected, and for higher compressive strengths, for which behavior tends WREHPRUHEULWWOHWKHLPSURYHGFRQ¿QHPHQWSURYLGHGE having corners of hoops or seismic hooks supporting all 18.7.4.3 Over column clear height, longitudinal reinforce- ment shall be selected such that 1.25Ɛd”Ɛu/2. 18.7.4.4 Mechanical splices shall conform to 18.2.7 and welded splices shall conform to 18.2.8. Lap splices shall be permitted only within the center half of the member length, shall be designed as tension lap splices, and shall be enclosed within transverse reinforcement in accordance with 18.7.5.2 and 18.7.5.3. 18.7.5 7UDQVYHUVHUHLQIRUFHPHQW 18.7.5.1 Transverse reinforcement required in 18.7.5.2 through 18.7.5.4 shall be provided over a length Ɛo from each MRLQWIDFHDQGRQERWKVLGHVRIDQVHFWLRQZKHUHÀH[XUDO yielding is likely to occur as a result of lateral displacements beyond the elastic range of behavior. Length Ɛo shall be at least the greatest of (a) through (c): (a) The depth of the column at the joint face or at the VHFWLRQZKHUHÀH[XUDOLHOGLQJLVOLNHOWRRFFXU (b) One-sixth of the clear span of the column (c) 18 in. 18.7.5.2 Transverse reinforcement shall be in accordance with (a) through (f): (a) Transverse reinforcement shall comprise either single or overlapping spirals, circular hoops, or single or over- lapping rectilinear hoops with or without crossties. (b) Bends of rectilinear hoops and crossties shall engage peripheral longitudinal reinforcing bars. (c) Crossties of the same or smaller bar size as the hoops shall be permitted, subject to the limitation of 25.7.2.2. Consecutive crossties shall be alternated end for end along the longitudinal reinforcement and around the perimeter of the cross section. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 307 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 310. longitudinal bars is important to achieving intended perfor- mance. Where these conditions apply, crossties with seismic hooks at both ends are required. The 8 in. limit on hx is also intended to improve performance under these critical condi- tions. For bundled bars, bends or hooks of hoops and cross- ties need to enclose the bundle, and longer extensions on hooks should be considered. Column axial load Pu should UHÀHFWIDFWRUHGFRPSUHVVLYHGHPDQGVIURPERWKHDUWKTXDNH and gravity loads. In past editions of the Code, the requirements for transverse reinforcement in columns, walls, beam-column joints, and diagonally reinforced coupling beams referred to the same equations. In the 2014 edition of the Code, the equations and GHWDLOLQJUHTXLUHPHQWVGL൵HUDPRQJWKHPHPEHUWSHVEDVHG on consideration of their loadings, deformations, and perfor- mance requirements. Additionally, hx previously referred to the distance between legs of hoops or crossties. In the 2014 edition of the Code, hx refers to the distance between longi- tudinal bars supported by those hoops or crossties. xi xi xi bc1 bc2 xi xi The dimension xi from centerline to centerline of laterally supported longitudinal bars is not to exceed 14 inches. The term hx used in Eq. (18.7.5.3) is taken as the largest value of xi. Ash1 Ash2 6db ≥ 3 in. 6db extension Consecutive crossties engaging the same longitudinal bar have their 90-degree hooks on opposite sides of column Fig. R18.7.5.2²([DPSOH RI WUDQVYHUVH UHLQIRUFHPHQW LQ FROXPQV R18.7.5.3 The requirement that spacing not exceed one- fourth of the minimum member dimension or 6 in. is for FRQFUHWHFRQ¿QHPHQW,IWKHPD[LPXPVSDFLQJRIFURVVWLHV or legs of overlapping hoops within the section is less than 14 in., then the 4 in. limit can be increased as permitted by Eq. (18.7.5.3). The spacing limit as a function of the longi- tudinal bar diameter is intended to provide adequate longitu- dinal bar restraint to control buckling after spalling. (d) Where rectilinear hoops or crossties are used, they shall provide lateral support to longitudinal reinforcement in accordance with 25.7.2.2 and 25.7.2.3. (e) Reinforcement shall be arranged such that the spacing hx of longitudinal bars laterally supported by the corner of a crosstie or hoop leg shall not exceed 14 in. around the perimeter of the column. (f) Where Pu 0.3Ag fcƍ or fcƍ!SVL in columns with rectilinear hoops, every longitudinal bar or bundle of bars around the perimeter of the column core shall have lateral support provided by the corner of a hoop or by a seismic hook, and the value of hx shall not exceed 8 in. Pu shall be the largest value in compression consistent with factored load combinations including E. 18.7.5.3 Spacing of transverse reinforcement shall not exceed the least of (a) through (d): (a) One-fourth of the minimum column dimension (b) For Grade 60, 6db of the smallest longitudinal bar (c) For Grade 80, 5db of the smallest longitudinal bar (d) so, as calculated by: American Concrete Institute – Copyrighted © Material – www.concrete.org 308 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 311. 14 4 3 [ o h s − ⎛ ⎞ = + ⎜ ⎟ ⎝ ⎠ (18.7.5.3) The value of so from Eq. (18.7.5.3) shall not exceed 6 in. and need not be taken less than 4 in. 18.7.5.4 Amount of transverse reinforcement shall be in accordance with Table 18.7.5.4. The concrete strength factor kfDQGFRQ¿QHPHQWH൵HFWLYH- ness factor kn are calculated according to Eq. (18.7.5.4a) and (18.7.5.4b). (a) 0.6 1.0 25,000 f c k f = + ≥ ′ (18.7.5.4a) (b) 2 l n l n k n = − (18.7.5.4b) where nl is the number of longitudinal bars or bar bundles around the perimeter of a column core with rectilinear hoops that are laterally supported by the corner of hoops or by seismic hooks. Table 18.7.5.4—Transverse reinforcement for columns of special moment frames Transverse reinforcement Conditions Applicable expressions Ashsbc for rectilinear hoop Pu”Ag fcƍDQG fcƍ”SVL Greater of (a) and (b) 0.3 1 (a) g ch yt c A A f f ⎛ ⎞ − ⎜ ⎟ ⎝ ′ ⎠ 0.09 (b) yt c f f ′ 0.2 (c) u f n yt ch P k k f A Pu 0.3Ag fcƍRU fcƍ!SVL Greatest of (a), (b), and (c) ȡs for spiral or circular hoop Pu”Ag fcƍDQG fcƍ”SVL Greater of (d) and (e) 0.45 1 (d) g ch y c t A A f f ⎛ ⎞ ′ − ⎜ ⎟ ⎝ ⎠ 0.12 (e) yt c f f ′ 0.35 (f) u f yt ch P k f A Pu 0.3Ag fcƍRU fcƍ!SVL Greatest of (d), (e), and (f) 18.7.5.5 Beyond the length Ɛo given in 18.7.5.1, the column shall contain spiral reinforcement satisfying 25.7.3 or hoop and crosstie reinforcement satisfying 25.7.2 and 25.7.4 with spacing s not exceeding the least of 6 in., 6db of the smallest Grade 60 longitudinal column bar, and 5db of the smallest Grade 80 longitudinal column bar, unless a greater amount of transverse reinforcement is required by 18.7.4.4 or 18.7.6. 18.7.5.6 Columns supporting reactions from discontinued VWL൵PHPEHUVVXFKDVZDOOVVKDOOVDWLVI D DQG E R18.7.5.47KHH൵HFWRIKHOLFDO VSLUDO UHLQIRUFHPHQWDQG DGHTXDWHO FRQ¿JXUHG UHFWLOLQHDU KRRS UHLQIRUFHPHQW RQ deformation capacity of columns is well established (Sakai and Sheikh 1989). Expressions (a), (b), (d), and (e) in Table 18.7.5.4 have historically been used in ACI 318 to calcu- ODWHWKHUHTXLUHGFRQ¿QHPHQWUHLQIRUFHPHQWWRHQVXUHWKDW spalling of shell concrete does not result in a loss of column axial load strength. Expressions (c) and (f) were developed from a review of column test data (Elwood et al. 2009) and are intended to result in columns capable of sustaining a drift ratio of 0.03 with limited strength degradation. Expressions (c) and (f) are triggered for axial load greater than 0.3Ag fcƍ, which corresponds approximately to the onset of compres- sion-controlled behavior for symmetrically reinforced columns. The kn term (Paultre and Légeron 2008) decreases WKHUHTXLUHGFRQ¿QHPHQWIRUFROXPQVZLWKFORVHOVSDFHG laterally supported longitudinal reinforcement because such FROXPQVDUHPRUHH൵HFWLYHOFRQ¿QHGWKDQFROXPQVZLWK more widely spaced longitudinal reinforcement. The kf term LQFUHDVHVWKHUHTXLUHGFRQ¿QHPHQWIRUFROXPQVZLWKfcƍ! 10,000 psi because such columns can experience brittle IDLOXUHLIQRWZHOOFRQ¿QHGRQFUHWHVWUHQJWKVJUHDWHUWKDQ 15,000 psi should be used with caution given the limited test data for such columns. The concrete strength used to deter- PLQH WKH FRQ¿QHPHQW UHLQIRUFHPHQW LV UHTXLUHG WR EH WKH VDPHDVWKDWVSHFL¿HGLQWKHFRQVWUXFWLRQGRFXPHQWV Expressions (a), (b), and (c) in Table 18.7.5.4 are to be VDWLV¿HGLQERWKFURVVVHFWLRQDOGLUHFWLRQVRIWKHUHFWDQJXODU core. For each direction, bc is the core dimension perpen- dicular to the tie legs that constitute Ash, as shown in Fig. R18.7.5.2. Research results indicate that high strength reinforce- PHQWFDQEHXVHGH൵HFWLYHODVFRQ¿QHPHQWUHLQIRUFHPHQW Section 20.2.2.4 permits a value of fyt as high as 100,000 psi to be used in Table 18.7.5.4. R18.7.5.5 This provision is intended to provide reasonable protection to the midheight of columns outside the length Ɛo 2EVHUYDWLRQV DIWHU HDUWKTXDNHV KDYH VKRZQ VLJQL¿FDQW damage to columns in this region, and the minimum hoops or spirals required should provide more uniform strength of the column along its length. R18.7.5.6 ROXPQV VXSSRUWLQJ GLVFRQWLQXHG VWL൵ members, such as walls or trusses, may develop consider- able inelastic response. Therefore, it is required that these American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 309 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 312. (a) Transverse reinforcement required by 18.7.5.2 through 18.7.5.4 shall be provided over the full height at all levels beneath the discontinuity if the factored axial compres- VLYHIRUFHLQWKHVHFROXPQVUHODWHGWRHDUWKTXDNHH൵HFW exceeds Ag fcƍ. Where design forces have been magni- ¿HGWRDFFRXQWIRUWKHRYHUVWUHQJWKRIWKHYHUWLFDOHOHPHQWV of the seismic-force-resisting system, the limit of Ag fcƍ shall be increased to Ag fcƍ. (b) Transverse reinforcement shall extend into the discon- tinued member at least Ɛd of the largest longitudinal column bar, where Ɛd is in accordance with 18.8.5. Where the lower end of the column terminates on a wall, the required transverse reinforcement shall extend into the wall at least Ɛd of the largest longitudinal column bar at the point of termination. Where the column terminates on a footing or mat, the required transverse reinforcement shall extend at least 12 in. into the footing or mat. 18.7.5.7,IWKHFRQFUHWHFRYHURXWVLGHWKHFRQ¿QLQJWUDQV- verse reinforcement required by 18.7.5.1, 18.7.5.5, and 18.7.5.6 exceeds 4 in., additional transverse reinforcement having cover not exceeding 4 in. and spacing not exceeding 12 in. shall be provided. 18.7.6 Shear strength 18.7.6.1 Design forces 18.7.6.1.1 The design shear force Ve shall be calculated from considering the maximum forces that can be generated at the faces of the joints at each end of the column. These joint forces shall be calculated using the maximum probable ÀH[XUDOVWUHQJWKVMpr, at each end of the column associ- ated with the range of factored axial forces, Pu, acting on the column. The column shears need not exceed those calculated from joint strengths based on Mpr of the beams framing into the joint. In no case shall Ve be less than the factored shear calculated by analysis of the structure. 18.7.6.2 7UDQVYHUVHUHLQIRUFHPHQW 18.7.6.2.1 Transverse reinforcement over the lengths Ɛo, given in 18.7.5.1, shall be designed to resist shear assuming Vc = 0 when both (a) and (b) occur: (a) The earthquake-induced shear force, calculated in accordance with 18.7.6.1, is at least one-half of the maximum required shear strength within Ɛo. (b) The factored axial compressive force Pu including HDUWKTXDNHH൵HFWVLVOHVVWKDQAg fcƍ. FROXPQVKDYHWKHVSHFL¿HGUHLQIRUFHPHQWWKURXJKRXWWKHLU length. This covers all columns beneath the level at which WKHVWL൵PHPEHUKDVEHHQGLVFRQWLQXHGXQOHVVWKHIDFWRUHG IRUFHVFRUUHVSRQGLQJWRHDUWKTXDNHH൵HFWDUHORZ5HIHUWR R18.12.7.6 for discussion of the overstrength factor ȍo. R18.7.5.7 The unreinforced shell may spall as the column GHIRUPVWRUHVLVWHDUWKTXDNHH൵HFWV6HSDUDWLRQRISRUWLRQV of the shell from the core caused by local spalling creates a falling hazard. The additional reinforcement is required to reduce the risk of portions of the shell falling away from the column. R18.7.6 Shear strength R18.7.6.1 Design forces R18.7.6.1.1 The procedures of 18.6.5.1 also apply to FROXPQV$ERYHWKHJURXQGÀRRUWKHPRPHQWDWDMRLQWPD EH OLPLWHG E WKH ÀH[XUDO VWUHQJWK RI WKH EHDPV IUDPLQJ into the joint. Where beams frame into opposite sides of a joint, the combined strength is the sum of the negative moment strength of the beam on one side of the joint and the positive moment strength of the beam on the other side of the joint. Moment strengths are to be determined using a strength reduction factor of 1.0 and reinforcement with an H൵HFWLYHLHOGVWUHVVHTXDOWRDWOHDVW1.25fy. Distribution of the combined moment strength of the beams to the columns above and below the joint should be based on analysis. American Concrete Institute – Copyrighted © Material – www.concrete.org 310 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 313. 