Sensor "Memory" System: Faster, More Precise Damage Assessment
A new sensor system being developed at the University of Missouri-Rolla may help get rescue personnel to the scene faster the next time a tornado or terrorist damages a bridge or other structure because of its ability to “memorize” the location of the damage.
Unlike all other infrastructure-embedded sensors, which reset following the disaster, the distributed cable sensors under development at UMR 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.
“This is critical to making a rapid decision for emergency responses and evaluations immediately following the catastrophic event,” says Dr. Genda Chen, associate professor of civil engineering at UMR. “The current practice requires sending an engineer inspector to 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’s 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 many 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 inspection, when they opened up the structure joint. They had to open up every structure since then.”
Researchers tested a prototype cable sensor on a fifth-scale reinforced-concrete column inside a three-story high-bay structures laboratory on campus before installing the system in a Missouri bridge in fall 2003. Made from a Teflon-insulated copper wire surrounded by a solder-coated steel spiral layer, the cable sensor can be embedded in lengths of up to 100 feet.
Working with Chen on the project are Dr. David Pommerenke, associate professor of electrical and computer engineering at UMR, and Dr. James Drewniak, director of the UMR Materials Research Center and a professor of electrical and computer engineering. The team has received $240,000 over a period of three years from the National Science Foundation to support the research.
Based on the research team’s success, the New York Department of Transportation has asked the group to develop a pressure sensor that can monitor how much load a bridge bearing can carry.
In addition, the California Department of Transportation would like the team to use the sensor system to measure the performance of piles. “With this system, they could tell what’s going on underneath the ground – where you can’t see anything,” Chen adds.
Chen and his research team are also looking to develop a way to network the cable sensors for use in buildings.