Seismic isolation using sliding-elastomer bearing pads

Seismic isolation of nuclear power plants using sliding-elastomer bearing pads is reviewed. The foundation system involves a double raft interposed with reinforced neoprene pads and friction plates. All safety related structures are founded on the common (or connected) upper raft(s) which is in turn supported by a common lower raft founded on the subsurface soils. The pads act as a filter between the primary structures and the ground, limiting the horizontal earthquake forces and accelerations experienced by the structures. The low natural frequency of the predominant horizontal mode minimizes participation of higher structural modes. The performance and reliability of the system is demonstrated from the results of shaking table tests of scaled models, load and environmental tests of the bearings and various analytical studies. The characteristic features of the aseismic foundation system is shown to offer a number of advantages over conventionally designed structures in terms of performance, cost and safety. The system has been developed by Spie-Batignolles Bâtiment Travaux Publics in collaboration with Electricité de France, and has been incorporated into the design of a number of nuclear power plants.