GNGTS 2014 - Atti del 33° Convegno Nazionale

54 GNGTS 2014 S essione 2.1 constructed in accordance with a default elastic spectrum), simulated accelerograms (synthetic time-histories obtained by modelling the physical phenomenon), and instrumentally recorded accelerograms of real earthquakes. The use of the artificial accelerograms is not allowed in the dynamic analysis of geotechnical systems and, consequently, has not been considered in the following elaborations. Real time histories . Recorded accelerograms can be downloaded from national and international databases, and they should be representative of the seismicity of the site. Typically, the selection of the records is done according with the magnitude ( M ) and the epicentral distance ( D ), similar by to that of the design earthquake for the study site, and considering site conditions of the recording station similar to those observed in the study site. The identification of the design earthquake derives often by the deaggregation of the PSHA results for the return period of interest. In this work, 5 recordings have been selected, not necessarily related to different earthquakes, amounting to 15 accelerograms for each site: 2 for the horizontal components and one for the vertical one for each event. Horizontal and vertical response spectra of all the selected accelerograms (horizontal and vertical components) have been calculated (as in Fig. 2d) together with the average value (black line in Fig. 3a) and its standard deviation (grey dotted line in Fig. 3a). In the present paper, we show the elaborations referring to the horizontal components. Fig. 2d shows that the computed elastic spectrum of one of the selected real accelerograms remains Fig. 3 – Target and computed elastic response spectra: a) target spectrum corresponding to the average response spectrum of ten horizontal components of the five selected events (black curve), the grey dashed curves show one standard deviation, the red, green and yellow curves represent the UHRSs for a 1950-, 475- and 101-year return periods, respectively, for stiff soil, and the blue curve displays the 1950-year return period spectrum of Italian building code NTC08 for stiff soil; b) response spectra of the two horizontal components of a recorded earthquake made compatible with the spectrum of Italian building code NTC08 for stiff soil (blue curve); c) same as (b) but made compatible with the 1950-year return period UHRS calculated in this study (red curve); d) response spectra of a synthetic accelerogram made compatible with the target spectrum (red line) defined in (a).