Solution - dm2_080342

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(12) Determine the thickness of concrete required to carry the
shear.
Vu = 30,630 lb/in
vc = 288.5 psi
d = 30,630/288.5 = 106.2 in
(13) Determine the amount of flexural reinforcement required.
Main reinforcement:
Assume "a" block = 6 inches
As = Mub/fs (d - a/2)
Mu = 1,478,660 in-lb/in
b = 12 in
d = 106.2 in
a = assumed value of 6 in
fs = 60,000 psi
As = 1,478,660(12)/60,000(106.2 - 6/2)
= 2.87 in2/ft
a = Asfs/0.85bf'
f'c = 4,000 psi
a = 2.87(60,000)/0.85(12)(4,000)
= 4.22 in
As = 1,478,660(12)/60,000(106.2 - 4.22/2)
= 2.84 in2/ft
Amin = 0.0025bd = 0.0025(12)(106.2)
= 3.19 in2/ft
Use minimum steel:  As = 3.19 in2/ft
Area of No. 11 bar = 1.56 in2
Use two No. 11 bars, top and bottom, at 12-inch spacing.
These bars should extend from one end of the foundation
to the other end (see Figure 91).
Reinforcement in other direction:
As = 0.001bTc
Tc = 110 inches
As = 0.001(12)(110)
= 1.32 in2/ft
Use one No. 10 bar, top and bottom, at 12-inch spacing.
These bars should be placed in both extensions of the
foundation (see Figure 91).
2.08-325