Infrastructure Technology Institute
The ITI Research Engineering Group (REG) continues to be a leader in the area of practical applications of acoustic emission (AE) testing to steel highway bridges. AE testing employs special transducers to detect ultrasonic noises emitted by engineering materials under stress. In the experience of the REG, acoustic emission is particularly useful as a means to locate and characterize cracks and other defects in steel bridge details. By deploying an array of transducers around a known defect, or in a high-stress, fracture critical, or other area where a defect might be suspected, it is possible to locate an active crack or quantitatively determine whether a crack is actively growing or has been extinguished.
In October, 2008, members of the REG attended the 51st meeting of the Acoustic Emission Working Group, held in Memphis, Tennessee. ITI researcher David Kosnik presented his award-winning extended abstract, “A New Approach to Acoustic Emission Testing of Difficult-to-Reach Steel Bridge Details,” which documented the REG’s experience in AE evaluation of a crack in a fracture-critical steel bridge member. Previous AE work on highway bridges has been contingent on favorable field conditions – particularly access, weather, and power. To overcome these limitations, the REG developed a weatherproof enclosure and robust communication and control schemes to allow the collection of many hours of data from a detail that was accessible only by lift bucket during limited lane closure windows. The data showed that the crack was not growing; corroborating results were obtained from other, more traditional non-destructive evaluation techniques. In addition, the AE data indicated an additional defect near the crack. The presence of this defect, which is believed to be a slag inclusion, was confirmed by radiography, further validating the utility of AE testing of steel bridge details.