古建筑具有重要的历史价值，长时间暴露在自然环境中，其中构成古建筑的木质材料会发生老化，影响到古建筑的消防安全。为此，本文采用实验分析和理论分析相结合的研究方法，以古建筑营造常用的杉木为研究对象，利用人工加速老化实验制备不同老化程度样品，采用工业分析、元素分析、XRD、SEM、热物性测试等实验手段研究不同老化程度杉木的基础物理化学特性；自主搭建火蔓延参数测量实验系统，分析环境压力和放置角度对老化木材火蔓延过程的影响规律；结合固体火蔓延理论模型和热输运理论，建立干湿老化杉木顺流火蔓延模型，为木结构古建筑火灾危险性评估和火灾监测监控技术手段的发展提供理论依据。

首先，依据人工加速老化标准，结合古建筑木材自然老化因素，制备了7种干湿老化杉木，测试了干湿老化杉木的基础物理特征，表征了其干湿老化程度。研究表明，老化程度的加深降低了杉木水分和挥发分、但固定碳增加、灰分先增大后减小，而C、H、O元素的含量均小幅度变化；表面颜色逐渐加深，自身密度呈线性降低；纤维素结晶度降低，细胞壁变薄，壁间距离缩小，细胞结构挤压变形和破裂，表面弯曲、开裂以及变形；老化杉木局部的高温扩散到低温区的时间增长，木材本身的导热占据主导地位，传热能力增强，比热容与干湿老化程度之间的拟合关系曲线良好，自身材性对干湿老化木材火蔓延特性的影响增大。

其次，揭示了环境压力和放置角度对老化杉木火蔓延过程的影响规律。研究表明，压力的降低会导致火焰体破裂跳跃现象加剧，导致木材边界火焰蔓延程度不统一，火焰体加长加宽，火焰高度和宽度变化趋势逐渐减小，热解区长度相对较长，老化杉木的气固相温度峰值宽度逐渐变窄；杉木的火蔓延速度随环境压力的降低先增大后减小，随老化程度的增加先增大后减小再增大，低压下老化杉木火蔓延速度持续增大，高压下杉木燃烧所产生的氧气浓度有所下降，燃烧过程不充分，老化杉木的火蔓延速度开始减小。

放置角度的增加会使火焰体体积增大，与杉木表面的火焰夹角减小，火焰的热传导途径变长，火焰面积和热解区长度先增大后减小，火焰长度曲线增长趋势加快，火蔓延速度随之增大，气固相温度和老化程度的规律性减弱；水平条件下，气固相温度升温时间随着老化程度的增加依次前移；老化杉木的热扩散和热运输能力增强，热解区域固相传热阻力变小，老化程度越高的杉木经过火焰燃烧后，火焰长度的增长趋势减缓，夹角的波动程度减小，火焰面积逐渐增大，热解区长度变长，火蔓延速度相应下降。

最后，建立了干湿老化杉木顺流火蔓延模型。研究表明，干湿老化杉木为热薄性材料，火焰的对流热通量是火蔓延过程中的主要传热类型，比热容与老化程度的关系式为c_p=1.346+0.398∙e^(-W/22.031)∙sin[π(W+77.814)/66.678]，环境压力对干湿老化杉木火蔓延速度的影响较低，放置角度是影响火蔓延特性的主要外界因素。放置角度作用下的干湿老化杉木顺流火蔓延模型分为水平条件和倾斜条件两种情况，各自修正后的模型理论值与实验值对应良好。

Ancient architecture is the material expression of human history, symbolizing Chinese culture and history. Over time, natural factors such as wind, rain, and snow lead to the aging of wooden, which affects the fire safety of wooden ancient architecture. By preparing samples with different degrees of artificial accelerated aging, study the basic physical and chemical properties of fir at different degrees of aging, analyze the effect of pressure and angle on the fire spread of aging wood,  a model of downstream fire spread in dry and wet aging fir was established, provided a theoretical basis for the evaluation of fire risk, and the development of fire monitoring, and surveillance technology for wooden ancient architecture.

Firstly, the basic physical characteristics of the aging fir were tested, and the degree of dry and wet aging was characterized. The results showed that as the degree of aging increased, the moisture and volatile of the fir decreased, but the fixed carbon and ash content first increased and then decreased. The content of C, H, O changed slightly, the surface color gradually darkened, and the self-density decreased linearly. The crystallinity of cellulose decreased, the cell wall became thinner, the intercellular distance decreased, the cell structure compressed and deformed, and the surface curved and cracked, causing deformation. The time for high-temperature diffusion of aging fir from local to low-temperature areas increased, and the thermal conductivity of the wood itself dominated, enhancing its thermal transfer ability. The fitting relationship curve between specific heat capacity and the degree of dry and wet aging was good.

Secondly, the study revealed the influence of pressure and angle on the spread of aging fir wood fire. The results showed that the reduction of pressure leads to intensified flame fragmentation and jumping phenomenon, resulted in uneven propagation of boundary flames, elongation and widening of flame body, and a gradual decreased in the trend of flame height and width variations, as well as a relatively longer length of pyrolysis zone and a gradually narrowing peak width of gas-solid phase temperature in aging fir. The spreading speed of fir fire increased first and then decreased with the decrease of pressure, increased first and then decreased before increasing again with the increase of aging degree, and keeps increased under low pressure. The oxygen concentration produced by the combustion of fir decreased under high pressure, the combustion was incomplete, and the spreading speed of aging fir fire begins to decreasd.

The increase in angle of placement would result in an increase in flame volume, a decrease in the angle between the flame and the surface of the cedar wood, an elongation of the path of heat conduction in the flame, an initial increased and subsequent decreased in flame area and length of pyrolysis zone, an acceleration in the trend of increased in flame length curve, an increase in flame propagation speed, and a weakening of the regularity in temperature and aging of gas-solid phases. When the inclination angle was zero degrees, the time required for gas-solid phase temperature to rise increased with aging. The thermal diffusion and transport capabilities of aging wood enhanced, the thermal resistance of the solid-phase thermal transfer in the pyrolysis area decreased, and the trend of increase in flame length slows down for fir with higher levels of aging after combustion by the flame, resulted in a reduction in the degree of fluctuation in angle, a gradual increased in flame area, an elongation of the length of the pyrolysis zone, and a corresponding decreased in flame propagation speed.

Finally, a model for the propagation of fire downstream on dry and wet aged fir was established. The study showed that dry and wet aged fir wood was a material with low thermal conductivity, with convective heat flow being the main heat transfer mechanism during fire propagation. The relationship between specific heat capacity and degree of aging was described by the formula: c_p=1.346+0.398∙e^(-W/22.031)∙sin[π(W+77.814)/66.6 78]. The effect of ambient pressure on the speed of fire propagation on dry and wet aged fir wood was relatively low, while the placement angle was the main external factor affecting the characteristics of fire propagation. The downstream propagation model of dry and wet aging fir wood under the influence of placement angle can be divided into two conditions, horizontal and tilted, each of which has been well adjusted to fit both theoretical and experimental values.

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