Structural health monitoring under ambient vibrations: Accuracy of identification methods

Most of the techniques currently used in structural identification under ambient excitation typically require the hypothesis of stationarity, though, in the field of civil engineering, excitation may be markedly non stationary. This consideration prompted some proposals for new identification methods that, being based on special instantaneous estimators of modal parameters, were designed to handle current types of non-stationary excitation. Hence, a novelty is that identification is based solely on the properties of slowly modulated harmonics. The present paper briefly summarises the hypotheses and theories that constitute the basis of the main "output only" techniques. The problems usually encountered in this kind of identification will be stated and critically discussed. The final part of the paper reports a few numerical simulations.