Global-Global Interaction in Cold-Formed Steel Channel Columns: Relevance, Post-Buckling Behavior, Strength and DSM Design

Recently, in the context of numerical investigations dealing with the accuracy of the codified Direct Strength Method (DSM) column global design curve in predicting the ultimate strength of cold-formed steel columns failing in major-axis flexural-torsional modes, the authors (Dinis et al., 2018, 2019) unveiled the fact that, depending on the column geometry (length and cross-section shape/dimensions) and end support conditions, its failure load may be visibly eroded by the occurrence of interaction between the column first two global buckling modes: a major-axis flexural-torsional (critical) one and a minor-axis flexural one. To the authors’ best knowledge, such a global-global coupling phenomenon has only been investigated in the context of intermediate equal-leg angle columns, (e.g., Dinis et al. 2015, 2016, 2019), which exhibit a very peculiar structural behavior stemming from the fact that they are formed by just two outstand walls (very similar flexural-torsional and local deformations).

The aim of this work is to report the available results of an ongoing numerical investigation on the post-buckling behavior, strength and design of cold-formed steel channel columns experiencing global-global (G-G) interaction. In particular, the relevance of the G-G interaction is discussed, in order to assess when the column ultimate strength and/or failure mode are visibly affected by its development. It is necessary to identify ranges of (i) flexural-to-flexural-torsional buckling load ratios and (ii) squash-to-non critical global buckling load ratios that lead to non-negligible failure load erosion. Elastic and elastic-plastic post-buckling behaviors of different columns affected by several levels of G-G interaction are discussed and compared. The results presented consist of (i) relevant non-linear equilibrium paths, (ii) deformed configuration evolutions along those paths, evidencing G-G interaction, and (iii) figures providing the failure mode characteristics. Then, numerical failure load data are obtained and compared with their predictions by the available DSM-based column global strength curves and a few design considerations and/or guidelines are drawn from this comparison.

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