A mechanics-based design approach to local buckling of thin-walled cross-sections

A new methodology for the design of thin-walled cross-sections against local buckling is presented. Unlike the currently codified approaches (the Effective Width Method and the Direct Strength Method), which are based on empirical curve-fitted equations, the new method is rational in nature: a differential equation governing the post-local buckling behaviour of thin-walled cross-sections is established, combined with a failure criterion based on first yield of the membrane stresses, and solved using a finite element scheme. Owing to its solid theoretical fundamentals, the approach is applicable across all possible cross-sectional shapes. To provide an initial proof-of-concept of the new method, an experimental campaign was devised, comprising 22 axial compression tests on cold-formed steel stub columns with a wide range of cross-sectional geometries. All specimens failed by local buckling. The average ratio of the predicted to the experimentally measured capacity was 0.96, with a standard deviation of just 2.9%, and the new approach clearly outperformed the current design standards.