The Huey P. Long Bridge has spanned the Mississippi River and served the New Orleans area since 1935. A unique structure, this bridge not only carries vehicular traffic, but also rail lines. Because of these features and functionality, it was determined that the bridge would be widened instead of replaced when upgrades were needed. The plan specified three 11-foot lanes in each direction and inside and outside shoulders on each side of the road. This four-phase project has been greatly anticipated by local communities and is thought to be vital to the recovery of the Greater New Orleans area.
Post-tensioning was built into the design of this project and the responsibilities of the post-tensioning provider include supply and installation of more than 100-tons of 0.6-inch diameter post-tensioned strand for the retrofit of the piers that will support the widened bridge, along with the ducts and anchorages for the bonded multistrand system. The five piers range in height from 48 feet to 67 feet high. Prior to enlargement, the width of each is approximately 50 feet. When work is complete, the width will be increased to 80 feet.
Post-tensioning was specifically selected as the reinforcement system because it easily accommodates the challenge of reinforcing the widening the existing piers. It is a very effective method of providing circumferential reinforcement and the high strength (270 ksi) and flexibility of the strand around the radii of the corner of the piers lends itself to an efficient, durable and aesthetically attractive design. Additionally, the horizontal post-tensioned tendons provide effective reinforcement at the ends of the piers where the thickness of the concrete increases.
A special anchor was selected for use on this project. This particular anchor, known as the Z anchor, is designed for those tendons where the ends cannot be anchored using normal anchorages. By using this anchor, the widening procedures can be completed without buttresses or pilasters which results in simplified concrete forming and improved structural aesthetics. Another unique feature of the anchorage is that it moves along the tendon axis during the stressing operation within a block-out. When the strands are completely stressed, the block-out is poured back with concrete to create a seamless finish.
Work by the post-tensioning contractor on each pier began with the perimeter tendons. Once the ducts and all the reinforcing steel were installed and the concrete poured by the general contractor in all locations other than the block-outs, the post-tensioning contractor moved in to install the perimeter tendons. These tendons were then stressed using the special anchorages. To stress the tendons, specially designed curved jack chairs were placed and lubricated to guide the strands onto the jack. The 150-ton jack was then lowered using an electric chain hoist and secured into place. The gauge was anchored to the jack so that stressing could be accurately monitored. Tendons were stressed simultaneously from both ends, so careful coordination was required to ensure a smooth operation. Operators were in constant radio contact.
Meanwhile, the post-tensioning contractor moved to the nose tendons. The strands for these tendons were pushed through the ducts, stressed and grouted with a low-shrinkage, low-bleed flowable cementitious grout. The grout bonds the strands to the surrounding concrete and protects them from corrosion. When the nose tendons were completely stressed and the general contractor had completed the pour back of the perimeter tendons, the post-tensioning contractor moved back to perform the grouting of these tendons. Once the perimeter tendons were grouted, the post-tensioning contractor was finished with that pier's post tensioning work. In total, the concrete enlargements were performed in six lifts on each of the five piers.
Close cooperation with the general contractor was required to ensure a continuous operation. The post-tensioning contractor had to be prepared to be on-site and ready to work when the general contractor completed their portion of the work on each pier. Additionally, crews had the unique aspects of working in the middle of the Mississippi River - using boats to access all work areas and working under a fully functional bridge. To protect the crews from the overhead traffic and rail road debris, safety netting was installed and extended out 60 to 80 feet from the face of the piers.