Seismic Protection of Monolithic Objects of Art Using a Constrained Oscillating Base

Abstract

The model of rigid block is well known in literature. In the past, several papers analyzed the behaviour of rigid blocks under different kind of excitations because many monolithic objects of art, such as statues, obelisks and fountains, subject to earthquake excitation, can be modelled as rigid blocks. In [Shenton & Jones, 1991] a general bi-dimensional formulation of the rigid block has been obtained and rocking and slide-rock approximated conditions have been written. More recently this model has been used to describe the behaviour of monolithic bodies subject to base excitations as a one-sine pulse excitation in [Zhang & Makris, 2001; Makris & Black, 2004, Kounadis 2010] and earthquake excitation in [Agbabian et al., 1988; Pompei et al, 1998; Taniguchi, 2002]. Almost all the papers on rigid blocks subject to base excitation focus their attention on symmetric rigid bodies. Only a few papers concern non-symmetric rigid bodies that, usually, represent objects of art better than symmetric rigid blocks. In [Boroscheck & Romo, 2004] the influence of the eccentricity of the centre of mass on the motion of the system has been studied. In [Purvance, 2005; Purvance et al., 2008] an analytical and experimental estimation of overturning events under seismic excitations has been carried out, both for symmetric and non-symmetric rigid bodies. In particular, in [Zhang & Makris, 2001] for a one-sine pulse excitation and in [Purvance, 2005; Purvance et al., 2008] for seismic excitation, the existence of survival regions that lie above the PGA (Peak Ground Acceleration) associated with the first overturning occurrence have been shown. In recent years, methods to reduce the effects of seismic excitation on art objects have been studied in some papers. In [Fujita et al, 2008 ] a critical excitation problem for a rigid block subjected to horizontal and vertical simultaneous base inputs is considered. In [Vestroni & Di Cinto, 2000] a base isolation system has been used to protect statues from seismic effects. The work of art has been modeled through an equivalent elastic beam. In [Calio & Marletta, 2003] the same problem has been analyzed, but the art object has been modeled as a symmetric rigid block simply supported on an oscillating base connected to the ground by a visco-elastic device. The sliding of the body is prevented by special seismic restraints. These analyses have shown the effectiveness of the isolation system and the role of many parameters. To make things more realistic, in [Contento & Di Egidio, 2009], the model presented in [Calio & Marletta, 2003] has been enriched considering also the eccentricity of the centre of mass of the rigid body and the presence of security stops, able to prevent the breaking of the isolation device by limiting