Modal parameter identification of Tsing Ma Bridge during Typhoon Victor: EMD-HT approach

Abstract

There are several methods available for identifying modal parameters of a civil structure from its field measurement data. This chapter identifies the modal parameters of the Tsing Ma Bridge (TMB) from the bridge responses measured during Typhoon Victor using the newly-emerged empirical mode decomposition (EMD) method in conjunction with the Hilbert-transform (HT) technique. In the chapter, natural frequencies and modal damping ratios identified by the EMD-HT approach are first compared with those obtained by the traditional fast Fourier transform (FFT) method. The EMD-HT approach is then used to examine bridge modal parameters identified from different sensors at different locations. Finally, the EMD-HT approach is used to investigate variations of natural frequency and total modal damping ratio of the Bridge with vibration amplitude and mean wind speed. It is demonstrated that the EMD-HT approach is applicable to modal parameter identification of large civil structures using field measurement data, and the EMD-HT approach is better than the FFT method. The results show that the EMD-HT approach and the FFT method produce almost the same natural frequencies but the FFT method gave higher modal damping ratios than the EMD-HT approach in most cases. The consistent modal parameters are identified from different sensors at different locations. The results also demonstrate that the natural frequencies of the bridge decrease slightly with the increase of mean wind speed and vibration amplitude. The total damping ratios, however, exhibits an increasing trend with the increase of vibration amplitude and mean wind speed.