【作者】 李利军；

【导师】 胡兆同；

【作者基本信息】 长安大学 ， 桥梁与隧道工程， 2013， 博士

【摘要】 斜拉桥拉索和悬索桥主缆、吊索是主要承重构件，多采用平行钢束、钢丝绳或钢绞线作为承重材料。耐火性能差是钢结构的一个致命弱点。随着公路运输事业的发展，车辆火灾发生的频率越来越高，火灾规模越来越大，对结构物的破坏越来越严重。目前，对大跨径缆索承重桥梁的火灾研究尚处于空白阶段，开展大跨径缆索承重桥梁火灾对结构安全性能影响的研究极其必要，可为今后缆索承重桥梁的抗火设计提供重要的科学依据。本文主要研究内容如下：（1）在国内外研究工作的基础上，基于Ingason H.平方增长模型，提出了适用于公路桥梁火灾研究的车辆火灾和汽油池火灾的热释放率数学模型。（2）采用火灾动力学模拟软件FDS(Fire Dynamics Simulator)对公路火灾下缆索承重桥梁瞬态空间温度场进行数值模拟，并通过开放空间油罐火灾实验中实测的温度场数据与数值模拟的结果进行对比分析，证实了模拟过程中模型建立的正确性。（3）建立了公路火灾大气最高温度空间温度场。建立了公路桥梁火灾的物理模型，确定了车辆火灾和油池火灾各工况燃烧热源的尺寸和单位面积释热率。根据建立的物理模型，通过数值模拟得出了公路火灾大气温度场随释热率变化的规律、编制了各工况恒定温度场释热口平面上的温度值分布表格，给出空间温度场随高度变化的规律公式，从而模拟出整个空间大气温度场的最高温度分布。（4）建立了公路火灾下缆索承重桥梁承重构件瞬态空间温度场。根据建立的物理模型，通过数值模拟给出火灾各工况下悬索桥主缆、吊索以及不同直径斜拉索表面温度及热流密度随火灾的发展过程而变化的规律公式，并编制了最大燃烧持时处的温度及热流密度表格，从而建立了承重构件瞬态空间温度场。通过温度场的建立，得出了钢构件截面尺寸对其表面温度及热流密度变化过程的影响；同一火灾工况下，不同直径的悬索桥主缆不同位置具有相同的Tt2时，可以采用相同的表面温度及热流密度随火灾的发展过程而变化的规律公式。（5）通过对国内外已有的高温下钢材材料特性的研究做了详细比较，确定采用欧洲规范EUROCODE4规定的预应力钢筋的高温强度和弹性模量降低系数和高温下钢材的应力-应变关系Rubert-Schaumann模型进行缆索承重桥梁(悬索桥和斜拉桥)在火灾下的全过程分析。（6）给出了公路火灾下缆索承重桥梁承重构件的安全距离，明确了其抗火设计范围。通过热—结构耦合分析，确定了火灾各工况作用下悬索桥0.4～1.0m范围内不同直径主缆的安全距离、悬索桥吊索的安全距离、斜拉桥0.05～0.2m范围内不同直径斜拉索的安全距离；安全距离之内的构件，火灾对其力学性能不会造成影响，不需要考虑抗火设计。（7）根据建立的缆索承重桥梁承重构件瞬态空间温度场，采用ANSYS有限元程序，选择间接耦合法进行斜拉桥和悬索桥实例的热—结构耦合全过程数值模拟，分析了结构的温度场分布、内力和位移特征以及破坏模式，得到了不同火源模型下结构的极限状态。不同缆索承重桥梁在公路火灾下的极限状态可根据本文建立的承重构件瞬态空间温度场进行热—结构耦合的全过程数值分析。综上所述，公路火灾最不利状态下会对缆索承重桥梁的安全造成隐患，火灾如果得不到及时扑救，将使其丧失正常使用功能，严重时会导致大桥的损毁；火灾对悬索桥的影响是致命的，悬索桥主缆是不可更换构件，一旦在火灾作用下主缆发生较大的伸长变形，将会导致加劲梁的变形，使其丧失使用功能。本文的研究成果，对缆索承重桥梁抗火设计和工程实践具有重要的参考意义。更多还原

