Saturday, November 24, 2007

Engineer receives patent for laser testing bridge's structural health

Test by Tech engineer could help revent disasters such as the one in Minnesota

Argen Duncan El Defensor Chieftain Reporter

A New Mexico Tech engineer has received a patent for a system that could evaluate a bridge's structural health more accurately and quickly than current methods, possibly helping prevent disasters such as this summer's Minnesota bridge collapse.

Assistant Professor of Mechanical Engineering Ashok Ghosh has invented a laser-based testing system that can check a bridge's safety while vehicles use the structure.

"Traffic will never notice this is getting tested right now," Ghosh said.

A laser gun mounted on one of the bridge's unyielding supports shoots a cross-shaped beam to a pixel board attached to a span, or an area between two supports.

The pixel board is wirelessly connected to a computer and registers which pixels the laser beam hits.

The board's movement as vehicles pass allows the laser beam to eliminate different pixels, showing the deflection, or movement, of that span of the bridge.

The system would be on the bridge and collect data for several hours.

Engineers would know from the bridge's design what the deflection should be, and compare it to the data from the laser-based system.

The laser-based system can be used at any time of day instead of only in the morning, as regulations now require for load testing of bridges.

"So that way you have more time to do the test, so you can do more tests," Ghosh said.

Ghosh said his system could allow engineers to test every span in a bridge instead of just one.

The invention could test spans over water, as well as taking less time than some other methods, Ghosh said. The evaluation could also be done remotely.

Ghosh believes bridges should be tested during evening rush hour traffic because collapses, such as the Minnesota bridge failure, often occur then.

"If the traffic is on and you do the test, that is more representative," Ghosh also said.

Ghosh said testing for several hours also gives engineers indications of problems they might not see otherwise.

"And that can be done with this system and within the time that you have," he said.

Ghosh said the laser testing system should have good application. He needs to fine-tune and nicely package it to make it commercially attractive.

Ghosh hopes to get state Department of Transportation funding for the task, but in the meantime, he plans to make a small model with money he already has.

In the future, Ghosh would like to combine the laser system with a system he invented to tests truck weights as the vehicles drive.

The system would sense the weight of trucks moving over a particular place in a bridge and photograph any that were heavier than regulations allow.

Inspectors would receive the pictures and stop only the trucks with the photographed license plates.

Ghosh developed the weighing system in light of the North American Free Trade Agreement because Mexican trucks, which would come over the border due to the agreement, can be significantly heavier than American laws allow.

aduncan@dchieftain.com

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