DSM design of CFS columns subject to distortional buckling at elevated temperatures

Cold-formed steel (CFS) columns are subject to distortional buckling unlike hot-rolled steel columns. Many experimental and numerical investigations have been conducted on the distortional buckling behaviour and capacity of CFS columns at ambient and elevated temperatures. However, constitutive laws of CFS at ambient and elevated temperatures are different with varying levels of nonlinear stress-strain characteristics. Thus, the ultimate distortional buckling capacities predicted by the elevated temperature design rules can be unconservative when the ambient temperature design equations are used with elevated temperature mechanical properties. However, no study has fully incorporated the effects of nonlinear stress-strain characteristics of CFS at elevated temperatures. Therefore, this research study investigated the effects of nonlinear elevated temperature stress-strain characteristics on the distortional buckling capacities of CFS columns using three parameters, namely, nonlinearity, strain hardening and yield strength to Young’s modulus ratio, through a numerical parametric study. A comparison of ultimate capacities from the parametric study with those predicted by the current AS/NZS 4600 direct strength method (DSM) showed that the current design equations cannot accurately capture the effects of nonlinear elevated temperature stress-strain characteristics. Consequently, modified DSM equations were proposed to accurately predict the distortional buckling capacities of CFS columns at elevated temperatures