Performance-Based Fire Safety Assessment Mechanism for High-Rise Timber Ancient Pagoda Buildings Based on Fire Dynamics Simulator

Fire protection remains one of the key challenges in the field of architectural heritage conservation, particularly for heritage buildings dominated by timber structures, which face greater difficulties in fire prevention and risk assessment. To systematically evaluate the fire safety performance of high-rise timber heritage buildings, this study takes the Shengjin Pagoda, a typical brick–timber pavilion-style ancient tower in Jiangxi Province, China, as the research object. A three-dimensional performance-based fire assessment framework was developed using Fire Dynamics Simulator (FDS) and PyroSim. Based on field survey data and historical documentation, the geometric characteristics, material properties, and vertical circulation system of the pagoda were reconstructed. Three representative fire scenarios, including bottom-floor ignition, simultaneous multi-level ignition, and wind-driven top-floor ignition, were established to investigate smoke propagation, thermal insulation degradation, and the thermal response of critical timber components under different fire conditions. The results show that brick walls provide effective thermal insulation during the early stages of fire, with efficiency exceeding 90%, but this decreases to approximately 55% in upper regions due to chimney-effect-driven smoke accumulation. Under wind-driven top-floor ignition, exposed dougong components can reach temperatures of 782 °C, resulting in a progressive “top-down and outside-in” failure mechanism. The study reveals the dominant smoke-driven heat transfer pathways and the failure sequence of critical load-bearing elements. Based on these findings, a performance-based fire protection strategy incorporating vertical virtual smoke control zoning and fire-resistance enhancement of key structural components is proposed to support the sustainable conservation of historic high-rise timber structures.