Numerical Investigation of the Wan’an Bridge Fire and the Protection Effect of Intumescent Flame-Retardant Coatings

The Wan’an Bridge, the longest wooden lounge bridge in China with a history of more than 900 years, was devastated by a catastrophic fire in 2022. This tragic event underscores the susceptibility of historical wooden structures to fire damage. In this article, the bridge’s intricate structure and the development of the fire incident are introduced in detail. To gain a deeper insight into the patterns of fire propagation across the bridge and assess the reliability of fire simulations in predicting fire spread in historical wooden structures, we utilized the Fire Dynamics Simulator (FDS), with a sophisticated pyrolysis model and thermal response parameters specifically tailored to ancient fir wood. The modeling results reveal that the FDS simulation reflects the actual fire spread process well. Both the investigation and simulation findings indicate that once the flame reaches above the bridge deck, it enters a rapid three-dimensional propagation phase that is exceptionally challenging to control. Furthermore, the modeling results suggest that the application of intumescent fire-retardant coatings can significantly delay fire spread, reduce heat release rates, and suppress smoke production, thereby making them an effective fire prevention measure for historical wooden buildings.