Research On Identification And Application Of Bridge Modal Parameters Based On Instantaneous Frequency Of Vehicle-bridge System

As important dynamic property of bridge structures,modal parameters(frequency,damping,and mode shape)are widely used in bridge damage detection,finite element model(FEM)updating and optimization design.Increasing attention has been paid to modal identification techniques in recent years.Conventional approaches utilize a large number of sensors to measure the structural dynamic responses,and followed by signal processing tools to obtain the modal parameter.However,the conventional approaches require large data processing workload,large number of sensors and result low accuracy mode shape.To reduce the sensor installation and data processing workload and improve mode shape identification accuracy,this paper proses a modal identification method for bridge structures based on the instantaneous frequency of the vehicle-bridge system.The basic principle of this method is that the frequency change of the vehicle-bridge system reflects the characteristics of the model parameters of the bridge.A small number of sensors are installed on the bridge to measure dynamic response of the system,and the instantaneous frequencies of the system are identified by synchroextracting transform to estimate the bridge modal parameters.The proposed method is investigated by numerical and experimental examples in terms of the effectiveness,and further applied to the FEM updating.The main work and conclusions are as follows:(1)Conventional modal identification approaches,modal identification methods based on a small number of sensors,and the application of bridge modal parameters in FEM updating are introduced in detail.(2)The essential physical relationship between the instantaneous frequency of the vehicle-bridge system and the bridge mode shape is derived.The principle of estimating the instantaneous frequency of the vehicle-bridge system through synchroextracting transform is introduced in detail.A modal identification method based on the instantaneous frequency tracking of vehicle-bridge system is proposed accordingly.Thus the bridge mode shape identification has been transformed into vehicle-bridge system frequency identification,which is meaningful in improving identification the accuracy and efficiency.(3)The proposed method is verified by numerical and experimental examples.Numerical examples are designed using simply supported beam and continuous beam.Responses of the vehicle-bridge system are measured by a small number of sensors installed on the beam are used to estimate the mode shapes and frequencies.The effects of the moving vehicle parameters and sensor positions on identification results are investigated.Experimental vehicle and bridge model are set up and the modal parameters are identified by measuring the system frequencies.The results of the numerical and experimental examples clearly indicated the effectiveness and superiority of the proposed modal identification method.(4)The modal parameters identified by the proposed method are then applied to the bridge FEM updating.The updating results manifest that the modal parameters identified by the proposed method have high accuracy,which can provide reliable data for bridge FEM updating.