How base isolation originated
Dr Bill Robinson of Robinson Seismic, the inventor of the lead rubber bearing, talks about how he developed the bearing while he was working with Ivan Skinner at the Department of Scientific and Industrial Research in the early 1970s.
Transcript
DR BILL ROBINSON I became interested in earthquake engineering when I met Ivan Skinner and he was telling me about their research using what they called energy absorbers for structures, which seismically isolated. Now I found this fascinating and so I thought I am sure that steel is not the best material for absorbing energy. And so I went back to my office sat down with the periodic table and worked through that looking for a material which had a relatively low melting point, it was readily available at high purity and also had the other property of face centre cubic. Now the only material that satisfies all those conditions is lead, then I thought what sort of device can make use of those properties.
The device I came up with was the lead extrusion damper. This is a damper, now with a motor vehicle you have two parts, you have springs and you have shock absorbers, you can’t just bolt your wheels or your axles straight onto the chassis of a car, it would be horrendously uncomfortable. Now what we are doing with seismic isolation is the same sort of thing. We are putting a suspension system under the building so you are not allowing the shocks of the earthquake to pass directly into the building. So its just a suspension system and so what we need is we need springs, and for the lead rubber bearing you've got layers of rubber and steel, that is the spring and the shock absorber or the damper is the lead plug down the middle. So you have got those two components, and for seismic isolation to do a really good job you need both of those.
If you had a building sitting straight on a rubber bearing then you would get less shock going through but the displacements would be huge, if there was a big earthquake it would be a metre. If you put in some damping you can bring down to 200 millimetres. It’s the same with a motor vehicle if you don't have any dampers your vehicle will bounce around all over the place.
Acknowledgements: Capital & Coast District Health Board The Fletcher Construction Company Ltd Parliamentary Service (New Zealand) Robinson Seismic Limited
