Instantaneous Identification of Degrading Hysteretic Oscillators Under Earthquake Excitation

This article presents a technique for the structural identification of hysteretic oscillators that are characterized by degradation in stiffness. The main assumption of the proposed procedure is that it is possible to replace the expression of the time derivative of the restoring force with a polynomial approximation, characterized by time-varying coefficients. The work aims at generalizing a method that the authors have proposed for hysteretic nondegrading systems: system parameters are evaluated from instantaneous estimates of the time-varying coefficients. The instantaneous estimation, based on optimization techniques, is made possible through the temporal localization of frequency components, i.e., the representation in the joint time—frequency domain. A numerical application consisting of the instantaneous identification of a Bouc-Wen model with stiffness degradation under earthquake excitation is presented and discussed. Although the sensitivity of the estimation to exogenous noise is greater than in the nondegrading case, the global accuracy of the identification is satisfactory.