PPT Unit-1 DS-III.pdf

RCE -701
DESIGN OF STRUCTURE – III
Sem:- VII (CE)
1

Syllabus
UNIT ‐ I : Introduction:
Introduction to steel structures. Advantages and
Disadvantages of Steel as a Structural Material.
Stress‐Strain Curve for Mild Steel, Rolled Steel Sections,
Convention for Member Axes, Loads, Dead Load, Live
Loads, Environmental Loads, Seismic Forces, Snow and
Rain Loads, Erection Loads, Basis for Design, Design
Philosophies, Local Buckling of Plate Elements.
Introduction to Limit State Design Limit States of
Strength, Limit States of Serviceability, Actions (Loads),
Probabilistic Basis for Design.
2

UNIT ‐ II : Connections:
Introduction to Riveted, Bolted and Pinned Connections, Riveted
Connections, Patterns of Riveted Joints, Bolted Connections, Types of
Bolts, Types of Bolted Joints, Load Transfer Mechanism, Failure of Bolted
Joints, Specification for Bolted Joints, Bearing‐Type Connections, Prying
Action, Tensile Strength of Plate, Efficiency of the Joint, Combined Shear
and Tension, Slip‐Critical Connections, Combined Shear and Tension for
Slip‐Critical Connections, Working Load Design, Design of eccentric
bolted connections . Simple Welded Connections, Types, Symbols,
Welding Process, Weld Defects, Inspection of Welds, Assumptions in the
Analysis of Welded Joints, Design of Groove Welds, Design of Fillet
Welds, Fillet Weld Applied to the Edge of A Plate Or Section, Fillet Weld
for Truss Members, Design of Intermittent Fillet Welds, Plug and Slot
Welds, Stresses Due To Individual Forces, Combination of Stresses,
Failure of Welds, Distortion of Welded Parts, Fillet Weld Vs Butt Weld,
Welded Jointed Vs Bolted and Riveted Joints, Design of eccentric welded
connections.
3

UNIT – III : Tension Members
Introduction to Tension Members, Types of Tension
Members, Net Sectional Area, Effective Net Area, Types of
Failure, Design Strength of Tension Members, Slenderness
Ratio (λ), Displacement, Design of Tension Member, Lug
Angles, Splices, Gusset Plate.
UNIT – IV :Compression Members
Introduction to Compression Members, Effective Length,
Slenderness Ratio (λ), Types of Sections, Types of Buckling,
Classification of Cross Sections, Column Formula, Design
Strength, Design of Axially Loaded Compression Members,
Built‐Up Columns (Latticed Columns), Lacing, Batten,
Compression Member Composed of Two Components
Back‐to‐Back, Splices, Design of Column Bases.
4

UNIT – V : Flexural Members
Introduction to Beams, Types of Sections, Behaviour of
Beam in Flexure, Section Classification, Lateral Stability of
Beams, Lateral‐Torsional Buckling, Bending Strength of
Beams, Laterally Supported Beams, Laterally
Unsupported Beams, Shear Strength of Beams, Web
Buckling, Bearing Strength, Web Crippling, Deflection,
Design Procedure of Rolled Beams, Built‐Up Beams
(Plated Beams), Purlins, Beam Bearing Plates, Effect of
Holes in Beam, Introduction to Plate Girder , Introduction
to Gantry Girder.
5

Text Books
Design of Steel Structures
Dr. Subramanian Narayanan - Oxford Publication
Limit State Design of Steel Structures
S. K. Duggal –Tata McGraw Hill
6

References Books
Design of Steel Structures
by Elias G. Abu-Saba
– CBS Publishers and Distributors
Design of steel structures
by E.H. Gaylord, C.N. Gaylord
& J.E. Stallmeyer – McGraw Hill.
Structural Steel work: Analysis and Design
by S. S. Ray – Blackwell Science
7

