Structural Dynamic Parameters Identification Based On Time-varying Analysis Of Vehicle-bridge Interaction System

Bridges are the key hub in the transportation infrastructure network,and the safety performance of bridges is of great practical significance for ensuring the smooth operation of the national economy and social life.However,a large number of bridges are in a "sub-health" state for a long time due to lack of targeted maintenance and understanding of performance status.Therefore,it is an urgent problem to be solved that how to evaluate the current performance of bridges.Vibration test is a convenient method commonly used in current structural performance assessment,but traditional ambient vibration test and driving vibration test only focus on identifying the basic modal information of the structure and cannot serve the bridge safety assessment,and the impact vibration test is complicated and limited.In this thesis,these strengths of ambient vibration test,impact vibration test and driving vibration test are combined,and then a structural dynamic parameters identification method based on the time-varying analysis of the vehicle-bridge coupling system is proposed for structural deflection prediction and performance assessment.The main research contents and innovations of this thesis are shown below:(1)Based on the moving mass unit and moving mass-spring-damper unit vehicle models,the vehicle-bridge interaction vibration analysis theory is derived respectively,and the dynamic equations of the vehicle-bridge interaction system for single and multiple vehicle units are established.Then the numerical calculation method of vibration response,road surface roughness simulation method and vehicle-bridge interaction model parameters used in the analysis are introduced,and the effects of different vehicle parameters and road surface roughness on the structural vibration response are analyzed.(2)Based on the vehicle-bridge interaction model of moving mass unit and moving mass-spring-damper unit,respectively,the mapping relationships between the basic modal parameters of the structure,the time-varying modal parameters of the vehicle-bridge interaction system,the vehicle parameters and the displacement shape function are derived.A deep level dynamic parameter identification method of the structure is presented then.These modal parameters are analyzed and identified from the structural response in the proposed method,and further parameters of the testing vehicles as the excitation source are combined to identify the structural mode scaling factor,so that the mass-normalized mode shape of the can be calculated,and then the true displacement frequency response function and flexibility matrix of the structure is reconstructed,which can be utilized to predict the elastic deformation of the structure under static load and evaluate the performance of bridges.(3)In order to improve the applicability of the proposed method and avoid the trouble of the basic modal parameters without vehicles of the structure,a structural parameter identification method based on time-varying dynamic characteristics at different times is further proposed.Ambient vibration test is unnecessary in this method but only the vibration test is carried out to analyse and achieve the structural mode scaling factor.At the same time,in view of the fact that it is hard to measure the vehicle parameters in practice,a method for simultaneously identifying vehicle parameters and structural parameters based on multiple time-varying dynamic characteristics is proposed,which can be used to obtain the vehicle parameters and structural mode scaling factor.(4)A series of finite element model numerical experiments are performed to verify the correctness of the theoretical methods proposed above.At the same time,the effects of identification frequency deviation,vehicle model parameters,and road surface roughness on the identification results of instant frequency and mode scaling factor are analyzed through numerical experiments.Finally,the field test including ambient vibration test,impact vibration test,driving vibration test and static load test were carried out on a three-span prestressed concrete continuous beam bridge.The results prove the effectiveness and feasibility of identifying the structural mode scaling factor and displacement flexibility matrix by the proposed method,which can be applied to further evaluate the current structural safety performance and effectively serve the maintenance and management of bridges.