GNGTS 2014 - Atti del 33° Convegno Nazionale

438 GNGTS 2014 S essione 2.3 in order to quantify the periods of vibration. Single station tests were performed using the instrument Tromino (Micromed) and Lennartz Seismometer (with 1 Hz sensors). The results obtained with the two different instruments are basically in agreement (Fig. 2). The H/V analysis performed show no clear peaks, that suggests the absence of impedance contrasts and therefore the gradual velocity increase with depth (Fig. 2). The amplification of about 2.5 Hz, recognizable at all sites can be interpreted as a layer of over consolidated gravel deposit (bedrock–like), which is supposed to have an S-wave velocity of about 800 m/s. Design spectra. The simplified procedure of Malhotra et al. (2000) proposed in Eurocode 8 uses spectra calculated over a 2% and 0.5% damping in order to evaluate the base shear stress, the overturning moment and the sloshing wave height. However, it is not possible to define the spectra according to the legislation formula with a damping ratio lower than 5%, since the factor involved in the relations (depending on the damping ratio) is defined only above this value. Therefore, it was necessary to use accelerograms to define the elastic design spectra needed to the simplified computations. Fig. 1 – Theoretical and experimental dispersion curve (a); velocity ground model (b); HVSR fitting (c).