Research on Fire Dynamics in Historical Timber Lounge Bridges with Different Roof Forms

Historical timber lounge bridges in China are irreplaceable cultural heritage assets. Throughout history, they have differentiated into distinct roof forms, which influence fire development patterns. Therefore, this study selected three roof forms of historical timber lounge bridges that respectively exhibit single roof, tripartite roof, and variant roof. Naturally aged timber was subjected to cone calorimeter, testing to obtain the pyrolysis parameters directly importable into Fire Dynamics Simulator (FDS). Moreover, FDS was employed to build full-scale bridge models with different roof forms. Fire development patterns, Heat release rate (HRR) curves and smoke spread patterns were compared. The rate of HRR indicated that the bridge with variant roof experienced the most rapid fire growth, followed by the single-roof bridge, whereas the bridge with tripartite roof showed the slowest growth. Smoke spread analysis revealed that roof form determined the smoke spread velocity. Further, a fire risk assessment system was adopted, resulting in a clear fire risk hierarchy. The single-roof form was the highest, followed by the variant roof, and the tripartite roof was significantly safer. The findings elucidate how variation in roof forms governs the fire risk of historical timber lounge bridges and provide a quantitative base for targeted preventive conservation.