Infra-red thermography systems that have been developed over the last few years offer great potential to locate and discover flaws in steel highway bridge structures at a relatively early stage in their development. Under ideal conditions, the use of infra-red instrumentation should allow bridge inspection personnel to rapidly scan the structure and determine if a potential structural problem has developed. If a problem spot is located by the infra-red camera, then the trouble spot can be examined carefully to determine the need for corrective maintenance. The primary purpose of this research study is to evaluate the accuracy and reliability of sensitive infra-red equipment for detecting fatigue cracks in steel highway bridge structures and components. The performance and sensitivity of one particular infra-red system was explored by conducting tests on two different specimen types in the laboratory, followed by a check of the equipment under field conditions. Crack detection sensitivity in the laboratory was evaluated using a center-hole test coupon geometry as well as a welded attachment plate detail. The test samples were subjected to cyclic loading to initiate and propagate a fatigue crack. Control variables for the infra-red system were then varied to evaluate the optimal conditions. The field tests were conducted to assess the equipment limitations and performance under field conditions. The detail inspected involved a vertical plate that was welded to the web of a beam member and used to attach transverse diaphragm cross-frame members; the diaphragm connection plate was selected for inspection because it was known that fatigue cracks had developed at the end of a number of the vertical plates. It was found that infra-red inspection could be used successfully to detect fatigue cracks in steel bridge members and components if the crack had propagated through the thickness. Consequently, the crack size that could be reliably and consistently detected was not significantly different from that which could be detected from a careful visual inspection. Moreover, a number of difficulties were encountered when using infra-red inspection in the field. Limitations were encountered in the field related to mobility of the equipment, calibration requirements, operator skill level required, and the variable effects of environmental factors that influence the detection capabilities.

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fatigue crack, inspection, nondestructive evaluation (NDE), infra-red thermography, thermal profile, steel, bridge, SPR-2203

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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