钢框架整体结构在火灾下的热—结构响应分析
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摘要
钢结构及其组合结构具有轻质、高强、安装方便、施工工期短等特点,因此被广泛应用于实际工程中。但是此类结构对于火灾比较敏感,需要对其抗火性能进行特别的关注。本文针对钢框架整体结构的抗火问题,从以下几方面发展了一些高效可靠的计算方法,并将这些方法应用于实际结构的有限元抗火分析中:
1、混凝土楼板是工程结构中常用部件,为了准确计算其在火灾下的温度场,必须同时考虑板平面上和板厚度方向的温度梯度,因此本文提出了一种考虑厚度方向温度梯度的温度板单元。其基本思想是将楼板在平面上用有限元离散,温度沿厚度方向假设为线性分布函数。在热传导方程的推导过程中,利用楼板厚度方向平均温度(以开尔文为单位)一般比温差(以开尔文为单位)大得多的假定,实现了平均温度和温差的解耦,将问题的求解分解为两步:(1)求解关于楼板节点平均温度的非线性常微分方程组;(2)在已知每一时间步的节点平均温度基础上,求解温差满足的非线性常微分方程组。单元每个节点包含两个自由度:厚度方向的平均温度和温差。数值算例表明该单元具有精度好、计算效率高的优点。
2、在热变形计算时,本文推导了板壳温度场导致的等效温度载荷,其中板厚方向的温差将引起板的热弯曲,数值算例表明了热弯曲计算的准确性。
3、根据上述理论和方法,本文编制了钢框架整体结构在火灾情况下的瞬态温度场、弹性热变形和弹性热应力计算的有限元程序,用于结构抗火的计算。通过数值算例,讨论了结构整体效应对于抗火性能的影响。
With features of lightweight, high-strength, convenient adjustment and short construction period, the steel structure and composite structure are widely used in practical construction. But these structures are very sensitive to fire. Special concern should be gave to their fire resistance. Considering the problem of fire resistance of steel structure with concrete slabs, some efficient and reliable numerical methods are presented from the following aspects and applied to the fire resistance analysis of practical structures.
1. Concrete floor is commonly used in engineering structure. In order to calculate the temperature field in the floor, the temperature gradient in the plane and along the direction of thickness should be considered. And a kind of temperature element is presented here by considering its temperature gradient along thickness. With this element, the floor is decomposed in the plane, and the temperature distribution was assumed linear along the direction of thickness. Considering the assumption that the temperature difference(measure in K) are far less than the mean temperature(measure in K), the mean temperature and temperature difference are decoupled in process of deducing the heat conduction equation. So that the temperature field can be calculated by the following two steps: (1) solving nonlinear ordinary differential equations of average temperature; (2) solving the nonlinear ordinary differential equations of difference temperature based on knowing the average temperature of every time step. Two degrees of freedom are employed for node of element: average temperature and difference temperature. The numerical examples show that the present element can be calculated fastly and effectively.
2. The equivalent force caused by temperature field of plate are presented in structural analysis. The thermal flexure are caused by difference temperature along plate thickness. Numerical examples prove the accuracy of thermal flexure calculation.
3. Based on the method above, the finite element programs are applied to calculate the transient temperature field, elastic thermal deformation and elastic heat stress of steel structure with concrete slabs in fire, and applied in calculation of structural fire resistance. The effect of whole structure which influence the fire resistance performance of the structure are discussed in numerical examples.
1、混凝土楼板是工程结构中常用部件,为了准确计算其在火灾下的温度场,必须同时考虑板平面上和板厚度方向的温度梯度,因此本文提出了一种考虑厚度方向温度梯度的温度板单元。其基本思想是将楼板在平面上用有限元离散,温度沿厚度方向假设为线性分布函数。在热传导方程的推导过程中,利用楼板厚度方向平均温度(以开尔文为单位)一般比温差(以开尔文为单位)大得多的假定,实现了平均温度和温差的解耦,将问题的求解分解为两步:(1)求解关于楼板节点平均温度的非线性常微分方程组;(2)在已知每一时间步的节点平均温度基础上,求解温差满足的非线性常微分方程组。单元每个节点包含两个自由度:厚度方向的平均温度和温差。数值算例表明该单元具有精度好、计算效率高的优点。
2、在热变形计算时,本文推导了板壳温度场导致的等效温度载荷,其中板厚方向的温差将引起板的热弯曲,数值算例表明了热弯曲计算的准确性。
3、根据上述理论和方法,本文编制了钢框架整体结构在火灾情况下的瞬态温度场、弹性热变形和弹性热应力计算的有限元程序,用于结构抗火的计算。通过数值算例,讨论了结构整体效应对于抗火性能的影响。
With features of lightweight, high-strength, convenient adjustment and short construction period, the steel structure and composite structure are widely used in practical construction. But these structures are very sensitive to fire. Special concern should be gave to their fire resistance. Considering the problem of fire resistance of steel structure with concrete slabs, some efficient and reliable numerical methods are presented from the following aspects and applied to the fire resistance analysis of practical structures.
