Civil Engineering Reference
In-Depth Information
2.3.2
Example: Frame Analysis by Coefficients
Determine factored moments and shears for the joists of the standard pan joist floor system of Building #1
(Alternate (1)) using the approximate moment and shear coefficients of ACI 8.3.3. Joists are spaced at 3 ft on center.
(1)
Data:
Width of spandrel beam = 20 in.
Width of interior beams = 36 in.
Floors: LL = 60 psf
DL = 130 psf
w
u
= 1.2 (130) + 1.6 (60) = 252 psf
3 ft = 756 plf
(2)
Factored moments and shears using the coefficients from Figs. 2-3, 2-4, and 2-7 are summarized in Fig. 2-8.
30'-0"
30'-0"
15'-0"
8"
1'-
0"
˜
n
= 27.5'
3'-0"
˜
n
= 27.0'
3'-0"
˜
n
= 27.0'
Sym. about
C
L
Total Load
w
u
˜
n
= 0.76 x 27.5
= 20.9 kips
0.76 x 27.0 = 20.5 kips
0.76 x 27.0 = 20.5 kips
Coefficient
from
Fig. 2-7
Shear V
u
1.15/2
1
/
2
1
/
2
1
/
2
1
/
2
10.3 kips
10.3 kips
10.3 kips
10.5 kips
12 kips
w
u
˜
n
2
Coefficient
from
Fig. 2-3
Pos. M
u
574.8 ft-kips
554 ft-kips
554 ft-kips
1
/
14
1
/
16
1
/
16
34.6 ft-kips
41.1 ft-kips
34.6 ft-kips
˜
w
u
˜
n
2
Coefficient
from
Fig. 2-3
Neg. M
u
27.5 ft
27.25 ft*
27.25 ft*
27.0 ft
27.0 ft
574.8 ft-kips
564.3 ft-kips
564.3 ft-kips
554 ft-kips
554 ft-kips
1
/
11
1
/
24
1
/
10
1
/
11
1
/
11
56.3 ft-kips
24 ft-kips
51.3 ft-kips
50.4 ft-kips
50.4 ft-kips
*Average of adjacent clear spans
Figure 2-8 Factored Moments and Shears for the Joist Floor System of Building #1 (Alternate 1)
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