Huey P. Long Bridge Widening Phase 1
The Huey P. Long Bridge spans the Mississippi River and has served the New Orleans area since 1935. This unique bridge structure carries vehicular traffic and rail lines. Because of the 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 had a high anticipation by local communities and vital to the recovery of the Greater New Orleans area.
Post-tensioning was selected as the reinforcement system because it easily accommodates the challenge of 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 aesthetic design. Additionally, the horizontal post-tensioned tendons provide effective reinforcement at the ends of the piers where the thickness of the concrete increases.
STRUCTURAL TECHNOLOGIES provided the post-tensioning supply and installed 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 and each was increased in width – from 50 feet to 80 feet.
A special anchor, known as the Z anchor, was designed and utilized for tendons where the ends could not be attached with normal anchorages. By using this anchor, the widening procedures were completed without buttresses or pilasters, resulting 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 crews – in all locations other than the block-outs, the perimeter tendons were installed. These tendons were stressed using the Z anchors. 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 and operators were in constant radio contact.
The strands for the nose 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 pour back of the perimeter tendons was completed, the tendons were grouted.
Close cooperation with the general contractor was required to ensure a continuous operation. The post-tensioning contractor was prepared and ready to work when the general contractor completed their portion of the work on each pier. Additionally, crews had the unique challenge 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.
In total, the concrete enlargements were successfully performed in six lifts on each of the five piers.