Local-distortional interaction in cold-formed steel columns: Non-linear behaviour, ultimate strength and DSM design

This paper provides an overview of the most recent research activity concerning the (i) nonlinear behaviour (elastic and elastic-plastic), (ii) ultimate strength and (iii) Direct Strength Method (DSM) design of cold-formed steel columns experiencing local-distortional (L-D) interaction. After briefly introducing and illustrating this mode coupling phenomenon, both numerical (Abaqus 4-node shell finite element analysis) and experimental results are presented, compared and discussed. The numerical investigation make it possible to characterise the L-D interactive behaviour and failure of columns with different cross-section shapes (lipped channels, hats, zeds and racks) and includes fairly extensive parametric studies, carried out in order to (i) assess how the relevance of the L-D interaction effects varies with the ratios between the competing (local and distortional) critical buckling stresses and the steel yield stress, and (ii) gather a substantial ultimate strength data bank. Then, the experimental tests, dealing with lipped-channel and rack-section columns, provides experimental (i) evidence of the occurrence of clear L-D interaction and (ii) failure loads and collapse mechanisms. Next, after showing the inadequacy of the current DSM local and distortional column strength curves to predict L-D interactive failures, the paper presents and assesses the merits of recently developed DSM-based design procedures against such interactive column failures. Finally, the paper closes with some concluding remarks and a few comments on developments planned for the near-to-intermediate future.