EARTHQUAKE ENGINEERING OF THE DAY: Base isolation
That thought also occurred to a very smart New Zealand engineer back in the 1970s, Dr Bill Robinson (right), and in 1976 he developed a system to do it that is now implemented in around 3,000 buildings and bridges worldwide—including, unfortunately, Wellington’s parliament buildings (simultaneously protecting its inhabitants, and making the idea of a Wellington earthquake far less attractive).
Robinson’s basic system is essentially a lead-rubber bearing (left) placed between the ground and a buildings foundations either during original construction (as with Te Papa) or afterwards (as with the parliament buildings) to reduce the force exerted on the building by the ground’s movement. The outer rubber “sandwich” gives the bearing flexibility, while the lead damps down the movement and absorbs the earthquake’s kinetic energy, turning it into heat.
Working together in the same way a car’s springs and dampers do, they reduced the earthquake force in buildings and bridges in both the Northridge and Kobe quakes to about one-fifth the seismic force that un un-isolated building or bridge would suffer—allowing bridges, hospitals and buildings necessary after a major shake to to ride out the earthquake undamaged, even while all around them is a sea of destruction.
You can see how effective it is in these videos of building models on a “shake table” set up to compare buildings that have been base-isolated and those which haven’t. It’s a pretty persuasive demonstration.
Since Robinson’s invention of the lead-rubber bearing, many other systems have been developed following the same principle—including base-isolated tables designed to protect fragile objects during a quake. And there’s even one Canterbury economist who’s protecting his child right now with what he calls “a Gerry-rigged earthquake base isolation unit” for his 4 month old, which has successfully kept Eric Crampton’s youngster safe through two aftershocks.
There’s a neat video here at the Science Learning site where Robinson explains the life-saving concept of his lead-rubber bearing and how he came up with it—and there’s plenty more links there to take you further…