Codes
▪ Code of practice for general construction in
steel → IS: 800 - 2007
▪ Handbook for structural engineers
→ SP: 6(1) – 1964 (Reaffirmed 2003)
▪ IS 808 : 1989 (Reaffirmed 2004)
▪ Steel Tables of any standard publication.
▪ Code of practice for design loads (other than
earthquake) for buildings and structures
→ IS 875 : Part I to V : 1987
▪ IRC for vehicle load etc. in Bridge structures
8

Introduction
◼ Steel has made possible some of the grandest structures both in
the past and in the present days
▪ Structural steel is widely used in making:
◼ Transmission towers
◼ Industrial buildings
◼ Bridges
◼ Storage structures
◼ Water tanks
9

Anatomy
➢Beams
➢Columns
➢Floors
➢Bracing
➢Systems
➢Foundation
➢Connections
10

Indian Standard Junior Beam (ISJB) – JB
Indian Standard Light Beam (ISLB) – LB
Indian Standard Medium Weight Beam (ISMB)– MB
Indian Standard Wide Flange Beam (ISWB) – WB
Indian Standard Heavy Weight Beam (ISHB)– HB
Indian Standard column section (ISSC) – SC
ROLLED STEEL SECTIONS
11

ROLLED STEELSECTIONS
I-Section
12

Indian Standard Junior Channel (ISJC) – JC
Indian Standard Light Channel (ISLC) – LC
Indian Standard Medium Weight (ISMC) – MC
Indian Standard parallel flange Channel (ISMCP)-MCP
Channel – Sections
12
13

Indian Standard Equal Angel (ISA)
Indian Standard Unequal Angel (ISA)
Angle – Sections
14

Indian Standard Normal Tee Bars (ISNT) – ISNT– NT
Indian Standard Deep Tee Bars (ISDT) – ISDT – DT
Indian Standard Light Tee Bars (ISLT) –ISLT – LT
Indian Standard Medium Tee Bars (ISNT) –ISMT – MT
Indian Standard Heavy Tee Bars (ISHT) –ISHT – HT
Tee – Sections
16

Rolled Steel Bar Section
Indian Standard Round Section-ISRO
Indian Standard Square Section-ISSQ
17

Rolled Steel Sections are designated as follows
ISRO100 means a round section of diameter 100mm,
while ISSQ50 means a square section each side of
which is 50mm.
100mm 50mm
18

Rolled Steel sheets & strip
Indian Standard Steel Sheet Section- ISSH-SH
Indian Standard Steel Strip Section- ISST-ST
Rolled steel flats are designated by width of
the section in mm followed by the letter F &
thickness. Thus, 50 F 8 means a flat of
width 50 mm & thickness of 8 mm.
19

Hollow section pipe
20
Square hollow section

• Better quality control
• Lighter
• Faster to erect
• Reduced site time - Fast track Construction
• Large column free space and amenable for alteration
• Less material handling at site
• Less percentage of floor area occupied by structural
elements
• Has better ductility and hence superior lateral load
behavior; better earthquake resistance
Advantages of steel design
21

• Skilled labor is required.
• Higher cost of construction
• Maintenance cost is high.
• Poor fireproofing, as at 1000oF (538oC) 65% & at
1600oF (871oC) 15% of strength remains
• Electricity may be required.
Disadvantages of steel design
22

Chemical composition of steel:
Grade C Mn S P Si Carbon
Equivalent
Fe410WA 0.23 1.50 0.050 0.050 0.40 0.42
Fe410WB 0.22 1.50 0.045 0.045 0.40 0.41
Fe410WC 0.20 1.50 0.040 0.040 0.40 0.39
Fe 440 0.20 1.30 0.05(0.04) 0.05(0.04) 0.45 0.40
Fe 490 0.20 1.50 0.05(0.04) 0.05(0.04) 0.45 0.42
Fe 590 0.22 1.80 0.045(0.04) 0.045(0.04) 0.45 0.48
Notes:
1. Carbon Equivalent = (C+Mn)/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
2. The terms in the bracket denotes the maximum limit for the flat products. 4
Steel is an alloy which mainly contains iron and carbon. Apart from
the carbon a small percentage of manganese, silicon, phosphorus,
nickel and copper are also added to modify the specific properties of
the steel.
Chemical composition of structural steel (IS 2062-1992 & IS 8500)
23

