Civil Engineering Reference
In-Depth Information
For the roof:
Slab
= (121 ft)(61 ft)(0.122 ksf)
= 900 kips
Interior columns (8 columns)
= 8 (1.33 ft)(1.33 ft)(6 ft)(0.15 kcf)
= 12.8 kips
Exterior columns (12 columns)
= 12(1 ft)(1 ft)(6 ft)(0.15 kcf)
= 10.8 kips
Walls
= 2[(20.66 ft)(0.66 ft) + 2(7.33 ft)(0.66 ft)](6 ft)(0.15 kcf)] = 42 kips
Effective seismic weight (roof)
= 900 + 12.8 + 10.8 + 42
= 966 kips
The total effective seismic weight:
W = 1195 + 3(1179) + 966 = 5698 kips
Seismic Base Shear
V = C
s
W
V = 0.055
5698 = 313.4 kips
Vertical Distribution of the Base Shear
The vertical distribution of the base shear V can be calculated using ASCE Eqs. 12.8-11 and 12.8-12
(Section 12.8.3). For T = 0.45 second the distribution exponent k = 1. The calculations for the lateral forces
and story shear are shown in Table 11-3:
Table 11-3 Forces and Story Shear Calculations
y
Story
Weight
w
x
(kips)
Lateral
Force
F
x
(kips)
Story
Shear
V
x
(kips)
Height
h
x
(ft)
w
x
h
x
k
Level
5
63
966
60,858
88
88
4
51
1,179
60,129
87
176
3
39
1,179
45,981
67
242
2
27
1,179
31,833
46
288
1
15
1,195
17,925
26
314
∑
5,698
216,726
314
For building frame system the lateral force are carried by the shear walls. Gravity loads (dead load and live
load) are carried by the frames.
Distribution of the Seismic Forces to the Shear Walls in N-S Direction
For north south direction, consider that the lateral forces are carried by the two 248 in. by 8 in. shear walls. For
the symmetrical floor layouts the center of rigidity coincides with the center of mass at the geometric center of
the 120ft by 60ft floor area.
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