Assessment of the dynamic behaviour of an ancient masonry tower in Lucca via ambient vibrations

This paper reports on a seismic monitoring experiment conducted on the bell tower of the San Frediano Church in Lucca, Italy. The tower, dating back to the 11th century, has been fitted along its height with four triaxial seismometric stations which were then left active on the tower for four days. The data from the monitoring system have been processed via the Stochastic Subspace Identification Method, implemented in the MACEC code, which has allowed extracting the tower's natural frequencies, mode shapes and damping ratios and their variations over time. A finite element model of the structure has been created via the NOSA-ITACA code and updated to fit the experimental data. The analysis has proved the effectiveness of the tools employed to assess the dynamic behaviour of ancient masonry towers.