8 2. 30 ft 30 ft A partial roof plan of a reinforced concrete building is shown
ID: 1885134 • Letter: 8
Question
8 2. 30 ft 30 ft A partial roof plan of a reinforced concrete building is shown to the right. The roof is subjected to a dead load (D) O of 80 psf (which includes the self-weight of the roof slab and roofing materials, but not weight of girders), a roof live roof load (LR) of 35 psf, and a snow load (S) of 50 psf. The girders have nominal cross sectional dimensions of 10 x 18 in C1 Determine the factored load for a typical interior girder along Column Line B r Assume a concrete density of 145 lb/ft3. No need to consider live load reduction.Explanation / Answer
girder size = 10x18
self weight of girder = (10/12)*(18/12)*145/1000=0.18125 kip/ft
tributary width of typical east west beam = 30/2=15 ft
dead load = 80 psf
snow load=50 psf
Roof live load = 35 psf
uniform load on each East West beam due to dead load = 80*15=1200 lb/ft=1.2 kip/ft
uniform load on each East West beam due to snow load = 50*15=750 lb/ft=0.75 kip/ft
uniform load on each East West beam due to Roof live load = 35*15=525 lb/ft=0.525 kip/ft
dead load concentrated load on each girder along column line B due to each beam running East West = 1.2*30/2=18 kips
snow load concentrated load on each girder along column line B due to each beam running East West = 0.75*30/2=11.25 kips
Roof live load concentrated load on each girder along column line B due to each beam running East West = 0.525*30/2=7.875 kips
Total concentrated load on each girder along column line B due to dead load = 2*18=36 kips
Total concentrated load on each girder along column line B due to snow load = 2*11.25=22.5 kips
Total concentrated load on each girder along column line B due to Roof live load = 2*7.875=15.75 kips
per load combination of 1.2D+1.6(Lr or S), the factored concentrated load on girder will be governed by 1.2D+1.6S since Snow load is more than Roof live
Therefore, factored concentrated load on girder = (1.2*36)+(1.6*22.5)=79.2 kips
Factored uniform load on girder due to self weight of girder = 1.2*0.18125=0.2175 kip/ft
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