عنوان مقاله [English]
The aims of considering structural seismic design regarding various seismic risk levels are different. For example, the structure should be serviceable after weak earthquakes and should not collapse after strong motion. Seismic design goals depend on earthquake motion levels and expected performance levels. Therefore, in order to approach certain design objectives, the recognition of a range of seismic levels is highly essential. Based on seismic design codes, design based earthquake ground motion is usually recommended, though, for other earthquake levels, it has not been greatly considered. This research attempts to compare the conversion coefficients of design based earthquake ground motion (10%) to other earthquake acceleration levels (2%, 5%, 20%, 50% and 64%). For this purpose, two susceptible areas of Sari (Elburz zone) and Fereidoonshahr (Zagros zone) were chosen, and their design accelerations relevant to the various seismic levels were determined. Afterwards, the ratios of obtained ground-motion compared to design based ground-motion were calculated. For each of the above mentioned areas, available seismic data were collected and considered in a radius of 200 km for calculating seismic factors, based on the Kijko method. Major fault systems of the sites were reviewed and modeled using suitable attenuation parameters. SeisriskIII was employed as technical software for calculating the ground-motion peaks of different seismic risk levels by applying logic tree coefficients. Isoseismal maps were prepared for both areas, yielding the ratios of acceleration levels for various seismic designs. These ratios are (0.2, 0.28, 0.64, 1.51 & 2.41) and (0.36, 0.43, 0.74, 1.33 & 1.88) for Sari and Fereidoonshahr, respectively. Finally, the results of this study show good correlation with the proposed coefficients of the standard code. The results indicate that the Iranian Code of Practice for Seismic Design (Standard no. 2800) estimates well the design based acceleration for Sari and Fereidoonshahr.