Local Buckling of Compressed Cold-Formed Lipped Channels via Buckling Mode Shapes

The effective width method is the most well-known approach to determine the resistance of cold-formed members using design formulas, accounting for the effect of local and distortional buckling. Local buckling is usually the most dominant failure mode of compressed C channels. The usual codified design method to calculate the buckling resistance by Eurocode EN 1993-1-3 proceeds through the determination of effective widths of compressed plates of the cross-section. During this procedure the plates are considered separately, without consideration of possible interaction between each other. The Eurocode method assumes separately the pure load cases instead of considering the actual complex stress case, completed with possible bimoments and amplified second order stresses resulting from global imperfections. This paper presents a method which works with the full set of actual normal stresses acting on the cross-section. It is able to assign cross-section level buckling modes calculated with the help of finite strip analysis for the relevant plates of a compressed C section. Assignment is based on the determination of deformation energy balance. Effective width is calculated using the Eurocode buckling curve, from the plate slenderness obtained using the critical multiplier of the assigned buckling mode, at the actual design load level. The proposed method is part of a larger research project which aims to provide a complete Eurocode compatible design methodology considering local, distortional and global buckling of general shaped cold-formed members subject to arbitrary loading and support condition, to be implemented in computer software programs working with 14DOF thin-walled beam-column finite element. © 2022 The Authors. Published by Ernst & Sohn GmbH.