Civil Engineering Reference
In-Depth Information
Maximum allowable spacing of stirrups
p
h
70
from ACI Section 11.6.6.1
8
8
Say 8.75 in. or 12 in.
Minimum area of stirrups
A
v
by ACI Equation 11-23
c
b
w
s
f
yv
A
v
2
A
t
0.75
f
0.75
4000
(16)(7)
60,000
0.089 in.
2
(2)(0.20)
0.40 in.
OK
Use #4 stirrups @ 7 in.
(7) Selection of longitudinal torsion reinforcing
Additional longitudinal reinforcing required for torsion
f
yv
f
y
A
A
t
cot
2
s
p
h
(ACI Equation 11-22)
60,000
60,000
(1.00)
2
1.17 in.
2
(0.0167)(70)
c
A
cp
f
yt
5
f
p
h
f
yv
f
y
A
t
s
Min.
A
(ACI Equation 11-24)
with min
A
s
25
b
w
(25)(16)
60,000
0.00667
f
yv
(5
4000)(416)
60,000
60,000
60,000
(0.0167)(70)
1.02 in.
2
1.17 in.
2
OK
This additional longitudinal steel is spread out into three layers to the four inside corners of the
stirrups and vertically in between, with a spacing not in excess of 12 in.
Assume one-third in top
1.17/3
0.39 in.
2
, 0.39
3.52
3.91 in.
2
in bottom, and remain-
der 0.39 in.
2
in between.
Use two #4 bars (0.40 in.
2
) in top corner, two #4 bars in the middle, and five #8 bars (3.93 in.
2
)
at the bottom, as shown in Figure 15.14.
2 #4
#4 closed
ties @ 8
1
"
2
26
"
2 #4
5 #8
3
4 @ 2
= 11
4
2
1
2
1
16
"
Figure 15.14
Reinforcing selected for beam of Example 15.1.
