GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.2 371 In addition to the fundamental period, the damping ratio was computed as well, using the Random Decrement technique toolbox implemented in Geopsy (Fig. 3). The Random Decrement technique is based on the assumption that at each time step, the signal is the sum of a random signal and the impulse response function of the study-system. Stacking many time- windows with the same initial condition imply the enhancing of the impulse response function component with respect to the zero-mean random part. The algorithm selects all the windows of the given length starting with a 0 amplitude and a positive derivative and averages them. Then, the impulse response function is fitted by an exponentially decreasing sine function (starting at 0) depending on an amplitude α, the resonance frequency f=ω/2π and the damping ratio ξ (see for details: http://www.geopsy.org/ ). Fig. 3 – Examples of damping graphs obtained from measurements performed, for the NS and EW components, at the recording sites located at 5th floor of the building. Results and concluding remarks. The present study aims at evaluating the dynamic properties of Palazzo Boscarino. It was taken into account as a first example of the complete amount of surveys planned for the evaluation of the Catania University buildings asset vulnerability. These studies are quite important in investigating possible soil-to-structure resonance effects that can arise when the fundamental frequency of a building shares the same range as that of the site. The investigated building is the location of to the Department of Juridical Sciences and it shows a rectangular shape and it is formed by seven floors including both the ground and the underground floors. Its longitudinal section is NS oriented and it is erected on thin detritic layers and volcanics. The HSSR results point out that the fundamental frequency of the building is about 1.8 Hz. Inspection of the HSSR graphs, obtained from the measurements performed in the third to fifth floors, shows the presence of a secondary frequency at about 5.0 Hz that appears related to the vibration of an adjacent smaller edifice. The damping of the building, evaluated through the Random Decrement Method, showed