Local-distortional-global interaction in cold-formed steel lipped channel columns: Behavior, strength and DSM design

This work deals with the structural behavior and ultimate strength of fixed-ended cold-formed steel (CFS) lipped channel columns experiencing various levels of local-distortional-global (L-D-G) mode interaction. Initially, the paper addresses the selection of the column cross-section dimensions and lengths, intended to ensure various L-D-G interaction levels (more or less close critical stresses). Then, attention is turned to the experimental test campaign carried out at The University of Hong Kong, aimed at (i) providing experimental evidence and characterization of the occurrence of L-D-G interaction, and (ii) quantifying the associated failure load erosion. Next, the test results are used to develop and validate an Abaqus non-linear shell finite element model, subsequendy employed to perform a parametric study that is mostly intended to gather (numerical) failure load data - 368 fixed-ended columns exhibiting different geometries and various yield stresses, which ensure covering a wide slenderness range. Finally, the paper also assesses the quality of the failure load estimates provided by various design approaches, based on the Direct Strength Method (DSM), for CFS columns affected by the triple coupling phenomenon under consideration. This assessment is based on the comparison with both (i) the experimental and numerical failure loads obtained in this work, and (ii) additional ultimate strength values collected from the literature.