Millar Street Bridge

Years of rain and weather caused the existing timber bridge on Millar Street to reach the end of its service life. Shearer Design was contracted by the City of Ketchikan to provide an inspection, then any subsequent repair / replacement design. An inspection team was established, and Shearer Design compiled the field data into a bridge inspection report which included a repair/replacement analysis.

Due to the high number of bridge elements in poor condition, a quick repair was not feasible, and the bridge had to be closed all vehicular traffic. A complete closure for an extended period of time would obviously be a large inconvenience to local residents, so Shearer Design worked quickly with the City of Ketchikan to secure the most cost effective temporary bridge for the location.

The replacement bridge was constructed out of prestressed concrete voided slab girders with an HMA overlay. This superstructure system provides a much longer service life compared to the original timber, especially taking into account Ketchikan’s marine climate. Because of the limited access to the site, each structural component was sized to facilitate transport to the site.

One of the greatest challenges on the project was in the design of the substructure. The bridge is located in a narrow ravine where the bedrock is covered by a layer of overburden with varying thickness. Throughout construction, Shearer Design provided quick and effective modifications to the bridge’s foundation elements when field conditions changed as overburden was excavated.