My co worker thinks that we can use the AISC 360 provisions for W sections, calculating Lp and Lr from rx and ry for the entire composite shape. My worry is it will overestimate the LTB capacity. Capacity comes out to be governed by the plastic section (which he gets from adding Zx from one and Zy from another W24x55) so 552 k-ft
I would think to use the LTB capacity of a single W24x55, so 135 k-ft.
Intuitively, my idea is a lower bound and my co workers is an upper bound. The gap is wide. How would you do this?