Recommendation of new design spectra for Iran using modified Newmark method

Abstract

The Newmark design spectra are commonly adopted in seismic codes to calculate design spectra, while these spectra generally differ from the statistically driven ones. This study aims to re-construct the Iranian design spectra by implementing a modified Newmark method on an extensive database of previous earthquakes in Iran. Three sets of recorded earthquakes are considered to evaluate the effects of parameters such as source-to-site distance, magnitude of ground motion, and shear-wave velocity. Considering that the selected earthquakes have different frequency contents, the suitable frequency ranges for each earthquake category are obtained. Subsequently, a statistical approach is adopted to calculate amplification factors and spectral bounds of the site design spectrum of Iran for three different site categories as a function of ground motion's magnitude. The calculated coefficients can be used to modify the Newmark spectral values in displacement, velocity, and acceleration-sensitive regions to obtain suitable design spectra. The results indicate that, in general, the proposed design spectra can provide a better representative of the earthquakes in Iran compared to the current Iranian seismic design code.