Types of structural steel:
Different structural steel can be produced based on the
necessity by changing slightly the chemical composition and
manufacturing process.
1. Carbon steel: In this type of structural steel carbon and
manganese are used as extra elements.
2. High Strength Carbon Steel: By increasing the carbon
content this type of steel can be manufactured which
basically produces steel with comparatively higher
strength but less ductility.
3. Stainless Steel: In this type of steel mainly foreign
material like nickel and chromium are used along with
small percentage of carbon.
24

Properties of structural steel
The important mechanical properties of steel are:
ultimate strength, yield stress, ductility,
weldabilty, toughness, corrosion resistance and machinability.
The last four properties are important for durability of material
and often associated with fabrication of steel members.
The mechanical properties of steel largely depend on its
▪ Chemical composition
▪ Heat treatment
▪ Stress history
▪ Rolling methods
▪ Rolling thickness
25

Structural Steel
❖The steel used for structural works shall confirm to IS 2062 :
2011 (Hot Rolled Medium and High Tensile Structural Steel).
❖Most Commonly used grade is Fe 410.
❖Followings are few physical properties of structural steel (As
per clause 2.2.4.1 of IS 800 : 2007):
▪ Unit mass of steel, ρ = 7850 kg/m3
▪ Modulus of elasticity, E = 2.0 × 105 N/mm2
▪ Poisson’s ratio, µ = 0.3
▪ Modulus of rigidity, G = 0.769 × 105 N/mm2
▪ Co-efficient of thermal expansion, α= 12 × 10-6 /oc
26

Mechanical properties:
Following are the most important mechanical properties that are
Grade of
Steel
Yield Stress (MPa) Ultimate Tensile
Stress (MPa)
Elongation
Percentage
t<20 t = 20 to 40 t>40
Fe 410 250 240 230 410 23
Fe 440 300 290 280 440 22
Fe 490 350 330 320 490 22
Fe 540 410 390 380 540 20
frequently used in design of steel structures.
➢Yield stress, fy
➢Ultimate stress, fu
➢Minimum percentage elongation
These properties can be obtained by performing tensile tests of the steel
sample.
Mechanical properties of structural steel products (Table 1 of IS 800 : 2007)
27

Some other important mechanical properties of steel
(i)Ductility: It is defined as
the property of a material by
virtue of which it undergoes
large inelastic i.e. permanent
deformation without loss of
strength under the
application of tensile load.
(ii)Hardness: It is one of the mechanical properties of steel
by virtue of which it offers resistance to the indentation and
scratching. The hardness of steel is measured by
➢ Brinell hardness test
➢ Vickers hardness test
➢ Rockwell hardness test
28

(iii) Toughness: It is one of the mechanical properties of steel by
virtue of which it offers resistance to fracture under the action of
impact loading.
▪ Toughness = The ability to absorb energy up to fracture.
▪ Toughness is generally measured by the area under the stress-strain
curve.
(iv) Fatigue: It is defined as the damage caused by the repeated
fluctuation of stresses which leads to the progressive cracking of the
structural element.
➢Damage and failure of the material under the action of cyclic
loading.
(v) Resistance against corrosion:
In the presence of moist air corrosion of steel is an extremely important
aspect.
➢To avoid corrosion paint or metallic coating may be used
29

Few important terms associated with structural steel:
(a) Residual Stress:
Residual stresses are defined as the stresses which are locked into a
component or assembly of parts. At the time of rolling of steel
sections, fabrication of steel members, they are subjected to very
high temperature and after that they are allowed to cool which is
basically an uneven process. Due to this uneven heating and cooling,
residual stress in the structural member is generated.
(b) Stress Concentration:
Stress concentration indicates a highly localized state of stress at a
particular location of a member. Generally, if there exists an abrupt
change in the shape of the member like in the vicinity of notch or
holes, the stress generated at that location is several times greater
than the stress that would generate without that sudden change in
geometry.
30

