Post-fire mechanical properties of full-grouted sleeve connection with different grouting defects

The full-grouted sleeve connection (FGSC) is widely used in prefabricated structural connections, but the complexity of the grouting process often leads to defects, primarily grouting voids. The mechanical properties of FGSCs with these defects under fire exposure are not well understood. This study examines 144 FGSCs with various grouting voids exposed to specific temperatures before cooling to room temperature for static tensile testing. Key parameters include defect type, volume defect rates, and temperature. The study identifies two primary failure modes: rebar tensile and pull-out failures, influenced by void size, distribution, and temperature. Below 300 °C, tensile failure occurs when the defect rate is ≤0.05; above this rate, pull-out failure dominates. Above 300 °C, all specimens exhibit pull-out failure. Specimens with concentrated voids show lower bearing capacities. The research provides a bond stress-slip constitutive model for FGSCs and a fitting formula for characteristic points. A neural network model predicts the ultimate bond stress based on defect type, volume defect rate, temperature, and grouting material strength, with sensitivity analysis indicating the volume defect rate as a critical factor. This work offers a comprehensive theoretical foundation for studying the impact of grouting defects on FGSCs' post-fire mechanical properties.