Bill Robinson — Seismic Isolators

A morning tea discussion led to Bill Robinson's development of Earthquake 'shock absorbers'. These are able to protect buildings and structures from even the strongest of earthquakes.

It took only two hours after a morning tea discussion on how structures could best absorb the energy of an earthquake for Dr Bill Robinson, now of Penguin Engineering Limited, to come up with a solution to solve the problem. What he came up with that morning was the first step to an invention capable of protecting buildings, bridges or any other structure from even the strongest of earthquakes: the lead-rubber seismic bearing or 'earthquake shock absorber'.

Today many prominent buildings around the world are made safe from earthquakes by the lead-rubber bearing. It is a simple idea, says DR Robinson, which is what makes it such a good one, but one that no one else in the world had thought of before he came up with its final design in 1975.

The bearing is a lead core surrounded by interlayered sheets of steel and rubber. During an earthquake the lead deforms and is stretched sideways as the earth shakes. In fact, it is able to move sideways to a distance equal to its height — a few hundred millimetres being ample for even the most powerful of earthquakes.

The rubber and steel then pulls it back into shape ready for the next shock. A typical bearing is less than half a metre high. During an earthquake a structure fitted with the bearings will actually stay still, says DR Robinson, while the ground shakes beneath. They can be made to protect a building from an earthquake of any size, even one that would absolutely flatten other buildings.

DR Robinson, who has a PhD in Physical Metallurgy, the nature of metals, was working at the then DSIR, or Department of Scientific and Industrial Research in Gracefield, Wellington, on defects in metals when he joined in the morning tea discussion on energy absorption. It was his knowledge of metals and their crystalline make-up that made him realise lead would be the perfect material for the task of absorbing large amounts of energy.

DR Robinson explains: "Materials like metal and salt and many other materials are made of crystals with all the atoms lined up in neat rows." When a large lateral or sideways force is applied to the lead each neat layer of atoms slips sideways on top of the layer beneath it, so the top layer ends up a long way sideways from where it started.

If you stacked up a pile of $2 coins you could do the same by moving the top one a little, then the one underneath it, and the one underneath it and so on until the stack resembled a staircase with even steps from the top to the bottom.

DR Robinson says the successful idea he had was to combine the lead and the layers of rubber and steel. It was this which enabled the lead to work over and over again as well as support the weight of the building. The first structures to use the bearings were the William Clayton building in Wellington in 1981 and the Toe Toe and Waiotukupuna bridges also in 1981. DR Robinson has written a book on the subject of seismic isolation with two other scientists which has been translated into both Chinese and Japanese.

DR Robinson says there are three reasons for a building to be built with his seismic isolating devices. That the building itself is valuable, for example historically important like parliament buildings. That what the building contains is valuable, like Te Papa whose treasures rest on about 135 lead- rubber bearings. Or what goes on inside the building is important, like the Wellington Central Police Station.

There are great economic gains to be had from making buildings which don't fall down and are safe but the bearing DR Robinson invented also allows buildings to be made for less money as they do not have to be as strong as they otherwise would. Two recent earthquakes have proved the effectiveness of DR Robinson's seismic isolators. During the 1994 Los Angeles earthquake while other buildings and bridges collapsed, buckled, and swayed, the University of Southern California's teaching hospital was unaffected. Patients did not even realise there had been an earthquake despite the widely held belief that the 8 storey building's L-shaped design would be unsafe during an earthquake. Instead the seismic isolators it was built on allowed the ground to shake violently underneath while it remained calmly afloat. Objects did not even fall off the shelves. Nearby another hospital, which had been built for strength, did not fare so well. While the building itself was fine a waterpipe burst on the upper levels and flooded the floors beneath causing damage and obvious problems.

Some other prominent buildings and structures protected by DR Robinson's invention include the New Zealand Parliament building, The Museum of New Zealand, the San Francisco City Hall and the Golden Gate Bridge approach. There are over 800 structures around the world built with DR Robinson's invention in countries such as Japan, the United States, China and Italy.

In Kobe, Japan, in 1995 an earthquake, force 7.2 on the richter scale, hit the town killing 6000 people and destroying 70,000 homes. One building however was resting on the lead-rubber bearing and was completely unharmed while other buildings around it were destroyed by the quake.

The seismic bearings are made in New Zealand but are also manufactured overseas by license holding companies. The bearing remains the intellectual property of the New Zealand Government while Penguin Engineering Limited, which was set up by DR Robinson after his time at the DSIR, does some contract work on the testing of bearings and wins research contracts, including some for further work on energy absorption. Other Penguin engineering projects have included brakes and clutches which do not suffer from wear, and shock absorbers for stopping large moving vehicles such as ships, trains, trucks and aircraft.

Classroom activity - Testing Materials