LA TECNICA DELLA “TORRE NELLA TORRE”: DUE CASI A PAVIA

Ferdinando Zaccheo1, Lorenzo Jurina2

1 Architetto libero professionista, arch.zaccheo@libero.it

2 Politecnico di Milano- dip. ABC, lorenzo.jurina@polimi.it

ABSTRACT

In the Middle Ages, Pavia was characterized by the presence of several masonry towers, hence the name of "city of one hundred towers". Some of them are still existing in the historic center, while many others failed or were demolished in the past centuries. Since 1989, when the collapse of the Civic Tower occurred, the municipality of Pavia started a huge program of analysis and verifications for all the survived towers, in order to evaluate their residual resistance and to prevent further collapses. Many monitoring and diagnostic campaigns were conducted by ISMES in the Nineties, to determine the mechanical properties of the masonry and the actual state of stress. Results showed poor characteristics of masonry, composed by two brick layers and a thick un-coherent inner core, and high levels of stresses. Structural evidences required some consolidation interventions for three towers (San Dalmazio, Maino and Fraccaro). In this memory two similar interventions realized by the authors on the tower of San Dalmazio and Maino are presented. The consolidation solution is called "tower in tower", and consists in the insertion of a steel truss tower inside the masonry one, connected to the perimeter walls through more than 300 steel stays. Such elements are able to transfer part of the self weight of the masonry to the inner steel truss, reducing the compressive stresses at the base. A relevant strength contribution of the steel tower is offered even in presence of horizontal loads such as wind and earthquake, as demonstrated by a FE numerical Model. Another interesting consolidation solution is here shown, that applies some new steel diatones inside the existing “scaffolding holes”, incrementing the tri-axial compressive strength and the ductility of the masonry.

Parole chiave/Key-words:

Masonry towers, structural consolidation, monitoring, numerical modeling.