Thanks for all your information above! I finally get this problem fixed. The reason I made a mistake is that when I started a model, I selected "plane" instead of "space" to build a plane model in which I calculated the buckling about strong axis. The result I got was the bulking loads about...
Did anyone verify the buckling analysis in staad? I just tried a simple Example from "Steel Design" textbook, but theoretical Euler solution gives different results from that Staad does. The example is W12x50 beam, 20 ft long with two end pinned. Using Euler theory, the buckling load is 278.9...
