COV BASED MODIFIED SITE-SPECIFIC DESIGN SPECTRA DEVELOPMENT

摘要

A relatively reliable method of Site Specific Design Spectrum Development (SSDSD) has been presented. This method is based on an interpretation of coefficient of variation of spectral acceleration (COV= Sigma /Mean) as an index of Seismic Risk. According to current methods of seismic hazard analysis, SSDSD is rather hazard (probability of exceedence) based. Although this may lead to an almost definite level of safety but the deviation of spectral values and its variability with respect to structural period, will result in a variable level of seismic risk. It seems that a significant source of potential damage (Seismic Risk) is the deviation of spectral values from considered design spectrum. Studies have shown a high variation of COV of response spectral values, especially in low and moderate range of periods considering Site Specific Design Spectrum (SSDS) derived from a series of Site Specific Accelerograms resulted either from soil column analysis or less specific procedures. The propose of this paper is to suggest quantified criteria to develop and modify the Site Specific Spectra (SSS), considering the reliability basis of current seismic design practices, being acceptable. A short presentation of actual projects providing the necessary database is included.