ABSTRACT
One of the most widely implemented and accepted seismic protection systems is base isolation (Skinner et al. 1993; Naeim & Kelly 1999). The goal of base isolation is to simultaneously reduce inter-story drifts and floor accelerations to limit or avoid damage, not only to the structure but also to its contents, in a cost-effective manner. Based on observations from the January 17, 1994 Northridge earthquakes, some researchers (e.g., Hall et al. 1995; Heaton et al. 1995) have raised concerns as to the efficacy of seismic isolation during such events. With refer to these reports, design of seismic isolated buildings located at nearfault sites; the design engineer is faced with very large design displacements for the isolators. To reduce these displacements, supplementary dampers are often prescribed. These dampers reduce displacements, but at the expense of significant increases in inter-storey drifts and floor accelerations in the superstructure (Kelly 1999). The dilemma with regard to conventional isolation systems is the need to specify large amount of damping to mitigate very rare displacements, while this damping can be detrimental to the performance of the structure under occasional and rare events. A new innovative isolation system called double concave friction pendulum bearing has the ability to progressively exhibit different hysteretic properties at different stages of displacement response (Fenz et al. 2006; 2008a).