18.8—Joints of special moment frames 18.8.1 Scope 18.8.1.1 This section shall apply to beam-column joints of special moment frames forming part of the seismic-force- resisting system. 18.8.2 General 18.8.2.1 Forces in longitudinal beam reinforcement at the joint face shall be calculated assuming that the stress in the ÀH[XUDOWHQVLOHUHLQIRUFHPHQWLV1.25fy. 18.8.2.2 Longitudinal reinforcement terminated in a joint shall extend to the far face of the joint core and shall be developed in tension in accordance with 18.8.5 and in compression in accordance with 25.4.9. 18.8.2.3 Where longitudinal beam reinforcement extends through a beam-column joint, the depth h of the joint parallel to the beam longitudinal reinforcement shall be at least the greatest of (a) through (c): (a) 20 b d λ of the largest Grade 60 longitudinal bar, where Ȝ for lightweight concrete and 1.0 for all other cases (b) 26db of the largest Grade 80 longitudinal bar (c) h/2 of any beam framing into the joint and generating joint shear as part of the seismic-force-resisting system in the direction under consideration R18.8—Joints of special moment frames R18.8.2 General Development of inelastic rotations at the faces of joints of reinforced concrete frames is associated with strains in WKHÀH[XUDOUHLQIRUFHPHQWZHOOLQH[FHVVRIWKHLHOGVWUDLQ RQVHTXHQWO MRLQW VKHDU IRUFH JHQHUDWHG E WKH ÀH[XUDO reinforcement is calculated for a stress of 1.25fy in the rein- forcement (refer to 18.8.2.1). A detailed explanation of the reasons for the possible development of stresses in excess of the yield strength in beam tensile reinforcement is provided in ACI 352R. R18.8.2.2 The design provisions for hooked bars are based mainly on research and experience for joints with standard 90-degree hooks. Therefore, standard 90-degree hooks generally are preferred to standard 180-degree hooks unless unusual considerations dictate use of 180-degree hooks. For bars in compression, the development length corresponds to the straight portion of a hooked or headed bar measured from the critical section to the onset of the bend for hooked bars and from the critical section to the head for headed bars. R18.8.2.3 Depth hRIWKHMRLQWLVGH¿QHGLQ)LJ5 The column dimension parallel to the beam reinforcement in joints with circular columns may be taken as that of a square section of equivalent area. Research (Meinheit and Jirsa 1977; Briss et al. 1978; Ehsani 1982; Durrani and Wight 1982; Leon 1989; Aoyama 2001; Lin et al. 2000) has shown that straight longitudinal beam bars may slip within the beam-column joint during a series of large moment rever- sals. The bond stresses on these straight bars may be very large. To reduce slip substantially during the formation of adjacent beam hinging, it would be necessary to have a ratio of column dimension to bar diameter of approximately 32 for Grade 60 bars, which would result in very large joints. Tests demonstrate adequate behavior if the ratio of joint depth to maximum beam longitudinal bar diameter for Grade 60 rein- forcement is at least 20 for normalweight concrete and 26 for lightweight concrete. A joint depth of 26db for Grade 80 reinforcement is intended to achieve similar performance to that of a joint depth of 20db for Grade 60 reinforcement and normalweight concrete. The limits on joint depth provide reasonable control on the amount of slip of the beam bars in a beam-column joint, considering the number of anticipated inelastic excursions of the building frame during a major earthquake. A thorough treatment of this topic is given in Zhu and Jirsa (1983). American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 311 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 314. 18.8.2.3.1 Concrete used in joints with Grade 80 longitu- dinal reinforcement shall be normalweight concrete. 18.8.3 7UDQVYHUVHUHLQIRUFHPHQW 18.8.3.1 Joint transverse reinforcement shall satisfy 18.7.5.2, 18.7.5.3, 18.7.5.4, and 18.7.5.7, except as permitted in 18.8.3.2. 18.8.3.2 Where beams frame into all four sides of the joint and where each beam width is at least three-fourths the column width, the amount of reinforcement required by 18.7.5.4 shall be permitted to be reduced by one-half, and the spacing required by 18.7.5.3 shall be permitted to be increased to 6 in. within the overall depth h of the shallowest framing beam. 18.8.3.3 Longitudinal beam reinforcement outside the FROXPQFRUHVKDOOEHFRQ¿QHGEWUDQVYHUVHUHLQIRUFHPHQW SDVVLQJWKURXJKWKHFROXPQWKDWVDWLV¿HVVSDFLQJUHTXLUH- ments of 18.6.4.4, and requirements of 18.6.4.2, and 18.6.4.3, LIVXFKFRQ¿QHPHQWLVQRWSURYLGHGEDEHDPIUDPLQJLQWR the joint. 18.8.4 Shear strength 18.8.4.1 Joint shear force Vu shall be calculated on a plane at mid-height of the joint from calculated forces at the joint faces using tensile and compressive beam forces determined in accordance with 18.8.2.1 and column shear consistent ZLWKEHDPSUREDEOHÀH[XUDOVWUHQJWKVMpr. 18.8.4.2 ࢥ shall be in accordance with 21.2.4.4. 18.8.4.3 Vn of the joint shall be in accordance with Table 18.8.4.3. Requirement (c) on joint aspect ratio applies only to beams that are designated as part of the seismic-force- resisting system. Joints having depth less than half the beam depth require a steep diagonal compression strut across the MRLQWZKLFKPDEHOHVVH൵HFWLYHLQUHVLVWLQJMRLQWVKHDU Tests to demonstrate performance of such joints have not been reported in the literature. R18.8.2.3.1 Test data justifying the combination of light- weight concrete and Grade 80 longitudinal reinforcement in joints are not available. R18.8.3 7UDQVYHUVHUHLQIRUFHPHQW The Code requires transverse reinforcement in a joint regardless of the magnitude of the calculated shear force. R18.8.3.2 7KH DPRXQW RI FRQ¿QLQJ UHLQIRUFHPHQW PD be reduced and the spacing may be increased if beams of adequate dimensions frame into all four sides of the joint. R18.8.3.3 The required transverse reinforcement, or WUDQVYHUVHEHDPLISUHVHQWLVLQWHQGHGWRFRQ¿QHWKHEHDP longitudinal reinforcement and improve force transfer to the beam-column joint. An example of transverse reinforcement through the FROXPQSURYLGHGWRFRQ¿QHWKHEHDPUHLQIRUFHPHQWSDVVLQJ outside the column core is shown in Fig. R18.6.2. Additional detailing guidance and design recommendations for both interior and exterior wide-beam connections with beam rein- forcement passing outside the column core may be found in ACI 352R. R18.8.4 Shear strength The shear strength values given in 18.8.4.3 are based on the recommendation in ACI 352R for joints with members that are expected to undergo reversals of deformation into WKH LQHODVWLF UDQJH DOWKRXJK WKH $, 5 GH¿QLWLRQ RI H൵HFWLYH FURVVVHFWLRQDO MRLQW DUHD LV VRPHWLPHV GL൵HUHQW The given nominal joint shear strengths do not explicitly consider transverse reinforcement in the joint because tests of joints (Meinheit and Jirsa 1977) and deep beams (Hiro- sawa 1977) have indicated that joint shear strength is not sensitive to transverse reinforcement if at least the required minimum amount is provided in the joint. Cyclic loading tests of joints with extensions of beams with lengths at least equal to their depths have indicated similar joint shear strengths to those of joints with continuous EHDPV7KHVH¿QGLQJVVXJJHVWWKDWH[WHQVLRQVRIEHDPVDQG American Concrete Institute – Copyrighted © Material – www.concrete.org 312 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 315. Table 18.8.4.3—Nominal joint shear strength Vn Column Beam in direction of Vu RQ¿QHPHQW by transverse beams according to 15.2.8 Vn, lb[1] Continuous or meets 15.2.6 Continuous or meets 15.2.7 RQ¿QHG 20 c j f A λ ′ 1RWFRQ¿QHG 15 c j f A λ ′ Other RQ¿QHG 15 c j f A λ ′ 1RWFRQ¿QHG 12 c j f A λ ′ Other Continuous or meets 15.2.7 RQ¿QHG 15 c j f A λ ′ 1RWFRQ¿QHG 12 c j f A λ ′ Other RQ¿QHG 12 c j f A λ ′ 1RWFRQ¿QHG 8 c j f A λ ′ [1] ȜVKDOOEHIRUOLJKWZHLJKWFRQFUHWHDQGIRUQRUPDOZHLJKWFRQFUHWHAj shall be calculated in accordance with 15.4.2.4. 18.8.5 'HYHORSPHQWOHQJWKRIEDUVLQWHQVLRQ 18.8.5.1 For bar sizes No. 3 through No. 11 terminating in a standard hook, Ɛdh shall be calculated by Eq. (18.8.5.1), but Ɛdh shall be at least the greater of 8db and 6 in. for normal- weight concrete and at least the greater of 10dbDQGLQ for lightweight concrete. Ɛdh = fydb Ȝ c f ′ ) (18.8.5.1) The value of Ȝ shall be 0.75 for concrete containing light- weight aggregate and 1.0 otherwise. 7KHKRRNVKDOOEHORFDWHGZLWKLQWKHFRQ¿QHGFRUHRID column or of a boundary element, with the hook bent into the joint. 18.8.5.2 For headed deformed bars satisfying 20.2.1.6, development in tension shall be in accordance with 25.4.4, by substituting a bar stress of 1.25fy for fy. columns, when properly dimensioned and reinforced with ORQJLWXGLQDODQGWUDQVYHUVHEDUVSURYLGHH൵HFWLYHFRQ¿QH- ment to the joint faces, thus delaying joint strength deteriora- tion at large deformations (Meinheit and Jirsa 1981). R18.8.5 'HYHORSPHQWOHQJWKRIEDUVLQWHQVLRQ R18.8.5.1 Minimum embedment length in tension for deformed bars with standard hooks is determined using Eq. (18.8.5.1), which is based on the requirements of 25.4.3. The embedment length of a bar with a standard hook is the distance, parallel to the bar, from the critical section (where the bar is to be developed) to a tangent drawn to the outside edge of the hook. The tangent is to be drawn perpendicular to the axis of the bar (refer to Table 25.3.1). Because Chapter 18 stipulates that the hook is to be HPEHGGHG LQ FRQ¿QHG FRQFUHWH WKH FRH൶FLHQWV IRU concrete cover) and 0.8 (for ties) have been incorporated in the constant used in Eq. (18.8.5.1). The development length that would be derived directly from 25.4.3 is increased to UHÀHFWWKHH൵HFWRIORDGUHYHUVDOV)DFWRUVVXFKDVWKHDFWXDO stress in the reinforcement being more than the yield strength DQGWKHH൵HFWLYHGHYHORSPHQWOHQJWKQRWQHFHVVDULOVWDUWLQJ at the face of the joint were implicitly considered in the formulation of the expression for basic development length that has been used as the basis for Eq. (18.8.5.1). The requirement for the hook to project into the joint is to improve development of a diagonal compression strut across the joint. The requirement applies to beam and column bars terminated at a joint with a standard hook. R18.8.5.2 The factor 1.25 is intended to represent the poten- tial increase in stresses due to inelastic response, including strain hardening that may occur in beams of special moment frames. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 313 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 316. 18.8.5.3 For bar sizes No. 3 through No. 11, Ɛd, the devel- opment length in tension for a straight bar, shall be at least the greater of (a) and (b): (a) 2.5 times the length in accordance with 18.8.5.1 if the depth of the concrete cast in one lift beneath the bar does not exceed 12 in. (b) 3.25 times the length in accordance with 18.8.5.1 if the depth of the concrete cast in one lift beneath the bar exceeds 12 in. 18.8.5.4 Straight bars terminated at a joint shall pass WKURXJK WKH FRQ¿QHG FRUH RI D FROXPQ RU D ERXQGDU element. Any portion of ƐdQRWZLWKLQWKHFRQ¿QHGFRUHVKDOO be increased by a factor of 1.6. 18.8.5.5 If epoxy-coated reinforcement is used, the devel- opment lengths in 18.8.5.1, 18.8.5.3, and 18.8.5.4 shall be multiplied by applicable factors in 25.4.2.5 or 25.4.3.2. 