Savage Earth: Building Safer




		Build Smart, Not Hard by Daniel Pendick

		In sports, the best offense is sometimes a good defense. And that's how most engineers approach earthquake hazards, too: By building office towers, bridges, and apartment blocks to survive tremors, loss of life can be kept to a minimum. In small to moderate earthquakes, buildings and bridges can survive virtually unscathed with the help of bracing, reinforced joints, or even pads and rollers that allow the structure to move more freely when the ground starts to sway. The 1989 Loma Prieta quake made the upper floors of the Transamerica Pyramid building in downtown San Francisco sway more than a foot from side to side, but its earthquake-resistant construction allowed the landmark to survive without damage.


	But on the frontiers of earthquake engineering, some scientists are going on the offensive. There are technologies in the works that may allow buildings to aggressively resist earthquakes. In these "intelligent" systems, the structure adapts to the forces it experiences during an earthquake and avoids catastrophic damage.


	At the State University of New York at Buffalo, a team of scientists and engineers have developed a system based on hydraulic "tendons" controlled by computers. In one version, the tendons are anchored to a building's foundations and push or pull on wall beams to counteract swaying motions. Engineer Andrei Reinhorn, a member of the Buffalo team, compares this to a person leaning forward to counteract a blast of wind during a storm. The scientists are also investigating a "semi-active" system that incorporates special joints into the framework of a building that can tighten or loosen in response to motion. Using signals from sensors, a computer decides which joints to tighten or loosen. This could allow a building to ride out an earthquake and avoid major damage to its structure. Intelligent bracing can also be used in bridges.

The Transamerica Pyramid



				Seismic records from a 1984 earthquake show how much stress different parts of a roof may endure.

		Another system, under study at Buffalo and elsewhere, is based on a heavy weight inside the building that shifts in order to counteract swaying or twisting motions. When the building moves, pistons shift the position of the mass in the opposite direction. Some active systems are already in use to counteract the swaying of tall buildings caused by wind, which is unnerving to people inside and can even make them seasick. The Sendagaya INTES Building in Tokyo has such a system on its 11th floor, with one mass for counteracting swaying motions and another to resist twisting motions. Reinhorn believes that intelligent buildings are the way of the future in seismic engineering. One important advantage, he says, is the fact that a smart building can adapt to many types of ground motions -- possibly some unanticipated before the event. But, right now, building designers remain hesitant. One major issue is the reliability of the smart braces and the control systems. Should something break down in an actual quake, a building could suddenly become very dumb and very dangerous. For now, engineers will probably continue to build their high-rises and bridges like the stereotype of the football linebacker: not too bright, but really hard to knock over.

			Drawing: Courtesy of the U.S. Geological Survey.

		Article: All Stressed Out \| Sidebar One: Learning from Earthquakes \| Sidebar Two: Quake Prediction \| Sidebar Three: Build Smart \| ANIMATION Hell's Crust: Our Everchanging Planet \| The Restless Planet: Earthquakes Out of the Inferno: Volcanoes \| Waves of Destruction: Tsunamis

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