Naghavi - MS. Student, Dept. of Civil Engineering, Iran University of Science and Technology, Narmak ۱۶۸۴۴, Tehran, Iran,
Baziar - Professor, Dept. of Civil Engineering, Iran University of Science and Technology, Narmak ۱۶۸۴۴, Tehran, iran

Seismic ground response characteristics, generally defined as “site effects”, have a significant role on the design of structures for earthquake resistance. In other word, topography, local soil classification and earthquake characteristics affect amplification of ground motions and maximum surface acceleration. As a result, the shape of response spectra of a structure will be affected by site effect. In different national codes, site effects have been shown by amplification functions related to different soil classification, frequency range and intensity of bed rock motions. The objective of this study is to compare response spectra and site coefficients of the UBC97, IBC2000 and EC8 with Iranian 2800 Code, considering soil classification. Various representative models of realistic site conditions were analyzed. The input motions for analyses were selected from real earthquakes. Approximately 200 site models were analyzed with a set of Iranian well-documented strong motion recordings. Equivalent Linear one dimensional wave propagation analyses were performed in this study. In modeling of site conditions, special emphasis is given to the non-linear soil behavior, the impedance contrast between bedrock and soil deposits and the thickness of soil deposits. Finally, based on the above analyses and real earthquake motions, improved response spectra, considering soil classification and seismic ground motion intensity are proposed for Iranian code in this study.