The structural strengthening of the Garisenda Tower in Bologna, Italy

The Garisenda Tower, with its tilt toward South-East of 3.4 meters is the most tilted masonry tower in Italy. It was built in the XI century and it is 48 m high. Its cross-section is approximately square with a gradual decreasing along the height. From the date of its construction, the tower was subjected to various accidents (such as fires, lightings and earthquakes) that, together to its structural configuration, make the tower particularly vulnerable to the static and seismic actions. The aim of this paper is to present the strengthening interventions that have been effected on the Garisenda tower in the last decades. It has been possible to develop an appropriate strengthening design only after a deep knowledge of the tower obtained through historical, geometrical surveys and the materials properties characterization. The main strengthening interventions performed on the tower are: (i) masonry consolidation through substitution of the damage bricks and injection of high strength mortar, (ii) installation of steel frames in order to provide a connection between the two masonry layers and (iii) development/ installation of improved external steel ties in order to provide a lateral confinement to the masonry.