Preservation and monitoring of the Frari Bell Tower in Venice

The Frari bell tower, the second tallest in Venice after San Marco, has always been affected by structural problems since its construction in XIV century, mainly because of the slow but continuous differential settlement between the tower itself and the adjacent masonry structures of the basilica. In the last decade, within a comprehensive scheme of structural rehabilitation carried out by the Italian “Ministero per i Beni e le Attività Culturali” (Italian Ministry for Cultural Heritage and Activities), a rather innovative intervention of soil fracturing was carried out in order to improve the mechanical characteristics of the silty clay layer underlying the tower. Once the aim of improving the stability of the soil-foundation system had been achieved, a new solution was then required to reduce the damaging structural interaction induced by the foundation movements: a structural joint between the bell tower and the basilica was eventually carried out in order to improve the system deformability. The paper presents a well-documented history of such a complex and delicate intervention, since the preliminary accurate site investigation, highlighting not only the approach aimed at improving the overall safety without altering the original structure and modifying the current stress distribution but also the fundamental methodology, adopted throughout, of a flexible and modular design, constantly driven by the outcome of an extensive real-time monitoring system of the soil-structure interaction.