Cj34516519

Khan, M.A., Ahmed, F.S. / International Journal of Engineering Research and Applications
(IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 3, May-Jun 2013, pp. 516-519
516 | P a g e
Effect Of Web Reinforcement On Ultimate Strength Of
Reinforced Concrete Deep Beam
*Khan, M.A., **Ahmed, F.S.,
*(Lecturer, Department of Civil Engineering, Stamford University Bangladesh, Dhaka-1217)
**(Graduate Research Assistant, Department of Civil Engineering, The University of Texas at Arlington, USA)
ABSTRACT
It is observed that, reinforced concrete
beams failed due to flexure but in case of deep
beam failure occur due to shear. Deep beams
may be defined as the beam where shear span to
depth ratio less than 2. A number of researchers
already proposed various approach to predict
the ultimate strength of deep beams. In this
study a newer approach is developed to calculate
the ultimate shear strength of deep beams based
on strut and tie model. Deep beams of different
web reinforcement are used to predict the shear
strength. A new effectiveness coefficient has been
introduced to understand the contribution of
steel during failure of deep beam under
concentrated loads.
Keywords – deep beam, shear strength, concrete
strength.
I. Introduction
Shear strength of reinforced concrete deep
beam is composed of two components, nominal
shear strength provided by concrete and nominal
shear strength due to web reinforcement. Deep
beams used in this research composed of different
shear span to depth ratio, compressive strength of
concrete, longitudinal reinforcement ratio and
vertical reinforcement ratio. Though the prediction
of ultimate shear strength of different research
groups are not the same but some of the
characteristics remain same such as with the
increase of shear span to depth ratio the deep beam
become more and more slender and failure occur at
lower load. Tan et al (1998) proposed a shear
design equation for deep beams but it was so
conservative to use in practical. According to Sing
B. et al (2006), continuous deep beams also exhibit
the same tendency as simply supported deep
beams. Arabzadeh et al. (2009) describe a simple
sturt and tie model to predict shear strength. Lu et
al (2010) also proposed a new formula based on
sturt and tie model to predict the shear strength of
deep beams. W.W. kuo et al. (2010) also describes
the force transfer mechanism for deep beam based
on B and D region (ACI 318-05). Deep beams have
no B region and single D region. The diagonal
compression flows directly from the point of
applied load to the end support at an inclination
angle (θ).
According to the provision of ACI 318-05 Code,
the angle (θ) shall not be taken as less than 25°.
Therefore, the beam having shear span to
depth ratio greater than 2.0 are chosen as deep
beams for this research.
II. BEAM DATA
Simply supported, single span reinforced
concrete deep beam (Fig.1) data are used for this
research. Beam of different shear span to depth,
concrete strength and web reinforcement are
summarized to understand the behavior of deep
beams. Following notations are used to define
different parameters of deep beams:
a = shear span (distance from support to applied
load)
b = width of beam
d = effective width of beam
h = height of the beam
Vu = Theoretical ultimate shear strength
Ln = clear span
f′c = cylinder strength of concrete
fy = strength of steel
ρh = horizontal reinforcement ratio
ρv = vertical reinforcement ratio
ξ = softening coefficient of concrete
g = proposed coefficient
Vs = Steel contribution to share strength
Vexp = Experimental shear strength
Fig.1 Geometry of concrete deep beam
Material properties, experimental setup
and obtained test results are selected from different
researchers [9], [11] to prepare a deep beam
database. In selecting these data, following screens
were applied.

