Tests and design approach for plain channels in local and coupled local-flexural buckling based on eurocode 3

• Tests performed on coupled local-flexural buckling show how both instabilities interact with each other.
• The coupled buckling behaviour is crucially depending on the bending direction of single symmetric plain channels.
• Modified buckling coefficients which take into account the interaction of adjacent plates increase the accuracy of calculated effective cross-sections.
• Eurocode 3 design approach can be improved by an approximation of effective stiffness with respect to flexural buckling slenderness ratio.
• Eurocode 3 part 1-3 Annex D can be used for welded thin-walled sections as well.

Thin-walled plain channels are often subjected to coupled local and global flexural buckling. The objective of this paper is to verify and discuss the current design procedure of Eurocode 3 for plain channels in coupled instabilities. This paper deals with experimental investigations on plain channel stub columns subjected to local buckling only and long columns subjected to coupled local-flexural buckling. The test series consists of cold-formed and welded plain channels made of steel grade S355 and S460. Based on this experimental results modifications of the method of effective width (and thickness) as stated by Eurocode 3 Part 1-3 are discussed. Previously developed modified buckling coefficients, which take into account the rigidity of the connection of web and flange, are verified by comparative calculations. Additionally an approach for an approximation of effective stiffness for coupled instabilities is discussed as well.