Effect of hysteretic models on the inelastic design spectra

The design response spectrum has been widely used in seismic design to estimate force and deformation demands of structures imposed by earthquake ground motion. Inelastic Design Response Spectra to specify design yielding strength in seismic codes are obtained by reducing the ordinates of Elastic Design Response Spectrum by strength reduction factor (R). However, Inelastic Response Spectra (IRS) depend not only on the characteristics of the expected ground motion at the site, but also on the nonlinear characteristics of the structural system. IRS for the selected ground motions should be computed taking into account the different hysteretic characteristics according to the expected behavior of the type of structural system and materials to be used. The objective of this study is to investigate the effect of hysteretic models on IRS. For this purpose, IRS are obtained to attain a given target ductility ratio using nonlinear dynamic analyses of SDOF system for earthquakes. Forty ground motions recorded at stiff soil site are used. The considered hysteretic models are elasto perfectly plastic, bilinear, strength degradation, stiffness degradation, and pinching models. Results indicate that IRS are strongly dependent on hysteretic model as well as structural period and target ductility. Statistical studies are also performed to investigate the effect of the parameters of each hysteretic model on IRS. Based on the results of this parametric study the functional form of IRS (=LERS/R) is established. 1