Question

simply suppo 499 span s 20 ft· mid-pont. It is brated The steel is A992. しRFD 4mpet w14x99 the flange i's n Please calculate pMn f this baam. Pu cusiqn. ange is non- Compact =137.3 seb is campa T

Answer 1

The given cross-section is with Non-Compact flange and Compact web as classified by you and hence section F3 should be used to calculate the moment capacity of the member.

As per Section F3, the member may fail due to Lateral Torsional buckling and Compression Flange Local Buckling.

As Lb < Lp, Lateral torsional buckling does not occur .

Compression flange Local buckling :

As the section is with non compact flange, $Mn = Mp - (Mp - 0.7 *Sx*Fy)(\frac{\lambda -\lambda pf}{\lambda rf-\lambda pf})$

Given $\phi Mp =$ 646 , therefore Mp = 646/0.9 = 718 kip-ft = 8616 kip-in

Fy = 50 ksi ; Zx = 173 in^3 ;

therefore Mn = 8616 - [(8616-6055)(0.01270903)] = 8583.45 kip-in = 716 kip-ft

Therefore $\phi Mn =$ 0.9 * 716 = 644.4 kip-ft .