Numerical simulation and specification provisions for cruciform cold-formed steel built-up columns

Abstract

This paper addresses the nonlinear behavior of cruciform cold-formed steel (CFS) built-up columns formed by high-strength bolts and filler plates under axial compression. Nonlinear finite element modeling using ANSYS software is developed to simulate the behavior, including both geometric and material nonlinearities, and the numerical results are compared with the test results obtained by the authors and reported in another paper, showing good agreement. The finite element model in this paper predicts the ultimate loads and buckling modes of the specimens well. Following validation, the C89 series cross-section was selected for numerical and theoretical study using a varying slenderness ratio λ, plate thickness t and bolt spacing s. The results are compared with the nominal axial resistance calculated using the existing design standards, including the direct strength method (DSM) in the AISI Specifications and the effective width method (EWM) in the provisions of Chinese code GB50018-2002. The results show that the current AISI specifications have many overestimated resistance predictions for the cruciform CFS built-up columns, and the error decreases with the increase in the slenderness ratio, while the provisions in the Chinese code are overly conservative for predicting the resistance values of the cruciform CFS built-up columns. Therefore, a design procedure based on the effective width method is proposed for the resistance evaluation of axially compressed cruciform steel built-up columns.