517 | P a g e
1. The test specimens were reported to have
failed because of web compression failure,
not shear tension, bearing, or flexural
failures;
2. The shear span to depth ratio (a/d) was
less than 2.0;
3. The test specimens were simply
supported.
4. Loads and reactions were applied through
the bearing blocks with reported depth;
and
5. Horizontal and vertical web
reinforcements, if detailed, were
distributed uniformly.
III. APPROACH AND METHODOLOGY
Ultimate load carried by the concrete strut
and by the web reinforcement as shown in Fig 2.
Load carried by the concrete strut (C) is estimated
as following the formula provided by Lu et al.
(2010), which is based on strut and tie model. But
in this research, a new equation has been developed
to calculate the load carried by the web
reinforcement (F).
Fig.2 Load Transfer Mechanism of Deep Beams
Following Fig 2, it is estimated that, ultimate shear
strength,
Vu = C sinө + gF cosө 1
C = ξf′cAstr 2
F = bdfy {ρv(a/d)cosθ + ρhsinθ} 3
Equation 1 represents the basic theory of
calculating share strength by adding concrete
contribution with steel contribution. Here, g is a
proposed coefficient. Equation 2 represents the
capacity of concrete strut where, ξ is the softening
coefficient of concrete proposed by Lu et al (2010).
To calculate the active force provided by the
reinforcement during failure, equation 3 has been
introduced which represents equilibrium condition.
IV. COEFFICIENT OF EFFECTIVENESS OF
WEB REINFORCEMENT
To verify the equation with steel
contribution provided by Lu et al (2010) a new
coefficient g has been introduced. The coefficient g
represents the effectiveness of web reinforcement.
The value of g has been calculated as 0.3905. Fig 3
represents the value of steel contribution provided
by Lu et al. vs expected web steel contribution
calculated from equation 3. The slope of the
straight line represents the value of g, where a good
correlation of 0.9433 was observed.
Fig.3 Comparison of steel contribution with
predicted value
V. COMPARISON OF PREDICTED VALUE
Experimental data [7],[14] of 97 deep
beams are used to compare with theoretical value
obtained from Lu et al (2010), Arabzadeh et al.
(2011) and proposed formula based on three
categories; i) Vexp < 200 kip (Fig. 4) ii) 200 <
Vexp < 500 kip (Fig. 5) and iii) Vexp > 500 kip
(Fig. 6). It is observed that, shear strength can be
predicted from proposed formula with small
standard deviation for each of the three categories.
For high strength concrete where the ultimate value
is higher than 500 kip, the prediction of each of the
three formulas are very much similar. When the
ultimate shear strength is less than 200 kip
prediction of Arabzadeh et al. seems to be
inadequate where as for the shear strength greater
than 200 kip the prediction is quite conservative.
Fig.4 Vcal vs Vexp (Vu < 200 kip)

518 | P a g e
Fig.5: Vcal vs Vexp (200 kip < Vu < 500 kip)
Fig.6: Vcal vs Vexp (Vu > 500 kip)
1. Effect of concrete strength
Shear Strength of deep beams increases with the
increase of concrete cylinder strength. According to
Lu et al. (2010), the softened coefficient of
concrete is defined by ξ.
ξ = 0.52
4
Value of this coefficient decreases with
the increase of concrete cylinder strength. As a
result it is observed that, rate of increase of shear
stress decreases with the increase of concrete
cylinder strength as shown in Fig 7.
Fig.7: Effect of concrete strength on shear
stress.
VI. Effect of Vertical Web
Reinforcement
In case of normal beam where shear
strength to depth ratio is greater than 2.0, stirrup is
designed to carry the excess shear force that could
not be carried by the effective concrete section. In
case of deep beam, both vertical and horizontal
reinforcement is used. Deep beams were tested
keeping same compressive strength, f/
c, tensile
reinforcement ratio ρt, shear span to depth ratio a/d
and horizontal reinforcement ratio ρh but the
vertical reinforcement ratio ρv were varied to
understand the behavior. It is observed that, (see
Fig. 8) with the increase of vertical reinforcement
shear strength also increases.
Fig.8: Effect of vertical web reinforcement on
shear stress.
VII. Effect of Horizontal Web
Reinforcement
The contribution of horizontal
reinforcement cannot be ignored. According to Fig.
9 shown below it is obvious that at constant shear
span to depth ratio (1.25), compressive strength of
concrete, (50.67 Mpa), constant vertical
reinforcement ratio (0.0013), and ultimate shear
stress of the deep beam increases with the increase
of horizontal shear reinforcement. According to
Park J. W. and Kuchma D. (2007), if the web of a
deep beam is heavily reinforced, the failure will
controlled by strut crushing; however, without
sufficient reinforcement, failure can be occur
suddenly due to the splitting of concrete struts.
Park J. W. and Kuchma D. (2007) also observed
that horizontal web reinforcement is more effective
than vertical web reinforcement when a/d is less
than 0.75, and vertical web reinforcement is more
effective than horizontal web reinforcement when
a/d ratios are greater than or approximately equal to
1.0.
Fig.9: Effect of horizontal web reinforcement on
shear stress.

