Ambient Vibrations of Age-old Masonry Towers: Results of Long-term Dynamic Monitoring in the Historic Centre of Lucca

The paper presents the results of an ambient vibration monitoring campaign conducted on the so-called "Clock Tower" (Torre delle Ore), one of the best known and most visited monuments in the historic centre of Lucca. The vibrations of the tower were continuously monitored from November 2017 to March 2018 using high-sensitivity instrumentation. In particular, four seismic stations provided by the Istituto Nazionale di Geofisica e Vulcanologia and two three-axial accelerometers developed by AGI S.r.l., spin-off of the National Institute for Astrophysics, were installed on the tower. The measured vibration level was generally very low, since the structure lies in the middle of a limited traffic area. Nevertheless, the availability of two different types of highly sensitive and accurate instruments allowed the authors to follow the dynamic behaviour of the tower during the entire monitoring period and has moreover provided cross-validation of the results.