AE monitoring and structural modeling of the Asinelli Tower in Bologna

The Acoustic Emission (AE) technique was used to assess the structural stability of the Asinelli Tower, the tallest building in the city of Bologna, which, together with the nearby tower, named Garisenda, is the renowned symbol of the city. AE is a passive, non-destructive structural evaluation technique based on the spontaneous emission of pressure waves by evolving fracture processes. The monitoring program was carried out with the aid of a USAM tool, which is part of the equipment used at the Fracture Mechanics Laboratory of the Department of Structural Engineering at the Politecnico di Torino. This tool makes it possible to conduct a complete analysis of AE signals, acquire a huge quantity of data from on site monitoring, and identify the microcracks triggering the damage processes in a structure. In the second part of the paper, the results from a preliminary linear analysis are presented, in order to assess the structural behavior of the tower. The cracking and crushing strengths of the masonry have both been compared with the calculated stresses. The numerical analysis gives a valuable picture of the modal response of the tower, providing useful hints for the prosecution of structural monitoring.