Base isolation of heavy non-structural monolithic objects at the top of a masonry monumental construction

The present paper deals with the relevant topic of seismic protection of heavy non-structural monolithic objects, which are usually placed at the top of masonry monumental constructions for mainly decorative purposes, like pinnacles and heavy artwork. Even if, after seismic events, most of the losses are due to structural collapse of buildings and other structural systems, heavy non-structural objects of the kind considered in the present work represent a serious potential hazard for both human lives and cultural heritage. During earthquakes, such objects undergo large base accelerations, which may eventually cause their collapse by rocking and overturning. In the present contribution, the seismic protection of eleven ancient marble decorative pinnacles placed at the top of the three-arched masonry city gate in Ferrara (Italy) is illustrated as a case study. In particular, a method for assessing the safety level of these systems under the action of seismic excitations is outlined and base isolation is proposed as a very promising technique for the seismic retrofit of heavy non-structural monolithic objects. The dynamical response to seismic actions of the underlying masonry construction is assessed through time-history dynamic analyses and the amplification of the ground accelerations at the base of the pinnacles is evaluated. Furthermore, the pinnacles are modeled as rigid bodies and their rocking behavior under base excitations is discussed. Finally, the effectiveness of the proposed base isolation system is assessed through non-linear dynamic numerical simulations.