Rutgers Research Uses High-Tech Approach To Study U.S. Bridge System

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By Alex Padalka

A final report is pending on how technological advances can aid in the diagnosis, and ultimate rehabilitation, of the nation’s vast bridge network, based on an exhaustive study led by Rutgers University in New Jersey, involving teams from three continents.â?¨â?¨

The U.S. system includes some 600,000 bridges. This number does not include signature structures such as the Golden Gate Bridge, but it includes all the nameless small overpasses and short-span structures most commuters rely on daily. ��

This March the Federal Highway Administration (FHWA) reported that one out of nine bridges, or close to 70,000 structures nationwide, are "structurally deficient." Fixing them, according to an FWHA study in 2009, is expected to cost $70.9 billion, but only $5.2 billion is available.��

Since June 2010, the Rutgers’ Center for Advanced Infrastructure and Transportation (CAIT) has been engaged in the International Bridge Study: a "round-robin" analysis of one nameless steel stringer bridge on Route 23 near Wayne, N.J.â?¨â?¨

The CAIT project invited teams with disparate approaches to diagnosis. It pinned the Americans-who have little time to give to any one individual bridge-against teams from Japan, where it’s reasonable to spend two hours measuring just one bridge bearing, according to Dr. Franklin Moon, associate professor of Civil, Architectural, and Environmental Engineering at Drexel University. â?¨â?¨

Teams also came from Switzerland, the U.K., Austria, China, Korea and Canada. Up to 55 engineers worked on the project throughout the year, using Nondestructive Evaluation (NDE) methods, sensing technologies, information technology, and simulations. ��

The use of NDEs in particular can provide much better information at a significant reduction in cost, researchers say. The current method for testing for structural rigidity, for example, involves taking one to four drilled-out cylinders from the entire length of the bridge to a lab, and crushing them to measure the forces. A $30,000 machine can do 1,000 to 2,000 NDE samples in about half a day and eliminate the guesswork whether those 4 samples are indicative of the entire bridge, according to Dr. Nenad Gucunski, director of CAIT Infrastructure Condition Monitoring Program and chair of the Rutgers Dept. of Civil and Environmental Engineering.��

The $100,000 "Stepper" allows testing for density inconsistencies inside decks through impact echo recording. The job is currently done by literally dragging a chain across the deck and listening for changes in echo, and by hammer-sounding. While no doubt cheaper, the chain method can not detect early deck delamination, not to mention the inaccuracy of the readings given traffic noise.��

The main concern, however, is to come up with information that the DOT would be able to accept and use economically, according to Dr. Moon.��

"When these technologies became available in the late ’90s and early 2000s, [their designers] were saying, ‘These things are going to fix all your problems,’" Moon said. "There’s a great deal of skepticism [from the DOTs]-we’re been sold before, and we never saw any value. What I really hope for this project is that we begin to bend that curve back around. Yes, the technology is not the solution to all your problems, but yes, it is tools for the toolbox that makes sound and engineering sense."

��According to a preliminary report released in late June by CAIT, the nameless bridge "was deemed safe by all the researchers. Issues noted were fatigue cracking, issues with bearings, water infiltration, and presence of a gas line under the bridge that is "potentially problematic." However, most of the discussion focused on the excessive vibrations that were measured in ambient and induced load tests. High vibration amplitude and frequency of excitation could lead to accelerated deterioration, especially if trucks are creating or adding to the resonance-a vibrational "snowball effect"-which may worsen existing fatigue cracks and other problems. ��

The atypical vibration on the bridge could also account for pockets of delamination found in the deck, which Gucunski says is often seen on these kind of bridges.��

The CAIT team will release a final report outlining its findings and comparing all the different approaches to testing in August.

Fonte: Estadão


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