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Updated 2:30 PM July 7, 2005




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Wireless devices help sense cracks,
assess damage in buildings, bridges

Imagine a bridge that can self-diagnose cracks or a building able to assess its own health after an earthquake without any help from humans.

Networks of wireless sensors embedded in buildings, roads, bridges and other infrastructure hold that promise. In the first large-scale field test of the technology U-M researchers, in conjunction with Stanford University and the Korean Advanced Institute of Science and Technology, found that a wireless network of 14 sensors performed as well as traditional cable-based monitoring systems.
(Photo by Jerome Lynch)

To reach this conclusion, both tethered and wireless structural monitoring systems were tested simultaneously on the Geumdang Bridge in Icheon, South Korea, says Jerome Lynch, assistant professor with appointments in civil and environmental engineering, and electrical engineering and computer science. The results will be presented later this month at the International Conference on Structural Safety and Reliability in Rome.

There are several reasons scientists are trying to develop wireless networks to replace traditional cable-based monitoring methods used to assess the health or safety conditions of infrastructure, Lynch says. Wireless sensors are potentially less expensive, more functional, and take less time to install and maintain.

For instance, the wireless network on the Geumdang Bridge took just one hour to install, compared to an entire day for its cable-based counterpart, Lynch says.

The battery-powered sensors are about the size of a deck of cards and cost about $100 each or $1,400 for the entire system, compared with $10,000-$15,000 for the cable-based system.

Eventually, wireless monitoring systems could render obsolete the practice of sending engineers inside potentially unsafe buildings to assess damage after earthquakes, Lynch says. "You will be able to have untrained maintenance people install the sensors in all types of infrastructure systems," he says.

The sensors also can ferret out damage that isn't visible. For example, special sensors that emit electricity into structures can detect interior damage if an invisible internal crack disrupts the electrical current, Lynch says.

In the Geumdang experiment in late December, researchers took measurements for three days, recording the vibrations made by different-sized trucks driving over the bridge. Each sensor processes data locally and the unit communicates a few key data points to a central computer to reduce data glut and save battery power.

"If you want the system to determine its health, you want it to be self-sufficient computatively," Lynch says. The Michigan Department of Transportation (MDOT) will use the same set of wireless sensors this summer to measure potential crack patterns in a slab of Engineered Cement Composite (ECC), a new civil engineering material designed at the College of Engineering.

MDOT will use the ECC to retrofit a section of the Grove Street bridge deck over I-94 in Ypsilanti.

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