18.9—Special moment frames constructed using precast concrete 18.9.1 Scope 18.9.1.1 This section shall apply to special moment frames constructed using precast concrete forming part of the seismic-force-resisting system. R18.8.5.3 Minimum development length in tension for straight bars is a multiple of the length indicated by 18.8.5.1. Section 18.8.5.3(b) refers to top bars. Lack of reference to No. 14 and No. 18 bars in 18.8.5 is due to the paucity of information on anchorage of such bars subjected to load UHYHUVDOVVLPXODWLQJHDUWKTXDNHH൵HFWV R18.8.5.4 If the required straight embedment length RI D UHLQIRUFLQJ EDU H[WHQGV EHRQG WKH FRQ¿QHG YROXPH RI FRQFUHWH DV GH¿QHG LQ RU WKH required development length is increased on the premise that WKHOLPLWLQJERQGVWUHVVRXWVLGHWKHFRQ¿QHGUHJLRQLVOHVV than that inside. ƐGP = 1.6(Ɛd±Ɛdc) + Ɛdc or ƐGP = 1.6Ɛd±Ɛdc whereƐdm istherequireddevelopmentlengthifbarisnotentirely HPEHGGHGLQFRQ¿QHGFRQFUHWHƐd is the required development OHQJWKLQWHQVLRQIRUVWUDLJKWEDUDVGH¿QHGLQDQGƐdc LVWKHOHQJWKRIEDUHPEHGGHGLQFRQ¿QHGFRQFUHWH R18.9—Special moment frames constructed using precast concrete The detailing provisions in 18.9.2.1 and 18.9.2.2 are intended to produce frames that respond to design displace- ments essentially like monolithic special moment frames. Precast frame systems composed of concrete elements ZLWKGXFWLOHFRQQHFWLRQVDUHH[SHFWHGWRH[SHULHQFHÀH[XUDO yielding in connection regions. Reinforcement in ductile connections can be made continuous by using mechanical splices or any other technique that provides development LQ WHQVLRQ RU FRPSUHVVLRQ RI DW OHDVW WKH VSHFL¿HG WHQVLOH strength of bars (Yoshioka and Sekine 1991; Kurose et al. 1991; Restrepo et al. 1995a,b). Requirements for mechanical splices are in addition to those in 18.2.7 and are intended to avoid strain concentrations over a short length of reinforce- ment adjacent to a splice device. Additional requirements for shear strength are provided in 18.9.2.1 to prevent sliding on connection faces. Precast frames composed of elements with ductile connections may be designed to promote yielding at locations not adjacent to the joints. Therefore, design shear Ve, as calculated according to 18.6.5.1 or 18.7.6.1, may not be conservative. American Concrete Institute – Copyrighted © Material – www.concrete.org 314 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 317. 18.9.2 General 18.9.2.1 Special moment frames with ductile connections constructed using precast concrete shall satisfy (a) through (c): (a) Requirements of 18.6 through 18.8 for special moment frames constructed with cast-in-place concrete (b) Vn for connections calculated according to 22.9 shall be at least 2Ve, where Ve is in accordance with 18.6.5.1 or 18.7.6.1 (c) Mechanical splices of beam reinforcement shall be located not closer than h/2 from the joint face and shall satisfy 18.2.7 18.9.2.2 Special moment frames with strong connections constructed using precast concrete shall satisfy (a) through (e): (a) Requirements of 18.6 through 18.8 for special moment frames constructed with cast-in-place concrete (b) Provision 18.6.2.1(a) shall apply to segments between ORFDWLRQVZKHUHÀH[XUDOLHOGLQJLVLQWHQGHGWRRFFXUGXH to design displacements (c) Design strength of the strong connection, ࢥSn, shall be at least Se (d) Primary longitudinal reinforcement shall be made continuous across connections and shall be developed outside both the strong connection and the plastic hinge region (e) For column-to-column connections, ࢥSn shall be at least 1.4Se, ࢥMn shall be at least 0.4Mpr for the column within the story height, and ࢥVn shall be at least Ve in accordance with 18.7.6.1 Precast concrete frame systems composed of elements joined using strong connections are intended to experience ÀH[XUDO LHOGLQJ RXWVLGH WKH FRQQHFWLRQV 6WURQJ FRQQHF- tions include the length of the mechanical splice hardware as shown in Fig. R18.9.2.2. Capacity-design techniques are used in 18.9.2.2(c) to ensure the strong connection remains elastic following formation of plastic hinges. Additional column requirements are provided to avoid hinging and strength deterioration of column-to-column connections. Strain concentrations have been observed to cause brittle fracture of reinforcing bars at the face of mechanical splices in laboratory tests of precast beam-column connections (Palmieri et al. 1996). Locations of strong connections should be selected carefully or other measures should be taken, such as debonding of reinforcing bars in highly stressed regions, to avoid strain concentrations that can result in premature fracture of reinforcement. R18.9.2 General American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 315 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 318. (a) Beam-to-beam connection (b) Beam-to-column connection (c) Beam-to-column connection (d) Column-to-footing connection Connection length h h h h Critical section Plastic hinge region h h Strong connection Critical section Plastic hinge region Connection length Connection length Strong connection Critical section Plastic hinge region h h Connection length Strong connection Critical section Plastic hinge region Strong connection Fig. R18.9.2.2²6WURQJFRQQHFWLRQH[DPSOHV R18.9.2.3 Precast frame systems not satisfying the prescrip- tive requirements of Chapter 18 have been demonstrated in experimental studies to provide satisfactory seismic perfor- mance characteristics (Stone et al. 1995; Nakaki et al. 1995). 18.9.2.3 Special moment frames constructed using precast concrete and not satisfying 18.9.2.1 or 18.9.2.2 shall satisfy (a) through (c): American Concrete Institute – Copyrighted © Material – www.concrete.org 316 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 319. ACI 374.1GH¿QHVDSURWRFROIRUHVWDEOLVKLQJDGHVLJQSURFH- dure, validated by analysis and laboratory tests, for such frames. The design procedure should identify the load path or mechanism by which the frame resists gravity and earth- TXDNHH൵HFWV7KHWHVWVVKRXOGEHFRQ¿JXUHGWRLQYHVWLJDWH critical behaviors, and the measured quantities should estab- lish upper-bound acceptance values for components of the load path, which may be in terms of limiting stresses, forces, strains, or other quantities. The design procedure used for the structure should not deviate from that used to design the test specimens, and acceptance values should not exceed values that were demonstrated by the tests to be acceptable. Materials and components used in the structure should be similar to those used in the tests. Deviations may be acceptable if the licensed design professional can demonstrate that those deviations do QRWDGYHUVHOD൵HFWWKHEHKDYLRURIWKHIUDPLQJVVWHP ACI 550.3 GH¿QHV GHVLJQ UHTXLUHPHQWV IRU RQH WSH RI special precast concrete moment frame for use in accordance with 18.9.2.3. R18.10—Special structural walls R18.10.1 Scope This section contains requirements for the dimensions and details of special structural walls and all components including coupling beams and wall piers. Wall piers are GH¿QHG LQ Chapter 2. Design provisions for vertical wall segments depend on the aspect ratio of the wall segment in the plane of the wall (hw/Ɛw), and the aspect ratio of the horizontal cross section (Ɛw/bw), and generally follow the descriptions in Table R18.10.1. The limiting aspect ratios for wall piers are based on engineering judgment. It is intended WKDWÀH[XUDOLHOGLQJRIWKHYHUWLFDOUHLQIRUFHPHQWLQWKHSLHU should limit shear demand on the pier. Table R18.10.1—Governing design provisions for vertical wall segments[1] Clear height of vertical wall segment/length of vertical wall segment, (hw/Ɛw) Length of vertical wall segment/wall thickness (Ɛw/bw) (Ɛw/bw ” 2.5 (Ɛw/bw ” (Ɛw/bw) 6.0 hwƐw 2.0 Wall Wall Wall hwƐw• Wall pier required to VDWLVIVSHFL¿HG column design requirements; refer to 18.10.8.1 Wall pier required WRVDWLVIVSHFL¿HG column design requirements or alternative requirements; refer to 18.10.8.1 Wall [1] hw is the clear height, Ɛw is the horizontal length, and bw is the width of the web of the wall segment. R18.10.2 5HLQIRUFHPHQW (a) ACI 374.1 (b) Details and materials used in the test specimens shall be representative of those used in the structure (c) The design procedure used to proportion the test speci- PHQV VKDOO GH¿QH WKH PHFKDQLVP E ZKLFK WKH IUDPH UHVLVWVJUDYLWDQGHDUWKTXDNHH൵HFWVDQGVKDOOHVWDEOLVK acceptance values for sustaining that mechanism. Portions of the mechanism that deviate from Code requirements shall be contained in the test specimens and shall be tested to determine upper bounds for acceptance values. 18.10—Special structural walls 18.10.1 Scope 18.10.1.1 This section shall apply to special structural walls, including ductile coupled walls, and all components of special structural walls including coupling beams and wall piers forming part of the seismic-force-resisting system. 18.10.1.2 Special structural walls constructed using precast concrete shall be in accordance with 18.11 in addi- tion to 18.10. 18.10.2 5HLQIRUFHPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 317 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 320. Minimum reinforcement requirements in 18.10.2.1 follow from preceding Codes. The requirement for distributed shear reinforcement is related to the intent to control the width of inclined cracks. The requirement for two layers of reinforce- ment in walls resisting substantial design shears in 18.10.2.2 is based on the observation that, under ordinary construction conditions, the probability of maintaining a single layer of reinforcement near the middle of the wall section is quite low. Furthermore, presence of reinforcement close to the surface tends to inhibit fragmentation of the concrete in the event of severe cracking during an earthquake. The require- ment for two layers of vertical reinforcement in more slender walls is to improve lateral stability of the compression zone under cyclic loads following yielding of vertical reinforce- ment in tension. R18.10.2.3 Requirements are based on provisions in Chapter 25 ZLWK PRGL¿FDWLRQV WR DGGUHVV LVVXHV VSHFL¿F to structural walls, as well as to the use of high-strength reinforcement. Because actual forces in longitudinal rein- forcement of structural walls may exceed calculated forces, reinforcement should be developed or spliced to reach the yield strength of the bar in tension. Termination of longitu- dinal (vertical) reinforcement in structural walls should be VSHFL¿HGVRWKDWEDUVH[WHQGDERYHHOHYDWLRQVZKHUHWKHDUH QRORQJHUUHTXLUHGWRUHVLVWGHVLJQÀH[XUHDQGD[LDOIRUFH extending bars ƐdDERYHWKHQH[WÀRRUOHYHOLVDSUDFWLFDO approach to achieving this requirement. A limit of 12 ft is included for cases with large story heights. Bar termina- tions should be accomplished gradually over a wall height and should not be located close to critical sections where yielding of longitudinal reinforcement is expected, which typically occurs at the base of a wall with a uniform, or nearly uniform, cross section over the building height. Strain hardening of reinforcement results in spread of plasticity away from critical sections as lateral deformations increase. Research (Aaletti et al. 2012; Hardisty et al. 2015) shows WKDWODSVSOLFHVVKRXOGEHDYRLGHGLQZDOOVZKHUHÀH[XUDO yielding is anticipated, for example at the base of walls, because they may lead to large localized strains and bar frac- tures. Figure R18.10.2.3 illustrates boundary regions where lap splices are not permitted. At locations where yielding of longitudinal reinforcement is expected, a 1.25 multiplier is applied to account for the likelihood that the actual yield strength exceeds the spec- L¿HGLHOGVWUHQJWKRIWKHEDUDVZHOODVWKHLQÀXHQFHRI strain hardening and cyclic load reversals. Where transverse reinforcement is used, development lengths for straight and hooked bars may be reduced as permitted in 25.4.2 and 25.4.3, respectively, because closely spaced transverse rein- forcement improves the performance of splices and hooks subjected to repeated inelastic demands (ACI 408.2R). 18.10.2.1 The distributed web reinforcement ratios, ȡƐ and ȡt, for structural walls shall be at least 0.0025, except that if Vu does not exceed Ȝ ′ c f Acv, ȡt shall be permitted to be reduced to the values in 11.6. Reinforcement spacing each way in structural walls shall not exceed 18 in. Reinforce- ment contributing to Vn shall be continuous and shall be distributed across the shear plane. 18.10.2.2 At least two curtains of reinforcement shall be used in a wall if Vu 2Ȝ ′ c f Acv or hw/Ɛw•, in which hw and Ɛw refer to height and length of entire wall, respectively. 18.10.2.3 Reinforcement in structural walls shall be devel- oped or spliced for fy in tension in accordance with 25.4, 25.5, and (a) through (d): (a) Except at the top of a wall, longitudinal reinforcement shall extend at least 12 ft above the point at which it is no ORQJHUUHTXLUHGWRUHVLVWÀH[XUHEXWQHHGQRWH[WHQGPRUH than ƐdDERYHWKHQH[WÀRRUOHYHO (b) At locations where yielding of longitudinal reinforce- ment is likely to occur as a result of lateral displacements, development lengths of longitudinal reinforcement shall be 1.25 times the values calculated for fy in tension. (c) Lap splices of longitudinal reinforcement within boundary regions shall not be permitted over a height equal to hsx above, and Ɛd below, critical sections where yielding of longitudinal reinforcement is likely to occur as a result of lateral displacements. The value of hsx need not exceed 20 ft. Boundary regions include those within OHQJWKVVSHFL¿HGLQ D DQGZLWKLQDOHQJWKHTXDO to the wall thickness measured beyond the intersecting region(s) of connected walls. (d) Mechanical splices of reinforcement shall conform to 18.2.7 and welded splices of reinforcement shall conform to 18.2.8. American Concrete Institute – Copyrighted © Material – www.concrete.org 318 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 321. R18.10.2.4 This provision is based on the assumption that LQHODVWLFUHVSRQVHRIWKHZDOOLVGRPLQDWHGEÀH[XUDODFWLRQ at a critical, yielding section. The wall should be propor- tioned so that the critical section occurs where intended. If there is potential for more than one critical section, it is prudent to provide the minimum boundary reinforcement at all such sections. 