ASPIRE Spring 11 - Aspire - The Concrete Bridge Magazine

superstructure. These spans weredesigned to minimize the number ofbents used and minimize impacts toboat traffic on the lake.Part 3 consisted of twin, 1-milesections over the navigational channel.These portions of the twin bridgeswere designed to resist large bargeimpacts, provide higher navigationalclearance, and resist wave loads on thesubstructure elements. These sectionshave a significant number of abovewaterfootings. Parts 1 and 2 werein a single contract and Part 3 in asecond contract. Both contracts wereconventional design-bid-build.PrefabricationIn consideration of their location,size, and functional requirements,the bridges were designed to takeadvantage of prefabrication as theprimary construction method.Typical moment connections were madebetween piles and footings by placing6-ft-long reinforced plugs in the ends ofthe piles.PilesThe geological structure of the Louisianacoastal region favors large precast,prestressed concrete displacement piles.They are capable of developing largeaxial capacity with side friction, pilesetup, and sometimes point bearing.This project utilizes 36-in.-squarehollow piles containing twenty-eight0.6-in.-diameter strands. This pileshape and strand configuration arecapable of developing large momentcapacity. It also enables fabricationand transportation in long lengths thatvaried between 100 ft and 180 ft. Morethan 433,000 linear ft of piles wereused on the project.Pile-to-Cap andPile-to-Footing MomentConnectionDepending on specific designrequirements, the 36-in., precastconcrete pile hollow core was reinforcedby placing a 6-ft-long cast-in-placeconcrete moment plug in the top end.The project has atotal bridge length of 11miles.In other situations, the solid plug wasextended to 30 ft in length. Piles areexpected to resist moments and in somecases significant uplift loads.Precast Concrete CapsWhenever they could, the Contract1 contractor elected to use a precastconcrete pile cap alternate offered in theoriginal design. Working with the precastmanufacturer, Gulf Coast Pre-StressInc., and the owner, the original designwas modified to accommodate verticaland batter piles, as well as the momentconnection of the cap and restrainingwalls. The precast cap weighed about80 tons and contained conventionalnonprestressed reinforcement. Thesecaps were used for the majority of thespans where span length, bridge width,and pile configurations were the same.Over 20,000 yd 3 of concrete were usedin the 496 pile caps.The precast bridge elements include:• 36-in.-square hollow precast,prestressed concrete piles• 4 ft by 5.5 ft by 59.25-ft-longprecast concrete bent caps• 135-ft long, 78-in.-deep FloridaBulb-tee girders• stay-in-place precast concrete boxforms for the footings on the pilesThe majority of the spans were builtwith Florida Bulb-tee girders supportedby pile bents. The higher elevationsections of the bridges near the mainchannel crossing contain column bentstructures supported on two main pilefootings. The main navigational channelspans used steel plate girders.Precast concrete elements being readied for use as a stay-in-place footing form.TWIN, 5.5-MILE-LONG PRECAST, PRESTRESSED CONCRETE TRESTLES / LOUISIANA DEPARTMENT OFTRANSPORTATION AND DEVELOPMENT, OWNERprecasters: Gulf Coast Pre-Stress Inc., Pass Christian, Miss., a PCI-certified producer, Prestress Services Industries LLC, Memphis Tenn., a PCI-certifiedproducer, Boykin Brothers Inc., Baton Rouge, La., a PCI-certified producer, and Traylor, Kiewit, Massman JV, Slidell, La.bridge description: Parallel bridges that incorporate high-performance concrete in all of their components and include precast, prestressedconcrete piles, AASHTO I-beams, Florida Bulb-tee beams, precast concrete pile caps, and precast concrete footing formsBridge Construction Cost: $753 millionASPIRE, Spring 2011 | 31