Cross-section slenderness limits for columns with plastic rotations

•Braced frame construction with discontinuous columns explained•Full-scale discontinuous column tests conducted•New design method outlined•Current code slenderness limits shown to be optimistic for thin walled tubes

This paper reports on a study of local inelastic buckling in square hollow section columns with large plastic rotations. The study was conducted as part of the validation of a proposed design method for discontinuous columns in braced frames in which plastic rotations in the columns are used to limit the moments in the columns. The study included both testing of full-scale columns and a parametric study by finite element analysis. The results demonstrate that current codes permit cross section slenderness in plastic sections which are likely to lead to premature buckling in structures using plastic (inelastic) design if the rotations are large. Design limits are proposed for square hollow sections relating cross-section slenderness to column end rotations.