29-08-2017, 12:05 PM
Inelastic spectra (design) that characterize a seismic hazard are generally obtained by scaling the elastic spectra (design) through a set of response modification factors. The component of these factors, which explains the ductility demand ratio, is known as the resistance reduction factor (SRF), and the variation of this factor with the initial period of the oscillator is called the SRF spectrum. This study considers the scaling of the SRF spectrum in the case of an elasto-plastic oscillator with resistance and stiffness degradation characteristics. Two models are considered: one directly dependent on the characterization of the origin and site parameters and the other depending on the characterization of the normalized design spectrum of the seismic risk. The first model is the same as that proposed by the second author, and is given in terms of earthquake magnitude, duration of strong movement, predominant period, site geological conditions, ductility demand relation and parameter related to the supply of ductility. The second model is a new model proposed here in terms of the normalized values of pseudo-spectral acceleration (at peak acceleration of the peak unit), the ratio of ductility demand and the parameter related to the ductility supply. For each of these models, the least squares estimates of the coefficients are obtained by regression analysis of data from 956 accelerograms recorded in the western United States. Parametric studies carried out with the help of these models confirm the dependence of SRFs on the duration of strong movement and magnitude earthquake in addition to the prevailing period and site conditions. It is also observed that the degradation characteristics make a slight difference for high ductility demands and can lead to lower SRFs, unless the oscillators are very flexible.