ASPIRE Summer 08 - Aspire - The Concrete Bridge Magazine

Agency-Industry Collaboration MaximizesEconomic Benefits in CaliforniaTo meet this challenge, the designbuildteam worked with OCTA and theCalifornia Department of Transportation(Caltrans) to select a system of precast,prestressed concrete bridge beamsand stay-in-place (SIP) precast concretedeck panels with a composite concretetopping. Depending on the spanrange, bulb tees, California I-beams,and rectangular-shaped girders wereutilized. The latter were used forshorter spans, where vertical clearancenecessitated the use of bridge-specificgirder depths, and exterior bridgebeams to match the aesthetics of theexisting cast-in-place bridges. Continuityfor gravity and seismic loading wascreated with longitudinal reinforcementin the cast-in-place deck topping andbottom-flange continuity reinforcementmechanically coupled through the capbeammaking an integral connectionwith the columns. This system allowedthe design-build team to expeditedelivery economically while meeting thestructural performance and aestheticrequirements.One of the biggest challenges waswidening the State Route 22/I-5separation structure. This bridge spans17 lanes of I-5 traffic on a curvedalignment with a variable superelevationup to 6%, and on a 45-degree skew.The longest span is 170 ft, has an insideradius-of-curvature of 1300 ft andspans five lanes of mainline northboundI-5 traffic that had to remain openthroughout the duration of the project.The design-build team elected to usecurved precast, prestressed concretetub girders to span over these lanes oftraffic. These girders, measuring over100 ft in length and weighing over 250kips, were spliced with box girders caston falsework using continuous posttensioning.The contractor site-castthe curved tub girders using a cast-inplaceconcrete slab that was graded sothe soffit would match deck contoursincluding the variable super-elevationand camber. Vertical stems were usedto simplify the interface with the castin-placesections. After casting, thesegirders were transported from thecasting site, and lifted into place usinga single crane. Although not necessarilynew, the curved tub girder systemallowed for an innovative structurethat was economical, fit the aestheticrequirements of the site, and met theaggressive design-build schedule withminimum traffic interruptions. Savingsamounted to approximately 10% of theoverall bridge cost; however, this methodhad an added benefit of minimizing riskand providing a safer choice.The challenges faced by agenciesand industry, as more and more ofour transportation improvements inCalifornia include highly congestedurban interchanges, require innovativeand cost-effective solutions to meetCurved precast, prestressed concretespliced girders span I-5 at theinterchange with State Route 22.Photo: Rick Sharp, PBS&J.diminishing budgets. Constructionmaterials and reduced cost escalation haslargely outpaced inflation. To meet thesechallenges, agency-industry collaborationis essential in the delivery of sustainableconcrete bridges, and the benefits of thiscollaboration have been demonstratedwith successful delivery of the StateRoute 22 HOV widening.Aerial view of State Route 22 passing over I-5 during construction.Photo: © James A. Gallego.