Behaviour and design of cold-formed ultra-high-strength steel hollow section column members

Abstract

Cold-formed ultra-high-strength steel (UHSS) is gaining attention in the construction sector because of its high strength-to-weight ratio and affordability. However, limited research has been conducted on cold-formed UHSS tubular members under concentric axial loading. This study aims to propose a novel extension of deformation-based method namely; continuous strength method (CSM) and AISI based direct strength method (DSM) design methodologies for cold-formed UHSS columns. A nonlinear finite element (FE) model was developed using the ABAQUS package for cold-formed UHSS columns, incorporating initial geometric imperfections and material non-linearities. The developed FE model was then validated against experimental test results from the literature for cold-formed UHSS columns. Parametric studies were conducted on cold-formed UHSS hollow sections to comprehensively understand their axial behaviour, utilizing the validated FE model and to generate additional data sets. A total of 146 FE models were analyzed by varying the thickness of the cold-formed steel sheets (4, 5, 6, 8, 10 and 12 mm), as well as cross-section dimensions, to account for broad range of cross-sectional slenderness ratios. The obtained FE results were compared with the AISI based current DSM and also with CSM/DSM based design rules recommended by other researchers in the literature. The specimens considered in the present study demonstrated failure due to local buckling. The numerical results showed that existing standards lack precise design procedures for cold-formed UHSS hollow columns, indicating a need for further research to develop accurate design procedures. Therefore, the proposed rational extension of deformation-based CSM and DSM methodologies provides more precise and less scattered capacity estimations for cold-formed UHSS columns, as verified through reliability analysis.