Fire dynamic characteristics of historical timber lounge bridges considering enclosure shapes

Weatherboards, a unique feature of historical timber bridge heritages, create enclosed spaces affecting the fire dynamics. However, the influence of weatherboard height on the fire dynamic characteristics of timber bridge heritages remains poorly understood, and the relationship between weatherboard height and fire behavior has rarely been investigated. In this study, aged wood specimens were collected from a timber bridge and tested using cone calorimetry to establish a pyrolysis model for deteriorated wood. Subsequently, the fire development process in timber bridge heritages with five different weatherboard heights (no cover, 25 % cover, 50 % cover, 75 % cover and fully cover) was simulated using the Fire Dynamics Simulator (FDS). Parameters such as the total heat release rate (HRR), gas temperature, smoke layer height and internal gas flow were measured and analyzed. A novel theoretical model for smoke layer height in historical timber bridge heritages was proposed, which agreed well with the FDS results. Finally, statistical analysis of fire parameters was performed. Range analysis was employed to evaluate the sensitivity of different fire parameters to weatherboard height, while the entropy method was utilized to calculate the fire risk score (FRS) for the historical timber bridges with varying weatherboard heights. The experimental and simulation results, along with the proposed smoke layer thickness calculation model outputs, provided a reference for fire protection and fireproofing design of historical timber bridge heritages with different heights of weatherboards.