Civil Engineering Reference
In-Depth Information
Figure 12.4
cracks in between the two diagonal lines, is opposed by the squeezing or compression
caused by the downward wall load and the upward soil pressure. Outside this zone the
compression effect is negligible in its effect on diagonal tension. Therefore, for nonpre-
stressed sections shear may be calculated at a distance
d
from the face of the wall (ACI
Code 11.1.3.1) due to the loads located outside the section.
The use of stirrups in footings is usually considered impractical and uneconomical.
For this reason, the effective depth of wall footings is selected so that
V
u
is limited to the
desig
n
shear strength
V
c
that the concrete can carry without web reinforcing, that is,
(from ACI Section 11.3.1.1 and ACI Equation 11-3). The following expres-
sion is used to select the depths of wall footings:
c
b
w
d
2
f
V
u
d
c
)(
b
w
)
(
)(2
f
or for SI units
3
V
u
d
c
b
w
f
The design of wall footings is conveniently handled by using 12-in. widths of the
wall, as shown in Figure 12.5. Such a practice is followed for the design of a wall footing
in Example 12.1. It should be noted in Section 15.7 of the Code that the depth of a footing
above the bottom reinforcing bars may be no less than 6 in. for footings on soils and 12 in.
Figure 12.5
