A horizontal hollow rectangular mild steel tube 30mm x 50mm with 4mm wall thickness and 350mm long, which is part of a frame has 2 lengths of studding 300mm long , 180mm apart and equidistant from the ends, welded to the 50mm face of the tube. A total perpendicular load of 400Kgs is applied to the ends of the studding. By what amount the tube will twist? I am only interested in the twisting or torsion of the horizontal tube, as this is the weakest part of the frame. I also feel that it might simplify calculation if the load is considered at the midpoint of the tube. I have looked at various equations in Wikipedea but I am even more confused now than when I started to look at this problem. Is there a simple equation /s which I could use to calculate this?