Chris Gannon and Dr Bill Robinson of Robinson Seismic explain the base isolation principle. We can make buildings strong so they don’t fall down, but is that the best form of earthquake protection?
The main principal of base isolation is to try and isolate the structure from the ground movement so you could just about put it on ball bearings if you like and the ground could move underneath it and the building stays still.
DR BILL ROBINSON
Seismic isolation is important for two reasons, one it protects the structure, now it is possible always to build a strong enough structure, however it may not be economic. You can reduce the forces being transmitted to the building, in an earthquake, by following a seismic isolation approach. Now the most important thing is that seismic isolation protects the contents. In the Los Angeles earthquake there was a hospital which was built for strength and it survived but unfortunately the accelerations in the top floor were so great that a water pipe burst – broke – and that flooded the hospital and caused it to be evacuated. With the hospital that was mounted on lead rubber bearings it continued to operate and so it goes on with other products which you may have in a building, you want them to remain in place. If you have a library you don’t want all the books on the floor and so it goes on.
Museum of New Zealand Te Papa Tongarewa
National Information Service for Earthquake Engineering
Capital Coast District Health Board