Influence And Removal Of Moving Vehicles On Modal Parameter Identification Of Beam Bridge

The modal identification methods under ambient excitation are widely used in the field of bridge health monitoring,and the identified modal parameters are normally used for damage detection.However,the moving vehicles are usually deemed as part of the ambient excitation without considering their mass property.Thus the identified modal parameters belong to the vehicle-bridge system rather than the bridge itself,which would affect the effectiveness of subsequent damage detection.In this thesis,the effects of moving vehicles on the frequencies and mode shapes identified by stochastic subspace method under ambient excitation are investigated via finite element model(FEM).Then the empirical formulas of frequency and mode shapes are established to eliminate the influences of moving vehicle.Finally,the validity of the empirical formulas is verified by experiments.The main work and conclusions are as follows:(1)The analytical solution of bridge frequencies considering the vehicle-bridge coupling effects is derived.Then the influence of moving vehicle on the dynamic characteristics of bridge is investigated based on the theory of modal analysis.And the principle and process of identifying modal parameters by peak-picking method and random subspace method are introduced in detail.(2)The influence rule of moving vehicle on the frequencies and mode shapes identified by stochastic subspace method under ambient excitation are investigated with special attention on the vehicle mass and speed.The necessary of considering the moving vehicle influence is demonstrated by comparing the changes of frequencies and mode shapes induced by the moving vehicle and bridge damage.(3)Based on the influence rule of moving vehicle on the modal identification results,the empirical formulas of frequency variation coefficients and modal shape differences considering the moving vehicle mass,velocity and bridge span are established by using the orthogonal test and least square method.Numerical examples indicate that the proposed empirical formulas can eliminate the influence of moving vehicle on the identified modal parameters.(4)A vehicle and a simply supported beam model are created in lab for experiment.The acceleration responses of the beam with and without moving vehicle are obtained by sensors installed on the beam,and the frequencies and mode shape are identified by using the stochastic subspace method accordingly.The validity of theempirical formulas for eliminating the influence of moving vehicles is verified via the experimental results.