Wavelet-Based Modal Parameter Identification of Bridges-Application To Real Measurement Data

摘要

The wavelet transform is used as the time-frequency representation of operational measurement signals for the purpose of modal parameter identification of bridges. In this paper , the use of a new identification procedure,named wavelet-based identification technique of bridges modal parameters is discussed. The technique starts with the calculation of covariance from random response of the system that converted into the time-scale domain using a continuous Morlet wavelet transform. It can be shown that the ridges of the covariance wavelet coefficient magnitudes contain modal information of the system. The phase angles and the magnitudes of the covariance wavelet coefficients along the ridges are related to natural frequencies and viscous damping ratios. And the wavelet coefficients of the cross-covariance were used to estimate the mode shapes of the system. The case study is the Beichuan River Bridge,a concrete filled steel tubular arch bridge in Xining, China that was tested under ambient vibration excitation. The modal parameters such natural frequencies, damping ratios and mode shapes are successfully identified by proposed wavelet-based technique. The obtained results have been comparable with those previously obtained from the peak pick method in frequency domain and stochastic subspace identification in time domain. It is demonstrated that the wavelet transform is promising in the modal parameter identification of structures under operational measurements.