Stress-strain curve for mild steel
Stress,
f
Strain, ɛ
O
A
B
C D
Cʹ
Stress-Strain diagram for steel specimen is generally plotted by
performing tensile test, in which a specimen having gauge length
L0 and initial cross sectional area A0 is taken.
E
F
fy
fu
31

Part OA- In this region the stress is proportional to strain, and is called the
limit of proportionality.
Part AB- After reaching ‘A’, change in strain is rapid compared to that of
stress but still the material behaves elastically up to elastic limit ‘B’.
Cʹ - represents the upper yield point
C - represents the lower yield point.
Part CD- Beyond yield point the material starts flowing plastically without
any significant increase in the stress and material undergoes large
deformation.
Part DE- After reaching point ‘D’, the strain hardening in the material begins
which necessitates requirement of higher load to continue deformation. This
phenomenon is called ‘strain hardening’.
E represents the ultimate stress fu.
Part EF- When the stress reaches point ‘E’ that is the stress corresponding to
the ultimate stress, the necking in material begins.
F - represents breaking stress – the stress corresponding to the breakingload.
32

DESIGN PHILOSOPHIES
Safety at ultimate load and serviceability at working load
33

Working Stress Method:
Safety is ensured by limiting the stress of the material. The material is
assumed to behave in linear elastic manner. In this approach the stress-strain
behaviour is considered to be linear.
Permissible stress < (Yield stress / Factor of safety)
Details at: IS 800 – 1984.
Permissible stress in steel structural members
Types of stress Notation Permissible
stress (Mpa)
Factor of
safety
Axial tension σat 0.6fy 1.67
Axial compression σac 0.6fy 1.67
Bending tension σbt 0.66fy 1.515
Bending compression σbc 0.66fy 1.515
Average shear stress τva 0.4fy 2.5
Bearing stress σp 0.75fy 1.33
34

USM: It is also referred to Plastic Design Method. In this case
the limit state is attained when the members reach plastic
moment strength Mp and the structure is attained into a
mechanism. The safety measure of the structure is taken care of
by an appropriate choice of load factor. It is multiplied to the
working load and it is checked w.r.t to the ultimate load
corresponding to the member.
Working Load×Load Factor ≤Ultimate Load
LSM: In limit state design method, the structure is designed in
such a way that it can safely withstand all kind of loads that
may act on the structure under consideration in its entire design
life. In this approach, the science of reliability based design was
developed with the objective of providing a rational solution to
the problem of adequate safety. Uncertainty is reflected in
loading and material strength.
35

Factors
Governing
Ultimate
Strength
Stability
StabilityAgainst
Overturning
Sway Stability
Fatigue Plastic Collapse
Limit State of Strength
36

Limit State of Strength:
These are associated with the failure of the structure under the action
of worst possible combination of loads along with proper partial
safety factor that may lead to loss of life and property. As provided
in IS 800: 2007, Limit state of strength includes –
• Loss of equilibrium of the structure as a whole or in part.
• Loss of stability of the structure.
• Failure due to excess deformation or rupture.
• Fracture due to fatigue.
• Brittle fracture.
37

Check for
Serviceability
Limit States
Deflection
limit
Vibration
limit
Durability
consideration
Fire
Resistance
Limit State Serviceability
38

Limit State of Serviceability:
These are associated with the discomfort faced by the user while
using the structure.
• Excess deflection or deformation of the structure.
• Excess vibration of the structure causing discomfort to the
commuters.
• Repairable damage or crack generated due to fatigue.
• Corrosion and durability
39

