A small pedestrian bridge is supported by a rocker at an end (B) and a pin at the other (A). A 200-lb person is standing 4-ft out from point A. The bridge has a weight of 500-lb. Assuming the center of gravity is in the middle of the bridge, calculate the reaction at points A and B.
Solution
↻+ (clockwise positive)
↻+ΣMA=
0
200lb (4ft) + 500lb
(10) - By (20ft) = 0
By = 290 lb
B = 290 lb
↻+ΣMB=
0
Ax (0) + Ay (20ft) -
200lb (16ft) - 500lb (10ft) = 0
Ay = 410 lb
A = 410 lb
Check;
↑+ΣFy = 0
410 - 200 - 500 + 290 = 0
0 = 0
