Experimental investigation concerning lipped channel columns undergoing local–distortional–global buckling mode interaction

This work deals with the structural behaviour and ultimate strength of fixed-ended cold-formed steel lipped channel columns experiencing local–distortional–global buckling mode interaction, due to the closeness between the critical buckling stresses associated with these three buckling mode types. After briefly addressing the column specimen geometry selection and showing a few numerical elastic post-buckling results, the paper reports the results of an experimental investigation involving a set of 12 columns with several cross-section dimensions and yield stresses, which is aimed at (i) providing experimental evidence of the occurrence of the triple mode interaction under consideration and (ii) quantifying its effect on the column deformed configuration evolution and failure load erosion (drop). Various aspects concerning the test set-up and procedure are described in some detail before presenting and discussing the obtained column experimental results, which basically consist of (i) measured cross-section dimensions, lengths and initial displacements (geometrical imperfections), (ii) stress–strain curves and yield stresses determined from tensile coupon tests, (iii) recorded non-linear equilibrium paths (applied load vs. various relevant displacements) and ultimate strength values, and (iv) observed deformed configurations and collapse mechanisms.