07.13: On extending the direct strength method to the design of cold‐formed steel built‐up columns

Abstract

This paper presents a numerical investigation of the effects of discrete fasteners on the buckling behaviour of cold-formed steel (CFS) built-up columns and concludes with the assessment of the applicability of the current direct strength method (DSM) to the design of these members. To this end, the compound strip method is first utilised to accurately model the buckling behaviour of CFS built-up columns under axial compression via introducing connecting elements to represent the contribution of discrete fasteners. A series of elastic buckling analyses with different levels of composite action are carried out to obtain the "signature curves" corresponding to the considered CFS built-up sections. The performed studies comprise of variations in cross-sections, end boundary conditions and fastener spacing. Utilising the developed numerical techniques, the ultimate strength of the sections are estimated and an adjustment procedure is suggested to extend the current DSM equations to the design of CFS built-up columns. The proposed adjustment is verified against the existing experimental data and shown to be capable and accurate in capturing the expected behaviour of CFS built-up members with or without stiffeners.

Experimental study of the cross-sectional capacity of cold-formed steel built-up columns

“…The tests suggested that some degree of composite behaviour was present. Abbasi et al [9] further investigated this built-up geometry by carrying out a stability analysis using the compound strip method to study the effect of the connector spacing on the buckling behaviour of the columns, and showed that reducing the connector spacing enhanced the elastic local and global buckling stresses of the built-up member.…”