Engineers Teach 'Smart' Buildings To Foil Quakes
By SANDRA BLAKESLEE
Published: July 2, 1991
LAST week's earthquake in southern California may jolt even the building industry, notoriously slow to innovate, into experimenting with new kinds of earthquake resistant buildings. Among the most interesting are so-called smart buildings in which a system of computers, sensors and moving weights detects and moves to counteract the alarming motions generated by earthquakes and strong winds.
Traditionally, building engineers have taken a brute strength approach to structural safety. They use massive, heavy materials and build stiffness into a building's infrastructure to resist winds and earthquakes. To filter out shaking, some newer buildings have been constructed on huge rubber pads or materials that act as springs that help dissipate energy. It has taken 30 years to get such passive control systems into the building codes, because American construction companies are extremely slow to innovate, said Dr. Tsu T. Soong, a professor of civil engineering at the National Center for Earthquake Engineering Research at the State University of New York in Buffalo.
But in Japan, where destructive earthquakes are an ever-present threat, five major construction companies compete for contracts based on new technologies, and the company with the best new ideas tends to win more contracts. Japanese construction companies invest 10 percent of their gross income in research and development, said Dr. S. Chi Liu, program manager of the Earthquake Hazard Mitigation Project at the National Science Foundation in Washington. They are particularly interested in active and passive control systems to resist earthquakes and wind. U.S. companies invest virtually nothing.
As so often happens, Dr. Liu said, many of the most innovative ideas for such systems are originating in the United States but are being developed by the Japanese. To help spur American involvement, the foundation expects to award $5 million over the next five years to American researchers, Dr. Liu said. But whether American construction companies will use that research, he said, is hard to say.
The world's first building with an active control system was built on a sliver of land in a Tokyo suburb in 1989. The Kyobashi Seiwa office building is only 12 feet wide, 100 feet long and 11 stories high, he said, and the owners worried that wind would buffet the slender structure.
To stabilize the building, the construction company Kajima suspended a four-ton weight and a one-ton weight, one above another, on the building's roof. Sensors were embedded into the building's walls and base and attached to a computer. When the ground shakes or the wind blows, Dr. Liu said, the computer sends signals to hydraulic arms called actuators that move the weights to counteract the motions in the building.
Kajima claims that 80 percent of the building's motion has been dampened out by the active system, Dr. Liu said, although the building's performance has not been independently verified.
A second structure, also built in Tokyo in 1989, is a joint venture between between the Buffalo researchers and the Takenaka Corporation of Japan, another leading construction firm. It is a six-story, 600-ton building without walls that was built solely to demonstrate both weight and bracing systems, Dr. Soong said. Its performance is being monitored and will be published in scientific journals.
The weight consists of a six-ton slab of steel suspended on the roof. Sensors in the basement, third and sixth floor detect motion from earthquakes, wind and even local traffic and send the information to a computer that activates the actuators. The building's motion in strong wind and small earthquakes has been reduced by half, Dr. Soong said.
The bracing system is even more effective, Dr. Soong said, reducing motions by up to 70 percent. The braces are conventional steel tubes of the type that hold all buildings together, but these have been fitted with actuators at each end. When the computer sends its signals, the actuators lengthen or shorten the building's internal braces to accommodate motions from earthquakes and wind.
Both systems are capable of making the building shake, Dr. Soong said, so that one can be used to test the other's ability to dampen motion. Data will be collected for two more years.
The Tokyo buildings are performing very well, Dr. Liu said, and four more "smart" buildings are on the drawing board. But the technology is still in research and development stages, as safety, reliability, and cost questions are explored in the different designs.
People are going to need "a lot of convincing" before these concepts become acceptable in construction, Dr. Soong said. Whenever human lives are dependent on computers and mechanical systems, he said, people want to be sure about reliability.
Active control systems have long been used in airplanes, ships, spacecraft and other mobile structures. They are just beginning to be applied to stationary objects on land like buildings, bridges and elevated freeways. Disrupting Seismic Waves