PSI - Issue 44

Gianluca Standoli et al. / Procedia Structural Integrity 44 (2023) 2066–2073 G. Standoli et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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methods available, one of the techniques that mostly attracts the interest of researchers is the Ambient Vibration Testing (Pierdicca et al. (2019)), which consists in monitoring the environmental and anthropogenic vibrations induced on the structure in its operating conditions, and finally extracting the main dynamic parameters (frequencies, modal shapes, and damping factors) (Torres et al. (2017), Ramos et al. (2010)). Thanks to sensing evolution, it is now possible to monitor a structure in continuous, transmitting and analyzing real-time vibration data (Gentile et al. (2016), Giordano et al. (2020)). The correlation between the identified parameters and the environmental conditions (Ubertini et al. (2017), Ceravolo et al. (2021)), allows the filtering of these effects and the restitution of more precise dynamic parameters from which elaborate previsions models of the structural behavior. A particular application of this technique is the system, composed of four MEMS accelerometers, installed on the 4 th February 2020 in the bell towers of the Cathedral of Santissima Maria Annunziata of Camerino. This monument suffered severe damage during the seismic sequence of 2016 that stroked Central Italy, leading to reinforcement interventions that made the church an iconic case study for the development of a continuous monitoring system. In the paper, the first results of the modal parameters tracking are presented, automatically executed (Garcia-Macias and Ubertini (2020)) with a self-made Matlab© script, on the vibrations data acquired for the twin bell towers during two years of continuous monitoring activity.

Nomenclature CH

Cultural Heritage NDT Non-Destructive Tests AVT

Ambient Vibration Testing EFDD Enhanced Frequency Domain Decomposition SSI-cov Stochastic Subspace Identification - Covariance Based MAC Modal Assurance Criterion SNR Signal to Noise Ratio f̅ Mean Frequency f i i-th Frequency f Target Target Frequency

2. The case study: Camerino Cathedral bell towers 2.1. Localization and history

Fig. 1. (a) Localization of Camerino city; (b) a view of Santissima Maria Annunziata Cathedral

The city of Camerino (Fig. 1a) arises on a hill (661 m a.m.s.l.) of the Macerata Province, in the Marche region (Italy). In the main square is locate the Cathedral (Fig. 1b), nowadays known as Santissima Annunziata of Camerino, originally built during the V century d.C. as a Roman basilica dedicated to San Giuseppe. Starting from