18.10.2.4 Walls or wall piers with hw/Ɛw • that are H൵HFWLYHOFRQWLQXRXVIURPWKHEDVHRIVWUXFWXUHWRWRSRI wall and are designed to have a single critical section for ÀH[XUH DQG D[LDO ORDGV VKDOO KDYH ORQJLWXGLQDO UHLQIRUFH- PHQWDWWKHHQGVRIDYHUWLFDOZDOOVHJPHQWWKDWVDWLV¿HV D through (c). Wall intersection boundary region y be be x y Boundary region Note: For clarity, only part of the required reinforcement is shown. (b) Section A-A (a) Elevation be Critical section for flexure and axial loads Critical section Floor slab Longitudinal bar at boundary region No splice region A A ≥ min. 20 ft. ≥ d hsx x x Fig. R18.10.2.3²:DOOERXQGDUUHJLRQVZLWKLQKHLJKWVZKHUHODSVSOLFHVDUHQRWSHUPLWWHG American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 319 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 322. The requirement for minimum longitudinal reinforce- ment in the ends of the wall is to promote the formation of ZHOOGLVWULEXWHGVHFRQGDUÀH[XUDOFUDFNVLQWKHZDOOSODVWLF hinge region to achieve the required deformation capacity during earthquakes (Lu et al. 2017; Sritharan et al. 2014). )XUWKHUPRUHVLJQL¿FDQWOKLJKHULQSODFHFRQFUHWHVWUHQJWKV than used in design calculations may be detrimental to the GLVWULEXWLRQRIFUDFNLQJ D VSHFL¿HVWKHUHTXLUHG reinforcement ratio in the end tension zones, as shown for GL൵HUHQWZDOOVHFWLRQVLQ)LJ5 The longitudinal reinforcement required by 18.10.2.4(a) should be located at a critical section where concentrated yielding of longitudinal reinforcement is expected (typically WKHEDVHRIDFDQWLOHYHUZDOO DQGPXVWFRQWLQXHWRDVX൶- cient elevation of the wall to avoid a weak section adjacent to the intended plastic hinge region. A height above or below the critical section of Mu/3Vu is used to identify the length over which yielding is expected. R18.10.3 Design forces The possibility of yielding in components of structural walls should be considered, as in the portion of a wall between two window openings, in which case the actual shear may be in excess of the shear indicated by lateral load analysis based on factored design forces. (a) Longitudinal reinforcement ratio within 0.15Ɛw from the end of a vertical wall segment, and over a width equal to the wall thickness, shall be at least ′ 6 c y f f . (b) The longitudinal reinforcement required by 18.10.2.4(a) shall extend vertically above and below the critical section at least the greater of Ɛw and Mu/3Vu. (c) No more than 50 percent of the reinforcement required by 18.10.2.4(a) shall be terminated at any one section. 18.10.2.5 Reinforcement in coupling beams shall be devel- oped for fy in tension in accordance with 25.4, 25.5, and (a) and (b): (a) If coupling beams are reinforced according to 18.6.3.1, the development length of longitudinal reinforcement shall be 1.25 times the values calculated for fy in tension. (b)Ifcouplingbeamsarereinforcedaccordingto18.10.7.4, the development length of diagonal reinforcement shall be 1.25 times the values calculated for fy in tension. 18.10.3 Design forces Fig. R18.10.2.4—/RFDWLRQVRIORQJLWXGLQDOUHLQIRUFHPHQWUHTXLUHGE D LQGLৼHUHQWFRQ¿JXUDWLRQVRIZDOOVHFWLRQV w 0.15w 0.15w 0.15w 0.15w 0.15w 0.15'w 0.15w 0.15'w 0.15'w 0.15w 'w 'w American Concrete Institute – Copyrighted © Material – www.concrete.org 320 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 323. R18.10.3.1 Design shears for structural walls are obtained from lateral load analysis with appropriate load factors LQFUHDVHGWRDFFRXQWIRU L ÀH[XUDORYHUVWUHQJWKDWFULWLFDO sections where yielding of longitudinal reinforcement is H[SHFWHGDQG LL GQDPLFDPSOL¿FDWLRQGXHWRKLJKHUPRGH H൵HFWVDVLOOXVWUDWHGLQ)LJ57KHDSSURDFKXVHG WRGHWHUPLQHWKHDPSOL¿HGVKHDUIRUFHVLVVLPLODUWRWKDWXVHG in New Zealand Standard 3101 (2006). Because Mn and Mpr GHSHQGRQD[LDOIRUFHZKLFKYDULHVIRUGL൵HUHQWORDGFRPEL- QDWLRQVDQGORDGLQJGLUHFWLRQIRUÀDQJHGDQGFRXSOHGZDOOV the condition producing the largest value of ȍv should be used. Although the value of 1.5 in 18.10.3.1.2 is greater than the minimum value obtained for the governing load combina- tion with a ࢥ factor of 0.9 and a tensile stress of at least 1.25fy in the longitudinal reinforcement, a value greater than 1.5 may be appropriate if provided longitudinal reinforcement exceeds WKDW UHTXLUHG 'QDPLF DPSOL¿FDWLRQ LV QRW VLJQL¿FDQW LQ walls with hw/Ɛw 2. A limit of 0.007hwcs is imposed on ns to account for buildings with large story heights. The application of ȍV to Vu does not preclude the application of a redundancy factor if required by the general building code. 18.10.3.1 The design shear force Ve shall be calculated by: Ve ȍvȦvVu”Vu (18.10.3.1) where Vu, ȍv, and ȦvDUHGH¿QHGLQ and 18.10.3.1.3, respectively. 18.10.3.1.1 Vu is the shear force obtained from code lateral load analysis with factored load combinations. ȍv shall be in accordance with Table 18.10.3.1.2. Table 18.10.3.1.2—Overstrength factor ȍv at critical section Condition ȍv hwcsƐw 1.5 Greater of MprMu [1] 1.5[2] hwcsƐw” 1.0 [1] )RUWKHORDGFRPELQDWLRQSURGXFLQJWKHODUJHVWYDOXHRIȍv. [2] Unless a more detailed analysis demonstrated a smaller value, but not less than 1.0. 18.10.3.1.3 For walls with hwcs/Ɛw 2.0, Ȧv shall be taken as 1.0. Otherwise, Ȧv shall be calculated as: 0.9 6 10 1.3 1.8 6 30 s v s s v s n n n n ω = + ≤ ω = + ≤ (18.10.3.1.3) where ns shall not be taken less than the quantity 0.007hwcs. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 321 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 324. 18.10.4 Shear strength 18.10.4.1 Vn shall be calculated by: ( ) n c c t yt cv V f f A = α λ + ρ ′ (18.10.4.1) where: Įc = 3 for hw/Ɛw” Įc = 2 for hw/Ɛw• It shall be permitted to linearly interpolate the value of Įc between 3 and 2 for 1.5 hw/Ɛw 2.0. 18.10.4.2 In 18.10.4.1, the value of ratio hw/Ɛw used to calculate Vn for segments of a wall shall be the greater of the ratios for the entire wall and the segment of wall considered. 18.10.4.3 Walls shall have distributed shear reinforcement in two orthogonal directions in the plane of the wall. If hw/Ɛw does not exceed 2.0, reinforcement ratio ȡƐ shall be at least the reinforcement ratio ȡt. 18.10.4.4 For all vertical wall segments sharing a common lateral force, Vn shall not be taken greater than 8 ′ c f Acv. For any one of the individual vertical wall segments, Vn shall not be taken greater than 10 ′ c f Acw, where Acw is the area of concrete section of the individual vertical wall segment considered. 18.10.4.5 For horizontal wall segments and coupling beams, Vn shall not be taken greater than 10 ′ c f Acv, where Acw is the area of concrete section of a horizontal wall segment or coupling beam. R18.10.4 Shear strength Equation (18.10.4.1) recognizes the higher shear strength of walls with high shear-to-moment ratios (Hirosawa 1977; Joint ACI-ASCE Committee 326 1962; Barda et al. 1977). The nominal shear strength is given in terms of the gross area of the section resisting shear, Acv. For a rectangular section without openings, the term Acv refers to the gross area of the cross section rather than to the product of the width and the H൵HFWLYHGHSWK A vertical wall segment refers to a part of a wall bounded horizontally by openings or by an opening and an edge. For DQLVRODWHGZDOORUDYHUWLFDOZDOOVHJPHQWȡt refers to hori- zontal reinforcement and ȡƐ refers to vertical reinforcement. The ratio hw/Ɛw may refer to overall dimensions of a wall, or of a segment of the wall bounded by two openings, or an opening and an edge. The intent of 18.10.4.2 is to make certain that any segment of a wall is not assigned a unit strength greater than that for the entire wall. However, a wall segment with a ratio of hw/Ɛw higher than that of the entire wall should be proportioned for the unit strength associated with the ratio hw/Ɛw based on the dimensions for that segment. 7R UHVWUDLQ WKH LQFOLQHG FUDFNV H൵HFWLYHO UHLQIRUFHPHQW included in ȡt and ȡƐ should be appropriately distributed along the length and height of the wall (refer to 18.10.4.3). Chord reinforcement provided near wall edges in concentrated amounts for resisting bending moment is not to be included in determining ȡt and ȡƐ. Within practical limits, shear reinforce- ment distribution should be uniform and at a small spacing. If the factored shear force at a given level in a structure is resisted by several walls or several vertical wall segments of a perforated wall, the average unit shear strength assumed for the total available cross-sectional area is limited to 8 ′ c f with the additional requirement that the unit shear strength assigned to any single vertical wall segment does not exceed 10 ′ c f . The upper limit of strength to be assigned to any Moments from load combination, Mu Amplified moments, ΩvMu (d) Moment (c) Shear (b) Wall elevation (a) Lateral forces Critical Section (CS) Mpr,CS Mu,CS Vu,CS Vu,CS Vu,CS Vu,CS Mu,CS Mu,CS Mu,CS Mpr,CS Ve,CS Ve,CS Ωv = Heff = (b) (a) L Lateral f f tical ction (CS) Vu,CS V V Vu,CS V V Vu,CS V V Mu,CS M M ,CS Vu ΣFu,i = Vu { Ve Fig. R18.10.3.1²'HWHUPLQDWLRQRIVKHDUGHPDQGIRUZDOOVZLWKhw/Ɛw• 0RHKOHHWDO American Concrete Institute – Copyrighted © Material – www.concrete.org 322 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 325. 18.10.4.6 The requirements of 21.2.4.1 shall not apply to walls or wall piers designed according to 18.10.6.2. 18.10.5 'HVLJQIRUÀH[XUHDQGD[LDOIRUFH 18.10.5.1 Structural walls and portions of such walls VXEMHFWWRFRPELQHGÀH[XUHDQGD[LDOORDGVVKDOOEHGHVLJQHG in accordance with 22.4. Concrete and developed longitu- GLQDOUHLQIRUFHPHQWZLWKLQH൵HFWLYHÀDQJHZLGWKVERXQGDU HOHPHQWV DQG WKH ZDOO ZHE VKDOO EH FRQVLGHUHG H൵HFWLYH 7KHH൵HFWVRIRSHQLQJVVKDOOEHFRQVLGHUHG 18.10.5.2 Unless a more detailed analysis is performed, H൵HFWLYHÀDQJHZLGWKVRIÀDQJHGVHFWLRQVVKDOOH[WHQGIURP the face of the web a distance equal to the lesser of one-half the distance to an adjacent wall web and 25 percent of the total wall height above the section under consideration. one member is imposed to limit the degree of redistribution of shear force. Horizontal wall segments in 18.10.4.5 refer to wall sections between two vertically aligned openings (refer WR)LJ5 ,WLVLQH൵HFWDYHUWLFDOZDOOVHJPHQW rotated through 90 degrees.Ahorizontal wall segment is also referred to as a coupling beam when the openings are aligned vertically over the building height. When designing a hori- ]RQWDOZDOOVHJPHQWRUFRXSOLQJEHDPȡt refers to vertical reinforcement and ȡƐ refers to horizontal reinforcement. Horizontal wall segment Vertical wall segment Fig. R18.10.4.5—Wall with openings. R18.10.4.6 Section 21.2.4.1 does not apply because walls GHVLJQHGDFFRUGLQJWRDUHFRQWUROOHGEÀH[XUDO LHOGLQJDQGFRGHOHYHOVKHDUIRUFHVKDYHEHHQDPSOL¿HG R18.10.5 'HVLJQIRUÀH[XUHDQGD[LDOIRUFH R18.10.5.1 Flexural strength of a wall or wall segment is determined according to procedures commonly used for columns. Strength should be determined considering the applied axial and lateral forces. Reinforcement concentrated LQERXQGDUHOHPHQWVDQGGLVWULEXWHGLQÀDQJHVDQGZHEV should be included in the strength calculations based on a strain compatibility analysis. The foundation supporting the wall should be designed to resist the wall boundary and web IRUFHV)RUZDOOVZLWKRSHQLQJVWKHLQÀXHQFHRIWKHRSHQLQJ RURSHQLQJVRQÀH[XUDODQGVKHDUVWUHQJWKVLVWREHFRQVLG- ered and a load path around the opening or openings should EHYHUL¿HGDSDFLWGHVLJQFRQFHSWVDQGWKHVWUXWDQGWLH method may be useful for this purpose (Taylor et al. 1998). R18.10.5.2 Where wall sections intersect to form L-, 7RURWKHUFURVVVHFWLRQDOVKDSHVWKHLQÀXHQFHRIWKH ÀDQJHRQWKHEHKDYLRURIWKHZDOOVKRXOGEHFRQVLGHUHGE VHOHFWLQJ DSSURSULDWH ÀDQJH ZLGWKV 7HVWV Wallace 1996) VKRZWKDWH൵HFWLYHÀDQJHZLGWKLQFUHDVHVZLWKLQFUHDVLQJ GULIWOHYHODQGWKHH൵HFWLYHQHVVRIDÀDQJHLQFRPSUHVVLRQ GL൵HUVIURPWKDWIRUDÀDQJHLQWHQVLRQ7KHYDOXHXVHGIRU WKHH൵HFWLYHFRPSUHVVLRQÀDQJHZLGWKKDVOLWWOHH൵HFWRQ American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 323 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 326. 