Systematic Review of the Torsional Performance of Concrete-Filled Double Skin Steel Tube (CFDST) Members under Fire Conditions Following PRISMA Protocols

<ns3:p>Concrete-Filled Double Skin Steel Tubes (CFDST) have emerged as a promising composite structural system that integrates the mechanical advantages of steel and concrete while achieving enhanced energy dissipation, reduced weight, and improved post-fire resilience. Over the past two decades, substantial experimental and numerical efforts have focused on understanding the torsional and thermal performance of CFDST and related CFST members. However, an integrated synthesis of these findings under a unified systematic framework has been lacking. This study conducts a comprehensive systematic review of 37 selected experimental and analytical studies addressing the torsional and fire behavior of CFDST and CFST members, following PRISMA guidelines “the PRISMA methodology, a standardized framework for conducting systematic reviews that ensures transparency, rigorous screening, and unbiased selection of relevant studies through a structured flowchart process”. The review identifies key influencing factors, including section geometry, wall thickness, concrete type, steel grade, axial load level, and fire exposure duration. Comparative analysis reveals that torsional resistance increases with lower hollow ratios, thicker outer tubes, and confined concrete cores, while elevated temperatures significantly reduce torsional stiffness and residual strength. Despite considerable research on CFST under fire and torsion separately, the coupling effect of post-fire torsional performance remains underexplored. Based on the identified research gaps, a new experimental program is proposed to investigate the pre- and post-fire torsional performance of CFDST columns with varying cross-sections and steel thicknesses. The study concludes with future research recommendations focused on developing constitutive models, hybrid materials, and fire-torsion interaction design equations for CFDST systems.</ns3:p>