The Diefenbaker Bridge is a 7-span, 304m (1000 ft) long, fracture critical steel structure crossing the North Saskatchewan River in Prince Albert, Saskatchewan, Canada. The bridge is an important regional crossing and was constructed in 1959. On August 29th, 2011 a major fracture was found in one of the two steel girders of the southbound bridge. The crack extended from the bottom flange through the web of the girder, nearly full height of the girder and is one of the largest in-service bridge fractures to occur in Canada. The southbound structure was immediately closed and traffic was diverted to the parallel northbound structure. Full collapse was averted and there were no reported injuries. This paper describes the resulting fracture investigation and major structural repair implemented on the structure. Based on this investigation, the structure is believed to be susceptible to constraint-induced fracture (CIF). To repair the structure, the fractured bridge was supported on steel towers constructed on a river berm and raised to its original position. A section of the girder was then cut out and replaced with new steel and connected to the temporarily supported horizontal and vertical bracing. This intricate procedure required innovative engineering and construction procedures. Once the structure was reopened to traffic, attention was turned towards rehabilitation including retrofit methods to mitigate approximately 160 CIF susceptible details in the southbound and northbound structures. Construction consisting of retrofit of CIF details along with rehabilitation of joints and rocker bearings was completed between May and November, 2012. The methods used to retrofit the CIF details are described along with lessons learned. The paper will be of interest to bridge owners, designers, and anyone involved in inspecting and maintaining bridge infrastructure.
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