Study On The Detection And Evaluation Of Concrete Bridge After Fire

In recent years,fire accidents of concrete bridges are increasing with the expansion of our country's economic construction.The bridge fire accidents cause huge direct economic losses,and indirect economic losses like traffic blocking and public travel affecting.Therefore,the damage degree of the bridges should be detected and evaluated timely and scientifically when the fire occurs.Corresponding disposal measures should be taken according to the bridge bearing capacity to minimize the losses.In this paper,the method of detecting and evaluating of the reinforced concrete bridges after fire accidents was studied by means of experimental analysis and finite element simulation.The main contents are as follows:(1)By using of the finite element software ANSYS,the distribution law of the temperature field inside the concrete with one side exposed to fire under different fire temperatures and different exposure time was analyzed.Exponential model was proposed which was fitting well with the simulation results.By analyzing the composition of the model,a method was proposed to calculate the temperature field of the concrete with one side exposed to fire.The method was implemented by obtaining two feature points and the environment temperature before the concrete was exposed to fire.Then two feature points were obtained by analyzing the physical and chemical reactions of the concrete under different temperatures: carbide interface and burned layer interface.The feasibility of the method was verified by experiments.(2)Based on the method of temperature field calculation,the equivalent strength method and the equivalent section method were proposed for bending bearing capacity calculation of the reinforced concrete beam with one side exposed to fire beam.The applicable conditions of the two methods were analyzed.The four reinforced concrete beam which were not fired or fired under different fire degree were tested for the bending bearing capacity.And the bending bearing capacities of the tested beams were calculated using the bearing capacity calculating methods.By comparing with the measured results,it shows that the results obtained by the bending bearing capacity calculation of the reinforced concrete beam with one side exposed to fire is accurate when the tensile area was affected by the fire.(3)Combining with the temperature field calculation method and the bending bearing capacity calculation method,the process for detecting and evaluating of the concrete bridges after fire was drew up.A reinforced concrete box girder bridge under fire was detected and evaluated by using the process.According to the calculated results,the corresponding maintenance and reinforcement methods were put forward.As a validation,the technical conditions of the bridge after reinforced were good.