Distortional strength of end-bolted CFS lipped channel columns: Experimental investigation, numerical simulations and DSM design

This paper reports the results of an experimental investigation and numerical simulations concerning the influence of bolted end support conditions on the failure loads of cold-formed steel lipped channel columns buckling and failing in distortional modes, as well as on their prediction by means of the Direct Strength Method (DSM). The end supports consist of pairs of cylindrical high-strength bolts with hexagonal heads and nuts, which are inserted in standard-sized holes located at the intersections of the cross-section flanges with the minor principal centroidal axis (parallel to the web). After selecting the column geometries (cross-section dimensions and lengths) and yield stresses, the test set-up and procedure are described in detail, and the experimental results obtained are presented and discussed. Such results consist of initial imperfection measurements, equilibrium paths relating the applied load to key column displacements, deformed configurations (including the collapse mode) and failure loads. Next, those same experimental results are used to validate a previously developed shell finite model, which is subsequently employed to obtain additional numerical failure load data concerning the end-bolted columns under scrutiny. Then, attention is turned to assessing the merits of the available DSM column distortional design curves. Because it is concluded that these design curves clearly overestimate the failure load data obtained, new/modified strength curves are preliminarily proposed and shown to considerably improve the prediction quality (safety and reliability) of the end-bolted column failure loads, thus providing motivation and encouragement to continue the search for an efficient DSM-based design approach for end-bolted columns failing in distortional modes.