Progressive collapse resistance of self-resilient composite frames under fire conditions

Self-resilient composite frames exhibit robust resistance to progressive collapse and excellent seismic performance. However, their behavior under fire conditions is inadequately explored. This study investigates the collapse resistance mechanisms and response of self-resilient composite frame substructures (SRCFS) under fire-induced progressive collapse. A three-dimensional finite element model was developed, incorporating temperature-dependent thermal and mechanical properties of concrete and steel. Sequentially coupled thermal-mechanical analysis was conducted using the ABAQUS/Explicit solver in a quasi-static manner. Existing experimental data at both ambient and high temperatures were used to validate the proposed model. The study analyzed the contributions of steel beams and strands to vertical resistance, examining their impact on the collapse-resistance mechanism through a constant load-heating transient loading scheme. Structural responses under ambient and fire conditions were compared, focusing on different damage mechanisms. The effects of initial prestressing of strands, angle gauge length, angle thickness, and various heating curves on collapse resistance were evaluated. Findings suggest that the ISO-834 standard's failure criterion is overly conservative for SRCFS, as it neglects the enhanced load-carrying capacity provided by tensile catenary action. This mechanism offers additional escape time, enhancing personnel safety. The study identifies factors influencing the performance of SRCFS against progressive collapse under fire and proposes design recommendations.