Direct strength prediction of cold-formed steel fixed-ended singly-symmetric columns buckling in flexural–torsional modes

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The work reported in this paper is a sequel of previous numerical investigations carried out by the authors on the post-buckling behaviour, strength and Direct Strength Method (DSM) design of cold-formed steel (CFS) fixed-ended plain and lipped channel columns (both singly-symmetric with respect to the major-axis) buckling in flexural–torsional modes and experiencing global-global interaction – a coupling phenomenon involving major-axis flexural–torsional (FMT) and minor-axis flexural (Fm) buckling that was first unveiled in those studies. In the specific context of plain and lipped channel columns, a DSM-based design approach for columns buckling in FMT modes and failing in either pure FMT or FMT-Fm interactive modes was developed and shown to provide accurate, mostly safe and reliable predictions of the experimental (only a few) and numerical failure loads available. The success of this research effort encouraged the authors to extend the scope of the investigation to fixed-ended columns with other singly-symmetric cross-section shapes, namely return-lip, web-stiffened and web/flange-stiffened lipped channels, hat-sections and rack-sections (deemed representative of any arbitrary singly-symmetric cross-section). The results attained during this investigation are presented and discussed in detail – they concern the post-buckling behaviour, strength and DSM-based design of the columns analysed, including fairly extensive failure load sets (Ansys non-linear shell finite element models are used to obtain them). The main output of this work is a DSM-based design approach for arbitrary CFS fixed-ended singly-symmetric columns exhibiting pure FMT or FMT-Fm interactive failures.