Seismic risk assessment of a medieval tower: The case study of Craco

In the present paper the risk assessment of the medieval Norman tower of Craco (Matera, Italy) is discussed. Craco is a totally abandoned little town because of the activation of landslide motions of its soil depth. The medieval tower is one of the few buildings still standing as it is built on a fixed stiff foundation ground. Nevertheless, the tower is, indirectly, subjected to the movements of the close landslide. The tower is located in the highest and more stable part of the hill where the old town was built in the XII century for protection from enemy attacks. It is 20 m tall and has a (11 x 11) m2 square plan. The basement has a truncated pyramid shape; originally it had two masonry vaults, one barrel on the first floor, which no longer exists, and a still visible cruise at the second order, connected by a now destroyed internal staircase. In 1949 a reinforced concrete cistern was placed inside the tower. Craco is classified as a town with a medium level seismic hazard. The main aim of the present study is to evaluate the seismic risk by means of a Finite Element model, calibrated through dynamic tests performed on the tower and considering the historical value of the structure and the context in which it stands. In fact, the structure is characterized by several peculiarities: the presence of a reinforced concrete cistern, the interaction with the surrounding buildings, the closeness to the landslide, the topographical exposition, etc. Moreover, the structure has a great impact on the society due to its touristic interest, as it is an emblem of the, so-called, “ghost town” of the Appennino mountains. A new approach is proposed to evaluate the effects of all the previously cited features on the evaluation of the seismic risk of the tower, introducing also economical and sociological parameters.