Large Span Cfst Arch Bridge Modal Parameter Identification Methods Applied Research

In the construction stage and service period, the Concrete-filled Steel Tubular Arch bridge's dynamic testing is becoming more and more important, especially for those with long spans. Dynamic testing with ambient vibration has many advantages, such as no expensive excitation devices required, no interruption of the structure's service and less testing time. It is increasingly applied in the field of the identification of bridge's dynamic properties.First of all, the theory of Stochastic Subspace Identification (SSI) is applied to identify the modal parameters of a Concrete-filled Steel Tubular Arch Bridge-Bairiba Bridge in Luding County, Sichuan province. Then the wavelet transform identification (WTI) method is explored to the bridge. From the comparison, it can be seen that the estimated results using the above methods coincide well with those obtained from the finite element model.The main content is summarized as follows:1. A three-dimensional finite element model of Bairiba Bridge is developed to make modal analysis. Then the dynamic testing with ambient vibration is carried on this bridge. For getting the accurate dynamic properties of the structure, test scheme is carefully designed. The subsequent analysis shows that the testing provides ideal data for the identification of the bridge's dynamic properties. 2. In allusion to the insufficient of the traditional identification method in frequency domain, a program WABSS, which is based on the stochastic subspace identification method, are made to identify Bairiba Bridge's modal parameters. From the comparison, it can be observed that the results by SSI method are close to those by the finite element model.3. The classical Fourier transform is a global transform from time domain to frequency domain. It can gain full frequency information, while all information in the time domain is lost. To overcome this drawback, the wavelet transform, which has good localization property in both time and frequency domain, is introduced into the identification of the bridge's modal parameters.A program WABWT is made to apply the WTI method to deal with the measurement data from the ambient vibration, and estimate the Bairiba Bridge's modal parameters. From the comparison, it can be seen that the estimated results using the wavelet transform method agree well with those obtained from the finite element model and the stochastic subspace method, which implies the reliability and efficiency of these two identification methods.4. The modal analysis results obtained from the finite element model are compared with those estimated from the stochastic subspace method and the wavelet transform method. Good coincidence of results can be observed, which demonstrates that the built-up finite element model reflects the bridge's real dynamic properties, and can serve as a baseline model for its dynamic response analysis under complicated excitations, long-term health monitoring and structural service state assessment.