Lateral Stability of Unsymmetrical I-Beams And Trusses in Bending

An analysis is given herein of the lateral stability of unsymmetrical I-beams, both free and horizontally restrained along the bottom edge, and of beams of rectangular cross section horizontally restrained along the bottom edge. The cases of horizontally restrained beams apply to sheet stiffeners in bending. It is explained that the torsional rigidity of trusses and of thin-wall I-beams is smaller than would be expected from the use of the usual formulas for torsional stiffness. This is due to the fact that horizontal bending of such elements is accompanied by distortion of the cross section. For this reason, it is suggested that satisfactory, although slightly conservative, estimates of the critical loads of such beams may be obtained by neglecting the torsional rigidity entirely.