Behaviour of cold-formed steel channels bent about the minor axis

Abstract

The Direct Strength Method (DSM) in AISI S100 and AS/NZS 4600 is a newly developed alternative design method to the Effective Width Method in calculating the design moment capacity of cold-formed steel channels. The DSM uses elastic buckling stresses with an appropriate strength curve to calculate the design moment capacity. However, the current DSM design equation has been calibrated for channels bent about the major axis and is known to be conservative for channels bent about the minor axis with the web in compression. In order to extend the DSM for channels bent about the minor axis, it is necessary to prescribe and calibrate a DSM design equation for minor axis bending. This paper aims at deriving a new DSM design equation for cold-formed steel channels bent about the minor axis with the web in compression. For this purpose, the behaviour of 33 cold-formed steel channels bent about the minor axis inducing local buckling in the web are investigated using elastic finite strip buckling analysis and nonlinear finite element analysis. The cross-sectional dimensions such as thickness, web and flange widths are varied to cover a wide range of section slenderness. Deformed shapes and stress distributions at ultimate moment for various channels of different slenderness are described. Due to the considerable conservatism the current DSM design equation exhibited in comparison to the nonlinear finite element analysis results, a new DSM design equation for cold-formed steel channels bent about the minor axis is proposed.