PSI - Issue 64

Donato Fiore et al. / Procedia Structural Integrity 64 (2024) 740–748 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 7 – Example of the fluctuation of the maximum, residual and recovery to the 0 status during a static measurement

Static interferometric measurements were carried out continuously with the acquisition of 1 sample every 15 seconds for each station. The acquired data was managed online in real time and could be accessed at any time by anyone who had the credentials to access the system. It was possible to distinguish between the physical variables directly linked to the bridge and variables non-structural that anyway affected its behavior. The management software received, verified and processed all data in real time and transmitted the information to the storage system. This platform was able to send alert messages, when definite thresholds were exceeded, interrupting automatically the traffic. 3.3. Dynamic monitoring The objective of monitoring through dynamic analysis is to evaluate the invariance of the main resonance frequencies identified. It can indeed be demonstrated that, even using only ambient noise as an excitation source, the detection of collapse precursors is connected to changes in the main resonance frequencies of the structure even in the absence of significant movements or damage (monitoring in "ambient vibration testing" conditions, AVT). The results obtained (Fig. 9) demonstrate the ability of the method to indicate, through the measurement of the resonance frequencies of multiple points (corner reflectors) positioned along the viaduct, the following displacements: • Frequencies (Table 1) • Amplitude (Fig. 8) The instrumentation used continuously records the displacements over the period necessary for the stabilization of the loads and the unloading of the structure. A sampling frequency of 100 Hz has been chosen.

Table 1. Modal Frequencies (Hz) Modal Order

East Side (Hz)

West Side (Hz)

1 st

0.36

0.34 0.62 0.92 1.36

2 nd 3 rd 4 th

0.6

0.98 1.34