Torsional, flexural and torsional-flexural buckling of angle section members - an analytical approach

In the framework of the ongoing revision of EN 1993-3-1, the RCFS funded research project ANGELHY is currently performing experimental, numerical and theoretical studies on angle sections and lattice towers. This paper presents a particular aspect of the ANGELHY project and focusses on a theoretical study concerning the behaviour of angle section members. First, the elastic second order equation of such members subjected to axial compression is established. Then, this differential equation is solved based on different assumptions concerning geometric imperfections to determine second order displacements, rotations and internal forces and moments. The analytical second order solution is validated through comparisons to a numerical elastic second order analysis. Based on the validated analytical solution, it is then shown, that even if torsional/torsional-flexural buckling of angle section members was relevant according to the elastic critical loads, the member rather fails by flexural buckling only. The reason for this unexpected conclusion may be directly derived from the second order internal forces and moments as shown in the last part of this paper.