The seismic assessment of the Asinelli tower in Bologna

The Asinelli tower located in the city center of Bologna (northern Italy), whose construction began at the beginning of the XII century, is one of the tallest masonry towers in Italy, reaching a height of almost 100 m. Due to the large amount of stress induced at the basement, it experienced some soil settlement which leaded to a tilt toward West of 2.23 m. For its structural configuration, the tower appears prone to seismic-induced damages and, therefore, an assessment of its dynamic properties is of primary importance in order to evaluate its own safety against seismic actions. In the present paper, first an assessment of the main dynamic properties of the Tower (i.e. natural frequencies and mode shapes) is carried out by cross-correlating the response of different structural models (from simple continuum analytical models to more complex finite element models) with the results of a continuous dynamic monitoring performed in 2012 and 2013-2014 by the Italian Institute of Geophysics and Volcanology (INGV). Then, specific hazard analyses have been developed in order to identify the most probable earthquake scenarios which (i) occurred in the past and (ii) may probably occur in the future in the site of the monument. By making use of a nonlinear finite element models, the seismic vulnerability assessment of the actual state of the Asinelli tower has been conducted.