a highway tunnel photo from FHWAs "Public Roads" magazine

Acoustic Detectives Find Signatures of Loosening Bolts

A research paper being presented next week at the Acoustical Society of America's 157th Meeting in Portland, Ore., will detail preliminary results of work by Boise State University mechanical engineer Joe Guarino and colleagues that may detect loosening bolts in a built structure. Such an early warning system might prevent incidents such as the 2006 fall of concrete panels inside Boston's Big Dig tunnel, caused by faulty epoxy that allowed bolts in the tunnel's ceiling to work loose. The meeting will take place May 18-22 at the Hilton Portland & Executive Tower in Portland.

Guarino, Ph.D., P.E. ([email protected]), a faculty member at the Boise State University Center for Orthopaedic and Biomechanics Research, is scheduled to present "Acoustic detection of bolt detorquing in structures" at 10:30 a.m. May 20. He'll describe the BSU team's analysis of the varying sounds made by vibrating bolts and how certain frequencies in the noises could be monitored to check the health of bolts in buildings, bridges, and tunnels, according to ASA.

The team uses a full-scale structural model of bolted steel beams and girders, tapping the steel with a hammer as bolts are unscrewed to various degrees and recording those sounds with an electronic stethoscope. "Any slight relaxation in a joint can change the way it vibrates," Guarino said. A pattern detection technique named continuous wavelet transform indicates the signatures of unscrewing may be found in certain mid-to-high frequencies. ASA said Guarino hopes to take the research into the field. "If we're successful, this could lead to implanting permanent, inexpensive accelerometers that could monitor joints continuously," he said.

An abstract of Guarino's presentation is available at this site. For the meeting's full program, visit this site.

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