PSI - Issue 78

Daniele Storni et al. / Procedia Structural Integrity 78 (2026) 237–244

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M-A352 is only a bit noisier than the ES-T Episensor force-balance accelerometer by Kinemetrics. This makes both the M-A352 and the M-A552 well suited for seismological applications and structural vibration monitoring. The BAS01 station is part of the OSU urban seismic networks managed by the “Monitoraggio Sismico Urbano e delle Infrastrutture” group of INGV (Occhipinti et al., 2025). The expansion and enhancement of such urban networks, particularly in seismically active and densely populated areas, could substantially enhance seismic risk mitigation strategies while enabling the development and refinement of early warning systems. The bell tower partially interacts with the Basilica; this aspect influenced the sensor placement that was mounted at 29m, 36m and 47m from the base (Figure 4.a).

Fig. 4. The whole SHM system is defined by the a) location along the tower, b) placement of the M-A552 accelerometers and b) location of the OSU BAS01-INGV seismic station along with the station of the Italian National Accelerometric Network. 5 The dynamic behaviour of the bell tower Before starting to monitor the bell tower, an OMA analysis was performed for identifying the reference modal properties. Within this campaign, the modal shapes and frequencies reported in Figure 5 have been identified. The flexural behaviour is identified by the lower two frequencies, at 2.139 Hz and 2.593 Hz, respectively. Other two frequencies, at 3.444 Hz and 3.959 Hz, appear reliable and stable and are flexural second-order shapes that are not perfectly described due to the sensor position. It is worth noting that all the modal shapes describe an increment of modal displacements at the last level; this aspect is discussed in the next. Lastly, two torsional shapes appear at 5.469 Hz and 5.637 Hz. As Figure 5 shows, the torsional shapes clearly represent the absence of a floor or a ring beam at the top level.

a f Fig. 5. Identified modal shapes and frequencies. a) first flexural longitudinal, b) first flexural transversal, c) second order flexural longitudinal, d) second order flexural transversal, e) first torsional, f) second torsional b c d e