Post-buckling behaviour and strength of cold-formed steel lipped channel columns experiencing distortional/global interaction

This paper reports the results of a numerical investigation concerning the elastic and elastic-plastic post-buckling behaviour of cold-formed steel lipped channel columns affected by distortional/global (flexural-torsional) buckling mode interaction. The results presented and discussed were obtained by means of analyses performed using the finite element code Abaqus and adopting column discretisations into fine 4-node isoparametric shell element meshes. The columns analysed (i) are simply supported (locally/globally pinned end sections that may warp freely), (ii) have cross-section dimensions and lengths that ensure equal distortional and global (flexural-torsional) critical buckling loads, thus maximising the distortional/global mode interaction effects, and (iii) contain critical-mode initial geometrical imperfections exhibiting different configurations, all corresponding to linear combinations of the two ''competing'' critical buckling modes. After briefly addressing the lipped channel column ''pure'' distortional and global post-buckling behaviours, one presents and discusses in great detail a fair number of numerical results concerning the post-buckling behaviour and strength of similar columns experiencing strong distortional/global mode interaction effects. These results consist of (i) elastic (mostly) and elastic-plastic non-linear equilibrium paths, (ii) curves or figures providing the evolution of the deformed configurations of several columns (expressed as linear combination of their distortional and global components) and, for the elastic-plastic columns, (iii) figures enabling a clear visualisation of (iii"1) the location and growth of the plastic strains and (iii"2) the characteristics of the failure mechanisms more often detected in the course of this research work.

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