5 A W12x120 beamcolumn member with no holes and Fy 50ksi is

5. A W12x120 beam-column member with no holes and Fy 50ksi is subjected to factored second order compression demand of 720k and factored second order moment demand of 186.2k. Is the member satisfactory in LRFD if Lb-Lx Ly = 16, and Cb-1.0? (Hint: determine design strengths of com pression and morment. Use Chapter H to combine axial and moment).

Solution

compression capapcity of w12x120 for effective length of 16\' = 1200 kips

moment capacity of W12x120 for unbraced length of 16 = 698-[(698-428)/(56.5-11.1)]*(16-11.1)=668.8 kip-ft

compression demand = 720 kips

moment demand = 186.2 kip-ft

Therefore, intercation check is (720/1200)+(8/9)*(186.2/668.8)=0.85<1

Section is adequate