ASPIRE Summer 08 - Aspire - The Concrete Bridge Magazine

girder that would be fabricated and deliveredin three units, erected on temporary falseworkbents, and post-tensioned together once the deckwas placed. The span length is 197 ft and thegirders are 7.9 ft deep. The girders used HPC witha 28-day compressive strength of 8000 psi. Allpost-tensioned anchorages were placed in a castin-placeconcrete end diaphragm. At the time,this was the longest precast, spliced concretegirder in WSDOT’s inventory. This type of “SuperGirder” was developed in 1996 through a jointeffort between WSDOT and the Washington stateprecast, prestressed concrete industry.The Twisp River Bridge spliced “Super Girder.”Hood Canal Floating BridgeThe Hood Canal Bridge is the longest concretefloating bridge in the world over a saltwatertidal basin. The basin is up to 340 ft deep witha maximum tidal swing of 16.5 ft. On average,15,000 cars per day use this bridge, whichprovides a vital link to the northern part of theOlympic Peninsula. The bridge was originallybuilt in 1961. The west half sunk during a stormin 1979 and was replaced in 1982. WSDOTis currently in the middle of a $478 millionrehabilitation project to replace the east halffloating section along with both approaches,install new concrete floating anchors, and widenthe west half superstructure. The project beganin 2003 and is now about 73% complete. Furtherdetails of the bridge are provided in the articlebeginning on Page 16.WSDOT also owns and maintains three otherconcrete floating bridges, the Evergreen PointBridge on State Route 520, which is the world’slongest, and the Homer Hadley and Lacey V.Murrow Bridges on I-90.PGSuper Computer ProgramWSDOT has developed an in-house computerprogram for engineers to design precast,prestressed concrete girders. It is availablethrough a free download. (See ConcreteConnections on Page 44 for details.) PGSuperis our precast, prestressed concrete girder designand analysis software. It can be used to designand to check designs in accordance with theAASHTO LRFD Bridge Design Specification andWSDOT criteria. The flexural design featurecomputes the number and configurationof prestressing strands and the minimumrequired concrete release strength. The sheardesign feature determines the number, size,and spacing of transverse reinforcement forvertical shear, horizontal shear, bursting, andstrand confinement. Specification checkingevaluates girders for compliance with strength,serviceability, and detailing criteria. Girdersare evaluated for stresses and stability duringhandling and transportation. Temporaryprestressing to control camber, improve stability,and reduce concrete release strengths may alsobe input. The program has been designed toallow for future expansion and updating asdesign criteria and user expectations change.______________________Jugesh Kapur is bridge and structures engineerand DeWayne Wilson is bridge managementengineer with the Washington State Department ofTransportation.For more information on Washington Statebridges, visit www.wsdot.wa.gov/eesc/bridge.Prestress girders rolled into position on the Hood Canal Bridge approaches.Hood Canal floating bridge.48 | ASPIRE, Summer 2008