Civil Engineering Reference
In-Depth Information
Use
c
approximately
0.18
f
(0.18)(3000)
60,000
0.009
f
y
M
u
bd
2
(from Table A.12)
482.6 psi
bd
2
(12)(92,472)
(0.
9)(48
2.6)
2555
2555
12
d
14.59
h
14.59
2
1
2
17.09
Say 18
(
d
15.50
)
M
u
(12)(92,472)
(0.90)(12)(15.5)
2
427.7
bd
2
0.00786 (from Appendix Table A.12)
A
s
(0.00786)(12)(15.5)
1.46 in.
2
Use #8 @ 6
(1.57 in.
2
)
1.57
(12)(15.5)
0.0084
1.57
(12)(15.5)
0.0084
Minimum vertical
by ACI Section 14.3
0.0015
OK
Minimum horizontal
A
s
(0.0025)(12)(average stem
t
)
12
18
2
(0.0025)(12)
0.450 in.
2
(say one-third inside face and two-thirds outside face).
Use #4 at 7
2
outside face and #4 at 15
inside face
Checking Shear Stress in Stem
Actually,
V
u
at a distance
d
from the top of the footing can be used, but for simplicity.
V
u
H
1
H
2
9734
29
95
12,729 lb
c
bd
(0.75)(2
3000)(12)(15.5)
V
c
2
f
15,281 lb
12,729 lb
OK
Design of Heel
The upward soil pressure is conservatively neglected, and a load factor of 1.2 is used for calculating
the shear and moment because soil and concrete make up the load.
V
u
(22.5)(6.2
5)(100
)(1.2)
(1.5)(6.25)(150)(1.6)
19,125 lb
V
c
(0.75)(2
3000)(12)(14.5)
14,295
19,125
No good
Try 24-in. Depth (
d
20.5 in.)
Neglecting slight change in
V
u
with different depth
V
c
(0.75)(2
3000)(12)(20.5)
20,211
19,125
OK
6.25
2
M
u
at face of stem
(19,125)
59,766 ft- lb
M
u
(12)(59,766)
(0.9)(12)(20.5)
2
bd
2
158
min
Use
0.00333
