Effect of In-Plane Deformation on Lateral Buckling

In the classical analysis of the flexural-torsional buckling of beams, beam columns and rigid-jointed plane frames, it is assumed that the major axis rigidity is very large, so that the small in-plane deformations can be neglected. The effects of the in-plane deformations on lateral buckling are investigated in this paper for determinate beams and cantilevers, beam columns, continuous beams, and portal frames. This is done by deriving more accurate governing differential equations, and by obtaining closed form or numerical solutions of these. The results obtained indicate that the classical critical loads or moments are generally conservative, except for the members which are highly restrained laterally. The sources of error in the classical analysis are also studied, and their effects are demonstrated. The results of experiments on small scale beams, which are in close agreement with the theoretical predictions, are reported.