Fully Automated Operational Modal Identification Using Continuously Monitoring Data of Bridge Structures

Abstract

Structural modal identification for providing dynamic properties, including frequencies, damping ratios, and mode shapes, plays an important role in structural health monitoring and safety assessment. Automated modal parameter identification techniques have become increasingly important to process continuously monitored data. In this study, an improved frequency-domain method for automated modal identification of bridge structures is proposed by enhancing frequency-domain decomposition through time-related modal assurance criterion and free-decaying segment determination. First, a method using ratios in the frequency domain for determination of the cutoff frequency is proposed to reduce the computational cost and improve the accuracy. Second, time-related modal assurance criterion is proposed to select physical modes. Third, damping ratios are estimated by combining the continuous wavelet transform and free-decaying segment selection to improve the accuracy of damping ratio estimation, especially for closely spaced modes. The results of the numerical studies show that the proposed method is robust to noise and efficient for identification of closely spaced modes. Moreover, the results for the practical bridge demonstrate the effectiveness and feasibility of the proposed method for performing automated modal identification in practical bridge structures.