Theoretical And Parametric Study On Vehicle Response Based Modal Identification Of Girder Bridges

The vibration-based modal identification is an important and useful tool for damage diagnosis and health monitoring of bridges.The bridge modal information(e.g.,frequencies,modal shapes,damping,etc.)contains much information that allows the evaluation of damage condition and operation status of the bridge.Therefore,the accuracy of the identified modal parameters of the bridge significantly affect the evaluation result.Compared to the conventional modal identification methods,the indirect method identifies the bridge modal parameters based on the dynamic responses of moving vehicles mounted with a single or very few sensors,which is a very good idea.This method is particularly suitable for rapid inspection of small and medium span bridges on a large scale,which does not require special excitation equipment,does not interrupt traffic,and greatly reduces the number of sensors.However,current research on the indirect method has mainly focused on the application on a single type of bridge and cannot be applied to a large number of bridges.The present study focused on the optimization of vehicle parameters that could be used for the indirect modal identification of different types of bridges.The main work and conclusions are as follows.(1)Considering the effect of unevenness of the bridge deck,the theoretical equation is used to simulate the vertical vibration of the vehicle itself when passing through the simply supported beam,and the vehicle response is processed by Fast Fourier Transform(FFT)to extract the bridge frequency information contained therein,and the theoretical analytical solution is verified through finite element simulation of vehicle-bridge coupling vibration and field tests.(2)To improve the detection of vehicle recognition,vehicle power parameters,vehicle speed,and bridge parameters are analyzed.The results show that for the bridge low order frequency,the bridge frequency recognition effect is better when the trailer frequency is 0.8～0.9(or 1.1～1.2)times of the bridge frequency.Vehicle speed on the frequency recognition results of the regularity is not obvious,take lower vehicle speed is more appropriate.In addition,also need to pay attention to two trailers spacing on the recognition results of the influence.For a large number of simply-supported girder bridges,it is recommended that the parameters of the test vehicle be reasonably selected according to the cross-sectional area,cross-sectional shape and span of the bridge,which can improve the accuracy of the frequency recognition based on the indirect method.(3)A simplified vehicle-bridge coupled vibration system was used to derive a theoretical formulation for modal identification of continuous girder bridges based on vehicle response,and the indirect method was successfully applied to continuous girder bridges of three spans and above.The feasibility of the method for structural parameter identification and system response estimation of multi-span continuous girder bridges is also verified by means of finite element numerical simulation analysis and a field test of a continuous girder bridge.(4)In order to optimize the testing vehicle parameters,the number of continuous girder bridge spans,single span spans,as well as the testing vehicle power parameters,operating speed and other parameters are analyzed.The results show that the frequency recognition accuracy is higher when the number of spans of a continuous girder bridge is small.The frequency recognition of continuous girder bridges is better when the vehicle frequency varies between 3.5 ～ 6.5 Hz,but care needs to be taken to avoid resonance between the test vehicle and the bridge.When using the indirect method for modal recognition of continuous girder bridges,it is recommended that the speed of the moving test vehicle should not be taken too large.