Strength of Cold-Formed Sigma Section Subjected to Bending Moment Using Direct Strength Method

Abstract

In this research, the behavior of cold-formed steel sigma section beams subjected to bending moment about the major axis was extensively studied. A comprehensive literature review was performed to investigate the recent researches related to the Direct Strength Method and sigma section. It was demonstrated that the Direct Strength Method classified the cross-section into two groups: prequalified beams, not prequalified beams. Prequalified beams, like C and Z sections, are supported by enough experiments and investigations. In contrast, other beams are not supported by enough investigations like sigma section. Consequently, the author worked on filling this gap in knowledge. In order to study the flexural behavior of sigma beams, a finite element model was developed utilizing Abaqus/CAE 2016.The finite element model considered geometric imperfections, material, and geometric nonlinearities. In addition, a finite strip analysis model was developed using CUFSM4. Both models were verified using existing test results that were presented in the literature review. Sigma sections, subjected to bending moments about the major axis, were analyzed and compared to C-sections to investigate the feasibility of using sigma beams as an alternative to C-sections. Besides, the relation between the nominal flexural capacity (Mn.) and critical buckling moment (Mcr.) was investigated and compared to AISI equations. Consequently, the sigma section can be considered as a prequalified section; thus, more economic design can be achieved.