Numerical investigation and strength prediction of core-enhanced cold-formed steel hexagonal columns

Cold formed steel columns are extensively used due to their high strength to weight ratio. However, their thin-walled section is susceptible to local buckling, which limits their load-carrying capacity. This study is a numerical investigation of core-enhanced cold formed steel hexagonal columns with internal stiffeners and inner core for improving buckling resistance and structural performance. In contrast to early research that mainly focused on hollow hexagonal sections using existing design approaches, this study evaluates the structural performance of the proposed Core-Enhanced Hexagonal Sections (CEHS) and formulates modified Effective Width Method and CSM design equations for axial compression design. A validated nonlinear finite element model considering material nonlinearity, geometric imperfections and appropriate boundary conditions was employed to develop a numerical database comprising of 154 Finite Element models. The effects of width, thickness, slenderness ratio and core configuration on the ultimate capacity and failure modes were studied through a parametric study. The results show that the presence of a core improves the local buckling resistance, modifies the buckling response and increases the axial capacity with respect to unstiffened hollow hexagonal sections. The responses are influenced by local and local-global buckling interaction. The predicted strengths were thoroughly compared to design methodologies, the Effective Width Method (EWM) and Continuous Strength Method (CSM). On the basis of the numerical database revised equations for the CSM and EWM were proposed. The equations showed better agreement with the results obtained from the finite element analysis, with the mean values close to unity and reduced scatter. The proposed formulations provide more reliable basis for predicting the axial capacity of core-enhanced cold formed steel hexagonal columns.