Developments and Comparisons on the Definition of an Instantaneous Damping Estimator for Structures under Natural Excitation

Abstract

Accurate identification of damping constitutes a relevant issue for structural health monitoring. In fact, high modal or localized damping ratios are often associated with the presence of structural damage. This question may become even more challenging when identifying a structure from its natural vibration (due to wind, traffic etc.). This article describes the results of the latest studies, conducted by this research group, focusing on the definition of an instantaneous estimator of damping for the identification of structures under unknown non-stationary excitation. A method is presented, in particular, which is based on instantaneous curve-fitting applied directly to time-frequency representations of dynamic response signals. One of the strong points of this technique is its flexibility: from each signal, in fact, a time function of damping is extracted, providing punctual information on estimate stability. A series of numerical applications to Multiple Degree of Freedom (M-DOF) systems is presented; the performance of the method is examined under increasing levels of non stationarity of the excitation. Finally, the results are compared with those obtained, on the same data, through the use of three known time-domain identification methods: Direct System Parameter Identification (DSPI), Eigensystem Realisation Algorithm (ERA), Polyreference Time Domain (PRTD). The latter two were used with the Random Decrement function.