Failure mechanism and reliability prediction of CFS built-up columns considering distortional buckling

Abstract

This paper aims to investigate the instability mechanism, the assembly effect, the critical buckling stress, and ultimate capacity of the CFS built-up box section (CFSBBS) column. The design rules for distortional buckling related to the CFSBBS column are presented. Additionally, the distortional buckling behavior of the examined members is briefly discussed. The theoretical models are established, including the mutual mechanical interaction between plates and boundary simplification. The shear slip deformation of the connection interface and the effect of discrete screw constraints are considered in the theoretical model. The calculation formula of the critical distortional buckling stress is proposed based on the equilibrium differential equation, deformation compatibility conditions, and the corresponding equation obtained using the Galerkin method. Subsequently, the influence of extensive parameters such as boundary conditions, geometric dimensions of the cross-section, and screw spacing on the critical distortional buckling stress is revealed. Finally, an approach for predicting ultimate capacity is carried out by substituting the proposed design method into the direct strength method. Conclusions regarding the applicability and reliability of the presented method for determining the ultimate capacity of the CFSBBS column under investigation are derived. This proposal also suggests a design procedure for the built-up sections experiencing distortional buckling, which is not explicitly stipulated in current design standards or previous studies.