Research On Model Updating Of Medium And Small Span Bridge Using Influence Line And Its Bearing Capacity Evaluation Method

Under the effects of long-term load,environmental factors,and material aging,in-service small and medium-span bridges will inevitably appear structural damage and resistance degradation.How to quickly and effectively evaluate the carrying capacity of bridges is an urgent problem that needs to be solved in the work of bridge inspection and maintenance.This Subject focuses on small and medium-span bridges with a large volume and a wide range.Based on the actual measured response influence line,the bridge finite element model is updated to obtain a finite element model that can represent the actual bearing capacity of the bridge,and then the bridge’s bearing capacity evaluation is realized based on the corrected model.This article is based on the National Natural Science Foundation of China’s general project(52078102): Research on quantitative identification of joint damage of fabricated slab girder bridges based on spatial response feature inversion.The main research work is as follows:(1)Programming realization of the correction method of influence line model based on MATLAB platform.The objective function,parameter selection,optimization algorithm and evaluation index of influence line model modification are sorted out.A general calculation program for the influence line of the bridge was written using the spatial beam element,the plate shell element and the spring element.The results were compared with the solution results of the commercial software ANSYS,and the correctness of the general program was verified.The pattern search algorithm is introduced into the influence line model correction,and the steel-concrete composite beam bridge example is compared with the genetic algorithm to verify the global optimization and fast convergence advantages of the pattern search algorithm.The MATLAB script function of the influence line model modification method and its implementation method are introduced,and the process and framework of the influence line finite element model modification of small and medium-span bridges are given.(2)The influence line is used to study the correction of the finite element model of typical small and medium-span bridges under damage.The hollow slab girder bridge and the steel-concrete composite girder bridge are taken as examples for model correction.By comparing the difference between several common virtual beam value methods and the solution results of the solid model,the virtual beam stiffness value method is given,and the optimization index of hinge damage is proposed.At the same time,a method to modify the finite element model of the hollow slab girder bridge under hinge damage is given.The method first locates the hinge damage through the influence line,and then constructs the objective function to damage the damage based on the residual of the relative displacement influence line on both sides of the hinge.The finite element model of the hollow slab girder bridge was revised,and the effectiveness of the method was verified by numerical examples of multiple damage joints.Finally,the measured influence line is used to analyze the model correction of the steel-concrete composite beam bridge under the degradation of the shear bond.The shear force transmission between the steel beam and the concrete slab is simulated by the eccentric beam element,and the influence line residual error is used to construct the target The function modifies the finite element model of the steel-concrete composite beam bridge.(3)Based on the modified bridge finite element model,a virtual load bearing capacity evaluation method is introduced.The methods of carrying capacity evaluation between China and the United States are compared from the aspects of carrying capacity evaluation formula,load rating grade,live load model and so on.On the basis of the modified model,the pseudo-load test method is introduced,and the existing joint damage hollow slab girder bridge obtained after the modification is taken as an example,the structure verification coefficient is obtained by arranging the virtual loading of the load condition.the structure verification coefficient is less than 1 shows that the bearing capacity of the hollow slab girder bridge is better than the theoretical state.In addition,the American LRFR method was used for the graded evaluation of the steel-concrete composite beam bridge,which verified the applicability of the quasi-load test method based on the modified model for the evaluation of the bearing capacity of the steel-concrete composite bridge.