Modal Identification of High-Speed Railway Bridges through Free-Vibration Detection

AbstractIn the dynamic characteristic analysis of high-speed railway bridges, free-vibration responses after a train passes are valuable for modal identification. However, distinguishing between free- and forced-vibration segments requires user intervention, which hinders the reliable and continuous identification of modal parameters, thereby impeding the vibration-based structural state assessment. This paper proposes a free-vibration detection technique whose basis is that the envelope function of each modal component decomposed from the free-vibration data decays exponentially. To extract the modal component adaptively, iterative variational mode decomposition is proposed where the signal is iteratively decomposed into two components until a single-degree-of-freedom component is obtained. Subsequently, the estimated free-vibration data are adopted to identify the modal parameters by the eigensystem realization algorithm with data correlation. A numerical simulation illustrates that the proposed method can provide the optimal free-vibration data for modal analysis. To verify the effectiveness of the proposed method in practice, the accelerations of the railway bridge during the passage of a train are analyzed. The modes can be identified from the estimated free-vibration data but not from the combination of forced- and free-vibration data, which indicates that the separation of forced and free vibration is necessary and can be achieved by the proposed method.