Instances of mixed buckling and post-buckling of steel RHS beams

Simply supported steel beams with rectangular hollow section (RHS) are investigated, taking into account large twist and cross-sections distortions. A closed-form expression for the critical value of external couple inducing lateral torsional buckling is found; homotopy perturbation method (HPM) used to investigate post-buckling non-linear path. The linear paths given by HPM compared those of: i) a Newton–Raphson algorithm arc length; ii) commercial FEM code Abaqus. Some numerical examples presented.