DSM-based prediction of distortional failure loads of cold-formed steel columns at elevated temperatures

Abstract

This work is dedicated to investigate the structural behavior, strength and Direct Strength Method (DSM) design of cold-formed steel columns failing in distortional modes at elevated temperatures. The numerical results, obtained by means of ANSYS shell finite element analyses (SFEA), concern columns with (i) two end support conditions (fixed and pinned end supports), (ii) lipped channel cross-section shape with different dimensions (bw/bf equal ~ 0.7, 1.0 and 1.4), (iii) several room temperature yield stresses (distortional slenderness range up to ~ 3.5), (iv) critical-mode (distortional) initial geometrical imperfections with small amplitudes, and (v) subjected to eight uniform temperatures (up to 800 oC). It is shown that the currently codified DSM distortional design equations are unable to predict adequately failure loads under fire conditions. The temperature dependence of the steel material properties is simulated using the model prescribed in part 1.2 of Eurocode 3 (EC3-1.2) for cold-formed steel. The column failure load data obtained are used to appraise how the quality of the predictions provided by the existing DSM distortional strength curves is influenced by the temperature-dependent steel constitutive model. Finally, modified curves are developed for fixed and pinned end members, exhibiting a significant improvement of the DSM distortional design in estimating the ultimate strength of the CFS columns submitted to elevated temperatures.