Since the Silver Bridge collapsed in 1967, detection of cracks in steel highway bridges has been an area of great concern to the inspection and maintenance community. This research examines the use of eddy currents to detect cracks and fabrication induced flaws in fillet welds on highway bridges. A specially designed commercial probe is utilized to overcome the spatially varying magnetic properties typically associated with the weld area in ferromagnetic steel. Laboratory testing was performed on specimens of structural steel commonly found in highway bridges. EDM notches were detected and characterized through both conductive and nonconductive coatings typical of highway bridges. Field testing was conducted on a painted, high strength welded box girder with fabrication induced defects. Results of the field testing indicated that the method was effective for detecting cracks under paint, and that the cracks could generally be distinguished from other welding defects, such as rollover or undercut. The performance of the specially designed probe is compared with a traditionally designed probe for cracks found on the box girder bridge. Recommendations for the field application of the eddy current method for highway bridges are included in the results.
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