EFFECTIVE PEAK ACCELERATION, ATTENUATION RELATIONSHIPS AND SHAPE OF SPECTRA

Abstract

Prediction of a design response spectra at a site is difficult because of large uncertainties associated with it. The present work deals with the site-dependent spectra for aseismic design of structures for rock and soil sites by analysing earthquake data recorded in Western United States. Six different criteria for normalisations have been considered. A further normalisation has been carried out by equating the area under the average spectra corresponding to different normalisations and the equivalent standard deviations evaluated. It has been found that effective peak acceleration (EPA) as defined by Bolt and Abrahamson give least standard deviation. Besides this, attenuation relationships have been developed for all the normalising parameters and their standard errors evaluated, Bolt's EPA has been found to give least standard error. Attenuation formulae reported in literature give values with 50 percent exceedence ptobability. In design of Nuclear structures mean plus sigma spectra is required for design. In this study, therefore, attenuation formula corresponding to 16 percent exceedence probability have been evaluated at soil site. It has also been found that at soil site Bolt's EPA give lowest magnification for mean and mean plus sigma speetra.Comparison of design spectra at three example sites show that Bolt's EPA should be used in design rather than the peak acceleration criterion.