Finite element analysis and design of cold-formed steel built-up closed section columns with web stiffeners

This paper presents a numerical investigation and design of cold-formed steel built-up closed section columns with web stiffeners. A finite element model (FEM), considering the initial geometric imperfections and nonlinear material properties, was developed to simulate the structural behaviour of fixed-ended built-up closed section compression members. The comparison between the numerical results and the available test results show that this FEM can provide good predictions for both the ultimate strength and the failure modes of the test specimens. The verified FEM was used to conduct an extensive parametric study for the investigation on the structural behaviour of cold-formed steel built-up closed sections with web stiffeners. The parametric study was designed to investigate the effect of web stiffeners as well as to evaluate the current design method. The column strengths obtained from the finite element analysis and the test results were compared with the design strengths calculated using the direct strength method in the North American Specification and the Australian/New Zealand Standard for cold-formed steel structures. Design curves modified from the current direct strength method are proposed for flexural, local and distortional buckling. The reliability analysis was used to assess the current design rules and the modified design curves. It is shown that the modified direct strength method is generally conservative and reliable for the design of cold-formed steel built-up closed section compression members.