NDT Applications Utilized in Hoan Bridge Failure

摘要

The Hoan Bridge, Located in Milwaukee Wisconsin failed on December 13, 2000. The bridge is approximately two miles long and has and ADT of about 32,000. It is a major interstate artery in downtown Milwaukee. The bridge has three 12' lanes of traffic in each direction. Each set of lanes has a 10' and 12' shoulder. The bridge consists of three different girder geometry's. There is an arch span over the main harbor channel, three girder approach spans adjacent to the arch, and the lower approach spans are multi-girder. The bridge opened to traffic in 1978. The failure occurred in the three girder portion of the structure. There is approximately 1,800' of three girder span on each end of the arch span. Two of the three girders in the longest three girder span failed completely and the third girder had three significant cracks. The span could not be saved and had to be demolished. An extensive failure analysis was performed by a team of experts from Lichtenstein Engineers, Lehigh University, and Federal Highway Administration. Also contributing were Michigan Tech University with a weigh-in-motion study and Northwestern University with strain gauge studies. The failure occurred at a lower lateral connection plate and was determined to be a brittle fracture with no fatigue indications noted in the failure. It is an un-inspectable failure. The steel girders are fabricated from A36 web material and A588 flange material. The material properties of the existing material would meet current zone 3 non-fracture critical requirements. The failed spans on the Hoan Bridge are not fracture critical but were inspected as such by Wisconsin DOT. A temporary retrofit was performed on the adjacent three girder spans and the bridge was opened up to a single lane of traffic in each direction, 4 ton maximum load, in February 2001. The Hoan Bridge was completely rehabilitated and was placed back into full service in October 2001. Nondestructive testing was performed at approx, 2,500 locations for the temporary retrofit and for the permanent repair. Nondestructive methods utilized were visual, video taping, ultrasound, magnetic particle, acoustic emission, and strain gauges.