Research On Existing Continuous Concrete Bridge Safety Performance Evaluation Based On Model Updating By Response Surface Method

Bridge is an important part of traffic line,and it is the key to ensure the whole line through.Due to the defects of design and construction,degradation of material properties,improper use and natural disasters,there are more and more problems in existing bridges,such as structural damage,reduction of bearing capacity,safety and reliability decline.In order to ensure the safety and smooth flow of traffic,understand the actual working conditions of the bridge,it is necessary to make a reasonable assessment and prediction of the actual bearing capacity and safety reserves of existing bridges until it is almost too late.In this paper,combined the development of computer,communication and sensing technology in recent years and the results obtained by the structural finite element model revision,using the static and dynamic load test of an existing viaduct on a city's main road as the engineering background.Using ANSYS finite element software to construct the finite element model of the test bridge.Comprehensively use the dynamic weighting coefficient and combined with the static and dynamic load test data to construct the objective function,use the response surface method to modify the initial finite element model,and use the benchmark finite element model obtained after the model updating to carry out the operational safety performance assessment of the existing bridge.The concept of equivalent check coefficient based on model updating and the method of evaluating the bearing capacity of real bridges using equivalent check coefficient are proposed.The validity of the method is verified by the load test of real bridges.The research results can be used as reference for similar projects.The main research work of the paper is as follows:1.Field static load and dynamic load tests were carried out.Vehicle load was used to obtain the measured values of deflection and stress of the main measuring points under three static loading conditions and the first three vertical natural frequencies and modes under dynamic load test conditions.A solid finite element model of a four-span prestressed concrete continuous box girder was established based on the design drawings and the design values of material parameters,and then the theoretical analysis results of the initial finite element model are compared with the actual field measurements.2.The variance analysis method is used to analyze the significance of the modified parameters,and the parameters that have a significant effect on the static and dynamic characteristics of the structure are selected: concrete elastic model,concrete density,Poisson's ratio of concrete,and asphalt pavement thickness as parameters to be modified.The objective function is constructed by using the dynamic weighting coefficient as well as the static and dynamic load test data.Taking the deflection of the main measuring points under all static load conditions and the first three vertical frequencies of the structure under dynamic load conditions as the state variables at the same time,a basic model for model updating is constructed.3.The central composite experiment design method was used to arrange the extraction of numerical samples.The least squares method was used to fit the quadratic polynomial response surface equations of each response of the structure.Using the response surface model instead of the finite element model to modify the initial finite element model of the bridge,a reference finite element model reflecting the actual working condition of the bridge was obtained.4.Based on the benchmark finite element model,the bridge safety performance evaluation method is studied.The concepts and meanings of equivalent calibration coefficient and initial calibration coefficient were proposed.The feasibility and accuracy of using the equivalent check coefficient instead of the initial check coefficient to evaluate the bearing capacity of the bridge were verified by the deflection of the static load test and the measured value of the stress.