Partial Safety Factor for Load
(Clause 5.3.3, Table 4, IS 800: 2007)
𝑄𝑑 = 𝛾𝑓𝑘𝑄𝑐𝑘
𝑘
Where, 𝛾𝑓 = the partial safety factor for kth load or load effect, 𝑄𝑐
= Characteristic load or load effect, 𝑄𝑑 = Design load or load
effect.
Note
Characteristic values (loads/stresses) are defined as the values
that are not expected to be exceeded within the life of the
structure with more than 5% probability.
Generally partial factor of safety considered is in all cases higher
than unity. Whereas for serviceability limit states unit factor of
safety is considered as it is checked under the action of service
load for structure. 40

Combinatio
ns
Limit State of Strength Limit State of Serviceability
DL LL WL/
EL
AL DL LL WL/
EL
Leadin
g
Accompa
nying
Leading Accomp
anying
DL+LL+CL 1.5 1.5 1.05 - - 1.0 1.0 1.0 -
DL+LL+CL
+WL/EL
1.2 1.2 1.05 0.6 - 1.0 0.8 0.8 0.8
1.2 1.2 0.53 1.2 -
DL+WL/EL 1.5
(0.9)
- - 1.5 - 1.0 - - 1.0
DL+ER 1.2
(0.9)
1.2 - - - - - - -
DL+LL+AL 1.0 0.35 0.35 - 1.0 - - - -
Notes:
(i) DL=dead load, LL=imposed (live) load, CL=crane load, WL=wind load, EL=earthquake
load, AL=accidental load.
(ii) During simultaneous action of different live loads one which has greater effect on the
member under consideration is considered as the leading live load.
(iii)Value in the bracket should be considered when dead load contributes to the stability
against overturning or it causes reduction in stress due to other loads.
Partial Safety Factor for Loads, 𝜸𝒇 (Table 4, IS 800: 2007)
41

Partial Safety Factor for Material
Partial safety factor for material
𝑆𝑑 = 𝑆𝑢/𝛾𝑚
Where, 𝛾𝑚 = Partial safety factor for material as given in Table 1.5.
𝑆𝑢 = Ultimate strength of the material, 𝑆𝑑 = Design strength of the
material.
Generally, a factor of unity (one) or less is applied to the
resistances of the material.
42

Definition Partial Safety Factor
Resistance governed by yielding, 𝛾𝑚0 1.10
Resistance of member to buckling, 𝛾𝑚0 1.10
Resistance governed by ultimate stress,
𝛾𝑚1
1.25
Resistance of connection Shop
Fabrication
Field
Fabrication
(a) Bolts, friction type, 𝛾𝑚𝑓 1.25 1.25
(b) Bolts, bearing type, 𝛾𝑚𝑏 1.25 1.25
(c) Rivets, 𝛾𝑚𝑟 1.25 1.25
(d) Welds, 𝛾𝑚𝑤 1.25 1.50
Partial safety factor for material, 𝜸𝒎 (Table 5, IS 800: 2007)
43

Type of
Building
Deflection Design
Load
Member Supporting Maximum
Deflection
Industria
l
Buildings
Vertical
LL/WL Purlins and
girts
Elastic Cladding Span/150
Brittle Cladding Span/180
LL Simple span Elastic Cladding Span/240
LL Cantilever
span
Elastic Cladding Span/120
LL/WL Rafter
supporting
Profiled Metal sheeting Span/180
Plastered sheeting Span/240
CL(manual operation) Gantry Crane Span/500
CL (electric operation up to50t) Gantry Crane Span/750
CL (electric operation over50t) Gantry Crane Span/1000
Lateral
No cranes Column Elastic Cladding Height/150
Brittle Cladding Height/240
Crane + wind Gantry
(lateral)
Crane(absolute) Span/400
Relative displacement
between rails
supporting crane
10mm
Crane + wind Column/fra
me
Gantry(Elastic cladding,
pendant operated)
Height/200
Gantry(Brittle cladding, cab
operated)
Height/400
Deflection Limits (Table 6, IS 800: 2007)
44

