The next time the New Madrid fault zone produces a strong earthquake, buildings in the Midwest may see less damage if they use a new device developed by a researcher at the University of Missouri-Rolla.
Dr. Genda Chen, associate professor of civil engineering at UMR, has spent the past five years developing a "smart" damper that can adapt to external disturbances such as earthquakes and keep buildings from shaking as much. His most recent findings are included in an upcoming issue of the Journal of Structural Control and Health Monitoring, available Sept. 12. Earlier findings were reported in the March 2004 issue of the International Journal of Structural Engineering and Mechanics and the April 2004 issue of the American Society of Civil Engineers’ Journal of Engineering Mechanics.
Chen’s damper operates much like the brakes of an automobile. "When you drive and go too fast, you press the brake to slow down a little bit," Chen explains. "Then you release the brake so you can keep your speed in a comfortable range. We’re using the same concept for a building. If, during an earthquake, the building shakes too much, we would like to brake it using a friction device."
A prototype damper has been tested on a quarter-scale building structure inside a three-story high-bay structures laboratory on campus, Chen says. "My goal is to build and test a 10-ton, full-scale damper in the near future, which can be used to mitigate seismic responses of actual buildings," he adds.
In a mathematical study, Chen found that a 20-story building would need more than 80 block-sized dampers placed between floors. A V-shaped bracing support would be needed between each floor to keep the building stable.
During an earthquake, sensors embedded in structure members would measure the amount of the building’s movement. If the motion is outside the acceptable limits, a computer would send a signal to a piezoelectric actuator damper a device that generates a counter-earthquake force when an electrical charge is applied. Once the motion was reduced, the damper would be lifted to allow the building to finish shaking at a much lower vibration level.
The piezoelectric actuator dampers can adjust or adapt to various responses, unlike the passive visco-elastic dampers used in the former World Trade Center to reduce the amount of swaying from high winds.
"The former World Trade Center had more than 20,000 visco-elastic dampers in it," Chen explains. "But once visco-elastic dampers are installed, they are fixed. If a wind comes much stronger than the designed value for the damper, the dampers won’t be able to provide the additional help needed because there’s no intelligence involved."
For the past five years, Chen’s work has been supported through a $330,000 CAREER award from the National Science Foundation. The CAREER program supports the early career development of teacher-scholars who are to become academic leaders.