Distortional Post-Buckling Behavior and Strength of Cold-Formed Steel Columns: How does the Cross-Section Geometry Affect it?

This paper reports the available results of a numerical research effort currently under way and whose final goal is to assess and mechanically interpret the influence of the cross-section geometry and end support conditions on the elastic distortional post-buckling behavior and strength of cold-formed steel columns. This work deals only with simply supported (pinned end sections that can warp freely) columns exhibiting lipped channel, hat and zed cross-sections, which share common critical distortional buckling loads (for the same length and cross-section dimensions, of course) − i.e., the columns eligible for this investigation are grouped into various column triplets. Initially, the paper presents the column geometry selection (cross-section dimensions and lengths), which involves sequences of “trial-and-error” buckling analyses based on Generalized Beam Theory (GBT) and leads to column triplets buckling in “pure” distortional modes and purposely exhibiting a wide range of cross-section proportions. Taking advantage of the GBT modal decomposition features, the buckling analyses are also used t mechanically characterize the various column critical bucking modes − in particular, their most relevant modal participations are identified and quantified, which may help in predicting the column post-buckling behavior and strength. Then, the paper presents and discusses results concerning the elastic post-critical strength of the selected column triplets, obtained from ANSYS shell finite element analyses − a representative sample of the corresponding equilibrium paths and post-buckling deformed configurations are also shown. In particular, the post-critical strength data are used to attempt identifying key parameters (e.g., cross-section dimension ratios or critical buckling mode mechanical characteristics), in the sense that they play a pivotal role in influencing the features exhibited by the column distortional post-buckling behavior and strength. Finally, the paper closes with a few concluding remarks that also address the next steps of the current research effort. 

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