Local buckling of cold-formed steel lipped Z section beams under pure bending

This paper investigates the local buckling of cold-formed steel lipped Z sections under pure bending. Several series of four-point bending tests available from previous research have been used to develop and verify numerical models with special reference to geometric imperfections. Once verified, the local buckling response of lipped Z sections under flexure is investigated using comprehensive parametric studies with varying lip sizes and flange widths. Lateral-torsional buckling mode is effectively restricted using lateral restraints. Local buckling occurs prior to distortional buckling using the lowest Eigenmode representing local buckling as the shape of initial imperfections. Comparing the results with the predictions of existing European and British codes demonstrates that both are rather conservative in predicting the pure bending moment capacity of lipped Z sections, especially, for sections with smaller flange to thickness ratios.