18.10.6 %RXQGDUHOHPHQWVRIVSHFLDOVWUXFWXUDOZDOOV 18.10.6.1 The need for special boundary elements at the edges of structural walls shall be evaluated in accordance with 18.10.6.2 or 18.10.6.3. The requirements of 18.10.6.4 DQGVKDOODOVREHVDWLV¿HG 18.10.6.2 Walls or wall piers with hwcs/Ɛw• that are H൵HFWLYHOFRQWLQXRXVIURPWKHEDVHRIVWUXFWXUHWRWRSRI wall and are designed to have a single critical section for ÀH[XUHDQGD[LDOORDGVVKDOOVDWLVI D DQG E (a) Compression zones shall be reinforced with special boundary elements where 1.5 600 u w wcs h c δ ≥ A (18.10.6.2a) and c corresponds to the largest neutral axis depth calcu- lated for the factored axial force and nominal moment strength consistent with the direction of the design displacement įu. Ratio įu/hwcs shall not be taken less than 0.005. (b) If special boundary elements are required by (a), then L DQGHLWKHU LL RU LLL VKDOOEHVDWLV¿HG (i) Special boundary element transverse reinforcement shall extend vertically above and below the critical section a least the greater of Ɛw and Mu/4Vu, except as permitted in 18.10.6.4(i). (ii) ≥ 0.025A w b c (iii) įc/hwcs•įu/hwcs, where: 1 1 4 100 50 8 c w e wcs c cv V c h b b f A ⎛ ⎞ δ ⎛ ⎞ ⎛ ⎞ = − − ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ ′ ⎝ ⎠ A (18.10.6.2b) The value of įc/hwcs in Eq. (18.10.6.2b) need not be taken less than 0.015. the strength and deformation capacity of the wall; therefore, WRVLPSOLIGHVLJQDVLQJOHYDOXHRIH൵HFWLYHÀDQJHZLGWK EDVHGRQDQHVWLPDWHRIWKHH൵HFWLYHWHQVLRQÀDQJHZLGWKLV used in both tension and compression. R18.10.6 %RXQGDUHOHPHQWVRIVSHFLDOVWUXFWXUDOZDOOV R18.10.6.1 Two design approaches for evaluating detailing requirements at wall boundaries are included in 18.10.6.1. Provision 18.10.6.2 allows the use of displace- ment-based design of walls, in which the structural details are determined directly on the basis of the expected lateral displacements of the wall. The provisions of 18.10.6.3 are similar to those of the 1995 Code, and have been retained because they are conservative for assessing required trans- verse reinforcement at wall boundaries for many walls. Provisions 18.10.6.4 and 18.10.6.5 apply to structural walls designed by either 18.10.6.2 or 18.10.6.3. R18.10.6.2 This section is based on the assumption that LQHODVWLFUHVSRQVHRIWKHZDOOLVGRPLQDWHGEÀH[XUDODFWLRQ at a critical, yielding section. The wall should be propor- tioned and reinforced so that the critical section occurs where intended. Equation (18.10.6.2a) follows from a displacement- based approach (Moehle 1992; Wallace and Orakcal 2002). The approach assumes that special boundary elements are UHTXLUHG WR FRQ¿QH WKH FRQFUHWH ZKHUH WKH VWUDLQ DW WKH H[WUHPH FRPSUHVVLRQ ¿EHU RI WKH ZDOO H[FHHGV D FULWLFDO value when the wall is displaced to 1.5 times the design displacement. Consistent with a displacement-based design approach, the design displacement in Eq. (18.10.6.2a) is taken at the top of the wall, and the wall height is taken as the height above the critical section. The multiplier of 1.5 on design displacement was added to Eq. (18.10.6.2) in the 2014 Code to produce detailing requirements more consis- tent with the building code performance intent of a low prob- ability of collapse in Maximum Considered Earthquake level shaking. The lower limit of 0.005 on the quantity įu/hwcs requires special boundary elements if wall boundary longi- tudinal reinforcement tensile strain does not reach approxi- PDWHO WZLFH WKH OLPLW XVHG WR GH¿QH WHQVLRQFRQWUROOHG beam sections according to 21.2.2. The lower limit of 0.005 on the quantity įu/hwcs requires moderate wall deformation FDSDFLWIRUVWL൵EXLOGLQJV The neutral axis depth c in Eq. (18.10.6.2) is the depth calculated according to 22.2 corresponding to development RIQRPLQDOÀH[XUDOVWUHQJWKRIWKHZDOOZKHQGLVSODFHGLQ the same direction as įu. The axial load is the factored axial load that is consistent with the design load combination that produces the design displacement įu. The height of the special boundary element is based on estimates of plastic hinge length and extends beyond the zone over which yielding of tension reinforcement and spalling of concrete are likely to occur. American Concrete Institute – Copyrighted © Material – www.concrete.org 324 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 327. Equation (18.10.6.2b) is based on the mean top-of-wall drift capacity at 20 percent loss of lateral strength proposed by Abdullah and Wallace (2019). The requirement that drift capacity exceed 1.5 times the drift demand results in a low probability of strength loss for the design earthquake. The expression for b in (ii) is derived from Eq. (18.10.6.2b), assuming values of Vu/(8Acv ′ c f ) and įu/hwcs of approxi- mately 1.0 and 0.015, respectively. If b varies over c, an average or representative value of b should be used. For H[DPSOHDWWKHÀDQJHGHQGRIDZDOOb should be taken equal WRWKHH൵HFWLYHÀDQJHZLGWKGH¿QHGLQXQOHVVc extends into the web, then a weighted average should be used for b.$WWKHHQGRIDZDOOZLWKRXWDÀDQJHb should be taken equal to the wall thickness. If the drift capacity does not exceed the drift demand for a trial design, then changes to the design are required to increase wall drift capacity, reduces wall drift demand, or both, such that drift capacity exceeds drift demand for each wall in a given building. R18.10.6.3 By this procedure, the wall is considered to be acted on by gravity loads and the maximum shear and moment induced by earthquake in a given direction. Under this loading, the compressed boundary at the critical section resists the tributary gravity load plus the compressive resul- tant associated with the bending moment. Recognizing that this loading condition may be repeated many times during the strong motion, the concrete is to be FRQ¿QHGZKHUHWKHFDOFXODWHGFRPSUHVVLYHVWUHVVHVH[FHHG a nominal critical value equal to 0.2fcƍ. The stress is to be calculated for the factored forces on the section assuming linear response of the gross concrete section. The compres- sive stress of 0.2fcƍ is used as an index value and does not necessarily describe the actual state of stress that may GHYHORS DW WKH FULWLFDO VHFWLRQ XQGHU WKH LQÀXHQFH RI WKH actual inertia forces for the anticipated earthquake intensity. R18.10.6.4 The horizontal dimension of the special boundary element is intended to extend at least over the length where the concrete compressive strain exceeds the FULWLFDO YDOXH )RU ÀDQJHG ZDOO VHFWLRQV LQFOXGLQJ ER[ shapes, L-shapes, and C-shapes, the calculation to deter- mine the need for special boundary elements should include a direction of lateral load consistent with the orthogonal FRPELQDWLRQVGH¿QHGLQ$6(6(,. The value of c/2 in 18.10.6.4(a) is to provide a minimum length of the special boundary element. Good detailing practice is to arrange the ORQJLWXGLQDO UHLQIRUFHPHQW DQG WKH FRQ¿QHPHQW UHLQIRUFH- ment such that all primary longitudinal reinforcement at the wall boundary is supported by transverse reinforcement. A slenderness limit is introduced into the 2014 edition of this Code based on lateral instability failures of slender wall boundaries observed in recent earthquakes and tests (Wallace 2012; Wallace et al. 2012). For walls with large cover, where spalling of cover concrete would lead to a 18.10.6.3 Structural walls not designed in accordance with 18.10.6.2 shall have special boundary elements at bound- aries and edges around openings of structural walls where WKH PD[LPXP H[WUHPH ¿EHU FRPSUHVVLYH VWUHVV FRUUH- VSRQGLQJWRORDGFRPELQDWLRQVLQFOXGLQJHDUWKTXDNHH൵HFWV E, exceeds 0.2fcƍ. The special boundary element shall be permitted to be discontinued where the calculated compres- sive stress is less than 0.15fcƍ. Stresses shall be calculated for the factored loads using a linearly elastic model and gross VHFWLRQSURSHUWLHV)RUZDOOVZLWKÀDQJHVDQH൵HFWLYHÀDQJH width as given in 18.10.5.2 shall be used. 18.10.6.4 If special boundary elements are required by RU D WKURXJK N VKDOOEHVDWLV¿HG (a) The boundary element shall extend horizontally from WKH H[WUHPH FRPSUHVVLRQ ¿EHU D GLVWDQFH DW OHDVW WKH greater of c – 0.1Ɛw and c/2, where c is the largest neutral axis depth calculated for the factored axial force and nominal moment strength consistent with įu. E :LGWKRIWKHÀH[XUDOFRPSUHVVLRQ]RQHb, over the horizontal distance calculated by 18.10.6.4(a), including ÀDQJHLISUHVHQWVKDOOEHDWOHDVWhu/16. (c) For walls or wall piers with hw/Ɛw•WKDWDUHH൵HF- tively continuous from the base of structure to top of ZDOOGHVLJQHGWRKDYHDVLQJOHFULWLFDOVHFWLRQIRUÀH[XUH and axial loads, and with c/Ɛw•ZLGWKRIWKHÀH[- ural compression zone b over the length calculated in 18.10.6.4(a) shall be greater than or equal to 12 in. G ,QÀDQJHGVHFWLRQVWKHERXQGDUHOHPHQWVKDOOLQFOXGH WKHH൵HFWLYHÀDQJHZLGWKLQFRPSUHVVLRQDQGVKDOOH[WHQG at least 12 in. into the web. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 325 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 328. VLJQL¿FDQWO UHGXFHG VHFWLRQ LQFUHDVHG ERXQGDU HOHPHQW thickness should be considered. A value of c/Ɛw • LV XVHG WR GH¿QH D ZDOO FULWLFDO section that is not tension-controlled according to 21.2.2. A minimum wall thickness of 12 in. is imposed to reduce the likelihood of lateral instability of the compression zone after spalling of cover concrete. :KHUH ÀDQJHV DUH KLJKO VWUHVVHG LQ FRPSUHVVLRQ WKH ZHEWRÀDQJHLQWHUIDFHLVOLNHOWREHKLJKOVWUHVVHGDQG may sustain local crushing failure unless special boundary element reinforcement extends into the web. Required transverse reinforcement at wall boundaries is based on column provisions. Expression (a) of Table 18.10.6.4(g) was applied to wall special boundary elements prior to the 1999 edition of this Code. It is reinstated in the 2014 edition of this Code due to concerns that expression (b) of Table 18.10.6.4(g) by itself does not provide adequate transverse reinforcement for thin walls where concrete FRYHUDFFRXQWVIRUDVLJQL¿FDQWSRUWLRQRIWKHZDOOWKLFN- ness. For wall special boundary elements having rectangular cross section, Ag and Ach in expressions (a) and (c) in Table J DUHGH¿QHGDVAg = Ɛbeb and Ach = bc1bc2, where dimensions are shown in Fig. R18.10.6.4b. This considers that concrete spalling is likely to occur only on the exposed IDFHV RI WKH FRQ¿QHG ERXQGDU HOHPHQW 7HVWV Thomsen and Wallace 2004) show that adequate performance can be achieved using vertical spacing greater than that permitted by 18.7.5.3(a). The limits on spacing between laterally supported longitudinal bars are intended to provide more uniform spacing of hoops and crossties for thin walls. RQ¿JXUDWLRQUHTXLUHPHQWVIRUERXQGDUHOHPHQWWUDQV- verse reinforcement and crossties for web longitudinal reinforcement are summarized in Fig. R18.10.6.4a. A limit is placed on the relative lengths of boundary element hoop legs because tests (Segura and Wallace 2018; Welt et al. 2017; Arteta 2015) show that a single perimeter hoop with supplemental crossties that have alternating 90-degree and GHJUHHKRRNVDUHQRWDVH൵HFWLYHDVRYHUODSSLQJKRRSV and crossties with seismic hooks at both ends if Ɛbe exceeds approximately 2b. These tests also show that loss of axial load-carrying capacity of a wall can occur immediately following damage to the wall boundary elements if web vertical reinforcement within the plastic hinge region is not restrained. Use of web crossties outside of boundary elements also results in a less abrupt transition in transverse reinforcement used to provide FRQFUHWHFRQ¿QHPHQWDQGUHVWUDLQEXFNOLQJRIORQJLWXGLQDO reinforcement, which addresses potential increases in the neutral axis depth due to shear (diagonal compression) and uncertainties in axial load. Requirements for vertical extensions of boundary elements are summarized in Fig. R18.10.6.4c (Moehle et al. 2011). The horizontal reinforcement in a structural wall with low shear-to-moment ratio resists shear through truss action, with the horizontal bars acting like the stirrups in a beam. (e) The boundary element transverse reinforcement shall satisfy 18.7.5.2(a) through (d) and 18.7.5.3, except the transverse reinforcement spacing limit of 18.7.5.3(a) shall be one-third of the least dimension of the boundary element. The maximum vertical spacing of transverse reinforcement in the boundary element shall also not exceed that in Table 18.10.6.5(b). (f) Transverse reinforcement shall be arranged such that the spacing hx between laterally supported longitudinal bars around the perimeter of the boundary element shall not exceed the lesser of 14 in. and two-thirds of the boundary element thickness. Lateral support shall be provided by a seismic hook of a crosstie or corner of a hoop. The length of a hoop leg shall not exceed two times the boundary element