Axial compression behaviour of cruciform cold-formed steel built-up columns: Shape optimization and experimental study

Abstract

In this paper, the cruciform CFS built-up cross sections are formed through four identical multi-roll lipped channels connected at their webs with high-strength bolts and filler plates. An optimization algorithm is primarily proposed that integrates sequential quadratic mathematical programming methods and finite strip analysis. It is desirable to effectively improve the buckling behaviour of cruciform CFS built-up columns without increasing the material volume. Eight different areas of built-up sections were optimized, each built-up open section was formed by fold-lines of the steel plate, and the width and angle of the constituent elements of the built-up section were selected as the main design variables. To simplify the optimization task and provide more practical structural components, usage constraints and practical manufacturing limits were imposed on the selected built-up sections during the optimization process. The results show that the adopted optimization process significantly increased the critical local buckling stress of the cruciform CFS built-up columns by 26.2%–58.9%. The design strength calculated according to the AISI standard was increased by 2.76%–18.15%. The axial compression bearing capacity tests with two different optimized cross sections were conducted, and the test loading capacities and failure modes of each specimen were obtained. The test results show that the failure modes were mainly driven from local and distortional buckling to torsional and flexural buckling with increasing slenderness, and the deformations were concentrated in the region near the end of column. Finally, the axial compression strengths of such cruciform CFS built-up columns obtained from the tests were used to assess the applicability of AISI standards. For columns failed by local and distortional buckling, AISI standard were un-conservative, whereas for torsional and flexural, AISI standard were conservative.