On the influence of local-distortional interaction in the behaviour and design of cold-formed steel web-stiffened lipped channel columns

This work reports the results of a numerical (Abaqus shell finite element analysis) investigation on the influence of local-distortional (L-D) interaction in the ultimate strength and design of fixed-ended cold-formed steel web-stiffened lipped channel columns, hereafter termed “WSLC columns”. These results concern columns with various geometries and yield stresses, ensuring a wide variety of combined ratios between (i) the distortional and local critical buckling stresses, and (ii) the yield stress and the higher of the above two buckling stresses. The objectives of the work are two-fold: (i) acquire in-depth knowledge on the mechanics underlying the L-D interaction in the WSLC columns analysed, all selected to ensure that local buckling is triggered by the flanges, and also (ii) provide a first contribution towards the efficient Direct Strength Method (DSM) design of these columns. The results presented and discussed concern the (i) post-buckling behaviour (elastic and elastic-plastic), (ii) ultimate strength and (iii) failure mechanisms of WSLC columns undergoing L-D interaction. Special attention is paid to the comparison between the ultimate strength erosion, stemming from L-D interaction, exhibited by web-stiffened and plain lipped channel columns (the latter were studied earlier by the authors). The paper closes with some considerations about the impact of the findings reported in this work on the design of cold-formed steel columns experiencing different levels of L-D interaction.