thickness, and adjacent hoops shall overlap at least the lesser of 6 in. and two-thirds the boundary element thickness. (g) The amount of transverse reinforcement shall be in accordance with Table 18.10.6.4(g). Table 18.10.6.4(g)—Transverse reinforcement for special boundary elements Transverse reinforcement Applicable expressions Ashsbc for rectilinear hoop Greater of 0.3 1 g ch yt c A A f f ⎛ ⎞ − ⎜ ⎟ ′ ⎝ ⎠ (a) 0.09 yt c f f ′ (b) ȡs for spiral or circular hoop Greater of 0.45 1 g ch yt c A A f f ⎛ ⎞ − ′ ⎜ ⎟ ⎝ ⎠ (c) 0.12 yt c f f ′ (d) K RQFUHWHZLWKLQWKHWKLFNQHVVRIWKHÀRRUVVWHPDW WKHVSHFLDOERXQGDUHOHPHQWORFDWLRQVKDOOKDYHVSHFL¿HG compressive strength at least 0.7 times fcƍ of the wall. (i) For a distance above and below the critical section VSHFL¿HGLQ E ZHEYHUWLFDOUHLQIRUFHPHQWVKDOO have lateral support provided by the corner of a hoop or by a crosstie with seismic hooks at each end. Transverse reinforcement shall have a vertical spacing not to exceed 12 in. and diameter satisfying 25.7.2.2. (j) Where the critical section occurs at the wall base, the boundary element transverse reinforcement at the wall base shall extend into the support at least Ɛd, in accordance with 18.10.2.3, of the largest longitudinal reinforcement in the special boundary element. Where the special boundary element terminates on a footing, mat, or pile cap, special boundary element transverse reinforcement shall extend at least 12 in. into the footing, mat, or pile cap, unless a greater extension is required by 18.13.2.4. American Concrete Institute – Copyrighted © Material – www.concrete.org 326 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 329. Thus, the horizontal bars provided for shear reinforcement PXVWEHGHYHORSHGZLWKLQWKHFRQ¿QHGFRUHRIWKHERXQGDU element and extended as close to the end of the wall as cover requirements and proximity of other reinforcement permit. The requirement that the horizontal web reinforcement be DQFKRUHGZLWKLQWKHFRQ¿QHGFRUHRIWKHERXQGDUHOHPHQW and extended to within 6 in. from the end of the wall applies to all horizontal bars whether straight, hooked, or headed, as illustrated in Fig. R18.10.6.4c. The requirements in 18.10.2.4 apply to the minimum longitudinal reinforcement in the ends of walls, including those with special boundary elements. (k) Horizontal reinforcement in the wall web shall extend to within 6 in. of the end of the wall. Reinforcement shall be anchored to develop fyZLWKLQWKHFRQ¿QHGFRUHRIWKH boundary element using standard hooks or heads. Where WKH FRQ¿QHG ERXQGDU HOHPHQW KDV VX൶FLHQW OHQJWK WR develop the horizontal web reinforcement, and Asfy/s of the horizontal web reinforcement does not exceed Asfyt/s of the boundary element transverse reinforcement parallel to the horizontal web reinforcement, it shall be permitted to terminate the horizontal web reinforcement without a standard hook or head. b bc be 1 ≤ 2bc Horizontal web reinforcement, Av Through web crosstie Supplemental crossties Perimeter hoop Longitudinal web reinforcement (a) Perimeter hoop with supplemental 135-degree crossties and 135-degree crossties supporting distributed web longitudinal reinforcement (b) Overlapping hoops with supplemental 135-degree crossties and 135-degree crossties supporting distributed web longitudinal reinforcement be Horizontal web reinforcement, Av Through web crosstie Hoop #2 Hoop Overlap at least min. of (6 in. and 2b/3) Hoop #1 Supplemental crossties 1 ≤ 2bc 2 ≤ 2bc b bc Longitudinal web reinforcement Fig. R18.10.6.4a²RQ¿JXUDWLRQVRIERXQGDUWUDQVYHUVHUHLQIRUFHPHQWDQGZHEFURVVWLHV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 327 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 330. ≤ 6 in. ≥ dh or dt as appropriate bc1 be bc2 b ≤ 6 in. ≥ d of the horizontal web reinforcement Option with standard hooks or headed reinforcement (a) Option with straight developed reinforcement (b) Confined core Horizontal web reinforcement, Av Horizontal web reinforcement, Av Boundary element reinforcement, Ash Fig. R18.10.6.4b²'HYHORSPHQW RI ZDOO KRUL]RQWDO UHLQ- IRUFHPHQWLQFRQ¿QHGERXQGDUHOHPHQW American Concrete Institute – Copyrighted © Material – www.concrete.org 328 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 331. Ties not required Ties per 18.10.6.5 Special boundary element ≥ 12 in. ρ fy 400 ρ ≥ fy 400 Max.≥ w Mu ( ) 4Vu critical section Boundary element near edge of footing or other support Critical section per 18.10.6.2 Boundary element not near edge of footing ≥ d for 1.25fy (or hook as req’d.) (a) Wall with hw /w ≥ 2.0 and a single critical section controlled by flexure and axial load designed using 18.10.6.2, 18.10.6.4, and 18.10.6.5 Develop for fy past opening, top and bottom σ ≥ 0.2f′c Special boundary element required σ ≤ 0.2f′c ρ fy 400 Ties per 18.10.6.5 ρ ≤ σ 0.15f′c fy 400 Ties not required σ 0.15f′c ρ fy 400 Ties per 18.10.6.5 b ≥ hu 16 σ 0.2f′c Special boundary element required, See Notes. Notes: Requirement for special boundary element is triggered if maximum extreme fiber compressive stress σ ≥ 0.2f′c. Once triggered, the special boundary element extends until σ 0.15f′c. Since hw /w ≤ 2.0, 18.10.6.4(c) does not apply. (b) Wall and wall pier designed using 18.10.6.3, 18.10.6.4, and 18.10.6.5. b ≥ hu 16 If c w ≥ 3 8 then b ≥ 12 in. , ; Fig. R18.10.6.4c²6XPPDURIERXQGDUHOHPHQWUHTXLUHPHQWVIRUVSHFLDOZDOOV American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 329 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 332. R18.10.6.5 Cyclic load reversals may lead to buck- ling of boundary longitudinal reinforcement even in cases where the demands on the boundary of the wall do not require special boundary elements. For walls with moderate amounts of boundary longitudinal reinforcement, ties are required to inhibit buckling. The longitudinal reinforce- ment ratio is intended to include only the reinforcement at the wall boundary, as indicated in Fig. R18.10.6.5. A greater spacing of ties relative to 18.10.6.4(e) is allowed due to the lower deformation demands on the walls. Requirements of 18.10.6.5 apply over the entire wall height and are summa- rized in Fig. R18.10.6.4c for cases where special boundary elements are required (Moehle et al. 2011). The addition of hooks or U-stirrups at the ends of hori- zontal wall reinforcement provides anchorage so that the UHLQIRUFHPHQWZLOOEHH൵HFWLYHLQUHVLVWLQJVKHDUIRUFHV,W will also tend to inhibit the buckling of the vertical edge reinforcement. In walls with low in-plane shear, the devel- opment of horizontal reinforcement is not necessary. Limits on spacing of transverse reinforcement are intended to prevent bar buckling until reversed cyclic strains extend well into the inelastic range. To achieve similar performance capability, smaller spacing is required for higher-strength longitudinal reinforcement. h h x a x 14 boundary longitudinal bars Distributed bars Ab ρ = 14Ab h(2x + a) s Distributed bars, Ab, at equal spacing s ρ = 2Ab hs Fig. R18.10.6.5²/RQJLWXGLQDO UHLQIRUFHPHQW UDWLRV IRU typical wall boundary conditions. R18.10.7 RXSOLQJEHDPV Coupling beams connecting structural walls can provide VWL൵QHVVDQGHQHUJGLVVLSDWLRQ,QPDQFDVHVJHRPHWULF limits result in coupling beams that are deep in relation to their clear span. Deep coupling beams may be controlled by VKHDUDQGPDEHVXVFHSWLEOHWRVWUHQJWKDQGVWL൵QHVVGHWH- rioration under earthquake loading. Test results (Paulay and Binney 1974; Barney et al. 1980 KDYHVKRZQWKDWFRQ¿QHG diagonal reinforcement provides adequate resistance in deep coupling beams. 18.10.6.5 Where special boundary elements are not required ERU D DQG E VKDOOEHVDWLV¿HG (a) Except where Vu in the plane of the wall is less than Ȝ ′ c f Acv, horizontal reinforcement terminating at the edges of structural walls without boundary elements shall have a standard hook engaging the edge reinforcement or the edge reinforcement shall be enclosed in U-stirrups having the same size and spacing as, and spliced to, the horizontal reinforcement. (b) If the maximum longitudinal reinforcement ratio at the wall boundary exceeds 400/fy, boundary transverse rein- forcement shall satisfy 18.7.5.2(a) through (e) over the distance calculated in accordance with 18.10.6.4(a). The vertical spacing of transverse reinforcement at the wall boundary shall be in accordance with Table 18.10.6.5(b). Table 18.10.6.5(b)—Maximum vertical spacing of transverse reinforcement at wall boundary Grade of SULPDUÀH[XUDO reinforcing bar Transverse reinforcement required Maximum vertical spacing of transverse reinforcement[1] 60 Within the greater of Ɛw and MuVu above and below critical sections[2] Lesser of: 6db 6 in. Other locations Lesser of: 8db 8 in. 80 Within the greater of Ɛw and MuVu above and below critical sections[2] Lesser of: 5db 6 in. Other locations Lesser of: 6db 6 in. 100 Within the greater of Ɛw and MuVu above and below critical sections[2] Lesser of: 4db 6 in. Other locations Lesser of: 6db 6 in. [1] In this table, dbLVWKHGLDPHWHURIWKHVPDOOHVWSULPDUÀH[XUDOUHLQIRUFLQJEDU [2] ULWLFDOVHFWLRQVDUHGH¿QHGDVORFDWLRQVZKHUHLHOGLQJRIORQJLWXGLQDOUHLQIRUFH- ment is likely to occur as a result of lateral displacements. 18.10.7 RXSOLQJEHDPV 18.10.7.1 Coupling beams with (Ɛn/h • shall satisfy the requirements of 18.6, with the wall boundary interpreted as being a column. The provisions of 18.6.2.1(b) and (c) need QRWEHVDWLV¿HGLILWFDQEHVKRZQEDQDOVLVWKDWWKHEHDP has adequate lateral stability. 18.10.7.2 Coupling beams with (Ɛn/h) 2 and with Vu• Ȝ ′ c f Acw shall be reinforced with two intersecting groups of diagonally placed bars symmetrical about the midspan, unless it FDQEHVKRZQWKDWORVVRIVWL൵QHVVDQGVWUHQJWKRIWKHFRXSOLQJ American Concrete Institute – Copyrighted © Material – www.concrete.org 330 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 333. beams will not impair the vertical load-carrying ability of the structure, the egress from the structure, or the integrity of nonstructural components and their connections to the structure. 18.10.7.3 Coupling beams not governed by 18.10.7.1 or 18.10.7.2 shall be permitted to be reinforced either with two intersecting groups of diagonally placed bars symmetrical about the midspan or according to 18.6.3 through 18.6.5, with the wall boundary interpreted as being a column. 18.10.7.4 Coupling beams reinforced with two inter- secting groups of diagonally placed bars symmetrical about the midspan shall satisfy (a), (b), and either (c) or (d), and the requirements of 9.9QHHGQRWEHVDWLV¿HG (a) Vn shall be calculated by Vn = 2Avd fyVLQĮ” c f ′ Acw (18.10.7.4) ZKHUHĮLVWKHDQJOHEHWZHHQWKHGLDJRQDOEDUVDQGWKH longitudinal axis of the coupling beam. (b) Each group of diagonal bars shall consist of a minimum of four bars provided in two or more layers. (c) Each group of diagonal bars shall be enclosed by recti- linear transverse reinforcement having out-to-out dimen- sions of at least bw/2 in the direction parallel to bw and bw/5 along the other sides, where bw is the web width of the coupling beam. The transverse reinforcement shall be in accordance with 18.7.5.2(a) through (e), with Ash not less than the greater of (i) and (ii): (i) 0.09 c c yt sb f f ′ (ii) 0.3 1 g c ch yt c A sb f A f ⎝ ′ ⎛ ⎞ − ⎜ ⎟ ⎠ For the purpose of calculating Ag, the concrete cover in 20.5.1 shall be assumed on all four sides of each group of diagonal bars. The transverse reinforcement shall have spacing measured parallel to the diagonal bars satisfying 18.7.5.3(d) and not exceeding 6db of the smallest diagonal bars, and shall have spacing of crossties or legs of hoops measured perpendicular to the diagonal bars not exceeding 14 in. The transverse reinforcement shall continue through the intersection of the diagonal bars. At the intersection, it is permitted to modify the arrangement of the transverse reinforcement provided the spacing and volume ratio requirements are VDWLV¿HG$GGLWLRQDO ORQJLWXGLQDO DQG WUDQVYHUVH UHLQ- forcement shall be distributed around the beam perim- eter with total area in each direction of at least 0.002bws and spacing not exceeding 12 in. (d) Transverse reinforcement shall be provided for the entire beam cross section in accordance with 18.7.5.2(a) through (e) with Ash not less than the greater of (i) and (ii): Experiments show that diagonally oriented reinforcement LVH൵HFWLYHRQOLIWKHEDUVDUHSODFHGZLWKDODUJHLQFOLQD- tion. Therefore, diagonally reinforced coupling beams are restricted to beams having aspect ratio Ɛn/h 4. The 2008 edition of this Code was changed to clarify that coupling beams of intermediate aspect ratio can be reinforced according to 18.6.3 through 18.6.5. Diagonal bars should be placed approximately symmetri- cally in the beam cross section, in two or more layers. The diagonally placed bars are intended to provide the entire shear and corresponding moment strength of the beam. Designs deriving their moment strength from combinations of diagonal and longitudinal bars are not covered by these provisions. 