Civil Engineering Reference
In-Depth Information
3.6
DESIGN FOR SHEAR REINFORCEMENT
In accordance with ACI Eq. (11-2), the total shear strength is the sum of two components: shear strength
provided by concrete (
φ
V
c
) and shear strength provided by shear reinforcement (
φ
V
s
). Thus, at any section of
the member, V
u
≤ φ
V
c
+
φ
V
s
. Using the simplest of the code equations for shear strength of concrete, V
c
, can
be calculated as follows:
V
c
=
φ
2
λ
f
c
ʹ
b
w
d
ACI Eq. (11−3)
where
λ
is a modification factor to account for the reduced mechanical properties of lightweight concrete.
λ
= 0.85 for sand-lightweight concrete and 0.75 for all-lightweight
concrete. Figure 3-6 shows the values for nominal shear strength provided by concrete (V
c
) for a rectangular
section, for normal and light weight concrete and for different concrete strengths. Figure 3-7 and Table 3-7
summarize ACI 318 provisions for shear reinforcement.
= 1.0 for normal weigh concrete,
λ
0.18
φ
v
c
b
w
d
V
c
=
0.16
Sand lightweight
0.14
Normal weight
All lightweight
0.12
0.1
0.08
3
4
5
6
7
8
f'
c
(ksi)
Figure 3-6 Nominal Shear Strength Provided by Concrete V
c
(Kips)
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