Profitability through Innovation: Structural Repair of George N. Wade Memorial Bridge, USA
The 6 lane wide George N. Wade Memorial Bridge, over Susquehanna River is an important element of Interstate 81 in Harrisburg, Pennsylvania, USA. The structure is 1,581m (approx. 5,188ft) long and was built between the end of the 60’s and the beginning of the 70’s.
Within the framework of its comprehensive inspection program, the Pennsylvania Department of Transportation (PennDOT) determined that the reinforcement in the pier caps was no longer able to handle the current traffic load of approx. 32,000 vehicles per day. PennDOT contracted the construction company J.D. Eckman Inc. to carry out comprehensive repair and retrofit of the bridge substructure.
The as-advertised contract documents called for external post-tensioning using ten Ø 36mm, GR150 external double corrosion protected (DCP) post-tensioning tendons per pier cap. At the outer side of each of the pier caps, five tendons were to be installed in order to supplement the existing eight post-tensioning bars that had been installed for reinforcement years ago.
DSI presented a technically proven alternative to the general contractor that only required six Ø 46mm, GR150 DCP DYWIDAG Tendons per pier cap. The special solution provided a significant reduction in material and labor costs for the contractor, and ultimately the Owner, PennDOT.
The DSI design included a re-designed end anchorage which facilitated installation. DSI designed rolled (radius bent) steel end cap anchorages that were installed at the ends of the pier caps. Since these anchors are curved, yet the pier caps ends are flat, the space between was filled with an engineered self-consolidating concrete mix to provide proper bearing capacity for the larger diameter bars.
In addition, DSI installed DYNA Force® sensors on the tendons in order to ensure efficient and reliable long-term monitoring, in place of the as-advertised conventional load cells. The DYNA Force® sensors allow for force monitoring of the post-tensioning bars at any point of time with the help of a readout box that captures the data. This technology is far superior to traditional load cell tests and also eliminates the need for lift-off testing, which can be cumbersome and expensive.
The repair and retrofit of the pier caps started in autumn 2010. DSI experts first installed and stressed DCP DYWIDAG Tendons on the 34 pier caps accommodating the northbound lanes of traffic. Afterwards, the bar tendons on the southbound lane pier caps were installed and stressed. Repair and strengthening of the piers will be completed in the fall of 2011.