PSI - Issue 78

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

486

Table 2. Sensor type, locations and measure of interest for church and bell tower.

Area

Symbol

Type

Transmission Channels Config,

Location

Measure and purpose Seismic and micro seismic input Translational response of the colonnade (in- and out-of-plane) Internal temperature, data acquisition, storage and processing Translational response of the nave and loggia Translational response of the transept and the dome

F1

FB accelerometer

Wired

3

Tri-axial

Ground level, right aisle First level of the right colonnade

F2

FB accelerometer

Wired

2

Bi-axial

Church

AU1, PU

Acquisition Unit + Temperature probe, Processing Unit

Wired

6 (up to 9)

-

Matroneum

I2

HS MEMS Accelerometer with Integrated AU HS MEMS Accelerometer with Integrated AU HS MEMS Accelerometer with Integrated AU

Wi-Fi

2

Bi-axial

Top of the loggia, north-west corner Top of the dome L2 - Seminarians' hall (putlog hole) L5 - Tower terrace

I3

Wi-Fi

2

Bi-axial

I1

Wi-Fi

2

Bi-axial

Interaction with the church

Bell tower

M1, M2 HS MEMS

Wired

3

Uni- and bi-axial

Roto-translational response of the bell tower External temperature, data acquisition

Accelerometers

AU2

Acquisition Unit + Temperature probe

6 (up to 9)

-

L5 - Base of the drum

Local modes of other structural macroelement (for example, the matroneum) or nonstructural atop elements vulnerable to seismic actions (pinnacles) have been taken into account by predisposing a scalable system, capable of accepting other sensors in the future. The installation of an extensive monitoring system in such an old and important monument poses critical challenges. This is particularly true for a heritage-protected structure, in which all the interventions should minimize the impact on existing architectural and decorative assets. Furthermore, several areas of interest for the monitoring are also open to visitors, so all the instrumentation should be, if possible, concealed or, at minimum, protected. In this regard, data transmission is a crucial aspect of the measurement chain, as it is often impractical or even impossible to rely on wired systems given the challenges of routing cables over long distances in such a complex structure. Conversely, wireless (Wi-Fi) transmission faces significant limitations when traversing thick masonry walls and necessitates local digitization. To overcome these challenges, the system has been designed as a hybrid system, leveraging the benefits of both wired and wireless approaches (Figure 3). Remote MEMS sensors, such as those installed on the main dome, in the loggia, and in the bell tower, are equipped with an Integrated acquisition system (indicated as INT. in Figure 3) that acquires, digitizes, and transmits data to a nearby Wi-Fi Access Point (AP). Conversely, measurements acquired at the base of the structure and at the top of the bell tower are, given their critical importance, transmitted via cable to local Acquisition Units (AU in Figure 3) and subsequently via a wired local area network to the central Processing Unit (PU), where data is permanently stored and processed. All acquisition units are equipped with a 24-bit A/D converter enabling local data storage, a 32 GB memory providing a redundant data backup, and a GNSS receiver for synchronization (precision of 1 µs), all directly powered by mains electricity through a battery backup. To enable real-time data transmission to the central processing unit while minimizing archiving space, time series data are compressed using the miniSEED format and streamed via the SeedLink protocol. Preliminary results obtained in the first phases of the installation show that embedded HS MEMS (Figure 4a) are effectively capturing the global dynamics of the structure (Figure 4b), demonstrate the feasibility of current high-end MEMS accelerometers for operational vibration monitoring and SHM of cultural heritage structures.