Seismic engineering expert Ian Aiken wants more structures around the world to be protected against the possibility of a devastating earthquake by setting them on state-of-the-art seismic isolation bearings.
Growing up in the geologically volatile region around Rotorua on New Zealand’s North Island, Ian Aiken dreamed of becoming a volcanologist. It took a cousin’s advice for the teenager to follow his aspirations and set him on the path of becoming a civil engineer.
“That’s a profession where you can actually earn a living,” Aiken recalls of his career decision. Subsequently he has become one of the most sought-after experts in the field of advanced earthquake proofing for buildings and bridges large and small around the world.
Aiken still keeps detailed tabs on the tremors and rumblings around the “Ring of Fire” – the horseshoe of countries ringing the irascible tectonic plates of the Pacific Rim from Oceania to Japan, over the Aleutian chain and then down again to California and Chile. But these days, Aiken serves as arbiter of the latest advancements in structural soundness when it comes to retrofitting existing buildings like the Los Angeles City Hall and San Diego’s Coronado Bay Bridge, both in the U.S., or the City Hall in the Romanian capital city of Bucharest.
Aiken’s company, Seismic Isolation Engineering (SIE), based in Emeryville, California, near San Francisco, specializes in the design, analysis and testing of seismic isolation bearings. These act to decouple buildings from the ground during an earthquake.
“It’s an irony of our work that we spend a lifetime preparing structures for something we hope never happens, and when it happens it’s over in a matter of 20 or 30 seconds,” says the researcher-turned-consultant.
And there is plenty of prep work out there. Never before have quake experts had access to such a wealth of data from sensors that are everywhere, cameras and eyewitness reports to refine their models and simulations, always in the hope of saving more lives and protecting more structures next time around.
To be fair, experts like Aiken don’t speak of “earthquake proofing.” They prefer to say they make structures “earthquake resistant,” helping them to withstand large and violent horizontal movements that can topple even a low building.
“If you consider different technologies, base isolation is the gold standard, designed to withstand maximum credible earthquakes that are expected to occur only once every 2,500 years, or even longer,” explains Aiken.
Code requirements for ordinary buildings commonly set a lower bar, designed for quakes with a more frequent recurrence probability of once every 500 years.
Seismic isolation is a fairly new weapon in the civil engineer’s arsenal. It involves putting a building or bridge on large shock absorber-type devices, which can even be slid under the weight-bearing columns of existing buildings. Made from dozens of vulcanized layers of rubber and steel plates and often reinforced with a lead core, these bearings can have a diameter of up to one and a half meters. They are designed to carry thousands of tons of weight while allowing a structure to gently sway up to 75 or more centimeters each way. Isolation is most appropriate to secure mid-level buildings of up to 12 stories,
Aiken explains, but there are plenty of taller structures and even high-rises that have been put on specially designed bearings.
The technology has been around since the late 1970s and was first installed in a government building in New Zealand in 1981, but it is still a high-end niche market. By Aiken’s reckoning, Japan has the highest number of isolated structures with around 2,000 large buildings, an additional 3,000 to 4,000 smaller wood-frame houses and several thousand bridges.
The United States, by contrast, has used the technology for only about 150 buildings, notably big public buildings that are of historic significance or serve critical functions, such as hospitals, fire stations or police headquarters, plus another 300 to 400 bridges. Unlike Japan’s hundreds of residential towers, Aiken knows of few private residences globally that sit on elastomeric bearings.
“Add in China and some other countries, and we’re looking perhaps 8,000 to 10,000 isolated structures worldwide, but that’s only a drop in the bucket,” he says.
The cost factor and a lack of a sense of urgency have kept seismic isolation from making major inroads outside of Japan, says Aiken.
“In Japan earthquakes are a national threat to all society, as we’ve seen so vividly recently.”
But, he says, that general awareness may change after the recent devastating quakes in Chile, New Zealand and Japan.
Seismic isolation has come a long way since the 1980s, due to better data, which in turn allows better computer modeling and simulation. Today there is a standardized bundle of almost identical offerings and services around the world. Aiken’s company consults and works with structural engineers and the global community of manufacturers such as Trelleborg, whose ANDRE bearings are still hand-fabricated in small quantities and individually tested before being installed.
Still, says Aiken, there is another way to look at the growing role of seismic isolation in the future.
“The big move in recent years toward sustainable construction has to go beyond merely looking at material and energy costs and take into better account the true life cycle cost of a building,” he says. “Destruction, downtime and recovery costs after a quake can put a company out of business, and they can devastate the entire economy.”
That’s why the back of his business card has four words of advice. The first three in green, the last one printed in bright blue: “Reduce. Reuse. Recycle. Isolate.”
Protecting the Infrastructure
Trelleborg’s Andre elastomeric steel composite bearings are the leaders in earthquake isolation of buildings. The horizontal stiffness and displacement capacity of each bearing is determined by the combined height of the rubber layers within the bearing. Those specifically designed for seismic isolation have a high vertical stiffness, achieved using comparatively thin rubber layers. Trelleborg’s seismic isolation projects include the Cathedral of Our Lady of the Angels in Los Angeles and one of the bridges in Istanbul, Turkey.
For more information visit www.trelleborg.com.