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Posted 11 August 2016
Originally constructed in 1928, the Dakota Creek Bridge is a two-lane, 335-foot-long bridge just south of Blaine in Whatcom County, Washington. It was part of the old Pacific Highway, which was regarded as the most important north-south highway in Washington at the time, connecting from the Oregon border up to Canada. (Later renamed Portal Way because it was used by travelers to reach the Peace Portal Arch at the Canadian border.) However, in 1963, the Ferndale-to-Dakota Creek segment of Interstate 5 (I-5) officially opened; as a result, the older highway became an auxiliary route that was used less frequently.
As part of one of the key routes in Washington State’s original highway system, Dakota Creek Bridge is eligible for listing on the National Register of Historic Places. When Whatcom County identified structural and seismic deficiencies at the bridge, the County sought funding to preserve this historically significant structure. Additionally, this route would be critical for the mobility of freight into Canada in case of an emergency shutdown of I-5. Therefore, the project goal was to design retrofits that would bring the bridge up to date on current standards and extend its service life.
As civil/structural and seismic consultant on the team, BergerABAM provided engineering services to identify and design the bridge seismic retrofits and provided support during construction. The analysis and design was done following methods outlined in the Federal Highway Administration’s Seismic Retrofit Manual for Highway Structures, and supplemented with the AASHTO Guide Specifications for LRFD Seismic Bridge Design.
The project faced several challenges during construction. For instance, the bridge is located at the mouth of Dakota Creek near Birch Bay, home to many fish species, including three on the Federal Endangered Species list. This limited the construction schedule to a short in-water work window between July and October. Also, the site is heavily influenced by tidal action. During construction, the water level would fluctuate between a few feet to over 12 feet at times at the site, creating less than favorable conditions to work on the lower sections of the piers.
Despite the difficult work schedules and conditions, including in-water work, work over water, restricted work space underdeck, and night shifts, construction was completed in approximately six months and the final construction cost was under budget. The project was recently honored as the recipient of the American Public Works Association, Washington Chapter, Project of the Year in the category of historical restoration/preservation.