Cushing Bridge is located on a major east-west truck route within the City of Calgary's southeast industrial area and is a vital link in the City and Provincial road network. The bridge consists of westbound and eastbound structures, constructed in 1956 and 1965 respectively. The structures are generally similar and consist of three spans: two anchor spans and a central suspended span. The suspended spans are connected to the anchor spans using pin and hanger assemblies and provide a classic case of a major bridge with non-redundant, fracture-critical pin and hanger supports. The City recognized that the structures were vulnerable to sudden failure of the pin hanger supports and retained Associated Engineering to study, analyze and develop retrofit options to manage the risk by retrofitting the pin and hanger supports. Project scope also included visual inspection and non-destructive testing of the pin and hanger connections and determination of the critical pin and hanger assemblies' residual fatigue life. The study established that the full fatigue design life of the hangers had been exhausted. The study further concluded that vulnerability of the pin hanger connection was exacerbated by corrosion and "freezing" of the pin hanger connections, high stresses in the hangers, and the significant volume of truck traffic on the bridge. The study recommended that best value risk mitigation would be achieved through immediate re-articulation of the existing girders by connecting the suspended span to the anchor spans and creating a continuous 3-span girder system. Retrofit work commenced in the spring of 2011 with completion in the fall.
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