The new 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," explains Genda Chen, associate professor of civil engineering at UMR. “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.

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.

Helping first responders

Chen’s research may also help get rescue personnel to the scene faster the next time a terrorist or natural disaster damages a bridge or other structure. His new sensor system could “memorize" the most severe damage that occurred during a prior catastrophic event, allowing for an immediate assessment of the structure’s performance and integrity. Following a disaster, current infrastructure-embedded sensors can again pick up damages due to a more severe earthquake in the future.

This is critical to making a rapid decision for emergency responses and evaluations immediately following the catastrophic event," Chen says. “The current practice requires sending an engineer to inspect every bridge along the emergency vehicle route to get into the striking area to rescue people. In the future, you could use a hand-held piece of equipment to detect whether there is damage or not. We can detect the location and severity of damage areas within two inches."

The same distributed sensor system can also find cracks and other damage not seen during visual inspection, Chen says. “The problem with visual inspections is that much of this damage in columns can’t be seen after the earthquake or disaster is over," Chen explains. “Cracks on the columns are typically closed immediately after an earthquake due to gravity loads. You won’t be able to see them with your eyes – but this sensor can pick them up."

The distributed sensor system could provide a more accurate damage assessment, Chen says. For example, when the 1994 Northridge earthquake shook residents of the Los Angeles area, it also caused widespread damage to sections of major freeways, parking structures and office buildings. However, a visual inspection found some areas did not appear to be affected by the strong seismic movements.

“Most of the steel-beam column weld areas were cracked severely," Chen says. “But you couldn’t see that from the outside because those areas had a fireproof cover and architecture covering the bare steel material. People didn’t know about the cracks until after in-depth inspection, when they opened up the structure joint. They have had to open up most structure joints since then."