This document presents the Operational Modal Analysis and finite element update of the bell tower of the church of Castro (BG), in Italy. This procedure was adopted to identify the actual state of structural damage following the widespread carbonation and oxidation of the surface concrete layer and the significant localized damage of the rebars detected by visual inspections. The 39m high structure is a reinforced concrete tower with a hollow section with a double concavity and a tapered section in elevation. Four uniaxial piezoelectric accelerometers were adopted to record environmental vibrations for dynamic identification using the roving technique. After performing dynamic identification, two types of 3D structural models were compared, namely with shell elements and beam elements. Finally, a calibration of the shell finite element model was carried out to identify the boundary conditions and the extension of the damage. The knowledge of the actual state of the structural damage enables the definition and the design of the retrofit strategy aimed at guaranteeing both static and seismic safety, as well as the future preservation of the structure.
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