Acoustic Emission Monitoring of Fatigue Cracks in Steel Bridge Girders

Project summary:

Cracks in fracture critical members pose a serious threat to a bridge structure. If these members fail in fatigue, a catastrophic collapse of the structure is possible. However, many cracks found in bridges are self-extinguishing - they grow far enough in a given direction to relieve the overstress in the member. These types of cracks do not endanger the structure. Acoustic emission monitoring can be employed to determine if a crack is self-extinguishing or not. Members with cracks that are not self-extinguishing, must be retrofit to ensure the safety of the structure. One such method of repair is to bolt angle splices to the web. The effectiveness of this repair method will be evaluated by examining the stress range after repair in the cracked member and in the angle splice. The objectives of this project will be to determine, by employing acoustic emission monitoring, if previously identified fatigue cracks in steel bridge girders are self-exhausting fatigue cracks or are growing fatigue cracks and by performing standard strain measuring techniques, the effectiveness of the splice retrofit.