Unveiling the complexity of twin church bells dynamics using ambient vibration tests

On the Italian territory, many monumental structures need to be preserved. Given their great historical and architectural value, it is essential to use minimally invasive, but effective, techniques able to evaluate their current structural capabilities and monitor their structural health. The technique that currently appears most appropriate is the ambient vibration monitoring, which, through the analysis of recorded accelerometric time-histories in operating conditions, returns the current dynamic properties of the structure. This work shows the results of the short-term monitoring carried out on the two towers of the San Francesco Church, located in the city of Ascoli Piceno. Modal identification allowed obtaining its frequencies, modal shapes, and damping. With these data, the finite element model of the complex was calibrated, acting on the elastic parameters of the masonry, making numerical modal shapes and frequencies match with the experimental results.