Earthquakes kill thousands of people and cause billions of dollars in damage every year. Reinforced concrete and special trusses have toughened large buildings, but mechanisms that actually reduce the shake from a quake are still relatively new.
Building codes require structures to provide “life safety”—that is, they should not collapse, so people can evacuate. But the real challenge is economic. “We could design a building with conventional techniques that would survive the largest earthquake without damage, but it would be so expensive no one would build it,” says André Filiatrault, deputy director of the Multidisciplinary Center for Earthquake Engineering Research at the State University of New York at Buffalo. More and more, building owners are considering the incremental cost to minimize damage to the structure, to its mechanical systems, to the contents inside and, ultimately, to allow for immediate reoccupancy. “In a hospital, for example,” Filiatrault says, “the structure accounts for only 10 percent of the total cost. The other 90 percent is equipment, and designing for life safety won’t spare it.”
The leading techniques “try to absorb a lot of the ground motion energy so the building doesn’t have to,” says James Malley, senior principal at Degenkolb Engineers in San Francisco. That often means inserting heavy-duty fixtures between the building and its foundation, such as base isolators that act as rubber mats, viscous fluid dampers that operate like shock absorbers, or slide bearings that allow the building to sway instead of snap. Much of the hardware is adapted from military gear for hardening missile silos, ship decks and submarines against bombs and missiles, and it is being rolled out by contractors looking for civilian work, notes Douglas P. Taylor, CEO of Taylor Devices in North Tonawanda, N.Y.
A few researchers are examining novel technologies, such as actuators that would pull on tendonlike beams to counteract ground motion or electrorheological fluids in a foundation that would turn from liquid to gel to filter out shock waves. In the meantime, installations at new sites and retrofits to old ones are booming. Even in California, most buildings are not yet outfitted.
Did You Know
- SHARE A SHAKE: In 1999 the National Science Foundation launched the Network for Earthquake Engineering Simulation to research how best to protect structures against earthquakes. The NSF will spend more than $100 million over 15 years at almost 20 university research centers. The centers, which are building gigantic shake tables and wave tanks, will run experiments at one another’s facilities over high-speed networks that should be fully operational this fall.
- IT TAKES A DISASTER: Work on structural isolation techniques has accelerated sharply because of two disasters. The January 1994 Northridge earthquake near Los Angeles took 60 lives and caused $20 billion in damage. The January 1995 quake in Kobe, Japan, killed more than 5,000 people and crippled more than 50,000 buildings. History repeats: the 1971 San Fernando Valley quake in California prompted codes requiring steel-reinforced concrete in buildings.
- ILL WIND: Even light skyscrapers can withstand strong winds. Still, they may sway at a frequency that can make occupants feel seasick. Builders can cancel the movement by installing huge roof tanks with water that swishes to counter the motion (and is available to quench fires). Alternatively, slide bearings can support the roof, allowing it to rock back and forth. This technique can also isolate the heavy mass during a quake, lessening stress on vertical columns.
This article was originally published with the title Shock Absorbed.