Civil Engineering Reference
In-Depth Information
Figure 8.15
Determination of number of stirrups for 'contribution of steel'
V
s
8.3.3.2 'Contribution of Steel' (
V
s
)
The
V
s
term in Equation (8.15) must be based on the observed failure crack of approximately
45
◦
as shown in Figure 8.13. In the ACI Code, the 45
◦
crack is located in the manner shown
in Figure 8.15(a). This ACI concept of smearing the stirrups results in an average number
of stirrups
d/s
crossing the crack. A more realistic concept, however, is to seek a crack that
produces a 'minimum shear resistance' among a series of individual stirrups, as shown in
Figure 8.15(b). This concept by Loov gives the number of stirrups crossing the crack as
(
d/s
- 1), and the
V
s
term as:
A
v
f
y
d
1
V
s
=
s
−
(8.16)
Besides being more rational and conservative, Equation (8.16) has an additional practical
advantage: all the tedious 'stirrup spacing limitations' to guard against the unsafe nature of
the 'smeared stirrups' assumption can be eliminated.
