Research
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Drivers using the new Interstate 25 interchange at the village of Doña Ana north of Las Cruces may notice the distinctive art work on the outside of the bridges, but most will be unaware of the cutting-edge technology on the inside of the southbound bridge.
The Doña Ana bridge has a system of fiber-optic sensors embedded in its concrete beams and deck to monitor stresses within the bridge. It’s the latest “smart bridge” project of NMSU civil engineering Professor Rola Idriss.
“Instead of relying on visual inspections of the bridge, the sensors will tell us on a continual basis how much the bridge is stressed and how it is performing under load,” Idriss says.
Idriss and civil engineering doctoral student Zhiyong Liang conducted a series of tests at the bridge to get baseline measurements as a heavy New Mexico Department of Transportation (NMDOT) truck drove across the bridge at different speeds. After the bridge opened to traffic, data is being collected on a weekly basis from computer equipment in a protective cabinet at the bridge site.
The fiber-optic sensors, built into the concrete girders during the fabrication process, send beams of light through the structures, measuring changes in temperature and shape that indicate stress within the bridge. On a shorter-term basis, other sensors in the deck of the bridge are monitoring humidity as the concrete cures.
The technology is not only improving bridge safety, Idriss says, but also “allowing us to get more information on the new materials that are being used in bridge construction. The Department of Transportation is using newer high-performance materials, such as high-strength concrete, and we need to know more about those materials.”
Wil Dooley, division bridge engineer for the Federal Highway Administration, which provided $400,000 for the smart bridge research, says the research is expected to result in more efficient bridge maintenance and design.
“Most of our information on how these new materials perform under load has come from lab tests,” Dooley says. “The reactions under real service is lesser known. What the NMSU technology does is actually instrument these girders and allow us to see how they perform in the field.”
The sensors already have provided measurements of stresses during fabrication and transportation of the girders and during construction of the bridge, he says. Over the life of the bridge, the data collected will show how the materials perform under long-term stress.
“We have multiple girders in a bridge, and when a load is driven across the bridge we assume the load is distributed in a certain fashion,” Dooley says. “This technology tells us exactly how the load is flowing through the bridge to its foundation. All this information is presented to AASHTO (the American Association of State Highway and Transportation Officials). They maintain the bridge design codes, so research like this is instrumental in making changes to those codes.”
Gilbert Clemente, project manager for NMDOT, says the smart bridge technology will improve preventive maintenance and extend the life of the bridge.
The bridge is over NM-320 (Thorpe Road) at Exit 9 north of Las Cruces. Jim Camp, state bridge engineer for NMDOT, says it is the third smart bridge to result from Idriss’ research, and it uses the most advanced sensor technology. The other projects are an Interstate 10 bridge at the Main Street interchange in Las Cruces and an Interstate 40 frontage road bridge over the Rio Puerco west of Albuquerque.
“I don’t know of any other state using fiber optics in this way,” Camp says. The bridge features art work by Jenny Carbajal of Doña Ana. On the walls of the bridge are relief sculptures representing Doña Ana, the historic figure for whom the village and the county were named, and also depicting the region’s Spanish, Indian and Mexican influences. The walls along the underpass display wild horses that appear to be running with the traffic.