Document Type : Research Article
Preparation of site-specific spectra for alluvium and design of tall and special structures are needed.Due to placement of the city of Ardabil on the alluvium and developing of construction in the central part of the city, preparing of site-specific design spectra is inevitable and worthwhile. In this paper, according to the geotechnical boreholes and tests to a depth of 40 meters in different parts of the city, beside probabilistic risk analysis, site- specific spectra for central part of the city are developed. Based on the distribution of boreholes, the area is divided into 15 districts, with an area of one square kilometer. Through the probabilistic risk analysis, design acceleration of 0.32g is obtained for earthquakes with a return period of 475 years, which is 6 % higher than that proposed by Building Design Codes for Earthquakes - Standard 2800.
Design spectra are obtained using three methods of ground response analysis, statistical analysis of different earthquakes and uniform hazard spectra. Using the data from geotechnical measurements, soil types in the different areas of the city center is designated. The soil types in the most parts of studied area are classified as type III of the standard 2800 classification. Comparison of the obtained spectrum with the proposed spectrum of standard 2800, showed that in the range of constant acceleration, the values of site-specific design spectra is 25 % higher than those proposed by the standard 2800.