Indirect Identification Of Bridge Modal Parameters Based On Vehicle Response And Time-frequency Analysis

Bridge modal parameters(i.e.,frequency,damping and modal shape)are the important basis for bridge health monitoring,system identification,and damage diagnosis.The traditional bridge modal identification method is through measuring the dynamic response of the structure itself by directly placing sensors on the bridge.This method needs to install a large number of sensors on the bridge,which is difficult for the application on the short and medium span bridges.It is thus important to develop more efficient modal identification methods.The indirect method by measuring the dynamic response of moving vehicles is an efficient and fast method to identify bridge modal parameters.However,the dynamic response of moving vehicles not only contains the vibration information of bridges,but also the vibration information caused by vehicle vibration and environmental factors.Therefore,the present study proposed a method based on empirical mode decomposition(EMD)and time-frequency analysis to process the vehicle response signals so as to improve the accuracy of bridge modal identification,followed with the verification using finite element analysis,scaled model test,and field bridge test.The main research contents and conclusions are as follows:(1)Bridge modal identification method based on vehicle response and si gnal processing.A signal processing method based on EMD and time-frequency analysis was proposed to identify bridge modal parameters.The effective separation of vehicle vibration signals was realized by EMD,and the high-resolution modal shapes of bridges were constructed by time-frequency analysis technology,and the basic flow of the method was established.(2)Verification using the finite element models of one-dimensional beam element and three-dimensional solid element.For the construction of bridge modal shapes,three time-frequency analysis methods,namely,short-time Fourier transform(STFT),Wigner-Ville distribution(WVD),and continuous wavelet transform(CWT)are adopted for comparison.The results show that the bridge modal shapes constructed by CWT are more accurate and smooth than those constructed by STFT and WVD.(3)Parametrical analysis of various factors on the identification.The results show that when the frequency of the trailer is lower than the first-order frequency of the bridge,the identification results are better.Random traffic flow can excite the bridge more sufficiently,which is beneficial for the indirect identification of bridge modal parameters.The proposed method has good robustness for bridges w ith road roughness,noise and different cross section types.(4)Verification using scaled model test and field experiments.The scaled test of a simply supported T-beam bridge was carried out to verify the reliability of the proposed method for identifying bridge frequencies and mode shapes.Finally,a field test was carried out on a hollow slab bridge.The first two frequencies of the bridge are identified and the first mode shape is constructed.The research results show that the indirect identification method of bridge modal parameters based on vehicle responses and signal processing techniques can effectively improve the accuracy of bridge modal identification and provide support for the rapid detection and evaluation of short and medium span bridges.