Study On The Fire Spreading Characteristics Of Wooden Structure Buildings In Southwest China

There are a large number of wooden buildings in southwest China,mainly pine,fir and other materials.Due to the limited terrain and topography,the fire control planning of houses in village and town areas is not perfect,the wooden buildings are connected,and the risk of fire is large.Once the fire occurs,the fire is extremely easy to spread between buildings,resulting in disastrous consequences.Current research mostly adopts numerical simulation research methods,focusing on the combustion characteristics of wood itself or the fire developing process of single buildings.However,relatively little attention has been paid to the process of fire spread between wooden buildings in villages and towns,and the research on the influencing mechanism of fire spread between buildings is relatively weak.Aiming at the characteristics of wooden buildings in villages and towns in southwest China,such as large fire loads and compact building layout,this paper adopts a combination of field research,scaled(1:10)wood structure experiments,numerical simulation,and full-scale test to consider the fire spread mechanism between different buildings,focusing on the impact of spacing and slope on flame heat transfer,and reveals the impact mechanism of spacing and slope on fire spread,key impact parameters are identified.Based on two aspects of flame radiation heat transfer and wood heat transfer,the fire propagation model between buildings was constructed,and then the fire spread time under the corresponding boundary conditions is derived.Finally,the full-scale solid wood structure building fire physical experiment was conducted,and the results show that the model predicted value conforms well with the test results.The specific research work mainly includes the following aspects:(1)The fire load field investigation of wooden structures was carried out,the material combustion characteristics of white pine wood commonly used in southwest China were tested,the current situation of wood structure buildings in villages and towns in southwest China was analyzed,and the characteristics of topography,building spacing,external rescue conditions,construction years,building structure and fire hazards in villages and towns in southwest China were clarified.(2)Based on the basic theories formed by predecessors on flame radiation heat transfer and wood heat transfer,and combined with the field research results of this study,a fire spread heat transfer model between wood buildings in southwest villages and towns was constructed,through which the spread time between buildings can be predicted.(3)According to the common 2-story wooden structure building form in Southwest China,white pine was used as the main material,a 1:10 scaled-down wooden structure building was designed and built,and a scaled-down physical fire experiment was carried out.The fire development process of the burning wooden structure was analyzed.By changing the distance between the fire building and adjacent buildings,the fire spread process between buildings under different distances was studied,and the change rules of parameters such as temperature distribution,radiation distribution and spread time with the building interval were obtained.The relationship between dimensionless flame temperature and height was established,and the theoretical value of the fire separation distance between wooden structures is proposed.The fire dynamics software FDS was used to simulate the fire spread process between wooden structures at different distances,and the transformation law of parameters such as temperature distribution,radiation distribution and spread time with building distances were obtained.Based on the fire spread model between buildings,the fire spread prediction time calculated at different building space,the accuracy of the model was validated,and the deviation rate of the model is obtained by comparing with the scale-down experiment and FDS numerical simulation results.(4)The characteristics of the influence of slope on fire spread between buildings were studied.By changing the slope of the building on fire and adjacent buildings,the process of fire spread between buildings under different slope conditions was studied,and parameters such as temperature distribution,radiation distribution,and spread time were obtained.Variation law of building slope.The fire dynamics software FDS was used to simulate the fire spread process among wooden structures under different slope conditions,and the changing rule of parameters such as temperature distribution,radiation distribution and spread time with building slopes were obtained.Using the established fire spread model between buildings,the forecast time of fire spread under different building gradients is calculated,verified the accuracy of the model with reduced size experiment and FDS numerical simulation results,and obtained the model deviation rate.(5)The full-scale wooden buildings were built in southeast of China,and the solid fire experiment of fire spread between buildings was carried out.The fire development process in the wooden buildings and the fire spread process between buildings were analyzed,and the temperature distribution and radiation in and between buildings were obtained.The law of heat distribution is analyzed,and the influence of different building spacing and slope on the fire spread time between wooden structures is analyzed.The correlation of different factors on the fire spread among buildings was studied by cluster analysis and dimension reduction analysis.Using the established inter-building fire spread model,the fire spread time between full-scale wooden structures under the corresponding boundary conditions is measured and calculated.The predicted value is in good agreement with the test results,which proves the applicability of the model to fire spread in multi-scale wooden structures.To accurately evaluate the characteristic parameters such as spread time,flame temperature,and flame heat radiation in the process of fire spread in villages and towns of wooden structures in southwest China,and then realize the prediction and early warning of fire spread in wooden structures,which can be used for the development of village and town wooden structures.Building suitability fire safety strategy and guiding the overall fire safety layout provide theoretical and data support,which is of great significance to fire spread risk assessment and fire prevention and control of wooden structures in villages and towns in southwest China.