A steel bridge hanger with three fatigue cracks was monitored for acoustic emission (AE) using combined source location, strain gauge monitoring, and waveform analysis. AE activities from all three cracks were clearly identified and classified as crack growth or noise signals using location, strain magnitude, position on strain cycle, and uniqueness of waveforms as the primary criteria. A vast majority of AE from the cracks was found to be due to crack face rubbing and the crushing of corrosion products between the crack faces while limited crack growth emissions were detected. Results from laboratory tests on A588 compact tension specinlens under variable-amplitude tension-tension fatigue loading were used to aid in interpreting AE data from the hanger. Crack growth AEs from these tests were detected only on overload cycles mostly above 92% of the maximum load while AE due to crack face rubbing occurred throughout the load cycle.

The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a "clamp-on" strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of 1-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.

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