14 A W18x60 is used on a 36ft simple span to carry a uniform

14. A W18x60 is used on a 36-ft simple span to carry a uniformly distributed load. Determine the locations of the lateral supports in order to provide just enough strength to carry a design moment of 280 kip-ft. Use A992 steel.

Solution

Given beam section is W18x60

Beam strength required = 280 kip-ft
L_r of beam per Table 3-2 of AISC is 18.2 ft and M_r of beam is 284 kip-ft

since design moment is almost equal to M_r of beam, the unbraced length of beam should be equal to 18 ft

Since the beam span is 36 ft, unbraced length of 18 ft can be achieved by adding a lateral support at midspan of beam.