A SIMPLE METHOD FOR ESTIMATING THE MAXIMUM SOFTENING DAMAGE INDEX

A simple method is proposed for estimating the maximum softening damage index proposed earlier by DiPasquale and Cakmak. The index requires that the time variation of the fundamental period of an equivalent linear system be computed over the course of a damaging earthquake event. The proposed method estimates this variation by computing empirical transfer functions from fast Fourier transforms of moving windows on measured input and output time series. The method is applied to records from a scale model of a 10-story reinforced concrete building frame subjected to severe levels of damage. The computed damage indices are shown to agree well with those computed using a more elaborate time domain procedure. The proposed method is applicable to a large class of structures undergoing a damaging earthquake event.