LEAD RUBBER BEARINGS – A NEW ZEALAND INVENTION

The concept of “base isolation’ – placing rubber between buildings and the ground to isolate them from the strong earthquake ground shaking seemed at the time to be bold and unlikely to succeed, but has since been shown to work remarkably well.
Laminated lead-rubber bearings consist of an inner layered stack of rubber and steel sheets.  Each rubber sheet is c. 15 millimetres thick and each steel sheet c. 3 millimetres thick – typically, there are 20 off each, giving an overall height of a little under 40 centimetres.  A bearing for a large building measures 1 metres square and weighs several hundred kilograms, but can carry a load in excess of 2000 tonnes.  The final component, a vertical plug of lead to absorb seismic energy, was the critical breakthrough made by DSIR scientist Bill Robinson in 1976.  The bearings are placed in a layer between the base of a building and the ground.  If a strong earthquake shakes the ground under the bearings, they are able to flex and greatly reduce the seismic forces on the building.  The system has been thoroughly tested in the laboratory using large scale test machines.
There have been a number of real-life tests of base-isolaters  in actual earthquakes.  Of ten Los Angeles hospitals near the epicentre of the 1994 Northridge  earthquake, only the one on lead-rubber bearings remained functional.  Buildings and bridges on the bearings were subjected to strong ground shaking during the 1995 Kobe earthquake – all survived.  Also the Te Teko Bridge in the Bay of Plenty region was at the epicentre of the 1987 Edgecumbe earthquake.  It too survived.  This New Zealand invention is now being used in more than 200 buildings and 1000 bridges worldwide.  Prime examples  are the Museum of New Zealands, Te Papa Tongarewa, in Wellington City, which contains a viewing platform showing base-isolators in action, and New Zealand’s old Parliament building.

This was copied from the book
“A Continent on the Move
New Zealand Geoscience into the 21st Century.
Published by the Geological Society of New Zealand
In association with GNS Science.