4 - Output only modal identification and structural damage detection using timefrequency and wavelet techniques for assessing and monitoring civil infrastructures

Abstract

The primary objective of this chapter is to develop output only modal identification and structural damage detection. Identification of multidegree of freedom (MDOF) linear time invariant (LTI) and linear time variant (LTV – due to damage) systems based on time-frequency (TF) techniques – such as short-time Fourier transform (STFT), empirical mode decomposition (EMD), and wavelets – and also a newly-merging blind source separation (BSS) technique is discussed. STFT, EMD, and wavelet methods developed to date are reviewed in sufficient detail. In addition, a Hilbert transform (HT) approach to determine frequency and damping is also presented. In this chapter STFT, EMD, HT, and wavelet techniques are developed for decomposition of free-vibration response of MDOF systems into their modal components. Once the modal components are obtained, each one is processed using HT to obtain the modal frequency and damping ratios. In addition, the ratio of modal components at different degrees of freedom facilitate determination of mode shape. In cases with output only modal identification using ambient/random response the random decrement technique is used to obtain free-vibration response.