Identification of modal parameters of ambient excitation structures using continuous wavelet transform

Abstract : Continuous wavelet transform (CWT) has recently emerged as a promising tool for identification of modal properties such as natural frequencies, damping ratios and mode shapes through ambient excitation measurements of structures. This paper mainly discusses the capability of CWT method to identify the modal properties accurately using a numerical application in five storeys frame and two practical applications in a five storeys reinforced concrete structure with masonry in-fill walls and a three storeys masonry structure. Natural frequencies are identified by extracting windows paralleled to the frequency axis at wavelet ridges. Damping coefficients are estimated using the wavelet-based logarithmic decrement method. Finally, a conclusion can be drawn that the continuous wavelet transform used for the output-only system identification of ambient excitation structures yields a good agreement with results of the random decrement method and the finite element models.