How about using STAAD-Pro FEM package. This software can be used for modelling any type of structure with various load cases and support conditions. I heard of one company M/S Kirby building systems based in Kuwait who is pioneer in preengineered steel structures. I understand they use STAAD...
Formulae for Stress and strain by Roark is a very good reference book for the this problem. It gives formulae for considering various boundary conditions and load cases.