519 | P a g e
VIII. Conclusion
Behavior of deep beams is quite difficult
to understand and most of the researchers predict
the value of ultimate shear strength with method of
iteration. In this study simplified force transfer
mechanism is used to understand the beam
behavior. According to the proposed formula, it is
found that, 39% of the force acting perpendicular to
the diagonal cracks contributes to the shear strength
of deep beams. Softened coefficient for concrete of
medium strength does not vary and the value of the
softened coefficient of concrete having
compressive strength between 20Mpa to 40Mpa is
0.52. But for concrete of higher compressive
strength greater than 40Mpa the value of softened
coefficient decreases with the increase of
compressive strength of concrete. Further research
may be done to understand the deep beam behavior
with different end conditions. The value of mid
span deflection may be calculated which will not
be similar as normal beams
REFERENCES
[1] Lu W.Y., Hwang S. J., Lin I. J. (2010) ;
Deflection Prediction for reinforced
Concrete Deep Beams, Computer and
Concrete Journal, Vol. 7, No. 1, Page (1-
16).
[2] Arabzadeh A., Rahaie A. R., Aghayari R.
(2009) ;A Simple Sturt-and-Tie Model for
Prediction of Ultimate Shear Strength of
RC Deep Beams, International journal of
Civil Engineering, Vol. 7, No. 3, Page
(141-153)
[3] Tan K. H., Kong F. K., Weng L. W.
(1998) ; High strength Concrete Deep and
Short Beams: Shear Design Equations in
North American and UK Practice, ACI
Structural Journal, V. 95, No. 3,
[4] Sing B., Kaushik S.K., Naveen K.F., and
Sharma S. (2006), Design of continuous
deep beam using strut and tie model;
Asian Journal of Civil Engineering
(Building and Housing), Vol. 7, No. 5,
Page (461-477)
[5] Kuo W.W., Cheng T.J., Hwang S.J.,
(2010) Force transfer mechanism and
shear strength of reinforced concrete
beams. Engineering Structures 32, Page
(1537 - 1546).
[6] ACI Committee 318. Building code
requirements for structural concrete (ACI
318-02) and commentary (ACI 318R-02).
Farmington Hills (MI): American
Concrete Institute; 2002.
[7] Vecchio , F.J., and Collins, M.P. (1986) ;
Modified Compression Field Theory For
Reinforced Concrete elements Subjected
to shear, ACI Journal, V. 83, NO.2, Pages
(219-231).
[8] Quintero-Febres, C. G.; Parra-Montesinos,
G.; and Wight, J. K., Strength of Sturts in
Deep Concrete members Designed Using
Sturt-and Tie Method, ACI Structural
journal, V. 103, No. 4, July-AUG, 2006,
Pages (577-586).
[9] Smith, K. N., and Vantsiotis, A. S. (1982)
,Shear Strength of Deep Beams, ACI
journal. Proceedings V. 79, No. 3, Pages
(507-515).
[10] Park J. W., Kuchma D. (2007) ; Sturt-and-
Tie Model Analysis for Strength
Prediction of Deep Beams, ACI Structural
Journal, Vol. 104, No. 6, Page (657-666).
[11] Shin S. W. ,Lee K. S., Moon J. ,Ghosh S.
K. (1999); Shear Strength of Reinforced
High-Strength Concrete Beams with
Shear-Span-to Depth Ratios between 1.5
and 2.5, ACI Structural Journal, Vol. 96
,No. 4, Page (549-556)

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Cj34516519