PSI - Issue 64

Elide Nastri et al. / Procedia Structural Integrity 64 (2024) 153–160 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Historical structures serve as tangible connections to our past, providing insights into architectural, cultural, and technological advancements. However, preserving such monuments, especially in seismic regions, poses a complex challenge that balances conservation with public safety (Formisano et al. (2018), Uva et al. (2019)). Towers, iconic features of the Italian townscape, exhibit unique architectural traits and notable vulnerability to seismic forces due to their slenderness ratio and the limited capacity of masonry base materials to withstand horizontal loads (Curti et al. (2008) - Di Gennaro et al. (2023)). Damage assessments from recent seismic events in Italy highlight the heightened risk of severe damage to bell towers, particularly those associated with masonry churches (Casolo et al. (2011) – Chisari et al. (2024)). The seismic vulnerability assessment of these masonry bell towers has received attention at both territorial and structural levels, with Finite Element (FE) models being the most effective approach for evaluating seismic responses. Ambient Vibration Testing (AVT) (Sepe et al. (2008) – Zanotti et al. (2017)) and other monitoring techniques emerge as potent tools for dynamical characterization, facilitating the calibration and validation of numerical models through Operational Modal Analysis (OMA) (Ranieri et al. (2015) – Sun et al. (2023)). AVT helps identify principal vibrational modes and their natural frequencies, enabling model updating to closely reflect the dynamic attributes of the structure. This study focuses on a 13th-century bell tower of the San Michele Arcangelo Cathedral in Caserta Vecchia, Italy (Fig. 1a). Given the tower historical significance and potential vulnerability, characterizing its structural behaviour under seismic loading is vital for preservation efforts. Photogrammetric survey techniques document the current state of the tower, and analysis of recent interventions informs the study. An FE model calibrated using AVT data collected from tri-axial and bi-axial accelerometers, accounts for masonry material fracture and is validated against experimental tests. The model is subjected to various intensity limit state earthquakes to assess resilience, with seismic performance evaluated through damage evolution analysis. 2. Historical analysis and photogrammetric reconstruction The bell tower of the San Michele Arcangelo Cathedral in Caserta Vecchia is a significant architectural and historical landmark (Fig. 1b), characterized by its square-based structure measuring 7.60 meters per side and standing approximately 31.5 meters tall. Divided into five levels, each marked by distinctive architectural features, the tower exhibits a blend of form and function. The vertical dimensions of each level show considerable variation, as apparent upon initial inspection. Progressing from the base to the summit, the heights of the levels are 8.68 meters, 4.23 meters, 6.82 meters, 4.49 meters, and 4.35 meters, respectively. a b

Fig. 1. (a) Satellite view and location; (b) aerial view of the architectural complex.