Damage severity estimation of an elastoplastic single-degree-of-freedom oscillator from its ground and response accelerations

Structural health monitoring requires procedures for estimating seismic damage. An energy-based method is proposed for the estimation of occurrence in time and severity of damage of a damped elastoplastic single-degree-of-freedom oscillator from its absolute and ground accelerations, using ductility as the adopted damage index. This estimation requires the calculation of the yielding history, relative velocity and dynamic parameters of the oscillator. Oscillators of several frequencies, subjected to two different bandwidth motions, are examined. Yielding history is identified by the discrete wavelet transform (DWT) highest scale coefficients of the absolute acceleration. This identification is not possible in responses with high-frequency content. A DWT filter is proposed for this situation to enable this identification. A least-square method that acknowledges the unloading known from the yielding history is proposed to fit the velocity obtained from the time integral of the relative acceleration. The results show that the precision in estimated ductility is sensitive to the accuracy of the yielding history, as this history influences the calculation of the other parameters and variables required for the estimation of ductility. Small deviations in the actual yielding history generate important variations in estimated ductility. However, the proposed method successfully identifies the occurrence in time and severity of damage produced in most yielding stages.