Numerical Simulation Of Highway Fire Temperature Field And Analysis Of Long-span Cable Support Bridge Fire

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.