PSI - Issue 64

Alessandra De Angelis et al. / Procedia Structural Integrity 64 (2024) 327–334 De Angelis et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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connected by means of coaxial cables to a 4-channels dynamic signal acquisition module (model SCADAS XS) with a 24-bit ADC, provided with anti-alias filters. For each test, the acceleration time histories were recordered, using a sampling frequency of 100 Hz and an acquisition time of 3600 seconds. Sensors were positioned over the floors according to the layout shown in Fig. 5. Also for these tests, a pair of sensors located at the center of the second floor were adopted to investigate possible in plane floor deflections due to the slender rectangular plan shape as suggested by Pan et al. (2006). Since for the tests, more accelerometers than available were required, the AVTS were performed using two setups and merging the data on the basis of reference sensors (i.e., sensors named 3 and 4 in Fig. 5a) that are common to all the acquisitions.

Fig. 5. Layout of the sensors at a) third floor), b) second floor, c) first floor and d) ground floor The experimental modal parameters are identified though Operational Modal Analysis (OMA) starting from the recorded vibration measurements. The data recorded from sensors were pre-processed in MATLAB (2022) as the significant frequency content of signals is below 10 Hz, low pass filtering and decimation have been applied to the recorded data before using the identification tools. This allowed to reduce the sampling frequency from 100 Hz to 50 Hz. The extraction of the modal parameters from the recorded ambient vibration data were carried out by using the methods in domain available in the commercial software ARTeMIS (2019). In particular, the Frequency Domain Decomposition (FDD) was employed. In the FDD method (Brincker et al., 2001) the spectral density matrix is decomposed by Singular Value Decomposition (SVD) to obtain frequency values and mode shapes. The detected natural frequencies are summarized in Table 2 for AVT n.2 and n.3. Table 2. Natural frequencies and damping ratios (AVT n. 2 and n. 3). AVT n. 2 AVT n.3 Mode f [Hz] f [Hz] 1 2.466 2.099 2 3.296 2.913 3 3.833 3.027 4 6.543 5.989 5 10.059 9.195 2.3. Evolution of the dynamic behavior of the selected building The modal parameters of the building previously identified from the three performed AVTs are then monitored to evaluate the effects of the external and internal partition walls. Starting from the frequencies, in order to compare the results of each test the frequency discrepancy using equation (1) is calculated and reported in Table 3.