Compressive behavior of CFDST stub columns with inner corrugated tube after fire exposure

Currently, concrete-filled double-skin steel tubular (CFDST) columns incorporating inner corrugated tubes have been increasingly employed in engineering constructions due to their structural enhancing efficiency. Notably, the post-fire mechanical behavior of such members is critical for structural performance evaluation and strengthening design. However, the relevant research is insufficient. Therefore, this study experimentally investigated the elevated-temperature response and post-fire axial compressive behavior of ten CFDST stub columns with inner corrugated tubes. The key parameters included void ratio, fire exposure duration, and fire-protection coating type and thickness. Temperature field measurements indicated that decreasing the void ratio or applying fire-protection coatings effectively reduced the temperature rise within the cross-section. Meanwhile, GFC has the best thermal insulation performance. Axial compression results revealed that both the void ratio’s increment and prolonged fire exposure aggravated crack propagation in the core concrete and promoted interfacial debonding, thereby weakening the confinement and composite interaction between steel tubes and concrete. Consequently, reductions in axial bearing capacity, secant stiffness, and composite action were observed. Finally, A comparative evaluation of existing predictive methods for post-fire axial bearing capacity was conducted. The results demonstrated that the approach incorporating post-fire material strength degradation provided the highest prediction accuracy and the lowest dispersion. These findings provide valuable experimental evidence for evaluating and predicting the residual performance of CFDST columns with inner corrugated tubes after fire exposure.