【作者】 杜咏；

【导师】 李国强；

【作者基本信息】 同济大学 ， 结构工程， 2007， 博士

【摘要】 大空间建筑作为公共建筑广泛应用的一种空间形式,其建筑骨骼——结构在火灾作用下的安全性是结构工程师必须考虑的问题。,应确定火灾作用中表征能量输出的温度场（非定场）,然后再。目前,国内外对这两方面的研究或为空白或相当粗略。本文首先是研究用于大空间结构整体抗火计算与分析的温度场,提出大空间建筑火灾中空气升温的实用计算式;然后在实用计算式确定的空气升温条件下,得出有防火保护和无防火保护的钢构件升温简化计算方法,同时考虑火焰辐射引起的局部钢构件升温;由于钢构件的升温将导致钢材的材料性能变化和被约束构件的附加温度内力产生,因此,最后分析大空间建筑结构之一的正放四角锥网架在设定火灾作用下的结构反应,最终得到网架的实用抗火设计方法。具体的研究工作包括如下几个方面一、收集国内外对火灾特性的研究成果,充分认识火灾中空气升温的机理,确定用数值模拟方法预测建筑火灾中空气升温的温度场。二、确定大空间建筑火灾空气升温影响参数的定性变化规律,根据该参数变化规律,设计火灾场景,基于FDS非商业（美国NIST于2002年研发）火灾模拟计算机程序进行数值模拟实验。三、在对大空间建筑火灾中空气升温影响参数分析基础上,提出大空间建筑火灾中空气升温曲线的数学表达式,在大量数值模拟实验基础上,回归数学表达式中各项系数。得出实用大空间建筑火灾中空气升温计算分式,填补了目前研究中仅有小室火灾升温曲线,而无大空间建筑火灾升温曲线的空白。四,对于集总热容法建立钢构件的热平衡方程一般采用增量法求解的钢构件升温计算方法作进一步简化。将大空间建筑火灾下空气升温的实用计算方式导入基于集总热容法的钢构件热平衡方程,并对热平衡方程中各参数进行回归分析,得出有防火保护和无防火保护钢构件升温的简化计算方法。避免用增量法求解热平衡方程的繁琐。五、根据火焰的热物性（角系数、黑度）钢构件有效辐射表面系数概念,对集中热容法建立钢构件热平衡方程进行改进,通过对热平衡方程中的参数分析,提出不需考虑火焰辐射对钢构件升温影响的条件,在满足钢构件升温计算精度条件下,简化钢构件升温计算。六、基于通用有限元程序ANSYS对正放四角锥网架在恒载加温条件下的非线性结构（几何非线性,材料非线性）反应进行分析,模拟了在均匀温度场和非均匀温度场中,恒定加载下不同几何特性的正放四角锥网架整体结构反应,得到不同的参数条件下的正放四角锥网架在火灾中构件稳定破坏的临界温度T_cr0和整体结构丧失承载能力的临界温度T_cr。七、用有限元程序ANSYS进行网架在火灾中的结构全过程反应分析,得到不同参数条件下网架临界温度(T_cr0和T_cr)值,在对影响T_cr0和T_cr的参数分析基础上确定网架的临界温度T_cr0和T_cr值的简化计算方法,进而提出大空间建筑网架结构实用抗火设计方法。更多还原

【Abstract】 Large space building is widely used within public buildings. The fire safety of large space building structure must be researched by structural engineer. At first the temperature field which is attributed to energy dissipation must be determined, then analysis the behavior of large space structure imposed fire. However there is very limited research carried out. Researching temperature field used in large space structural design for fire safety, establishing utility temperature elevation empirical formula in large space fire, getting simply temperature calculation for protected or unprotected steel member based on utility temperature elevation empirical formula, considering local steel member elevated temperature by flame radiation are researched in this article. Because material properties may be changed with elevated temperature and internal strains may be induced by thermal expansion. As one of the large space structures regular pyramidic space structure behavior imposed design fire scenarios must be researched in order to get the utility method of fire resistance of regular pyramidic space structure. The specific works are outlined below.Based upon collected data of fire properties and recognized mechanics of elevated temperature in fire, estimated temperature field in building fire with arithmetic simulation can be gotten.The regularity of factor influencing elevated temperature of build fire must be obtained. Based upon the regularity of factor fire scenario can be designed. These scenarios may be simulated by computer programs "FDS" which use computational fluid dynamics researched by department of commerce of United States America in 2002.Simplified temperature variational field of large space fire through entire temperature elevation is established. Based on a great number of numerical experiments the mathematic model of temperature elevation in large space fire is presented . Finally, empirical formula of temperature elevation in large space fire is created, and the parameters of the empirical formula are fitted by regression analysis which fills up the space without the curve of temperature elevation in large space fire.The heat equilibrium equation based upon the lumped differential formulation usually be solved by iteration method. In order to simplify the iteration method The parameter of smoke temperature in heat equilibrium equation based upon the lumped differential formulation is substituted by the empirical formula of temperature elevation in large space fire, regression parameter, and analysis the parameters of heat equilibrium equation with regression method. Then the simplified analytical method to evaluate the temperatures of protected steel member and unprotected steel members can be obtained.The thermal properties parameters of flame （configuration factor、emissivity of the emitting surface、effective radiation area） are organized into heat equilibrium equation based upon the lumped differential formulation. The condition of neglected flame radiation in influencing elevated temperature of steel member can be gained by analyzed these thermal properties parameters of heat equilibrium equation based upon the lumped differential formulation.The geometrical nonlinearity and material nonlinearity behavior of regular pyramidic space structure under dead loading and elevated temperature is analyzed by the generic finite-element stress-analysis program "ANSYS". T₀ is the temperature at which member is buckling and T_cr is the temperature at which structure is failure . T₀ and T_cr can be gained by simulating the behavior of regular pyramidic space structures with diverse geometrical features under uniform and nouniform temperature field.The empirical value of T₀ and T_cr in varied condition can be gotten by analyzed the factors which influence the critical temperature (T₀ and T_cr) .If the empirical value of T₀ and T_cr are regarded as reference value, the T₀ and T_cr can be determined with interpolation method between these empirical values of T₀ and T_craccording to the geometrical feature of regular pyramidic space structure. If the time the structure load-bearing capacity lasting in the fire situation ruled by code and the smoke temperature in the same fire situation are presented, the T₀ and T_cr can be determined by the simplified analytical method to evaluate the temperatures of steel member. The T₀ and T_cr determined by the simplified analytical method to evaluate the temperatures of steel member is greater than the T₀ and T_cr determined with interpolation method between these empirical values of T₀ and T_cr according to the geometrical feature of regular pyramidic space structure, then structure is safety in fire,更多还原