Experimental Investigation of Cold‐formed Steel Built‐up Closed Columns using Frictional Interlocking

Abstract

This study explores the structural performance of innovative cold‐formed steel (CFS) built‐up columns developed using a friction‐based interlocking mechanism without mechanical fasteners. The proposed configuration is formed by lengthwise sliding of two tailored, fabricated unsymmetrical lipped channels, incorporating geometric overbends and flares to achieve secure interlocking. An extensive testing program was carried out, comprising 24 frictional tests with varying interaction lengths, and lip overbends, and 12 axial compression tests covering different slenderness ratios and interlock geometries. The frictional tests identified two primary failure mechanisms, with the resistance found to increase as the interaction length grew, mainly influenced by flange interference. Axial compression tests demonstrated three characteristic failure modes dominated by local buckling, with no evidence of separation or loss of interlock. The application of 3D‐DIC provided a deeper understanding of the deformation characteristics. Correlating the compression and frictional results confirmed that the interlocking mechanism significantly contributes to stability and strength, highlighting its promise as a practical alternative or complement to fastened connections for enhancing the efficiency of CFS built‐up members.