Civil Engineering Reference
In-Depth Information
Figure 18.5
Shear wall.
Shear is more important in walls with small height-to-length ratios. Moments will be
more important for higher walls, particularly those with uniformly distributed reinforcing.
It is necessary to provide both horizontal and vertical shear reinforcing for shear
walls. The Commentary (R11.10.9) says that in low walls the horizontal shear reinforcing
is less effective and the vertical shear reinforcing is more effective. For high walls the sit-
uation is reversed. This situation is reflected in ACI Equation 11-32, which is presented in
the next section. The vertical shear reinforcing contributes to the shear strength of a wall
by shear friction.
Reinforcing bars are placed around all openings, whether or not structural analysis in-
dicates a need for them. Such a practice is deemed necessary to prevent diagonal tension
cracks, which tend to develop radiating from the corners of openings.
18.6
ACI PROVISIONS FOR SHEAR WALLS
1.
The factored beam shear must be equal to or less than the design shear strength of
the wall.
V
u
V
n
2.
The design shear strength of a wall is equal to the design shear strength of the con-
crete plus that of the shear reinforcing.
V
u
V
c
V
s
3.
The shear strength
V
n
a
t a
ny horizontal section in the plane of the wall may not be
taken greater than (11.10.3).
4.
In designing for the horizontal shear forces in the plane of a wall,
d
is to be taken
as equal to 0.8
c
hd
10
f
w
is the horizontal wall length between faces of the sup-
ports, unless it can be proved to be larger by a strain compatibility analysis
(11.10.4).
5.
ACI Section 11.10.5 states that unless a more detailed calculation is made (as de-
scribed in the next paragra
ph
), the value of the nominal shear strength
V
c
used
may not be larger than
w
, where
c
hd
2
f
for walls subject to a factored axial compressive
