Question

2. A roof plan for a small building is shown below. The roof is composed of joists which frame beams or girders, which frame into into columns A, B, C, and D. The joists support a dead load 200 lb/ft2 and live load - 500 lb,/ft?. In Area ABEF there are 4 joists evenly spaced at 6 ft O.C. In Area FGHD there are 3 joists evenly spaced at 5 ft OC. Joists 5 ft 15 ft typ. typ. 6 ft typ B 6 ft typ. 30 Open 46 CH Provide the following: - If L 40 ft and B 30 ft, calculate the vertical loads columns A, B, C, and D must support. Neglect the self-weight of the joist and beams. Do not use live load reductions.

Answer 1

first convert all the slab load to live load acting on joint

6" spaced = 6X ( 500 + 200) = 4200 lb/ ft

5' spaced = 5 X 700 = 3500 lb/ft

load on beam AF and BE = 3 X 700 = 2100 lb/ft

load on beam FG and DH = 2.5 X 700 = 1750 lb/ft

6' joint = ( 20 X 4200) / 2 = 42000 lb / ft

5' joint = (15 X 3500) / 2 = 26250 lb each side

load on column A and F due to beam

(20 X 2100)/2 = 21000 lb on B and E

load on column F, D, G and H due to beam FD and GH = (15 X 1750) /2

312 S 2625o 2 000 u1 000

A = 105000 lb

B = 105000 lb

C = 0 lb

D = 39375 lb