“Modal updating of ancient heritage structures: The Rialto Bridge case”

The subject of the present thesis is the evaluation of the dynamic and seismic behaviour of the Rialto Bridge, located in Venice; this structure crosses the Grand Canal and is one of the major attractions of the city, a UNESCO World Heritage Site. The Code of Cultural Heritage and Landscape has fixed the guide concepts for the activities of knowledge and preservation of the structures of historical and artistical importance. To this purpose in Italy a permanent monitoring network has been established since 1995: it is managed by the Seismic Observatory of Structures (OSS) with the objective to evaluate the Structural Health Monitoring (SHM), which consists in the identification of sudden or progressive damage, but also the monitoring of the building's performance in operating conditions or during exceptional events, for example in the case of earthquakes. A structural monitoring system performs a process of periodic diagnosis of a structure by measuring the symptomatic characteristics of the phenomena under investigation and conducts their statistical analysis to determine the current status of the system. From an operational point of view, for the case in question, first of all surveys were carried out to identify the properties of the materials constituting the bridge and the degradation phenomena present.A finite element model of the bridge was then created using two-dimensional and three-dimensional elements to which numerical values of mechanical parameters were attributed; after the creation of the bridge geometric model, a modal analysis was carried out with the assistance of Ansys finite element software to obtain the trial values of the system parameters. The above mentioned initial values of the mechanical parameters were modified and adjusted in the second phase of the procedure, called modal updating phase, consisting in the calibration of the model aimed at identifying the frequencies and the modal displacements of the structure.