Study On Fire Resistance Of Simply Supported Steelconcrete Composite Box Girder Bridge

In recent years,with the rapid development of road traffic system,bridge fire accidents caused by the hydrocarbon transport vehicles,tankers and other flammable and explosive materials transport vehicles were reported commonly.The composite bridge,which was widely used in the Urban bridge and all kinds of small and medium span bridge,is prone to cause high temperature yield and strength degradation of steel when it is under fire accident.Furthermore,it will undergo a large deformation or even collapse.And because the city traffic network is intensive,it will cause a large range of traffic paralysis in a certain period of time once the bridge collapsed,which will cause unpredictable losses.However,the current research on the fire resistance of steel-concrete composite bridge is still at the initial stage,and there are many shortcomings in fire resistance design parameters,fire resistance factors and fire damage mechanism.Based on the national science foundation of china-study on effective prestress decay mechanism and load carrying capacity analysis of concrete bridge under fire,and the common steel-concrete composite box girder is selected as the research object,this paper analyzes the sensitive parameters of fire resistance of steel-concrete composite bridge under the action of hydrocarbon fire by ANSYS program for numerical simulation,and the variation law of the bending capacity of the section with the extension time is revealed.The main contents are as follows:(1)The transient heat transfer analysis model was established by the large-scale general procedure ANSYS,And the model reliability was verified by comparing the reported test data;According to the thermal parameters such as heat capacity and thermal expansion coefficient of the material specified in European Standard EC3,the temperature distribution characteristics and changing rules of the steel composite box girder under the bridge fire are revealed;(2)The nonlinear transient thermo-structural coupling analysis model was established by ANSYS program,and the model validation was carried out with reference to the related literature.This paper studied the effects of fire location,web stiffener and slenderness ratio on the fire resistance of steel-concrete composite box Girder Bridge,and the failure modes and characteristics of the beam under different hydrocarbon parameters are expounded.This paper also revealed the variation law and the change mechanism of the mid-span deflection of the steel-concrete composite box girder.According to the assumption of failure criterion,the fire resistance limit of steel composite box girder under the influence of parameters is determined.(3)Based on the principle of virtual layer cross-section equivalent of strength reduction,the cumulative burnt depth of concrete roof transverse bridge to different fire location is calculated.According to the strength degradation coefficient of structural steel and ordinary steel with temperature,the residual strength of the steel box composite box girder under the carbon and hydrogen fire is calculated.And the flexural capacity of the cross section with the delay time is revealed;and the fire resistance limit of the steel box under the local fire is corrected according to the fire resistance limit determined by the section resistance.