Fast Repair with Strand Tendons on the Plymouth Avenue Bridge
Following a 2010 routine inspection, the bridge was closed after corroded post tensioning tendons were discovered. Upon further evaluation, it was later determined that the post tensioning tendons had corroded due to a failure of the bridge’s drainage system. DYWIDAG has been awarded the supply and installation of the tendons used to repair the bridge.
Context
The Plymouth Avenue Bridge is a four lane, twin segmental box girder bridge carrying Plymouth Avenue over the Mississippi river on the north side of Minneapolis, Minnesota. The bridge has a total length of 287.4m (943ft), with the longest span reaching 43.6m (143ft). Built in 1983 using form travellers, it was the first segmental cast in place bridge in Minnesota.
Solution
The drainage pipes are located inside the box girders. Due to the failure, deicing chemical leakage accumulated in the interior of the box, thereby corroding both the rebar and the post-tensioning tendons in the structure’s bottom slab. A long-term and economical strengthening solution was needed to restore the bridge to service as quickly as possible. Corven Engineering proposed to install an additional external multistrand post tensioning system inside the hollow box girders.
The General Contractor hired DYWIDAG to provide a suitable post-tensioning system and to support the jobsite with engineering services and installation techniques. 5 new Type 12-0.6" DYWIDAG Strand Tendons were installed as external tendons in each hollow box girder. Each tendon was anchored in new concrete blisters created at the ends and running through new concrete deviators cast at the appropriate box floor slab locations.
The design required the steel embed ducts to deviate in two planes, creating difficulty in obtaining field measurements for the production and installation of these components. In addition, the concrete anchor blisters newly installed at the upper regions of the girder interior for anchoring the tendons left little space to maneuver a post-tensioning jack into position. Consequently, DYWIDAG was tasked with developing a unique stressing protocol for stressing each strand individually using monostrand jacks.
The special stressing system developed by DYWIDAG for accomplishing the tensioning work proved very successful so that the work was completed safely, on budget and within the limited schedule.
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