GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.3 315 the structural response of buildings (e.g., Nakamura et al. , 1999; Gallipoli et al. , 2004b, 2009; Parolai et al. , 2005; Fäcke et al. , 2006; Hans et al. , 2005; Luo et al. , 2008; Massa et al. , 2010). In this study, we apply spectral ratio techniques to study the structural response of some civil and historical buildings in the historic center of the city of Genoa (north-western Italy) that, during the second half of 2012, were subjected to intense vibrations induced by the blasting excavation of the sea bed in the Genoa harbor. The study focuses on three masonry structures (Fig. 1a): Vico Indoratori 2 (B1), Santa Maria di Castello (B2), and Piazza Cavour 4 (B3). B1 and B3 are civil buildings (B1 has been known since the half of the XIII century as it was the birthplace of St. Catherine of Genoa) while B2 is the monastery complex of Santa Maria di Castello, which was built around the IX and X century. Due to limited space available, the study will present results for site B3 (Fig. 1b-1d) only. The vibration modes of the buildings under study are determined through H/V spectral ratios computed either on microtremors and blast recordings. For site B3, where a reference station was installed on the ground level, SSRs are also computed. For this building, we also analyze the response to the incoming October 3, 2012 Piacenza earthquake ( M l = 4.5), which occurred at approximately 80 km from Genoa. The recordings of the Piacenza earthquake are also used to study filtering effects by comparing the experimental floor spectra with analytical ones. Structural response of B3, Piazza Cavour 4. This is a seven-story building inserted in a more complex aggregate (Fig. 1b). Systematic tie rods (Fig. 1c) are present at both lower and upper levels; the thickness of perimeter walls varies from about 0.5 to 0.9 m (passing from the ground floor to the top level). The building is located a few meters from the main road. Two seismic stations (Lennartz LE-3D/5s equipped with Lennartz MARSlite) were installed inside the building, one at level ground and one on the third floor. Thus, it was possible to calculate both H/V spectral ratios and SSRs. Fig. 2 – Comparison of H/V and standard spectral ratios along X (a) and Y (b) directions. SSRs relative to the vertical component are also displayed (c).