Behavior, strength and DSM-based design of cold-formed steel pin-ended columns buckling in flexural-torsional modes

Recently, the authors (Dinis et al. 2022, Cerqueira et al. 2023) studied the post-buckling behavior, strength and Direct Strength Method (DSM) design of cold-formed steel (CFS) fixed-ended singly symmetric columns buckling in major-axis flexural-torsional modes (FMT) and possibly experiencing interaction with minor-axis flexural (Fm) buckling -- FMT-Fm interaction. They developed an efficient DSM-based design approach to predict the failure loads of those columns, regardless of their failure nature (pure FMT or FMT-Fm interactive). The purpose of this work is to extend the scope of the above investigation to singly symmetric columns with three types of pin-ended support conditions, all fixed with respect to torsion and have warping fully prevented. Columns with seven cross-section shapes are considered and their wall dimensions, lengths and yield stresses are selected to ensure covering wide FMT slenderness ranges and various ratios between the Fm and FMT buckling loads. After investigating the elastic and elastic-plastic ostbucklingbehaviorsof the selected pin-endedcolumns, namely those affected by FMT-Fm interaction,a fairly extensive parametric study is carried out to gather pin-ended column failure load data, most of which are supposedly associated FMT-Fm interactive collapses. Then, the assembled numerical failure load data, together with failure loads previously reported by Dinis et al. (2020), are used (i) to show that none of the available DSM-based strength curves are able to predict all of them adequately and (ii) to develop and assess the merits of DSM-based design approaches to estimate the failure loads of pin-ended singly symmetric columns buckling in FMT modes and failing in either pure FMT or FMT-Fm interactive modes -- since no single design curve/approach can handle all the pin-ended columns considered, different strength curves are proposed for columns exhibiting each type of pin-ended support conditions.

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