7ZR FRQ¿QHPHQW RSWLRQV DUH GHVFULEHG $FFRUGLQJ WR 18.10.7.4(c), each diagonal element consists of a cage of longitudinal and transverse reinforcement, as shown in Fig. R18.10.7a. Each cage contains at least four diagonal EDUVDQGFRQ¿QHVDFRQFUHWHFRUH7KHUHTXLUHPHQWRQVLGH dimensions of the cage and its core is to provide adequate stability to the cross section when the bars are loaded beyond yielding. The minimum dimensions and required reinforce- ment clearances may control the wall width. Revisions were made in the 2008 Code to relax spacing of transverse UHLQIRUFHPHQW FRQ¿QLQJ WKH GLDJRQDO EDUV WR FODULI WKDW FRQ¿QHPHQWLVUHTXLUHGDWWKHLQWHUVHFWLRQRIWKHGLDJRQDOV and to simplify design of the longitudinal and transverse reinforcement around the beam perimeter; beams with these new details are expected to perform acceptably. The expres- sions for transverse reinforcement Ash are based on ensuring compression capacity of an equivalent column section is maintained after spalling of cover concrete. Section 18.10.7.4(d) describes a second option for FRQ¿QHPHQWRIWKHGLDJRQDOVLQWURGXFHGLQWKHRGH UHIHUWR)LJ5E 7KLVVHFRQGRSWLRQLVWRFRQ¿QH WKHHQWLUHEHDPFURVVVHFWLRQLQVWHDGRIFRQ¿QLQJWKHLQGL- YLGXDOGLDJRQDOV7KLVRSWLRQFDQFRQVLGHUDEOVLPSOLI¿HOG placement of hoops, which can otherwise be especially chal- lenging where diagonal bars intersect each other or enter the wall boundary. For coupling beams not used as part of the lateral-force- resisting system, the requirements for diagonal reinforce- ment may be waived. Test results (Barney et al. 1980) demonstrate that beams reinforced as described in 18.10.7 have adequate ductility at shear forces exceeding 10 ′ c f bwd. Consequently, the use of a limit of 10 ′ c f Acw provides an acceptable upper limit. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 331 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 334. (i) 0.09 c c yt sb f f ′ (ii) 0.3 1 g c ch yt c A sb f A f ⎝ ′ ⎛ ⎞ − ⎜ ⎟ ⎠ Longitudinal spacing of transverse reinforcement shall not exceed the lesser of 6 in. and 6db of the smallest diagonal bars. Spacing of crossties or legs of hoops both vertically and horizontally in the plane of the beam cross section shall not exceed 8 in. Each crosstie and each hoop leg shall engage a longitudinal bar of equal RUJUHDWHUGLDPHWHU,WVKDOOEHSHUPLWWHGWRFRQ¿JXUH KRRSVDVVSHFL¿HGLQ h α Line of symmetry A A n Wall boundary reinforcement Avd = total area of reinforcement in each group of diagonal bars Horizontal beam reinforcement at wall does not develop fy Note: For clarity, only part of the required reinforcement is shown on each side of the line of symmetry. Elevation Transverse reinforcement spacing measured perpendicular to the axis of the diagonal bars not to exceed 14 in. ≥ bw /2 bw Section A-A db Transverse reinforcement spacing measured perpendicular to the axis of the diagonal bars not to exceed 14 in. Fig. R18.10.7a²RQ¿QHPHQWRILQGLYLGXDOGLDJRQDOVLQFRXSOLQJEHDPVZLWKGLDJRQDOORULHQWHGUHLQIRUFHPHQW:DOOERXQGDU UHLQIRUFHPHQWVKRZQRQRQHVLGHRQOIRUFODULW American Concrete Institute – Copyrighted © Material – www.concrete.org 332 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 335. R18.10.8 Wall piers Door and window placements in structural walls some- times lead to narrow vertical wall segments that are consid- HUHGWREHZDOOSLHUV7KHGLPHQVLRQVGH¿QLQJZDOOSLHUVDUH given in Chapter 2. Shear failures of wall piers have been observed in previous earthquakes. The intent of this section LVWRSURYLGHVX൶FLHQWVKHDUVWUHQJWKWRZDOOSLHUVVXFKWKDW LQHODVWLFUHVSRQVHLILWRFFXUVZLOOEHSULPDULOLQÀH[XUH The provisions apply to wall piers designated as part of the seismic-force-resisting system. Provisions for wall piers not designated as part of the seismic-force-resisting system are JLYHQLQ7KHH൵HFWRIDOOYHUWLFDOZDOOVHJPHQWVRQWKH 18.10.8 Wall piers 18.10.8.1 Wall piers shall satisfy the special moment frame requirements for columns of 18.7.4, 18.7.5, and 18.7.6, with joint faces taken as the top and bottom of the clear height of the wall pier.Alternatively, wall piers with (Ɛw/bw) 2.5 shall satisfy (a) through (f): (a) Design shear force shall be calculated in accordance with 18.7.6.1 with joint faces taken as the top and bottom of the clear height of the wall pier. If the general building code includes provisions to account for overstrength of the seismic-force-resisting system, the design shear force h α Line of symmetry B B n Wall boundary reinforcement Avd = total area of reinforcement in each group of diagonal bars Horizontal beam reinforcement at wall does not develop fy Note: For clarity, only part of the required reinforcement is shown on each side of the line of symmetry. Elevation db Transverse reinforcement spacing not to exceed 8 in. Section B-B Transverse reinforcement spacing not to exceed 8 in. Note: Consecutive crossties engaging the same longitudinal bar have their 90-degree hooks on opposite sides of beam. Spacing not exceeding smaller of 6 in. and 6db Fig. R18.10.7b²)XOOFRQ¿QHPHQWRIGLDJRQDOOUHLQIRUFHGFRQFUHWHEHDPVHFWLRQLQFRXSOLQJEHDPVZLWKGLDJRQDOORULHQWHG UHLQIRUFHPHQW:DOOERXQGDUUHLQIRUFHPHQWVKRZQRQRQHVLGHRQOIRUFODULW American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 333 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 336. response of the structural system, whether designated as part of the seismic-force-resisting system or not, should be consid- ered as required by 18.2.2. Wall piers having (Ɛw/bw ” behave essentially as columns. Provision 18.10.8.1 requires that such members satisfy reinforcement and shear strength requirements of 18.7.4 through 18.7.6. Alternative provi- sions are provided for wall piers having (Ɛw/bw) 2.5. The design shear force determined according to 18.7.6.1 may be unrealistically large in some cases. As an alternative, 18.10.8.1(a) permits the design shear force to be determined using factored load combinations in which the earthquake H൵HFWKDVEHHQDPSOL¿HGWRDFFRXQWIRUVVWHPRYHUVWUHQJWK Documents such as the NEHRP provisions (FEMA P749), $6(6(, , and the 2018 IBC UHSUHVHQW WKH DPSOL¿HG HDUWKTXDNHH൵HFWXVLQJWKHIDFWRUȍo. Section 18.10.8.2 addresses wall piers at the edge of a wall. Under in-plane shear, inclined cracks can propagate into segments of the wall directly above and below the ZDOO SLHU 8QOHVV WKHUH LV VX൶FLHQW UHLQIRUFHPHQW LQ WKH adjacent wall segments, shear failure within the adjacent wall segments can occur. The length of embedment of the provided reinforcement into the adjacent wall segments should be determined considering both development length requirements and shear strength of the wall segments (refer to Fig. R18.10.8). need not exceed ȍo times the factored shear calculated by DQDOVLVRIWKHVWUXFWXUHIRUHDUWKTXDNHORDGH൵HFWV (b) Vn and distributed shear reinforcement shall satisfy 18.10.4. (c) Transverse reinforcement shall be hoops except it shall be permitted to use single-leg horizontal reinforcement parallel to Ɛw where only one curtain of distributed shear reinforcement is provided. Single-leg horizontal rein- forcement shall have 180-degree bends at each end that engage wall pier boundary longitudinal reinforcement. (d) Vertical spacing of transverse reinforcement shall not exceed 6 in. (e) Transverse reinforcement shall extend at least 12 in. above and below the clear height of the wall pier. (f) Special boundary elements shall be provided if required by 18.10.6.3. 18.10.8.2 For wall piers at the edge of a wall, horizontal reinforcement shall be provided in adjacent wall segments above and below the wall pier and be designed to transfer the design shear force from the wall pier into the adjacent wall segments. American Concrete Institute – Copyrighted © Material – www.concrete.org 334 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 337. Direction of earthquake forces Direction of earthquake forces Required horizontal reinforcement Edge of wall hw for wall pier w for wall pier Wall pier Edge of wall Wall pier Required horizontal reinforcement hw for wall pier w for wall pier Fig. R18.10.8²5HTXLUHGKRUL]RQWDOUHLQIRUFHPHQWLQZDOO VHJPHQWVDERYHDQGEHORZZDOOSLHUVDWWKHHGJHRIDZDOO R18.10.9 Ductile coupled walls The aspect ratio limits and development length require- ments for ductile coupled walls are intended to induce an energy dissipation mechanism associated with inelastic GHIRUPDWLRQUHYHUVDORIFRXSOLQJEHDPV:DOOVWL൵QHVVDQG VWUHQJWKDWHDFKHQGRIFRXSOLQJEHDPVVKRXOGEHVX൶FLHQW to develop this intended behavior. 18.10.9 Ductile coupled walls 18.10.9.1 Ductile coupled walls shall satisfy the require- ments of this section. 18.10.9.2 Individual walls shall satisfy hwcs/Ɛw• and the applicable provisions of 18.10 for special structural walls. 18.10.9.3 Coupling beams shall satisfy 18.10.7 and (a) through (c) in the direction considered. (a) Coupling beams shall have Ɛn/h• at all levels of the building. E $OOFRXSOLQJEHDPVDWDÀRRUOHYHOVKDOOKDYHƐn/h” in at least 90 percent of the levels of the building. F 7KHUHTXLUHPHQWVRIVKDOOEHVDWLV¿HGDWERWK ends of all coupling beams. American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 335 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 338. 18.10.10 Construction joints 18.10.10.1 Construction joints in structural walls shall be VSHFL¿HGDFFRUGLQJWR26.5.6, and contact surfaces shall be roughened consistent with condition (b) of Table 22.9.4.2. 18.10.11 Discontinuous walls 18.10.11.1 Columns supporting discontinuous structural walls shall be reinforced in accordance with 18.7.5.6. 18.11—Special structural walls constructed using precast concrete 18.11.1 Scope 18.11.1.1 This section shall apply to special structural walls constructed using precast concrete forming part of the seismic-force-resisting system. 18.11.2 General 18.11.2.1 Special structural walls constructed using precast concrete shall satisfy 18.10 and 18.5.2, except 18.10.2.4 shall not apply for precast walls where deforma- tion demands are concentrated at the panel joints. 18.11.2.2 Special structural walls constructed using precast concrete and unbonded post-tensioning tendons and not satisfying the requirements of 18.11.2.1 are permitted provided they satisfy the requirements of ACI ITG-5.1. 18.12—Diaphragms and trusses 18.12.1 Scope 18.12.1.1 This section shall apply to diaphragms and collectors forming part of the seismic-force-resisting system in structures assigned to SDC D, E, or F and to SDC C if 18.12.1.2 applies. 18.12.1.2 Section 18.12.11 shall apply to diaphragms constructed using precast concrete members and forming part of the seismic-force-resisting system for structures assigned to SDC C, D, E, or F. R18.11—Special structural walls constructed using precast concrete R18.11.2 General R18.11.2.2 Experimental and analytical studies (Priestley et al. 1999; Perez et al. 2003; Restrepo 2002) have demon- strated that some types of precast structural walls post- tensioned with unbonded tendons, and not satisfying the prescriptive requirements of Chapter 18, provide satisfactory seismic performance characteristics. ACI ITG-5.1GH¿QHVD protocol for establishing a design procedure, validated by analysis and laboratory tests, for such walls, with or without coupling beams. ACI ITG-5.2GH¿QHVGHVLJQUHTXLUHPHQWVIRURQHWSHRI special structural wall constructed using precast concrete and unbonded post-tensioning tendons, and validated for use in accordance with 18.11.2.2. R18.12—Diaphragms and trusses R18.12.1 Scope Diaphragms as used in building construction are structural HOHPHQWV VXFKDVDÀRRURUURRI WKDWSURYLGHVRPHRUDOORI the following functions: (a) Support for building elements (such as walls, parti- tions, and cladding) resisting horizontal forces but not acting as part of the seismic-force-resisting system (b) Transfer of lateral forces from the point of applica- tion to the vertical elements of the seismic-force-resisting system (c) Connection of various components of the vertical seismic-force-resisting system with appropriate strength, American Concrete Institute – Copyrighted © Material – www.concrete.org 336 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 339. 18.12.1.3 Section 18.12.12 shall apply to structural trusses forming part of the seismic-force-resisting system in struc- tures assigned to SDC D, E, or F. 18.12.2 Design forces 18.12.2.1 The earthquake design forces for diaphragms shall be obtained from the general building code using the applicable provisions and load combinations. 