Page 306 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch06.qxd 9/29/05 5:15 PM Page 6.28

DESIGN OF BUILDING MEMBERS

6.28 CHAPTER SIX

where C g = 1.6 for girders supporting joists connected to the girder flange (e.g., joist seats)
= 1.8 for girders supporting beams connected to the girder web
D g = girder transformed slab moment of inertia per unit width
3
4
= d e /12n, in /ft
D j = beam or joist transformed moment of inertia per unit width
4
= I g /S, in /ft
L g = girder span
D = 4315 ×12 = 143 85. in /ft
4
j
30
For this girder, C g = 1.8.
/
B = 18 ×  84 32.   14 × 30 = 47 245 ft < 2 × floor length
.
.
g
 4315 3
The girders are not affected by continuous action.
.
W = 1 853 × 47 25 30. × = 87 56. kips
g
30
Combined Vibration Investigation. The girder vibration calculations will be based on full com-
posite action and the shear deformations will not be included.
For the combined mode, the equivalent weight is
∆ ∆
W = j W + g W (6.37)
∆ j + ∆ g j ∆ j + ∆ g g

where ∆ j , ∆ g = beam, joist, or girder maximum deflection
If the girder span L g is greater than the joist or beam effective width B j , then the following adjust-
ment to the girder deflection is applicable but L g /B j ≥ 0.5:
L
∆ ′ = g ∆ ( ) (6.38)
g
B j g
Since L g /B j = 30/32.91 = 0.912 ≤ 1, then

∆ ′ = 30 (. = 0 246 in
.
0 269)
g
32 91
.
.
.
.
.
.
W = 0 447 88 76 + 0 246 87 56 = 88 327 kips
.
.
.
.
0 447 + 0 246 0 447 + 0 246
The combined natural frequency is calculated as follows:
386
.
f comb = 018 = 4 249. Hz
.
0 447 + 0 246.
For a typical modular office with small demountable partitions, β= 0.03 and P o = 65 lb.
a p = 65 × exp( −0 35 4 249) ×100% = 0 55% > 0 5 . % NG
× .
.
.
g 0 03 × 88 327 ×1000
.
.
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