21 Determine the adequacy of the following biaxial bending m

2-1: Determine the adequacy of the following biaxial bending members subject to the load conditions given assuming Cb- 1.0 MIx 200 MIx 425 MIx-845 Lb Oft a) W18x71 Fy-36 b) W12x120 Fy-50 b) W27x129 Fy50 Mry-30 kip-ft My 180 kip-ft Lb 18 ft Mry-53 kip-ft Lb 21 ft

Solution

a) moment capacity of w18x71 about major axis = 394.5 kip-ft

moment capacity of w18x71 about minor axis = 66.7 kip-ft

interaction ratio = (200/394.5)+(30/66.7)=0.96

section is adequate

b)moment capacity of W12x120 about major axis for unbraced length of 18 ft = 698-[(698-428)/(56.5-11.1)]*(18-11.1) = 657 kip-ft

moment capapcity of beam about minor axis = 320.2 kip-ft

intercation ratio= (425/657)+(180/320.2)=1.2

section is not adequate

c)moment capacity of W27x129 about major axis for unbraced length of 21 ft = 1480-[(1480-906)/(24.2-7.81)]*(21-7.841)=1019.1 kip-ft

moment capapcity of beam about minor axis = 216 kip-ft

intercation ratio= (845/1019.1)+(53/216)=1.07

section is not adequate