SEISMIC PROTECTION OF HEAVY NON-STRUCTURAL MONOLITHIC OBJECTS AT THE TOP OF A HISTORICAL MASONRY CONSTRUCTION THROUGH BASE ISOLATION

This contribution addresses the problem of earthquake protection of heavy nonstructural monolithic objects, which are usually placed at the top of historical masonry constructions for mainly decorative purposes like pinnacles, merlons, sculptures and heavy artwork. Such objects, when subjected to base accelerations due to seismic actions, may undergo rocking phenomena, which may eventually lead to the overturning of the whole body. In particular, the specific case of the seismic protection of ancient marble pinnacles placed at the top of a three-arched masonry city gate in Ferrara (ITALY) is illustrated. In a preliminary rocking analysis, the pinnacles have been idealized as rigid bodies in unilateral contact with the underlying moving base and the resulting rocking motion have been analyzed. The structural safety level of the pinnacles have thus been assessed. As a consequence of these considerations, a base isolation system designed around multiple double concave curved-surface steel sliders have been devised. The effectiveness of the proposed isolation system has been assessed through numerical simulations. The amplification effect of the ground acceleration due to the underlying three-arched structure has been established through time-history dynamic analyses, where masonry has been considered as a viscoelastic material. To this aim, an equivalent viscous damping coefficient has been calculated for masonry following an iterative procedure involving the computation of capacity curves for both inand out-of-plane load directions and the definition of simplified biand tri-linear inelastic load-displacement capacity curves for masonry panels.