Simplified design method of cold-formed steel columns with built-up box sections.

• The research on cold-formed steel columns with built-up box sections was conducted. • Tests on the built-up box section members were carried out. • The parametric analyses were conducted by the numerical simulation. • A simplified design method was proposed for the built-up box section columns. The built-up box section members in this paper consist of single cold-formed steel (CFS) C-section and U-section basic components, which are connected by self-drilling screws at the flanges. This study incorporates experimental and theoretical research on the buckling behavior and ultimate strength of axially loaded pin-ended CFS built-up box section columns as affected by local and local-flexural interactive buckling modes. In total, 28 specimens were prepared and tested under axial compression. The test results revealed visible local buckling or local-flexural interactive buckling for specimens. Thereafter, finite element models were established by the ABAQUS software and validated with the structural behavior of the test specimens. The effects of the slenderness ratio, web depth-to-thickness ratio and screw spacing on the ultimate strength of the built-up columns were investigated based on the numerical analysis. Finally, based on the test results of this research as well as previous works in the literature, a simplified design method was proposed to predict the ultimate strength of built-up box section columns. By comparing the predicted results against the test results, the proposed method was subsequently validated. [ABSTRACT FROM AUTHOR]