Results from the Seismometric Continuous Monitoring of an Ancient Bell Tower: The Arnolfo Tower, Palazzo Della Signoria, Florence, Italy

Florence (Tuscany, Italy) is one of the most visited cities of art in the world. Monuments, buildings, masterpieces from Renaissance are distributed everywhere in the historical center and they constitute an important heritage that is both of cultural and economic interest. It is of great importance to preserve the historical and cultural heritage of the city which constitutes an enormous wealth for the community. The first action for the protection of cultural heritage buildings is to increase the knowledge of their elastic characteristics. This allows to compensate for the lack of information regarding materials, construction techniques, and the geometries of the walls. In this context, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Dept. of Architecture of the University of Florence (DIDA) in December 2021 undertook a long term seismometric monitoring experiment, still in progress, of the Arnolfo Tower, the bell tower of the Palazzo della Signoria, the historic building that houses the Municipality of Florence. Two seismic stations were installed at the base and on the top terrace recording free vibrations to estimate the modal parameters of the structure. During the monitoring period, a short seismic sequence occurred which produced about more than 200 earthquakes with a maximum magnitude of 3.7, located about ten kilometers from the city and strongly felt by the population. The analyses of free vibrations made it possible to identify the main modal frequencies which constituted the experimental constraints for the comparison with the numerical model of the Tower. Continuous monitoring allows to record also moderate earthquakes than can produce effect on the structure, the results of the analysis of the seismograms recorded is presented.