Preliminary results from a one-week dynamic investigation of Giotto’s Bell Tower’s modal behavior using ambient vibration tests

Giotto’s Bell Tower, rising beside Brunelleschi’s Dome in the heart of Florence (Italy), is one of the most emblematic monuments of European architectural heritage. Its slender geometry, height, and complex masonry configuration make its dynamic behaviour of great interest for conservation planning, particularly in a seismic-prone country such as Italy. Although the tower has been previously investigated, most past studies relied on velocity-based modal identification, leaving scope for higher-resolution dynamic measurements. This work presents the first experimental campaign conducted using high-sensitivity piezoelectric accelerometers, marking an important advancement in the modal characterization of the tower. A one-week ambient vibration measurement program was carried out, during which acceleration time-histories were recorded at several levels along the tower. Data was processed using operational modal analysis techniques to estimate natural frequencies, modal damping and mode shapes. The experimental results enabled the identification of both fundamental and higher-order dynamic modes. To evaluate the meaning of these modes, the identified modal parameters were compared with those of an existing numerical finite element model calibrated on earlier vibration data. The results aim to contribute to long-term structural assessment strategies and represent an important reference for the development of continuous monitoring systems and seismic vulnerability studies for Giotto’s Bell Tower and similar heritage structures.