تفكيك خطر لرزه يي شاخص اتا در طيفهاي شرطي

Seismic Hazard Disaggregation of Eta in Conditional Spectra

انتخاب حركات زمين در بحث برآورد پاسخ غيرخطي سازه‌ها ــ?به گونه‌يي كه بتوان با كمينه‌ي تعداد حركات زمين، پاسخ قابل اطميناني از سازه به‌دست آورد?ــ تبديل به موضوعي كليدي در مهندسي زلزله براساس عملكرد و نيز نسل بعدي آيين‌نامه‌هاي لرزه‌يي شده است. براي بهبود انتخاب و نيز شناخت بهتر ويژگي‌هاي طيفي حركات زمين، پارامترهاي نوين طيفي از جمله اپسيلون شتاب طيفي و اِتا در ادبيات فني معرفي و در گام بعدي تلاش شده است تا با بهره‌گيري از اين پارامترها، طيف‌هاي مشروط براي بهبود تخمين پاسخ سازه معرفي شوند. كاربرد اِتا به دليل وابستگي به اپسيلون سرعت بيشينه، براي محاسبه‌ي طيف مشروط با مشكلاتي مواجه است. هدف اصلي اين پژوهش، تفكيك لرزه‌يي اِتاست، كه نتايج آن با روش‌هاي موجود در اين زمينه مقايسه شده است. نتايج بيان‌گر آن است كه تدقيق در محاسبه‌ي اِتاي هدف در ناحيه‌ي زمان تناوب‌هاي پايين طيف‌هاي شرطي موثر است.

Selection of appropriate ground motion is a key element within any seismic assessment of structures. Many methodologies have been developed in order to select and scale ground motion records for the purpose of response history analysis. UHS is one of those developments and has been widely used in performance based earthquake engineering. However, implementation of UHS is somewhat conservative when used as a proxy for ground motion selection processes, since it is very unlikely to find a record which has a spectrum as high as the UHS. Spectral shape indicators, including Epsilon and Eta, have been recently proposed in order to take a wide range of spectra into account. Additionally, conditional mean spectra have been obtained by the mentioned indicators which can be used as the target design spectra, e.g; Conditional Mean Spectrum (CMS) and Eta-based Conditional Mean Spectrum (ECMS). The Eta indicator uses the conventional epsilon in combination with the peak ground velocity epsilon. As the peak ground velocity epsilon is not convenient in seismic hazard disaggregation, a simple formula was proposed by Mousavi et al. to approximate the target peak ground velocity epsilon based on the conventional epsilon. However, this simple formula needs to be investigated more precisely. Therefore, a comprehensive seismic hazard disaggregation is proposed, in this paper, to explicitly obtain the target peak ground velocity epsilon. An ideal site, with a single linear fault, was assumed in order to obtain the target peak ground velocity epsilon. The results show that the exact target peak ground velocity epsilon is meaningfully different from the simple formula in this issue, and the resulted conditional spectra are sensitive to this refinement in the low period range when using the exact target peak ground velocity epsilon.