Jeff,
When I started using HSS, I called the tech department at RAM, who advised using A500 Grade B for structural use. The veteran at local Ceres Pipe & Metal told me, "A 500 Grade A is used only for architectural purposes. For structural applications, Grade B is used."
In fact, my structural software, RAM Advanse, does not even include A500 Grade A in the standard database of materials. Only Gr. B and Gr. C are listed.
Hope this helps, DairyDesigner