Cold-formed steel (CFS) products are highly adaptable and suitable for several structural applications. Recent experiments conducted by the authors have demonstrated that incorporating composite action within systems comprising built-up CFS beams and lightweight concrete (LWC) is viable and can significantly enhance structural performance. However, current design methodologies lack specific guidelines for innovative demountable CFSLWC composite beams, which are necessary to leverage the benefits of composite action under a sagging bending moment. The available composite design procedures are for steel beams and concrete slabs connected by welded shear studs, while in CFS-LWC composite beam systems, bolts are used as shear connectors, and the ratio of bolt diameter to the CFS top flange thickness is higher than 2.5 (limit provided by EN1994-1-1). This research aims to assess the possibility of extending the available design specifications to predict the bending resistance of CFSLWC composite beams. First, the numerical modeling procedure was provided for CFS-LWC composite beams, and its results were validated against the available experimental data. A large parametric study was undertaken by considering different beam spans, CFS and LWC geometries, and material properties. The numerical results were then compared with design predictions per EN 1994-1-1 and AISC-360. The findings indicate that the design specifications tend to overestimate the bending resistance of CFS-LWC composite beams due to the absence of suitable expressions to determine the shear resistance of bolted shear connectors and thin steel plates, where the local buckling of the CFS section is not considered. Therefore, the influence of the localized buckling was explicitly taken into account by conducting pushout simulations. A good agreement between numerical results and design predictions following EN 1994-1-1 and AISC-360 was observed when the shear resistance of the bolted shear connector was obtained by numerical pushout simulation.
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