Operational modal analysis of a damaged bell tower

This paper presents the operational modal analysis (OMA) and finite element (FE) modeling of the bell tower of the church of Castro located in Bergamo, Italy. This procedure was dictated by the need to identify the actual damage state of the structure detected by visual inspections. The 39m high reinforced concrete tower has a hollow section with a double concavity. Piezoelectric accelerometers were used to record ambient vibration in subsequent setups using the roving technique for high resolution system identification. After performing the system identification, two types of 3D structural models were considered compared, using shell and beam elements, respectively. Finally, the FE models were updated to identify the boundary conditions and the state of deterioration. The knowledge of the actual state of structural damage will be required to define the retrofit strategy.