Civil Engineering Reference
In-Depth Information
∞
26.16
"
code maximum
s
= =10
"
2
code maximum
s
= =5
"
7.18
"
4
theoretical spacing
4.41
"
4.54
"
d=20
"
16
"
36
"
36
"
80
"
Figure 8.17
8.11
ECONOMICAL SPACING OF STIRRUPS
When stirrups are required in a reinforced concrete member, the Code specifies maximum
permissible spacings varying from
d
/4 to
d
/2. On the other hand, it is usually thought that
stirrup spacings less than
d
/4 are rather uneconomical. Many designers use a maximum of
three different spacings in a beam. These are
d
/4,
d
/3, and
d
/2. It is easily possible to de-
rive a value of
V
s
for each size and style of stirrups for each of these spacings.
5
Note that the number of stirrups is equal to
d
/
n
and that if we use spacings of
d
/4,
d
/3,
and
d
/2 we can see that
n
equals 4, 3, or 2. Then the value of
V
s
can be calculated for any
particular spacing, size, and style of stirrup. For instance, for #3
stirrups spaced at
d
/2
0.75 and
f
y
with
60 ksi,
A
v
f
y
d
s
(0.75)(2
0.11)(60)(
d
)
d
/2
V
s
19.8 k
The values shown in Table 8.2 were computed in this way for 60-ksi stirrups.
Table 8.2
Values for 60-ksi Stirrups
Vs
for #3
Vs
for #4
s
stirrups (kips)
stirrups (kips)
d
/2
19.8
36
d
/3
29.7
54
d
/4
39.6
72
5
Neville, B. B., ed., 1984,
Simplified Design Reinforced Concrete Buildings of Moderate Size and Height
(Skokie, IL: Portland Cement Association), pp. 3-12-3-16.
