Civil Engineering Reference
In-Depth Information
EXAMPLE 14.1
Design the continuous slab of Figure 14.20 for moments calculated with the ACI coefficients. The
slab is to support a service live load of 170 psf in addition to its own dead weight.
3000 psi and
f
y
40,000 psi. The slab is to be constructed integrally with its spandrel girder supports.
c
f
SOLUTION
Minimum
t
for Deflection by ACI Code (9.5.2.1)
40,000
Deflection multiplier for 40,000
psi steel
0.4
100,000
0.80
(0.8)(12
13)
24
0.8
24
Minimum
t
for end span
5.2
Minimum
t
for interior span
0.8
28
(0.8)(12
13)
4.46
28
Loads and Maximum Moment Assuming 6-in. Slab (
d
4
4
in.)
6
12
w
D
slab weight
(150)
75 psf
w
L
170 psf
w
u
(1.2)(75)
(1.6)(170)
360 psf
1
10
1
10
n
(360)(13)
2
6084 ft- lb
Max
M
u
w
u
Computing moments,
values,
A
s
requirements, and selecting bars at each section, as shown in Fig-
ure 14.21.
For floor slabs we are not concerned with the design of web reinforcing. For continu-
ous beams, however, web reinforcing must be carefully designed. Such designs are based
on the maximum shears occurring at various sections along the span.
From previous discussions you will remember that to determine the maximum shear
occurring at Section 1-1 in the beam of Figure 14.22, the dead load would extend all across
the span while the live load would be placed from the section to the most distant support.
If the live load is placed so as to cause maximum shears at various points along the
span and the shear is calculated for each point, a maximum shear curve can be drawn.
Figure 14.22
