PSI - Issue 78

Daniele Sivori et al. / Procedia Structural Integrity 78 (2026) 481–488

485

10 2

10 1

10 0

10 -1

10 -2

10 -3

AVTs L5-L4-L3

AVTs L2-L1-L0

MEMS HS MEMS

PE

HS PE

FB

HS FB

10 -4

10 -1

10 0

10 1

10 2

Fig. 2. Comparison among the average spectral densities of ambient vibrations acquired at different levels of the church and the spectral noise of commercial accelerometers with different sensing technology (PE: PiezoElectric, FB: Force-Balance, MEMS: Micro Electro-Mechanical Systems, HS: high-sensitivity version, see Table 1). However, considering the potential level of ground shaking caused by an earthquake at the site and factoring in the tower's amplification effect, which can lead to accelerations exceeding gravitational acceleration at the top (see Degli Abbati et al. 2024), PE seismic sensors are severely limited by their full-scale range (see Table 1). Considering the advantages of HS MEMS in terms of dimensions, ease of installation, availability of fully integrated units with multi-axial channels and acquisition units (Section 3.2) and, crucially, their wide full-scale range, this solution appears optimal for measurements at higher elevations in both the church and the bell tower, balancing sensitivity, deployment time, and costs. Conversely, for internal and low-height measurements, the natural choice falls on FB accelerometers, owing to their unmatched sensitivity and dynamic range. Furthermore, their suitability as base seismometers allows for recording micro-tremors, earthquakes and soil-structure interactions. 3.2. Sensor placement and data management The choices related to sensors’ technology (Section 3.1) should be integrated with careful considerations related to sensor placement, which often intersects with the necessity of reducing the number of sensor but avoiding spatial aliasing (Pachón et al. 2020), achieve a robust data transmission and an efficient installation. This first system has been conceived to contain at maximum the cost of instrumentation, satisfying at the same time all the requirements declared at the beginning of the project (Section 3). Sensor location has been determined based on the results of preliminary AVTS conducted in May 2020 (Degli Abbati, Sivori et al. 2024) focusing on the measure of modes identified as global, involving the flexural and torsional behavior of the bell tower, as well as translational modes for the aisles, and promoting measurements in elevation. Table 2 reports the type, location and axial configuration for each sensor and the corresponding measure of interest.