Research Of Performance Of Steel-concrete Continuous Composite Girder Exposed To Tank Fire

The steel-concrete composite girder is a kind of mechanical structure which combines the upper concrete and the lower I-beam by shear connection installation.It can make full use of the mechanical performance of materials and it is more economical than pure steel structure.It is widely used in urban and highway traffic.With the development of transportation,the number of accidents of vehicles carrying inflammable materials in bridges is increasing.The damage of the bridge caused by the fire should be paid more attention.In fire,the steel beam heats rapidly,the material performance of steel-concrete composite girder decreases sharply in a short time,the bearing capacity of the original structure decreases rapidly,and the steel-concrete composite girder will seriously deflect or even collapse,which will cause great economic losses and adverse social effects.Scholars in China and abroad have done some research on the damage of structure caused by fire,mostly focuses on building structure and single beam experiment.There are few studies on the mechanical properties of steel-concrete composite continuous girder under fire.Based on previous studies,this paper establishes the finite element of the bridge of selected engineering background by using ANSYS software program,relying on the project of National Natural Science Foundation(51878057).The mechanical properties of steel-concrete composite continuous girder bridge are studied,which lays a foundation for mechanical properties evaluation and fire resistance design of steel-concrete composite continuous girder in fire.The main research work is as follows:(1)By summarizing the research results in China and abroad in the field of composite beam in fire,further study in the field of fire resistance of steel-concrete composite girder should be carried out.The corresponding ANSYS finite element heat analysis model and thermal-mechanical coupling analysis model are established for the problems to be solved in this paper.The elaborate establishment process,difficulties and parameters of establishment of thermal-mechanical coupling contact analysis model are given.(2)Based on ANSYS heat temperature model,the temperature time history of roof,common rebar,prestressing rebar,flange,web,bottom plate and other components of steel-concrete composite continuous beam under tank fire is studied.The temperature distribution of control section of steel-concrete composite continuous beam is compared and analyzed,and the temperature variation of gradient time history variation is tracked,building the foundation of the analysis of mechanical properties of steel-concrete composite continuous beams.(3)Based on the analysis of the thermal-mechanical coupling analysis model,the influence of fire source location and load level on the mechanical properties of steel-concrete composite continuous beams is studied.The failure models and performance of the beams are analyzed.The mechanical deflection and variation law of steel-concrete composite continuous beams with time of fire extension are revealed.The fire resistance limit of steel-concrete composite continuous beams under deflection analysis is obtained.(4)Based on the strength reduction of section equivalent principle and the strength reduction of steel and concrete varying with temperature,the time-history residual strength of materials in fire is calculated.The bending capacity of steel-concrete composite continuous beams under tank fire is calculated.The law of time-history variation of section bending capacity is revealed,the more applicable fire-resistance limit is obtained.The fire-resistance of steel-concrete composite continuous beams under fire is corrected by deflection analysis.(5)Through the analysis of thermal-mechanical coupled steel-concrete composite continuous beams in cooling stage,the restoring strength of steel in cooling stage is obtained,the variation law of ultimate bearing capacity in cooling stage is obtained,the calculation formula of ultimate bearing capacity in cooling stage is given,and the evaluation method of steel-concrete composite continuous beams in cooling stage is obtained.