1. Concrete floor is commonly used in engineering structure. In order to calculate the temperature field in the floor, the temperature gradient in the plane and along the direction of thickness should be considered. And a kind of temperature element is presented here by considering its temperature gradient along thickness. With this element, the floor is decomposed in the plane, and the temperature distribution was assumed linear along the direction of thickness. Considering the assumption that the temperature difference(measure in K) are far less than the mean temperature(measure in K), the mean temperature and temperature difference are decoupled in process of deducing the heat conduction equation. So that the temperature field can be calculated by the following two steps: (1) solving nonlinear ordinary differential equations of average temperature; (2) solving the nonlinear ordinary differential equations of difference temperature based on knowing the average temperature of every time step. Two degrees of freedom are employed for node of element: average temperature and difference temperature. The numerical examples show that the present element can be calculated fastly and effectively.
2. The equivalent force caused by temperature field of plate are presented in structural analysis. The thermal flexure are caused by difference temperature along plate thickness. Numerical examples prove the accuracy of thermal flexure calculation.
3. Based on the method above, the finite element programs are applied to calculate the transient temperature field, elastic thermal deformation and elastic heat stress of steel structure with concrete slabs in fire, and applied in calculation of structural fire resistance. The effect of whole structure which influence the fire resistance performance of the structure are discussed in numerical examples.
引文
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[3]李国强.钢结构抗火设计方法的发展[J].钢结构,2000,(3):47-49
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[6] Stark J W B, Bijlaard F S K. Structural Properties Connections in Steel Frame, Connections in Steel Structures Behavior, Strength and Design[M].Elsevier Applied Scienc Publishers, London, 1987.
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[8] Rahaman M U,Rowlands R E.Finite Element Analysis Multiple-Bolted Joints in Orthotropic Plate[J].Computer and structures,1993,46(5):2-5.
[9]魏东,孙秀山,刘应华,朱建明.钢结构抗火研究进展[J].建筑钢结构进展,2006, 8(4):17-22
[10]施丽彦.钢结构防火[J].重庆建筑大学学报.2002, 24(2): 15-18
[11]李国强,韩林海,楼国彪等.钢结构及钢-混凝土组合结构抗火设计[M].北京:中国建筑工业出版社,2006:13-50.
[12]赵金城,沈祖炎.钢结构抗火分析中的材性模型[J].工业建筑, 1996(9):3-6
[13]赵金城,沈祖炎.钢结构抗火设计的燃烧模型及温度传播[J].工业建筑, 1994(7):12-15
[14]马忠诚.火灾下钢筋混凝结构损伤评估与抗震修复[D].哈尔滨:哈尔滨建筑大学,1997:1-3.
[15]薛素铎,邱林波,冯淼.空间结构抗火性能研究进展[D].北京:北京工业大学空间结构研究中心,2009,11(3):29-36.
[16] International Standard ISO834,Fire-Resistance Tests Elements of Building Construction,Amendment1,Amendment2,1980
[17]郝淑英,杨秀萍.钢梁火灾下的虚拟仿真[J].天津理工学院学报,2004, 9(3) :9-12.
[18]陶元元,张卓,张敬宇.局部火灾下变截面门式钢刚架结构温度场的数值模拟[J].天津城市建设学院学报,2007,13(1):13-17
[19]罗轩忠,周焕廷.空间拱支索网结构抗火研究进展[J].中国水运,2009,9(3):231-233
[20]史健勇,赵金城.复杂空间钢结构整体性防火分析的系统方法研究[J].土木工程学报,2008,41(11):51-62
[21]唐兰,张系斌.火灾下钢框架结构的热-结构耦合非线性分析[J].吉林建筑工程学院学报,2008,25(3):39-42
[22]霍静思,韩林海. ISO834标准火灾作用后钢管混凝土的轴压刚度和抗弯刚度[J].地震工程与工程震动,2002,22(5):143-151
[23]张卓,魏金科,王杨.门式钢刚架斜梁和檩条在局部火灾下温度分布的试验研究[J].消防技术与产品信息,2009,4:3-5
[24]李兵,陈道政.钢框架结构抗火反应分析与研究[J].山西建筑,2009,35(1):78-79
[25]刘剑.钢结构建筑抗火设计及防火保护探讨[J].山西建筑,2009,35(2):88-89
[26]吴传伟,高轩能.钢与钢-混凝土组合结构抗火研究进展[J].防腐与防火,2009,1(24):69-73
[27]闫百慧,侯静.建筑钢结构的防火处理[J].建筑科学,2009,2:106-106
[28] Myllymaki J,Kokkala M.Experimental Correlation for the Thermal Analysis of Steel Beam in Localized Fire[A]. In: Proceedings of 9th Nordic Steel Construction Conference [C].Helsinki, Finland, 2001:549-556.
[29] Hasemi Y, Yokobayashi S, Wakamatsu T,et al. Fire Safty of Building Components Exposed to a Localized Fire [M]. ASIAFLAM 95. HongKong, 1995.
[30] Bostrom L, Polsson J, Heinz P. Experimental and Theoretical Analysis Of Temp-erature Response of Insulated Steel Columes Exposed to Fire [A]. In: Proceedings of 9th Nord -ic Steel Construction Conference[C].Helsinki, Finland,2001. 541~548.
[31] Asif Usmani. Fundamental Principles of Structural Behavio in Fire[C]. Proceedi-ng of the Tianjin Workshop on Structura Engineering for Fire Resistance, Tianjin,2002:3-4.
[32] Poh K W,Bennetts I D.Behavior of Steel Column at ElevateTemperature[J]. Journal of Structural Engineering,1995, 12 (4):676-684.
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