Wavelet energy ratio index for health monitoring of hysteretic dampers

Abstract

This paper presents new contributions to evaluate the damage suffered on a particular type of hysteretic damper called web plastifying damper (WPD) for the passive control of structures subjected to earthquakes. WPDs consist of several I-section steel segments arranged to form a brace-type structural element. Energy input by the earthquake is dissipated by the WPD through plastic deformations of the web of the I-sections. These devices, properly installed in reinforced concrete test models, were tested under successive seismic simulations of increasing magnitude with a shaking table. To assess the damage of the web of the I-section after each seismic simulation, a new damage index called wavelet energy ratio (WER) was developed; it uses the signals collected by piezoelectric sensors in simple vibration tests. The index is based on wavelet package decomposition and energy calculation of properly chosen wavelet coefficients. It was correlated with a mechanical energy-based damage index—ID—proposed in past research, which has proven to accurately characterize the level of damage yet requires costly instrumentation to acquire the load–displacement curve needed for its computation. The experiments reported in this paper demonstrate a good correlation between WER and ID indices in a realistic seismic loading scenario. On the basis of this correlation, it is possible to estimate ID indirectly from the WER, which involves much simpler and less expensive instrumentation, easily applicable for in situ continuous monitoring of the dampers.