Numerical analysis of the medieval Civic Tower of L’Aquila to prevent seismic pounding effects

The Civic Tower is one of the historical monuments damaged by the severe earthquake which struck the town of L’Aquila in 2009. Although it has been heavily modified during its long life, this masonry tower still represents one of the oldest monuments of L’Aquila. Presently, it forms a monumental complex with the adjacent lower building called “Palazzo Margherita”, the city hall of L’Aquila. The two structures are very close but separated to each other and exhibit a different seismic behaviour. This may trigger pounding effects during strong earthquakes. With the purpose of evaluating the extent of the pounding phenomenon, a three-dimensional model of the tower has been developed in the present paper. By referring to experimental data available in the literature, relevant to vibration-based tests made on the tower after the 2009 earthquake, the modal parameters of the numerical model have been identified. Different models of the tower were actually considered to assess the influence of some geometrical and material uncertainties. A code-based modal response spectrum analysis was carried out to determine the tower maximum displacements at the top level of the adjacent building. The distance that would accommodate the peak displacements of out-of phase oscillations under seimic design actions was thus calculated by taking also into account the peak displacements of “Palazzo Margherita”. Finally, the paper briefly examined some strategies to mitigate the pounding effects during future earthquakes.