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. To this end, three sets of earthquakes recorded at three different sites are considered. The effects of parameters such as source-to-site distance, the magnitude of ground motion, and the shear wave velocity are evaluated. Subsequently, the amplification factors are obtained through a statistical approach, and the spectral bounds are calculated for three site categories and two types of earthquake magnitudes. As a result, for the first time, the coefficients of the site design spectrum of Iran are presented as a function of ground motion’s magnitude for the aforementioned site categories. The calculated coefficients can be used to modify the Newmark spectral values in displacement, velocity, and acceleration-sensitive regions to obtain suitable design spectra. Finally, a comprehensive statistical study is conducted on earthquake parameters to assess the characteristics of the earthquakes in Iran from statistical perspective. The proposed design spectra can address most shortcomings of 4th edition of the Iranian seismic design code, and it is recommended to include them in the next revision.