Civil Engineering Reference
In-Depth Information
Checking Two-Way or Punching Shear around the Column
b
o
(2)(16
6.25)
(2)(12
6.25)
81
16
6.25
12
12
6.25
12
V
u
2
(20)(16)
(0.260)
82.47 k
82,47
0 lb
V
c
(0.75)(4
3000)(81)(6.25)
83,185 lb
82,470 lb
OK
Use
h
7
2
Calculate Static Moments
M
o
w
u
2
n
(0.260)(16)(20
1
12
)
2
181.2 ft- k
8
8
2
n
(0.260)(20)(16
1
12
)
2
8
M
os
w
u
1
146.2 ft- k
8
Proportion the Static Moments to the Column and Middle Strips and Select the Reinforcing
These calculations can be conveniently arranged, as in Table 16.6, which follows. This table is very
similar to the one used for the design of the continuous one-way slab in Chapter 14.
As the different percentages of moments are selected from the tables for the column and middle
strips of this slab, it will be noted that
t
0.
bd
2
values are some-
In the solution to Example 16.3 it will be noted that the
M
u
/
times quite small, and thus most of the
values do not fall within Table A.12 (see
Appendix). For such cases the author uses the temperature and shrinkage minimum
0.0018
bh
.
Actually, the temperature percentage includes bars in the top and bottom of the
slab. In the negative moment region, some of the positive steel bars have been ex-
tended into the support region and are also available for temperature and shrinkage
steel. If desirable, these positive bars can be lapped instead of being stopped in the
support.
The selection of the reinforcing bars is the final step taken in the design of this flat
plate. The Code Figure 13.3.8 (given as Figure 16.15 here) shows the minimum lengths of
slab reinforcing bars for flat plates and for flat slabs with drop panels. This figure shows
that some of the positive reinforcing must be run into the support area.
The bars selected for this flat plate are shown in Figure 16.16. Bent bars are used
in this example, but straight bars could have been used just as well. There seems to be
a trend among designers in the direction of using more straight bars in slabs and fewer
bent bars.