18.12.3 6HLVPLFORDGSDWK 18.12.3.1 All diaphragms and their connections shall be designed and detailed to provide for transfer of forces to collector elements and to the vertical elements of the seismic-force-resisting system. 18.12.3.2 Elements of a structural diaphragm system that are subjected primarily to axial forces and used to transfer VWL൵QHVVDQGGXFWLOLWVRWKHEXLOGLQJUHVSRQGVDVLQWHQGHG in the design (Wyllie 1987). R18.12.2 Design forces R18.12.2.1 In the general building code, earthquake GHVLJQ IRUFHV IRU ÀRRU DQG URRI GLDSKUDJPV WSLFDOO DUH not calculated directly during the lateral-force analysis that provides story forces and story shears. Instead, diaphragm design forces at each level are calculated by a formula WKDWDPSOL¿HVWKHVWRUIRUFHVUHFRJQL]LQJGQDPLFH൵HFWV and includes minimum and maximum limits. These forces are used with the governing load combinations to design diaphragms for shear and moment. For collector elements, the general building code in the 8QLWHG 6WDWHV VSHFL¿HV ORDG FRPELQDWLRQV WKDW DPSOLI earthquake forces by a factor ȍo 7KH IRUFHV DPSOL¿HG by ȍo are also used for the local diaphragm shear forces resulting from the transfer of collector forces, and for local GLDSKUDJPÀH[XUDOPRPHQWVUHVXOWLQJIURPDQHFFHQWULFLW RI FROOHFWRU IRUFHV 7KH VSHFL¿F UHTXLUHPHQWV IRU HDUWK- quake design forces for diaphragms and collectors depend on which edition of the general building code is used. The requirements may also vary according to the SDC. For most concrete buildings subjected to inelastic earth- quake demands, it is desirable to limit inelastic behavior of ÀRRU DQG URRI GLDSKUDJPV XQGHU WKH LPSRVHG HDUWKTXDNH forces and deformations. It is preferable for inelastic behavior to occur only in the intended locations of the vertical seismic- force-resisting system that are detailed for ductile response, such as in beam plastic hinges of special moment frames, or LQÀH[XUDOSODVWLFKLQJHVDWWKHEDVHRIVWUXFWXUDOZDOOVRULQ coupling beams. For buildings without long diaphragm spans between lateral-force-resisting elements, elastic diaphragm EHKDYLRU LV WSLFDOO QRW GL൶FXOW WR DFKLHYH )RU EXLOGLQJV ZKHUHGLDSKUDJPVFRXOGUHDFKWKHLUÀH[XUDORUVKHDUVWUHQJWK before yielding occurs in the vertical seismic-force-resisting system, the licensed design professional should consider providing increased diaphragm strength. For reinforced concrete diaphragms, $6(6(, Sections 12.10.1 and 12.10.2 provide requirements to determine design forces for reinforced concrete diaphragms. For precast concrete diaphragms in buildings assigned to SDC C, D, E, or F, the provisions of $6(6(, Section 12.10.3 apply. R18.12.3 6HLVPLFORDGSDWK R18.12.3.2 This provision applies to strut-like elements that occur around openings, diaphragm edges, or other American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 337 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 340. GLDSKUDJPVKHDURUÀH[XUDOIRUFHVDURXQGRSHQLQJVRURWKHU discontinuities shall satisfy the requirements for collectors in 18.12.7.6 and 18.12.7.7. 18.12.4 DVWLQSODFHFRPSRVLWHWRSSLQJVODEGLDSKUDJPV 18.12.4.1 A cast-in-place composite topping slab on D SUHFDVW ÀRRU RU URRI VKDOO EH SHUPLWWHG DV D VWUXFWXUDO diaphragm, provided the cast-in-place topping slab is rein- forced and the surface of the previously hardened concrete on which the topping slab is placed is clean, free of laitance, and intentionally roughened. 18.12.5 DVWLQSODFH QRQFRPSRVLWH WRSSLQJ VODE GLDSKUDJPV 18.12.5.1Acast-in-place noncomposite topping on a precast ÀRRU RU URRI VKDOO EH SHUPLWWHG DV D VWUXFWXUDO GLDSKUDJP provided the cast-in-place topping slab acting alone is designed and detailed to resist the design earthquake forces. 18.12.6 0LQLPXPWKLFNQHVVRIGLDSKUDJPV 18.12.6.1 Concrete slabs and composite topping slabs serving as diaphragms used to transmit earthquake forces shall be at least 2 in. thick. Topping slabs placed over precast discontinuities in diaphragms. Figure R18.12.3.2 shows an example. Such elements can be subjected to earthquake axial forces in combination with bending and shear from earthquake or gravity loads. A A Section A-A Wall Diaphragm opening Diaphragm Fig. R18.12.3.2²([DPSOH RI GLDSKUDJP VXEMHFW WR WKH UHTXLUHPHQWVRIDQGVKRZLQJDQHOHPHQWKDYLQJ FRQ¿QHPHQWDVUHTXLUHGE R18.12.4 DVWLQSODFHFRPSRVLWHWRSSLQJVODEGLDSKUDJPV R18.12.4.1 A bonded topping slab is required so that WKHÀRRURUURRIVVWHPFDQSURYLGHUHVWUDLQWDJDLQVWVODE buckling. Reinforcement is required to ensure the continuity of the shear transfer across precast joints. The connection requirements are introduced to promote a complete system with necessary shear transfers. R18.12.5 DVWLQSODFH QRQFRPSRVLWH WRSSLQJ VODE GLDSKUDJPV R18.12.5.1 Composite action between the topping slab DQGWKHSUHFDVWÀRRUHOHPHQWVLVQRWUHTXLUHGSURYLGHGWKDW the topping slab is designed to resist the design earthquake forces. R18.12.6 0LQLPXPWKLFNQHVVRIGLDSKUDJPV R18.12.6.1 The minimum thickness of concrete GLDSKUDJPV UHÀHFWV FXUUHQW SUDFWLFH LQ MRLVW DQG ZD൷H VVWHPVDQGFRPSRVLWHWRSSLQJVODEVRQSUHFDVWÀRRUDQG American Concrete Institute – Copyrighted © Material – www.concrete.org 338 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE CODE COMMENTARY Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 341. ÀRRURUURRIHOHPHQWVDFWLQJDVGLDSKUDJPVDQGQRWUHOLQJ on composite action with the precast elements to resist the GHVLJQHDUWKTXDNHIRUFHVVKDOOEHDWOHDVWLQWKLFN 18.12.7 5HLQIRUFHPHQW 18.12.7.1 The minimum reinforcement ratio for diaphragms shall be in conformance with 24.4. Except for post-tensioned slabs, reinforcement spacing each way in ÀRRURUURRIVVWHPVVKDOOQRWH[FHHGLQ:KHUHZHOGHG wire reinforcement is used as the distributed reinforcement WR UHVLVW VKHDU LQ WRSSLQJ VODEV SODFHG RYHU SUHFDVW ÀRRU and roof elements, the wires parallel to the joints between the precast elements shall be spaced not less than 10 in. on center. Reinforcement provided for shear strength shall be continuous and shall be distributed uniformly across the shear plane. 18.12.7.2 Bonded tendons used as reinforcement to resist FROOHFWRUIRUFHVGLDSKUDJPVKHDURUÀH[XUDOWHQVLRQVKDOOEH designed such that the stress due to design earthquake forces does not exceed 60,000 psi. Precompression from unbonded tendons shall be permitted to resist diaphragm design forces if a seismic load path is provided. 18.12.7.3 All reinforcement used to resist collector forces, GLDSKUDJPVKHDURUÀH[XUDOWHQVLRQVKDOOEHGHYHORSHGRU spliced for fy in tension. 18.12.7.4 Type 2 splices are required where mechanical splices on Grade 60 reinforcement are used to transfer forces between the diaphragm and the vertical elements of the seismic-force-resisting system. Grade 80 and Grade 100 reinforcement shall not be mechanically spliced for this application. 18.12.7.5 Longitudinal reinforcement for collectors shall be proportioned such that the average tensile stress over length (a) or (b) does not exceed ࢥfy where the value of fy is limited to 60,000 psi. roof systems. Thicker slabs are required if the topping slab is not designed to act compositely with the precast system to resist the design earthquake forces. R18.12.7 5HLQIRUFHPHQW R18.12.7.1 Minimum reinforcement ratios for diaphragms correspond to the required amount of temperature and shrinkage reinforcement (refer to 24.4). The maximum spacing for reinforcement is intended to control the width of inclined cracks. Minimum average prestress requirements (refer to 24.4.4.1) are considered to be adequate to limit the FUDFNZLGWKVLQSRVWWHQVLRQHGÀRRUVVWHPVWKHUHIRUHWKH maximum spacing requirements do not apply to these systems. The minimum spacing requirement for welded wire rein- IRUFHPHQWLQWRSSLQJVODEVRQSUHFDVWÀRRUVVWHPVLVWRDYRLG fracture of the distributed reinforcement during an earth- quake. Cracks in the topping slab open immediately above the ERXQGDUEHWZHHQWKHÀDQJHVRIDGMDFHQWSUHFDVWPHPEHUVDQG the wires crossing those cracks are restrained by the transverse wires (Wood et al. 2000). Therefore, all the deformation associ- ated with cracking should be accommodated in a distance not greater than the spacing of the transverse wires. A minimum spacing of 10 in. for the transverse wires is required to reduce the likelihood of fracture of the wires crossing the critical cracks during a design earthquake. The minimum spacing require- ments do not apply to diaphragms reinforced with individual bars, because strains are distributed over a longer length. R18.12.7.3 Bar development and lap splices are designed according to requirements of Chapter 25 for reinforcement in tension. Reductions in development or splice length for calculated stresses less than fy are not permitted, as indicated in 25.4.10.2. R18.12.7.5 Table 20.2.2.4(a) permits the maximum design yield strength to be 80,000 psi for portions of a collector, for example, at and near critical sections. The average stress in the collector is limited to control diaphragm cracking over the length of the collector. The calculation of average stress along the length is not necessary if the collector is American Concrete Institute – Copyrighted © Material – www.concrete.org PART 5: EARTHQUAKE RESISTANCE 339 CODE COMMENTARY 18 Seismic Frs|uljkwhg#pdwhuldo#olfhqvhg#wr#Xqlyhuvlw|#ri#Wrurqwr#e|#Fodulydwh#Dqdo|wlfv#+XV,#OOF/#vxevfulswlrqv1whfkvwuhhw1frp/#grzqordghg#rq#534038064#49=3;=64#.3333#e|##Xqlyhuvlw|#ri#Wrurqwr#Xvhu1 #Qr#ixuwkhu#uhsurgxfwlrq#ru#glvwulexwlrq#lv#shuplwwhg1
- 342. (a) Length between the end of a collector and location at which transfer of load to a vertical element begins (b) Length between two vertical elements 18.12.7.6 Collector elements with compressive stresses exceeding 0.2fcƍ at any section shall have transverse rein- forcement satisfying 18.7.5.2(a) through (e) and 18.7.5.3, except the spacing limit of 18.7.5.3(a) shall be one-third of the least dimension of the collector. The amount of transverse reinforcement shall be in accordance with Table 18.12.7.6. 7KH VSHFL¿HG WUDQVYHUVH UHLQIRUFHPHQW LV SHUPLWWHG WR EH discontinued at a section where the calculated compressive stress is less than 0.15fcƍ. ,IGHVLJQIRUFHVKDYHEHHQDPSOL¿HGWRDFFRXQWIRUWKH overstrength of the vertical elements of the seismic-force- resisting system, the limit of 0.2fcƍ shall be increased to 0.5fcƍ, and the limit of 0.15fcƍ shall be increased to 0.4fcƍ. Table 18.12.7.6—Transverse reinforcement for collector elements Transverse reinforcement Applicable expressions Ashsbc for rectilinear hoop 0.09 yt c f f ′ (a) ȡs for spiral or circular hoop Greater of: 0.45 1 g ch yt c A A f f ⎛ ⎞ − ′ ⎜ ⎟ ⎝ ⎠ (b) 0.12 yt c f f ′ (c) 18.12.7.7 Longitudinal reinforcement detailing for collector elements at splices and anchorage zones shall satisfy (a) or (b): (a) Center-to-center spacing of at least three longitudinal EDU GLDPHWHUV EXW QRW OHVV WKDQ LQ DQG FRQFUHWH clear cover of at least two and one-half longitudinal bar diameters, but not less than 2 in. (b) Area of transverse reinforcement, providing Av at least the greater of ′ 0.75 c w yt f b s f and 50bws/fyt, except as required in 18.12.7.6 18.12.8 )OH[XUDOVWUHQJWK 18.12.8.1 Diaphragms and portions of diaphragms shall EHGHVLJQHGIRUÀH[XUHLQDFFRUGDQFHZLWKChapter 12. The H൵HFWVRIRSHQLQJVVKDOOEHFRQVLGHUHG designed for fy of 60,000 psi even if Grade 80 reinforcement LVVSHFL¿HG R18.12.7.6 In documents such as the NEHRP Provi- sions (FEMA P750), $6(6(,, the 2018 IBC, and the Uniform Building Code (ICBO 1997), collector elements RIGLDSKUDJPVDUHGHVLJQHGIRUIRUFHVDPSOL¿HGEDIDFWRU ȍo to account for the overstrength in the vertical elements RI WKH VHLVPLFIRUFHUHVLVWLQJ VVWHPV 7KH DPSOL¿FDWLRQ factor ȍo ranges between 2 and 3 for most concrete struc- tures, depending on the document selected and on the type of seismic-force-resisting system. In some documents, the factor can be calculated based on the maximum forces that can be developed by the elements of the vertical seismic- force-resisting system. Compressive stress calculated for the factored forces on a linearly elastic model based on gross section of the structural diaphragm is used as an index value to determine whether FRQ¿QLQJUHLQIRUFHPHQWLVUHTXLUHG$FDOFXODWHGFRPSUHV- sive stress of 0.2fcƍ, or 0.5fcƍ IRU IRUFHV DPSOL¿HG E ȍo, is assumed to indicate that integrity of the entire structure depends on the ability of that member to resist substan- tial compressive force under severe cyclic loading. Trans- verse reinforcement is required at such locations to provide FRQ¿QHPHQWIRUWKHFRQFUHWHDQGWKHUHLQIRUFHPHQW R18.12.7.7 This sect