Civil Engineering Reference
In-Depth Information
Moments assuming
0.90
M
u
(1.2)(200)
(1.6)(425)
920 ft- k
M
u
0.90
920
M
n
0.90
1022 ft- k
Assuming a Lever Arm
z
(Note that the compression area in the slab is very wide, and thus its re-
quired depth is very small.)
z
(0.90)(24)
21.6
z
24
2
22.5
Trial Steel Area
A
s
(12)(10.22)
(60)(22.5)
9.08 in.
2
Checking Values of
a
and
z
A
c
(60)(9.08)
(0.85)(3)
213.6 in.
2
The stress block extends down into the web, as shown in Figure 5.11.
Computing the Distance
y
from the Top of the Flange to the Center of Gravity of
A
c
3.44
2
(162)(1.5)
(51.6)
3
y
2.28 in.
213.6
z
24
2.28
21.72 in.
A
s
(12)(1022)
(60)(21.72)
9.41 in.
2
The steel area required (9.41 in.
2
) could be refined a little by repeating the design, but space is
not used to do this. (If this is done
A
s
9.51 in.
2
)
54"
162 sq. in.
3"
y
51.6 sq. in.
24"
51.6
15
= 3.44"
15"
Figure 5.11
