Mode Interaction in Cold‐Formed Steel Members: State‐of‐Art Report

Abstract

AbstractThis work provides a state‐of‐art report on the most recent findings concerning the behaviour, strength and Direct Strength Method (DSM) design of cold‐formed steel (CFS) columns and beams affected by mode coupling phenomena not adequately covered by the current specifications for CFS members, namely local‐distortional (L‐D), local‐distortional‐global (L‐D‐G), distortional‐global (D‐G) and global‐global (flexural‐torsional/flexural ‐ FT‐F) interaction. The paper addresses experimental tests, numerical simulations and DSM‐based design approaches, intended to (i) acquire in‐depth knowledge on the non‐linear behaviour (elastic and elastic‐plastic), load‐carrying capacity and failure mode nature of the members under consideration, and (ii) make use of the above knowledge to develop, propose and assess the merit of efficient DSM‐based design approaches to estimate their failure loads or moments. Initially, illustrative column results are briefly presented to help grasp some fundamental concepts, namely the characterisation of the (i) above mode coupling phenomena, (ii) different sources of mode interaction that may lead to failure load/moment erosion and (iii) the most detrimental initial geometrical imperfections ‐ also presented are the currently codified DSM design curves, as well as two recently developed strength curves for column flexural‐torsional and beam distortional failures. Then, the paper addresses separately each mode coupling phenomenon dealt with, for columns, and only L‐D and D‐G interaction for beams. For columns undergoing L‐D and L‐D‐G interaction, beams experiencing L‐D interaction and angle columns susceptible to FT‐F interaction, the work reported includes experimental studies, numerical simulations and DSM‐based design considerations and/or guidelines. For the remaining coupling phenomena only numerical results are reported, but they unveil interesting (and unexpected) behavioural features that will help plan future test campaigns and achieve efficient design approaches. Finally, the paper closes with a few concluding remarks and a perspective about future developments in this field.