The Government of Yukon commissioned Ausenco Sandwell to evaluate the seismic performance of the Donjek River Bridge on the Alaska Highway. The Donjek River lies in a flood plain, which is fed by the Kluane Glaciers, and transports large quantities of sediment and debris. The bridge consists of eight 200 ft span steel through-trusses supported on steel rocker bearings on lightly reinforced concrete piers. The bridge, constructed in the 1950s, is in a region of relatively high seismicity, where the peak firm ground acceleration is 0.22g. Ausenco Sandwell selected the latest site specific Uniform Hazard Response Spectrum (UHRS) as a basis for the firm ground input motion.

Assessment techniques including elastic spectral analyses, nonlinear time histories and nonlinear pushovers were used to evaluate the structures. The bridge was found to have a number of seismic deficiencies, particularly in the piers and bearings. The site demonstrated significant susceptibility to liquefaction. In addition, the bridge foundations were found vulnerable to scour from large glacial outflow conditions. The evaluation included assessing the bridge to carry modern live loads. Several scenarios for live load evaluation were considered which included the possibility of installing a concrete overlay and performing a detailed inspection. A report detailing the retrofit concepts, retrofitting costs, rehabilitation costs and recommended load ratings was subsequently prepared.

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