Civil Engineering Reference
In-Depth Information
Figure 19.13
sume that the area of the prestressing steel is 1.0 in.
2
, the effective prestress force is 250 k, and
4000 psi.
c
f
SOLUTION
Approximate Method
w
u
(1.2)(1.2)
(1.6)(2.1)
4.8 k/ft
V
u
(10)(4.8)
(4)(4.8)
28.8 k
M
u
(10)(4.8)(4)
(4)(4.8)(2)
153.6 ft- k
V
u
d
(28.8)(24
3
3)
(12)(153.6)
M
u
0.281
1.0
OK
c
700
V
u
d
M
u
V
c
0.6
f
b
w
d
(ACI Equation 11-9)
[0.6
400
0
(700)(0.281)](12)(18)
50,684 lb
Minimum
V
c
(2
4000
)(12)(18)
27,322 lb
50,684 lb
Maximum
V
c
(5
4000)(12)(18)
68,305 lb
50,684 lb
V
c
50,684 lb
More Detailed Method
1
12
(12)(24)
3
13,824 in.
4
I
y
t
12
f
pe
compressive stress in concrete due to prestress after all losses
P
A
Pec
I
(250,000)(6)(12)
13,824
250,000
f
pe
(12)(24)
2170 psi
M
d
dead load moment at 4
point
(10)(1.2)(4)
(4)(1.2)(2)
38.4 ft- k
(12)(38,400)(12)
13,824
f
d
stress due to the dead load moment
400 psi
