GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.1 53 The UHRSs for each site and for the three return periods of 101, 475, and 1950 years obtained in the present study have been compared with those obtained by the MPS04 map (Stucchi et al. , 2011), referring to rock (comparison not shown in this paper), and with the reference spectra of the Italian building code NTC08 (��������� ����� ��������������� ����� ��� Ministero delle Infrastrutture, 2008) for stiff soil (Fig. 2d). It can be seen that the 1950-year return period UHRS exceeds that of the NTC08 only in the high frequencies (less than 0.4 s) while the spectra of the 2 components of the selected real accelerograms here shown remain well below both cited spectra. Seismic design parameter . According to the recent Italian technical dams code DM 2014 (Ministero delle Infrastrutture, 2014), for dams located in seismic areas with conventional hazard characterised by PGA greater than 0.15 g, a specific hazard study is mandatory; dam assessment must be performed using seismic input giving worst structural effects. Moreover, for dams located in areas with medium/high seismicity, dynamic analysis approaches (response spectrum and/or time history analyses) are suggested, with seismic action represented by acceleration time-series, i.e., a set of accelerograms (typically 3 to 7 in order to consider the effects on average) representative of the expected seismic event. DM 2014 (in agreement with the Italian building code, NTC08), defines three types of accelerograms to be used in the design: artificial accelerograms (synthetic time-histories, Fig. 2 – Computation scheme and results: a) logic tree composed by two seismogenic zonations (from Italian fault database DISS and the alternative OGS zonation), one seismicity model (HNH), one maximum magnitude ( M DISS / M K&G for DISS zonation and M W&C / M K&G for OGS zonation), 3 GMPEs [AMB = Ambraseys et al. (1996), C&F = Cauzzi and Faccioli (2008), S&P = Sabetta and Pugliese (1996)]; b) UHRSs for a 1950-year return period for stiff soil (1 = DISS zonation AMB GMPE, 2 = DISS zonation S&P GMPE, 3 = DISS zonation C&F GMPE, 4 = OGS zonation AMB GMPE, 5 = OGS zonation S&P GMPE, 6 = OGS zonation C&F GMPE); c) mean UHRSs for a 1950-year return period for the 6 dams; d) response spectra (pale and dark grey curves) of the two horizontal components of a recorded earthquake, the blue curve represents the 1950-year return period elastic spectrum of Italian building code NTC08 for stiff soil, the red curve represents the UHRS for a 1950-year return period for stiff soil.