Recent research and applications of seismic isolation in New Zealand

Abstract

In New Zealand, seismic isolation, the technique in which the structure is decoupled from earthquake-induced ground motions, has now advanced to the point where it is often considered for the protection of both new and existing buildings, bridges, and to a lesser extent, industrial plant. Many of the devices used in these applications have been developed in our laboratory. We describe here how the lead-based devices operate, and we give some examples of the application of seismic isolation to structures m New Zealand. Current interest is focused on the application of seismic isolation to three buildings in central Wellington. In July 1993, the construction of the seismically isolated Museum of New Zealand was started on the Wellington waterfront. All of the lead-rubber isolators have now been tested and installed. Nearby the NZ Parliament Building and Library have been retrofitted with a lead-rubber bearing system. To support the continuation of improvements to the seismic resistance of structures a number of research programs are operating in the Universities of Auckland and Canterbury, the Engineering Seismology Section of the NZ Institute of Geological and Nuclear Sciences, Works, a number of engineering consultants and in our company. Very strong support for the principles of seismic isolation is given by the fact that of the ten hospitals affected by the 1994 Northridge earthquake in Los Angeles, only the hospital seismically isolated by a lead-rubber bearing system was able to continue to operate. Further support is given by the excellent behaviour of two isolated buildings in the 1995 Hyogo Ken-Nanbu earthquake.