Recent Development in the Direct Strength Method of Design for Cold‐Formed Hat Sections under Localised Loading

Abstract The Direct Strength Method (DSM) of design for cold‐formed steel structural members has been well developed and incorporated into both the North American Specification (AISI S100) and the Australian/New Zealand Standard (AS/NZS4600). While DSM provides design provisions for compression, bending and shear, no rules are presented in these design codes for cold‐formed sections under localised loading, especially for hat sections. Recently, an experimental program has been performed by the authors at the University of Sydney to investigate the yielding behaviour of hat sections under various localised loading cases. Based on these findings, a comprehensive plastic mechanism model was proposed to determine the yield load for hat sections under localised loading. Subsequently, preliminary DSM design equations were developed using the derived yield load for each localised loading case. Although these equations showed strong agreement with the predictions for hat sections failing by yield‐arc mechanisms, they produced conservative results for sections failing by rolling mechanisms. This paper further studies the correlation between the hat sections' rounded corner radii and the overconservative predictions of the preliminary DSM design equations. Two advanced sets of DSM design equations, each based on distinct design concepts, are recommended for the DSM design of hat sections subjected to localised loading in this paper. The predicted results from the new DSM equations are discussed and validated against experimental results from the literature.