Experimental study of lead and elastomeric dampers for base isolation systems in laminated Neoprene bearings

Abstract

This report describes a series of experiments carried out on the shaking table at the Earthquake Simulator Laboratory of the Earthquake Engineering Research Laboratory, involving a base isolation system which incorporated multilayer isolation bearings of Neoprene, a polychloroprene rubber. Several forms of isolation system using the same basic bearing design but including inserts of different materials in a central hole in each bearing were studies. The inserts were used to enhance the damping properties of the system and to improve the response. The results indicate that there are no difficulties in designing an effective isolation system in polychloroprene rubber and that the multilayer elastomeric bearings can substantially reduce the seismic loads experienced by a building and its contents. Elastomeric inserts were effective in improving the response only to a limited extent. The use of lead inserts to enhance the damping was very effective in controlling the displacement. There is an increasing interest in the use of base isolation as a way of reducing the effects of earthquakes on structures. There is general acceptance of the concept but doubts about its implementation center on the question of suitable bearings. Experiments of the kind reported here, on large models where scaling effects are minimized, can allay the fears of the seismic engineering profession that bearings may not be available.