The Plymouth Avenue Bridge carries local traffic over the Mississippi River in downtown Minneapolis. The cast-in-place post-tensioned concrete box girder bridge was completed in 1983 and replaced an iron truss bridge built in 1886. Twin box girders carry two 12′ lanes of traffic in each direction. In 2010, during a routine inspection, tendon corrosion was found. Corven Engineering was hired to assess the condition of the post-tensioning system and the integrity of the bridge; and develop a design to restore the integrity of the bridge. The 934′ long bridge consists of two connected box girders with span lengths from 120′ to 260′. The total width is 75′-6″ and the box girders vary in depth from 10′ to 13′. The approach spans were cast-in-place on falsework and the center span was cast segmentally using form travelers advanced from each pier. All post-tensioning tendons are internal to the concrete.
Corven Engineering performed in-depth inspections to determine the condition of the bridge’s post-tensioning system. Structural analyses, replicating the construction of the bridge were performed to determine the current state of stress within the bridge. The results of inspections and structural analyses were used to develop detailed designs, plans and specifications for the rehabilitation of the bridge. During construction, Corven Engineering provided on-site assistance to address varying conditions as they were encountered. The project concluded with a load rating of the bridge in its as-built rehabilitated condition.