LOCAL / DISTORTIONAL / GLOBAL MODE COUPLING IN FIXED LIPPED CHANNEL COLUMNS: BEHAVIOUR AND STRENGTH

This paper reports the available results of an ongoing numerical and experimental investigation on the post-buckling behaviour and strength of fixed-ended cold-formed steel lipped channel columns affected by local/distortional/global (flexural-torsional) mode interaction. Initially, ABAQUS shell finite element results concerning columns exhibiting identical local, distortional and global buckling loads (their geometries are identified through preliminary buckling analyses) are presented and discussed  otherwise identical columns containing critical-mode initial geometrical imperfections with different configurations are analysed. These numerical results include (i) elastic and elastic-plastic post-buckling equilibrium paths, (ii) curves and figures providing the evolution, along a given path, of the column deformed configuration and (iii) the characterisation of the column collapse mechanism. Then, the paper addresses the experimental investigation currently under way at COPPE (Federal University of Rio de Janeiro) and to be fully reported in the near future  experimental and numerical results concerning one test are presented and discussed. Finally, the paper closes with some preliminary considerations concerning the applicability of the current Direct Strength Method (DSM) expressions to estimate the ultimate strength of cold-formed steel lipped channel columns experiencing local/distortional/global buckling mode interaction.

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