Author(s): C. D. Smith
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Abstract: In 1964 as part of a redevelopment program for downtown Saskatoon, the City acquired from the Canadian National Railway the six-span railway bridge over the South Saskatchewan River. The site was to be used for a new traffic bridge connecting the Idylwyld Freeway to the downtown core. In order to make room for a traffic flow interchange at each end of the bridge, it was necessary to shorten the length of the bridge from 294 m to 183 m. One suggestion was to replace the end spans with approach fills, and construct a new six-lane traffic deck on the existing piers. This would reduce the original six spans to four. A second suggestion was to construct new piers but with only three spans instead of four. Although there was never any trouble with ice at the existing CNR bridge, concern was expressed that the proposed reduction in the opening would increase the risk of ice jamming at the bridge during spring breakup. A model investigation was commissioned to assess this risk. This paper describes the design, construction and operation of the distorted fixed-bed ice flow model, and analysis of the results. The model covered a 2 km reach of the South Saskatchewan River upstream and downstream from the bridge site. Ice floes were simulated with paraffin blocks. It was found that the four-span proposal would not pass ice as well as the original six spans of the existing bridge. However, the capacity of the three-span bridge to pass ice was markedly superior, and pointed out that use of a large centre span would then compensate for a reduced total span. For this and other reasons the three-span proposal was accepted, and the bridge constructed accordingly. In 15 years of operation since construction ice flow has been passed without incident.
Year: 1981