Published Paper Details:

This paper presents an experimental investigation into the flexural performance of built-up cold-formed steel (CFS) closed-section beams under four-point bending, with a focus on the effect of composite action using Expanded Polystyrene Lightweight Concrete (EPS-LWC). Three full-scale beams were examined: a bare steel built-up section and two composite variants utilizing the same steel cross-sectional area. The first composite beam (Beam-2) was fully infilled and externally encased with EPS-LWC to assess the contribution of composite interaction. The second composite beam (Beam-3) included a novel configuration featuring outward-facing lipped flanges embedded within the concrete matrix, intended to enhance mechanical interlock and strain transfer. Experimental results showed that EPS-LWC encasement significantly improved the flexural capacity, stiffness, and ductility of the CFS beam. Moreover, Beam-3 demonstrated superior performance over Beam-2, attributed to improved interface bonding and strain compatibility through the lipped flange interlock. These findings confirm the structural viability of EPS-LWC for composite steel applications and highlight the potential of flange detailing innovations in maximizing composite action in thin-walled CFS members.