GNGTS 2016 - Atti del 35° Convegno Nazionale

458 GNGTS 2016 S essione 2.3 Free field survey. Free field surveys have highlighted a clear high amplitude frequency peak at a 1.5 Hz in all but one the testing sites, showing a significant impedance contrast between calcarenites and shallow sand and clay (Lupo and Gallipoli, 2011). Outside the Province building, instead, the peak was at 5.2 Hz, showing a more superficial layer of clay. Estimation of building vibrational modes. The buildings tested were: • “Duni” High School . The building has 4 floors. The measures have been performed along two vertical directions, with an instrument placed at each floor, and one along the horizontal direction at the 3rd floor (not at the top floor because it had different dimension in comparison to the others). In both configurations an instrument at the basement as been used as reference, to use the SSR technique. On the SSR curves, each floor shows two main vibration modes, one at 2.7 Hz for the transverse component and 4.2 Hz for the longitudinal one. The two sides of the building are not symmetric: the right side is stiffer than the left, because of the keystone building of the entrance stairs. This is confirmed by a rocking mode at 2.7 Hz, the peak is present also on the vertical component. Fig. 2 and Fig. 3 report the results for soil and building characterization. • “Loperfido” High School. Also this building has 4 floors, a rectangular shape with one side much longer than the other. Measures on two vertical directions have been performed in order to characterize both sides of the building, with an instrument at each floor, and one along the horizontal direction at the top floor. An instrument has been kept at the basement to be used as a reference for SSR analysis. The building shows an asymmetric behavior, especially noticeable at on the horizontal measure at the top floor. Mode frequencies were identified at 3.4 Hz and 5.7 Hz on the transversal direction and 4.3 Hz on the longitudinal direction, showing an asymmetrical behavior and a rocking mode at 3.4 Hz, which is evident on the extreme points of the horizontal measure, more flexible. • Firefighters head office. The building was under construction at the time of the survey. It is a structure designed with antiseismic criteria, regular in plan and in elevation. Also in this case measures have been performed along two vertical directions, one at the centre of the building close to the stairs and one at the left corner. Instruments have been placed at each floor, with the one at the basement used as a reference. At the top floor a measure has Fig. 2 – a) perspective view of the building and distribution of testing points inside the building and in free-field condition; b) HVSR curve.