Vol.10, No 3, 2012 pp. 259 - 274
UDC 624.042.7:550.34(497.11)(083.74)=111
DOI: 10.2298/FUACE1203259B
TOWARDS PREPARATION OF DESIGN SPECTRA FOR SERBIAN NATIONAL ANNEX TO EUROCODE 8 – PART II: USAGE OF THE UHS APPROACH INSTEAD OF NORMALIZED SPECTRAL SHAPES SCALED BY A SINGLE PSHA PARAMETER
Borko Đ. Bulajić1, Miodrag I. Manić2, Đorđe Lađinović3
1Highway Institute, Belgrade, Serbia
E-mail: borkobulajic@yahoo.com
2Faculty of Civil Construction Management, Union – "Nikola Tesla" University, Serbia
3University of Novi Sad, Faculty of Technical Sciences,
Department of Civil Engineering, Serbia
Eurocode 8 spectra are scaled by the peak ground acceleration values that are defined for the given site through a probabilistic seismic hazard analyses (PSHA). However, spectra that are created by combining the empirical shapes with the single PSHA-defined scaling factor will not represent the so-called Uniform Hazard Spectra (UHS). Moreover, the very shape (Type 1 or Type 2) of the Eurocode 8 elastic spectrum is selected with respect to the magnitude of the earthquakes “that will contribute most to the seismic hazard defined for the purpose of probabilistic hazard assessment…”. Such definition is somewhat obscure since these “most contributing” earthquakes are, even at the same site and for the same probability i.e. for the same “return period”, different (in a general case) for different vibration periods, while the whole Eurocode 8 spectrum is scaled by using only the PSHA estimate of the peak ground acceleration. In this Paper we present an illustrative example of the Uniform Hazard Spectra for the city of Belgrade and compare the obtained UHS spectra, as well as the scenario empirical spectra scaled for different earthquake parameters, to the corresponding Eurocode 8 spectra, further pointing out the intrinsic ambiguities in the current EC8 suggestions for creation of design spectra.
Key words: Eurocode 8, spectral scaling, probabilistic seismic hazard analysis, return period, Uniform Hazard Spectra.
KA PRIPREMI PROJEKTNIH SPEKTARA ZA SRPSKI NACIONALNI ANEKS NA EVROKOD 8 – DEO II: PRIMENA UHS PRISTUPA UMESTO SKALIRANJA EMPIRIJSKI DEFINISANIH SPEKTRALNIH OBLIKA JEDNIM PSHA PARAMETROM
Evrokod 8 spektri se skaliraju sa vrednostima maksimalnog ubrzanja tla koje su određene za zadatu lokaciju kroz probabilističku analizu seizmičkog hazarda (PSHA). Međutim, spektri koji nastaju kombinovanjem empirijskih oblika sa jednim jedinim PSHA faktorom za skaliranje, neće predstavljati tzv. Uniform Hazard Spektre (UHS). Štaviše, sam oblik (Tip 1 ili Tip 2) elastičnog spectra po Evrokodu 8 se bira u odnosu na magnitude zemljotresa “koji će najviše doprineti seizmičkom hazardu određenom za potrebe probabilističke ocene hazarda…”. Ovakva definicija je donekle nejasna jer su ovi zemljotresi “koji će najviše doprineti” (u opštem slučaju), čak i za istu lokaciju i istu verovatnoću tj. za isti “povratni period”, različiti za različite periode vibracija, dok se ceo Evrokod 8 spektar skalira korišćenjem samo PSHA ocene maksimalnog ubrzanja tla. U ovom radu predstavljamo jedan jednostavan ilustrativni primer Uniform Hazard Spektara za Beograd i poredimo dobijene UHS spektre, kao i scenario empirijske spektre skalirane za različite zemljotresne parametre, sa odgovarajućim spektrima po Eurokodu 8, dalje potencirajući suštinske nedoslednosti u postojećim sugestijama Evrokoda 8 u pogledu kreiranja projektnih spektara.
Ključne reči: Evrokod 8, skaliranje spektara, probabilistička analiza seizmičkog hazarda, povratni period, Uniform Hazard Spektri