Extraction of modal parameters through Wavelet Transform

The aim of this work is the comparison between results obtained through the processing of signals acquired during several dynamic tests with different methods. The wavelet transform (WT) is used as a time-frequency representation for the determination of modal parameters such as natural frequencies, damping ratios and mode shapes of real structures. Through the WT it is possible to investigate the behavior of a non stationary signal, and it is possible to define with sufficient accuracy the trend of the signal in the time domain and the spectrum of the same in the frequency domain by only one transform. For this reason in the latest years studies have been conducted on identification of modal parameters including natural frequencies, damping coefficients and mode shapes of structural systems using ambient and free vibration records without input measurements. In this context the WT are applied to identify the modal parameters of two bridges, one subjected to a free vibration test (Vasco da Gama Bridge) and the other subject to an ambient vibration test (Pinhão Bridge).