HOAN BRIDGE FORENSIC INVESTIGATION FAILURE ANALYSIS FINAL REPORT

Abstract

The Hoan Bridge (also know as the Milwaukee Harbor Bridge), opened to traffic in 1974, is located on interstate highway I-794 over the Milwaukee River in the city of Milwaukee, Wisconsin. I-794 is a major commuter route carrying 6 lanes of traffic to and from the city. Eighteen of the bridge spans are steel plate girder spans; the main unit is a three span tied arch crossing the river. On December 13, 2000, cracks were detected in the steel girders supporting one of the southern approach spans. Two of the three girders had full depth fractures, leaving the span near collapse. The entire roadway, both northbound and southbound, was immediately closed to traffic. On December 28, the most critically damaged section of the northbound roadway was removed by explosive demolition. The southbound roadway was re-opened to two way traffic on February 17, 2001, with weight and speed restrictions on bridge traffic. This report summarizes the results of the failure analysis and forensic investigation that was carried out on the three cracked girders from the Hoan Bridge. Valuable insight was also provided by examining cracked surfaces from two other cracked girder webs in the Hoan Bridge Structure. One was from northbound Unit S2A at Panel Point 9 of Girder D. The second was removed from southbound unit S2B at Panel Point 26 of Girder B. These latter crack surfaces were removed during the inspection and retrofit of southbound unit S2B and northbound unit S2A.