Evaluation of Fire Performance of Qing Dynasty Corridor-Style Timber Structures Under Different Surface Coating Treatments Using Cone Calorimeter and Fire Dynamics Simulator

To investigate the effects of different surface coating treatments on the fire resistance of Qing Dynasty traditional corridor-style timber structures, the Long Corridor of the Beijing Summer Palace was selected as the case study. Two representative timber species, red pine and larch, were examined under three treatment conditions, including no treatment, traditional treatment (“San-dao-hui” and “Yi-ma-wu-hui”), and composite treatment combining traditional treatment with modern flame-retardant coatings. Cone calorimeter (CC) testing and Fire Dynamics Simulator (FDS) simulation were used to systematically investigate their combustion performance and fire spread patterns. Results indicate a clear, gradual improvement in timber reaction to fire: composite treatment coating performed best, followed by plaster layer protection, and untreated wood performed the worst. Among these, the composite treatment of red pine with “Yi-ma-wu-hui” (one hemp layer and five lime plaster layers) combined with modern flame-retardant coating showed the highest overall efficacy. The time to ignition (TTI) reached 76.7 s, a 210.5% increase compared with untreated wood. Meanwhile, peak heat release rate and carbon monoxide production were both significantly reduced. Notably, the selected modern flame-retardant coating cures colorless and transparent, preserving the original appearance of the wood, and the composite treatment maintains the historical texture and color consistency required for heritage restoration. The flame-retardant efficiency of the “Yi-ma-wu-hui” plaster layer was superior to that of the “San-dao-hui” (three lime plaster layers), owing to its denser structure that provides a stronger physical barrier effect. Larch exhibited better inherent reaction to fire than red pine, and surface coating treatments effectively reduced differences between substrates. FDS simulations confirmed that the composite treatment could keep peak heat release rate below 6000 kW under the most adverse meteorological conditions, confining high temperatures and dense smoke near the ignition point and effectively restraining sequential fire spread in traditional corridor-style timber structures. These findings provide a scientific basis and practical guidance for the fire-resistant restoration of Qing Dynasty traditional corridor-style timber structures and similar heritage buildings.