Type of Building Deflection Design
Load
Member Supporting Maximum
Deflection
Other
Buildings
Vertical
LL Floor & Roof Elements not
susceptible to
cracking
Span/300
Elements
susceptible to
cracking
Span/360
LL Cantilever Elements not
susceptible to
cracking
Span/150
Elements
susceptible to
cracking
Span/180
Lateral
WL Building Elastic cladding Height/300
Brittle cladding Height/500
WL Inter story drift - Story
height/300
Deflection Limits (Table 6, IS 800: 2007)
45

Classification of Cross
Section
Class 1
Plastic
Class 2
Compact
Class 3
Semi-Compact
Cross Sectional Classification (Clause 3.7, Table 2)
46

Load and Load Combinations
• Dead loads – [IS:875 (Part-1)]
• Imposed loads (i.e. Live loads, Crane loads etc) – [IS:875 (Part 2)]
• Wind loads – [IS:875 (Part-3)]
• Snow loads - [IS:875 (Part-4)]
• Temperature, Hydrostatic, Soil pressure, Fatigue, Accidental,
Impact, Explosions etc and load combinations [IS:875 (Part-5)]
• Earthquake load – [IS:1893-2002 (Part-1)]
• Erection loads – [IS:800-2007 Cl. 3.3]
• Other secondary effects such as temperature change, differential
settlement, eccentric connections etc.
47

➢ In IS:800-2007 (Cl. 5.3.1) the loads/actions acting on a structural
system has been classified in three groups, these are as follows:
• Permanent actions (Qp) – Action due to self-weight of the structural
components, basically the dead loads.
• Variable actions (Qv) – Action due to loads at construction and
service stage such as all type of imposed loads, wind and earthquake
loads etc.
• Accidental actions (Qa) – Action due to accidental loads acting on
the structure such as due to explosion, due to sudden impact etc.
➢ While designing the steel structure following load combination
must be considered along with partial safety factors
• Dead loads + Imposed loads
• Dead loads + Imposed loads + Wind / Earthquake loads
• Dead loads + Wind / Earthquake loads
• Dead loads + Erection loads
48

Wind Load Calculation
Cl. 5.3, IS 875 (Part 3) 1987
The design wind speed (m/s) at any height z is
𝑉𝑧= 𝑘1𝑘2𝑘3𝑉𝑏
Where, 𝑉𝑏= Basic wind speed (Figure1)
𝑘1 = Probability factor (risk coefficient)
(Table 1)
𝑘2 = Terrain, height and structure size
factor (Table 2)
𝑘3 = Topography factor (Clause 5.3.3 )
Basic
wind
speed, m/s
Zone
55 I
50 II
47 III
44 IV
39 V
33 VI
49

The wind pressure at any height of a structure
depends on following.
➢Velocity and density of the air
➢Height above ground level
➢Shape and aspect ratio of the building
➢Topography of the surrounding ground surface
➢Angle of wind attack
➢Solidity ratio or openings in the structure
Design Wind Pressure
(cl. 5.4; IS 875 part 3)
Design wind pressure at any height above mean ground level
is obtained by
𝑧
𝑝𝑧 = 0.6𝑉2
50

Design Wind Force:
1. The total wind load for a building as a whole is given by
𝐹 =𝐶𝑓𝐴𝑒𝑝𝑧 [cl. 6.3 of IS 875 part-3 ]
Where, 𝐶𝑓=Force coefficient of the building
𝐴𝑒 = Effective frontal area
𝑝𝑧 = design wind pressure
2. Wind force on roof and walls is given by
𝐶𝑝𝑒 −𝐶𝑝𝑖
𝐹 = 𝐴𝑝𝑧 [cl. 6.2.1 of IS 875 part-3]
(cl. 6.2.2 of IS 875 part-3)
Where, 𝐶𝑝𝑒 = External pressurecoefficient
𝐶𝑝𝑖 = Internal pressure coefficient (cl. 6.2.3 of IS 875 part-3)
A = Surface area of structuralelement
51

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