ASPIRE Summer 08 - Aspire - The Concrete Bridge Magazine

The bridge was widenedfrom three lanes to fivein each direction.The project involved several key challengesthat required innovative thinking.constructed, reconstructed, widened,or modified the infrastructure along 12miles of highway. The overall projectwas undertaken on a design-build basisand bid as a lump sum contract.Widened by One-ThirdThe existing bridge, built in 1960, wasconstructed of cast-in-place, reinforcedconcrete box beams, as were manyof the bridges along the route. Theconstruction widened the six-lane bridgeby one-third to accommodate a total of10 lanes of traffic. Each side along thebridge’s 340-ft length was widened by28.75 ft, creating a total width of 170ft. The deck’s total area expanded by19,500 ft 2 to 57,800 ft 2 . The bridgefeatures two 61-ft-long end spans andtwo 108.75-ft-long main spans. Thestructure also includes a high skew angleof 59 degrees and a tangent-horizontalalignment, with a 1% grade.The project involved several keychallenges that required innovativethinking, says Syed Mohsin Kazmi,senior project manager for URS Corp.in Roseville, Calif., the bridge designer.These went beyond aesthetics to includeboth logistical and safety issues thatrequired close teamwork among thedesign and construction partners.Specifically, the city and Orange CountyTransportation Authority officials wantedto ensure traffic was not disruptedthroughout the project, build the projectquickly, blend it with other cast-in-placebridges along the highway, and keep itwithin tight budgetary restraints.To resolve these issues, the designersspecified two types of precast concretegirders for each of the four spans oneach side of the original bridge. Theoutside girder on each side is a 5-ft-deeprectangular, hollow, precast, prestressedconcrete girder. The three interior girderson each side are 5-ft-deep precast,prestressed concrete bulb-tee girders.Approximately 250 precast concretepanels were used for the deck, withfour precast domes used for decorativepilasters.The girders were erected on cast-inplacebent caps, which sit on cast-inplacecolumns and footings. They, inturn, are supported by 366 precast,prestressed concrete, driven piles thatwere 14 in. square. “The soil in this arearequired the addition of piles to providethe necessary support for the additionalloads of the columns for the widenedbridge,” Kazmi explains.“It was a huge challenge to design andconstruct this project, because of thevariety of concerns involved,” he adds.“The selection process for these projectsis very rigorous in any event, but welooked at many alternatives before wefound the one that provided the bestcombination of benefits. The challengewas especially to come up with astructure type that could be constructedquickly and without significant impactto the existing traffic.”The exterior beam is a rectangularsection to match other bridges,whereas, more economical bulb-teesare used for the interior beams.Precast, prestressed concrete girders and deck panels / California Department ofTransportation (Caltrans), OwnerBridge Description: Widening of a four-span cast-in-place concrete bridge with precast, prestressed concrete rectangular box beams,bulb-tee girders, and deck panelsStructural Components: Twenty-four, 5-ft-deep precast, prestressed concrete bulb-tee girders; eight, 5-ft-deep rectangularhollow precast, prestressed concrete girders; 250 precast, prestressed concrete deck panels, 366 14-in.-square precast, prestressed concretedriven piles; and four precast domes for decorative pilastersASPIRE, Summer 2008 | 31