Civil Engineering Reference
In-Depth Information
where I
s
= (12
12 + 6)(8.5)
3
/12 = 7,680 in.
4
C = larger value computed for the spandrel beam section (see Fig. 4-8).
x
1
= 8.5
y
1
= 23.5
C
1
= 3714
x
2
= 11.5
y
2
= 12
C
2
= 2410
x
1
= 12
y
1
= 20
C
1
= 7165
x
2
= 8.5
y
2
= 11.5
C
2
= 1260
C = 3714 + 2410 = 6124
C = 7165 + 1260 = 8425 (governs)
(b) Total panel moment M
o
:
M
o
= q
u
˜
2
˜
n
2
/8
where q
u
= 1.2(136) + 1.6(46.5*) = 238 psf
˜
2
= 24 ft
˜
n
(interior span) = 20 - 1.33 = 18.67 ft
˜
n
(end span) = 20 - 0.67 - 0.50 = 18.83 ft
Use larger value for both spans.
(c) Negative and positive factored gravity load moments:
Division of the total panel moment M
o
into negative and positive moments, and the, column strip
and middle strip moments involves direct application of the moment coefficients of Table 4-3.
Note that the moment coefficients for the exterior negative column and middle strip moments need to
be modified for
β
t
less than 2.5. For
β
t
= 0.29:
Column strip moment = (0.30 - 0.03
0.29)M
o
= 0.29M
o
Middle strip moment = 0.30M
o
- 0.29M
o
= 0.01M
o
End Spans
Interior Span
Slab Moments
(ft-kips)
Exterior
Negative
Positive
Interior
Negative
Positive
Total Moment
75.9
126.5
177.2
88.6
Column Strip
73.4
75.9
134.1
53.2
Middle Strip
2.5
50.6
43.1
38.1
Note: All negative moments are at faces of columns.
* Live load reduction: A
I
(4 panels) = 24
x
20 = 480 sq ft
L = 50(0.25 + 15/
480
) = 46.5 psf
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