Enhanced Lateral Strength and Ductility in Cold-Formed Steel Strap–Braced Walls with Composite Built-Up Chord Sections

Cold-formed steel (CFS) strap–braced walls are primary lateral force-resisting systems in light gauge steel (LGS) construction. However, their application in high seismic regions is limited by the premature buckling of traditional back-to-back chord studs, resulting in reduced lateral strength and ductility. This study introduces novel built-up chord (BUC) and composite built-up chord (C-BUC) configurations as substitutes for traditional chord studs to enhance both lateral load-carrying capacity and ductility of CFS strap–braced walls. The C-BUC configuration leverages lightweight concrete infill to significantly improve buckling resistance, enabling the use of higher-strength straps without compromising ductility. Axial compression tests were conducted to evaluate the load-bearing capacity and failure modes of the proposed chord configurations, followed by finite element analysis in ABAQUS for model calibration. A CFS strap–braced wall model was then developed and calibrated using existing experimental data. The validated CFS strap–braced wall model, incorporating optimized capacity-based strap design and calibrated BUC and C-BUC chords, was then used for parametric analyses under monotonic loading. Results demonstrate that the novel configurations increase lateral yield strength by up to 654.72% while maintaining ductility, effectively preventing brittle failures and meeting capacity-based design criteria within the AISI-S400 framework. Comparative analysis also reveals limitations in current AISI-S100 and AISC-360 design provisions, which underestimate C-BUC strength due to inadequate consideration of composite action and buckling behavior. These findings highlight the potential of composite built-up configurations to meet advanced seismic demands, advocating for their inclusion in design standards as effective lateral force-resisting systems for earthquake-resistant mid-to-high-rise LGS construction.