Numerical simulation analysis and residual load-bearing capacity of concrete beam bridges exposed to fire

Purpose Fire disasters pose severe threats to concrete beam bridges, potentially causing rapid performance degradation or collapse. This study aims to investigate the residual mechanical performance and load-bearing capacity of a hollow slab beam bridge in China following a specific fire accident. The primary objective is to accurately assess the post-fire structural safety by establishing a reliable temperature-damage mapping relationship. Furthermore, the study seeks to determine if the damaged bridge still meets serviceability limits to guide necessary maintenance, load restrictions, or strengthening measures. Design/methodology/approach Based on post-disaster field investigations, fire-affected zones were classified by temperature exposure. PyroSim software was used to simulate the spatial temperature distribution throughout the combustion process. The model's accuracy was validated by comparing simulated results with in-situ measurements and European standard material strength reductions. Subsequently, ABAQUS finite element analysis was employed to calculate the structure's mechanical response under a 35-ton vehicle load. The analysis focused on comparisons of mid-span deflection, reinforcement stress, and ultimate bearing capacity before and after the fire exposure. Findings Results indicate that temperatures exceeding 800 °C caused concrete compressive strength reductions of over 60%. The simulation aligned well with actual data, validating an average material strength reduction factor of 0.844. Under a 35-ton fleet load, the bridge exhibited a mid-load deflection of 25.4 mm and an eccentric-load deflection of 26.7 mm—approximately 6–7 times the pre-fire values. With reinforcement stress increasing by 150%, the analysis confirms that the structure no longer meets the normal service limit state, urgently requiring structural intervention. Originality/value This study bridges the gap between theoretical fire modeling and practical engineering assessment by analyzing a real-world fire accident on a hollow slab bridge. It establishes a comprehensive workflow integrating field investigation, PyroSim fire dynamics, and ABAQUS structural analysis. Uniquely, the research validates the temperature-damage mapping relationship using both in-situ measurements and material strength tests. The findings provide critical quantitative reference data for the residual bearing capacity of hollow slab bridges, offering valuable guidance for post-disaster safety assessment, load restriction strategies, and structural rehabilitation in similar infrastructure projects.