Buckling behaviour of cold-formed steel sigma and lipped channel beam–column members

Abstract

To determine the load-bearing capacity of cold-formed steel (CFS) beam–column members, closed formed interaction formulas are generally used in most current design guidelines by linearly combining axial load and biaxial bending moment effects. However, this approach ignores the nonlinear interactions between these actions. To evaluate this issue, in this research the structural behaviour of eccentrically loaded beam–column CFS lipped and sigma channel profiles are investigated experimentally and analytically under simultaneous effects of axial loads and biaxial bending moments. Detailed Finite Element (FE) models are developed using ABAQUS software by considering geometric imperfections and actual material properties obtained from coupon tests, and validated against experimental data to estimate the strength and buckling behaviour of CFS beam–column elements. A total of 4480 FE analyses are then performed on 500 mm and 2000 mm long CFS members with different lipped and sigma channel sections subjected to a wide range of eccentricity values in various directions. The results of the analyses indicate that the failure modes are mainly dependent on the stress distribution of the cross-section generated by the combined actions. It is also demonstrated that regardless of the selected load combination, using sigma sections for the short beam–column members generally results in higher strength by up to 42% compared to those with lipped channel sections. It is shown that AISI and Eurocode underestimate the capacity of CFS beam–column members, on average, by around %50 and %25, respectively. However, the recently proposed extended Direct Strength Method (DSM) can generally provide more accurate strength predictions, especially in the case of short beam–column elements.