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’Smart’ Bridge May Help Engineers Build Better Structures

Wed December 17, 2003 - National Edition
CEG



STAR CITY, WV (AP) Samir Shoukry works his way from the belly of the bridge to the slippery green rebar of its snow-covered back, talking about the 1,000-ft. (304.8 m) span over the Monongahela River as if it were alive.

And in a sense, it is. Though still unfinished, the Star City bridge is already loaded with 770 finely-tuned sensors, 28 data-collection boxes and a central unit called the brain. Together, they make up what Shoukry said is the smartest bridge in the world.

"Smart" bridges and roads that communicate with their makers through built-in sensors are becoming more common as engineers worldwide try to determine whether long-held construction assumptions are correct or whether there are better ways to build.

Several states have smart structures, and at least one span –– Florida’s Sunshine Skyway Bridge between St. Petersburg and Bradenton ––┬ámay have more sensors than Star City. "But if we’re talking about density," Shoukry said, "this would be the most. This is one of the most extensively instrumented bridges in the world."

The sensors measure minuscule, visibly undetectable changes in steel girders and support structures, in piers and abutments, in concrete and rebar. If a crack is about to occur, the sensors should detect it. If settling shifts the inclination by as little as one-millionth of a degree, that will be recognized and recorded.

"Intelligent structures are like the human body. It’s provided with millions of sensors that send signals to the brain when you’re in pain," said Shoukry, an engineering professor at West Virginia University.

"Basically, I want the structure to tell me where it hurts so I can make a quick response to the cry and come and repair it. We are providing the structure with the ability to have input,’ he said. "It’s like looking into the flesh and bones.’

The state Division of Highways is spending nearly $18 million on the bridge and decided to invest an additional $471,000 in Shoukry’s project to learn more about what causes stress and deterioration of expensive infrastructure.

The information may help the state make smaller, less costly repairs while problems are still manageable, Deputy Commissioner Norman Roush said.

"We wouldn’t be surprised to see people coming from all over the world to see this and use it," he said. "I don’t know of anybody worldwide who has done this much gauging and metering on a bridge."

Star City is West Virginia’s fourth and largest smart structure. Shoukry and his team of graduate students also installed sensors on a bridge deck in Evansville, Harrison County, in concrete pavement at a DOH facility in Monongalia County, and in a 450-ft. (137.2 m) section of the Corridor H highway near Elkins.

Roads and bridges face different problems. Roads have solid support and mainly move up and down as the load on the surface changes. Roads also can shift near the edge of the pavement, and inadequate drainage can affect their performance.

Bridges, meanwhile, are not rigid. "They bend, act and react under loads," Roush says. "Their actions are working with and against each other.’

Already, West Virginia’s demonstration projects have yielded results. On the Corridor H project, the state learned that concrete slabs 20 ft. (6.1 m) long are prone to crack, while those 15 ft. (4.6 m) are not. The state of Pennsylvania, which had problems with cracks on Interstate 81, is changing its slab length based on those results, Roush said.

Smart projects also may help engineers determine whether planning for worst-case scenarios has resulted in overdesigning.

Perhaps some assumptions are wrong, Shoukry suggests. Maybe steel and concrete don’t need to be quite as thick as the engineers think. If data were to prove that, designs could be more efficient and costs could be held down without sacrificing quality or safety.

Shoukry’s team has set up a weather station and two small sheds as a field laboratory at the bridge, just a mile or so from the engineering school. They collect environmental data 24 hours a day and readings from the bridge sensors every 20 minutes.

That makes for a unique lab, said David Martinelli, chairman of WVU’s civil and environmental engineering department.

Rather than read about devices in books, civil engineering students will be able to study real-world functioning on structures, Martinelli says. Mechanical and aerospace students will learn how to install instruments and analyze data. Computer science students will be able to develop and test better types of sensors and design databases for sharing the findings.

Smart structures are the way of the future, Shoukry says. The technology is there, and it only makes sense to use it.

"The cost is like medical insurance," he said. "You pay whether you use it or not, but it pays off when you get sick.’