10th Avenue NW Bridge Repair

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Status

Completed October 2016

10th Avenue NW Bridge Vicinity Map

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Background and History

The 10th Avenue NW Bridge was originally constructed in 1931 and is a two lane, 310 foot long concrete bridge built into the side of a hill along a ravine. The bridge was retrofitted in 1996 to address several deficiencies. Despite these measures, the bridge is classified as functionally obsolete due to the narrow deck width and has experienced deterioration of several components. Due to these deficiencies, the bridge is currently rated at 51.3 (bridges less than 50 should be considered for replacement).

The bridge as it currently exists has many concrete elements that are spalled or cracked, exposing reinforcing steel. The bridge railing is in poor condition and presents a hazard for vehicles due to the steep slopes. There are signs of soil sloughing around the foundation of the bridge. One footing has been exposed. The bridge was reinforced with wood supports to retain some of the soil and prevent cave-ins at the sidewalk above. A load rating determination has been recommended by King County to reassess the load carrying capacity of the bridge.

The bridge was evaluated in the spring of 2014 to update the bridge rating, reassess the load carrying capacity, evaluate the options for rehabilitation or replacement, and determine the potential for grant funding.  The evaluation conducted reduced the bridge rating from 51.3 to 43.7 (out of a rating of 100).  However, the evaluation did find that the bridge continues to be functionally obsolete (does not meet current design standards for bridges) but remains structurally sufficient (not in overall poor condition and able to carry modern design loads).  Since the bridge was not found to be structurally deficient, it does not qualify for funding assistance.  

Given the current status of the bridge, the evaluation recommended a series of repairs that will extend the life of the bridge.  Staff will be proceeding with a recommendation to the City Council to design and construct the recommendations for repair.

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