【Abstract】 Cables of cable-stayed bridge, and the main and suspender cables of suspension bridgeare the main bearing elements, which are usually made of parallel steel wires, wire rope orsteel strands. Poor fire resistance is a fatal weakness of steel structure. With the developmentof highway transportation, it is more and more likely to see vehicle fire accidents on thehighways and the fire scale is becoming bigger and bigger; consequently, the damage tostructure of bridge is becoming more and more serious. At present, studies on the fireaccidents on long-span cable bearing bridges are still in the blank stage. Therefore, it isextremely necessary to conduct researches on the effects of fire accidents on the structuralsafety performance, which can provide some important and valuable scientific bases for thefire resistance design of cable supporting bridge. The followings are what the present papermainly discusses in this research:（1）After reviewing and analyzing studies conducted at home and abroad, and based onthe Ingason H. Square Growth Model, this paper puts forward several kinds of thermal releaserate mathematical models, which are suitable for the fire studies of highway bridges, forvehicle and for gasoline pool fire.（2）In this research, the Fire Dynamics Simulator (FDS) is used to numerically simulatethe transient space temperature field of the cable bearing bridge in the highway fire. Bycontrasting and analyzing the measured data obtained from a tank fire experiment in the openspace and the data from the numerical simulation of temperature field, this study validates theaccuracy of modeling in numerical simulation.（3）Establish the space temperature field when the atmospheric temperature reaches thehighest in the highway fire.We build a physical model for highway bridge fire, and determine the size of combustionheat source and the heat release rate per unit area of the vehicle and pool fire in operatingconditions. Based on the established physical model, we obtain the regular pattern of how theatmospheric temperature field varies with the heat release rate change through the numericalsimulation, make a table of surface temperature distribution showing heat release in theconstant temperature field, and present the formula of how space temperature field varies withheight. Knowing that, we can simulate the highest temperature distribution of the wholeatmospheric temperature field.（4）Establish the transient space temperature field of bearing elements of cable bearingbridges in the highway fire.Based on the established physical model, we observe the trend of how the surfacetemperature and heat flux of main and suspender cables of suspension bridge as well asstayed-cable with different diameters changes with fire situation through the numericalsimulation, and create a table of temperature and heat flux at maximum combustion point.Therefore, the transient space temperature filed of bearing elements is established, from which we know the process of how the cross-section size of steel components influences itssurface temperature and heat flux. Under the same conditions of fire accidents, the sameformula of how the surface temperature and heat flux changes with fire situation can beapplied to main cables of suspension bridge with different diameters when they have thesameTt2at different places.（5）After a thorough comparison of existing studies on steel material properties at hightemperature home and abroad, we decide to employ the high temperature strength, the elasticmodulus decreasing coefficient and the stress-strain Rubert-Schaumann model at hightemperature, which is regulated by the European standard EUROCODE4, to analyzecompletely the cable bearing bridges (suspension bridge and cable-stayed bridge) under thefire occasion.（6）This study gives the safety distance of bearing elements of cable bearing bridgesand clarifies its design range of fire resistance.By the heat-structure coupling analysis, we determined the safety distance of main cableswith different diameters as well as suspender cable of suspension bridge (0.4~1.0m), and thesafety distance of stay cables with different diameters of cable stayed bridge (0.05~0.2m).As for those constructional elements within the safety distance, fire has no effect on theirmechanical properties, thus we need not take the fire resistance design into consideration.（7）Based on the transient space temperature filed of bearing elements of cable bearingbridges, and using ANSYS finite element software and indirect coupling method with whichwe conduct a practical and complete heat-structure coupling numerical simulation ofcable-stay brigade and suspension bridge, we studied the distribution of structural temperature,features of internal force and displacement and failure mode. From that we know the limitstate of cable structures in different fire models. According to the transient space temperaturefield of bearing elements established in this study, we can make a complete heat-structurecoupling numerical analysis of the different limit states of different cable bearing bridgesunder the highway fire.To sum up, fire, to the worst, could become a potential safety hazard to cable-supportedbridges. If it is not controlled and extinguished promptly, it could cause the bridge lose itsnormal functions, and even cause serious damage to the bridge. The influence of fire onsuspension bridge is fatal because main cables of suspension bridge are irreplaceable. Oncethe main cables, affected by fire, elongate and distort greatly, they will cause the deformationof the stiffening girder and make it lose its normal function. This paper has got somewhere inthis field, and we hope that the findings will be of great significance in fire-resistance designfor cable bearing bridges and engineering practice.更多还原