Civil Engineering Reference
In-Depth Information
Table 16.4
Percentages of Exterior Negative Design
Moment to Be Resisted by Column Strip
Table 16.5
Percentages of Positive
Design Moment to Be Resisted by
Column Strip
2
1
0.5
1.0
2.0
t
0
100
100
100
2
1
1
2
1
0.5
1.0
2.0
0
t
2.5
75
75
75
1
2
1
0
60
60
60
t
0
100
100
100
1
2
1
1.0
1
2
1
1.0
90
75
45
t
2.5
90
75
45
16.9
DESIGN OF AN INTERIOR FLAT PLATE
In this section an interior flat plate is designed by the direct design method The procedure
specified in Chapter 13 of the ACI Code is applicable not only to flat plates but also to flat
slabs, waffle slabs, and two-way slabs with beams. The steps necessary to perform the de-
signs are briefly summarized at the end of this paragraph. The order of the steps may have
to be varied somewhat for different types of slab designs. Either the direct design method
or the equivalent frame method may be used to determine the design moments. The de-
sign steps are as follows:
1.
Estimate the slab thickness to meet the Code requirements.
2.
Determine the depth required for shear.
3.
Calculate the total static moments to be resisted in the two directions.
4.
Estimate the percentages of the static moments that are positive and negative, and
proportion the resulting values between the column and middle strips.
5.
Select the reinforcing.
Example 16.3 illustrates this method of design applied to a flat plate.
EXAMPLE 16.3
Design an interior flat plate for the structure considered in Example 16.1. This plate is shown in Fig-
ure 16.13. Assume a service live load equal to 80 psf, a service dead load equal to 110 psf (includ-
ing slab weight),
f
y
60,000 psi,
c
f
3000 psi, and column heights of 12 ft.
SOLUTION
Estimate Slab Thickness
When shear is checked, the 7-in. slab estimated in Example 16.1 is not quite sufficient.
Try 7
2
in. slab
