Originally created 07/22/02

DOT looks at new test for bridges



Bridges throughout Georgia will soon undergo required strength tests - the result of a new state law that allows heavier truckloads on state routes.

"We're in the process of evaluating a whole lot of bridges," said Brian Summers, of the Georgia Department of Transportation. "A lot of our bridges that were in the marginal area may now require a (load restriction) posting."

The new law, which was passed July 1, increases the acceptable limit for truck shipments from 40,000 to 46,000 pounds per tandem (two) axles.

Officials say the possibility of new load-limit postings on bridges could have a negative economic effect on communities throughout Georgia. Mr. Summers said the postings often are seen as a hindrance by companies looking to locate in areas with easy access for trucks.

"If you have access in and out, it's definitely a plus for a business," he said.

Currently, Mr. Summers said, about 2,000 of Georgia's 6,441 state highway bridges have load-limit postings. He said it's uncertain how many more will be added after the upcoming evaluations are conducted.

But Georgia DOT officials say they are keeping their eye on a new way to monitor bridge strength, now being tested in South Carolina. Officials say it could someday give them more accurate data on the strength of bridges and eliminate the need for some of the postings.

"That's something that we may be thinking about in the future with the recent changes in the load-limit laws that the Legislature just passed," Mr. Summers said. "I'd be interested in seeing any reports South Carolina has on how accurate their tests are."

Currently, bridge inspections in Georgia and South Carolina are conducted visually. The South Carolina DOT is hoping to adopt a new test using stress sensors within six months.

"When you look at the current way DOT rates a bridge, it's based on conservative assumptions," said Scott Schiff, a civil engineering professor at Clemson University who is overseeing the new load test in South Carolina. "We typically underevaluate the strength of a bridge."

In South Carolina's protocol test, a strain gage - a 1-inch-by-3-inch aluminum stress sensor - is attached to a bridge in several areas, typically on the beams underneath the structure. Information is then sent via a wire to a computer. As a bridge flexes when a vehicle passes over it, the sensor bends and creates an electrical charge.

"We're trying to take out some of that estimating and get some hard numbers," Mr. Schiff said.

The new test could uncover evidence that a bridge could hold more weight, Mr. Schiff said.

And more accurate inspections could be a benefit to the economy and state budgets, said Lee Floyd, a bridge-inspection engineer for the South Carolina Department of Transportation.

"You avoid putting a burden on the local economy that way," he said, adding that companies that receive large shipments by truck could then have access to more bridges.

Mr. Floyd said the South Carolina test has been conducted on about four bridges in the Upstate.

"Some of the preliminary results are showing a benefit," he said.

The test also could save South Carolina and other states thousands of dollars.

"We're trying to have them not replace bridges that are still functional," Mr. Schiff said. "And if you can save $100,000 by spending $6,000 on a test and realizing that bridge doesn't have to be replaced, that's worth it."

In the meantime, officials in Georgia say they'll continue putting up postings until South Carolina's technology becomes available to them.

"At some point, we might be able to take down some of the posting signs that we're going to have to put up," Mr. Summers said.

Reach Preston Sparks at (706) 828-3904.



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