PSI - Issue 44

Corrado Chisari et al. / Procedia Structural Integrity 44 (2023) 1100–1107 Corrado Chisari et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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poor capacity in facing horizontal loads of the base material (masonry). As a matter of fact, damage reconnaissance after recent seismic events in Italy testified that, in masonry churches, bell towers are prone to suffer severe damage (De Matteis & Zizi, 2019; Ubertini et al., 2018; Zanotti Fragonara et al., 2017). The vulnerability assessment of masonry bell towers is a topic that found notable applications in the recent literature both at territorial (Cacace et al., 2022; Sepe et al., 2008; Shakya et al., 2018) and structural scales (Bali´cbali´c et al., 2021; Ceroni et al., 2009; Micelli & Cascardi, 2020). At the level of the single structure, the most appropriate methods for assessing the seismic response of masonry bell towers are based on numerical analyses, generally performed on Finite Element (FE) models. In this context, the dynamical characterisation by means of Ambient Vibration Test (AVT) is a powerful instrument for calibrating and validating the numerical models by means of Operational Modal Analysis (OMA) (Rainieri & Fabbrocino, 2014). In particular, by means of AVT the main vibrational modes and the relative natural frequencies are identified. Then, model updating is performed to calibrate a reliable numerical model simulating the dynamical characteristics of the investigated structures. This turns into an optimisation problem in which numerical-experimental discrepancies, in terms of both natural frequencies and vibrational shapes, are minimised. Notable examples of these methodologies applied to masonry bell towers can be found, among others, in (De Stefano et al., 2016; Standoli et al., 2021; Ubertini et al., 2017). The present study deals with a 13 th -century bell tower placed in the historical village of Casertavecchia (Campania region, Italy). The tower is adjacent to the Cathedral of St. Michele Arcangelo in the main village square (Rouhi et al., 2022). In particular, a dynamical characterisation of the tower is performed by means of AVT and a model updating procedure for the definition of a reliable numerical model is proposed in this study. 2. The bell tower 2.1. Geometrical description The structure under investigation is the bell tower of St. Michele Arcangelo Cathedral in Casertavecchia. It presents a total height of 32 meters from the ground level subdivided into an open base sector covering a road with an ogival vault and four additional sectors of different heights. Frontal and back views of the bell towers are provided in Fig. 1a and Fig. 1b, respectively.

Fig. 1. (a) Frontal and (b) back view of the bell tower of St. Michele Arcangelo.