Post-fire tensile behavior of blind-bolted hollow and concrete-filled steel tube connections: Experimental and analytical investigation

This study investigates the failure modes and load-bearing capacities of blind-bolted connections to hollow steel tube (HST) and concrete-filled steel tube (CFST) columns under tensile loading at room temperature and after exposure to high temperatures Based on the experimental data, analytical models were established to predict the initial stiffness, plastic resistance, and ultimate capacity of connections at different temperatures. The results indicate that under tensile loading, blind-bolted connections primarily exhibit three failure modes or their combinations: tube wall bending, bolt fracture, and bolt pullout. Temperature, anchorage length, and concrete infill collectively influenced the failure modes of the connections. After exposure to 500°C, the connections retained significant load-bearing and deformation capacities, with only slight reductions in stiffness and strength compared to room temperature. All connections to CFST column failed due to bolt fracture after exposure to 800°C. Increasing the anchorage length notably improved the stiffness and load-bearing capacity at room temperature and 500°C, while concrete infill consistently enhanced the performance of the connections across all temperature conditions. A comparison between experimental results and theoretical predictions confirmed the high accuracy of the proposed models in capturing the mechanical responses of blind-bolted connections under different temperature conditions. These findings provide experimental data and theoretical references for the design and evaluation of blind-bolted connections in fire-exposed structures.