An experimental acoustic emission (AE) device, the GARD Acoustic Emission Weld Monitor (AEWM), has been field tested on six bridges during this study. In addition, the device was used to test three other bridges under separate contracts from state highway agencies. The device was evaluated to determine if it could detect fatigue-crack growth on in-service steel bridges.

The AEWM employs a proprietary three-step model (filter) to reject noise-related AE activity and detect and locate defects subject to varying stress conditions. The unit uses built-in microprocessors to compare incoming data to the model. If defect-related AE activity is detected, the AEWM will notify the operator and locate the defect in relation to AE sensors placed on the test specimen.

The device rejects high background noise rates typical of bridges and detects and locates AE activity from known defects such as cracks and subsurface flaws. The AEWM functioned properly in every field test situation to which it was applied.

The device has demonstrated capability to perform AE tests on in-service bridges. It may be used to detect hidden defects or to assist in making repair decisions concerning detected discontinuities. The AEWM and AE testing have the potential for low-cost inspection of critical bridge members.

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