truss beam problem structural f32 i beam truss straight segment 2 5m wood columns trusses to steel beam i joist vs floor truss which is better beam to r c column connection in mrfs straight segments f32 i beam truss system deep trusses long span moment frames pre design of large span trusses l0 type soldering flu global truss america gp ib 10x20 f32 statically determinate indeterminate spatial structures