Selection of an optimum axially compressed closed cross-section thin-walled built-up column /

Abstract

This article focuses on the analysis of axially compressed thin-walled built-up closed cross-section columns. The built-up nature of the cross-section is carefully considered in the calculation procedures and optimization constraints, accounting for the connection of profiles through the flanges within the cross-section. The calculation procedures are based on Eurocode 3 [1], which encompasses local, distortional, and global buckling forms. Five types of closed column cross-sections, ranging in height from 2 to 4 m, and subjected to axial loads of 50, 100, 200, and 500 kN, were thoroughly analyzed and optimized. The first type of cross-section examined was a square cross-section without stiffeners, while the remaining types featured four web stiffeners with varying geometrical constraints. The constrained nonlinear optimization solver, fmincon in Matlab software, was selected for the optimization problem. The obtained optimal cross-section results indicate that the square cross-section consistently exhibited the lowest effectiveness across all column heights and axial load combinations. In contrast, the most effective cross-section type transformed to a form, similar to a circle. Moreover, cross-section types with deeper stiffeners were associated with thinner profile thickness. A comprehensive summary of the results demonstrates that the effective area ratio within the cross-section was higher for smaller column heights and larger axial loads across all cross-section types. In conclusion, this study provides valuable insights into the analysis and optimization of axially compressed thin-walled built-up closed cross-section columns. The findings underscore the superiority of cross-sections that adopt a circular form and feature deeper stiffeners, resulting in enhanced structural effectiveness.