عنوان مقاله [English]
Seismic hazard reduction requires precise response of the building based on PGA and site effects. Characteristics of site play an important role in building devastation. Based on the code of practice for seismic resistant design of buildings, exerted lateral load on a structure depends on the soil profile of the site. The classification mainly depends on the geological and geotechnical conditions which are determined by in situ and laboratory tests. In this regards, geoseismic studies based on average shear wave velocity from surface up to depth of 30m is necessary. Thickness, velocity and sequence of the layers, specifically a surface layer with low shear wave velocity underlain by stiffer material with high shear wave velocity have remarkable effects on design spectra. While a low velocity layer considered on a high velocity one, the soil profile postulated as soil type E according to the Eurocode. In this paper, soil type E defined by Eurocode and its effects on design spectra is examined. Further more consistency of design spectra resulted from case study (seismic microzonation of Bam city) with spectra based on soil type defined by Eurocode and Standard No. 2800 are evaluated. The results indicate, if terms and condition of class E is ignored. The site may be classified as type I (Standard No. 2800) or B (Eurocode). Obtained design spectra from case study match well with spectra from Eurocode for type E. Hence, it is inevitable to allocate a group of soil type within which a soft alluvium layer overlain hard layer.