ASPIRE Spring 11 - Aspire - The Concrete Bridge Magazine

BergerABAM value-engineered thedesign for a new bridge spanning SR520 in Redmond, Wash., to connecta new Microsoft campus with theoriginal one. Although the cityenvisioned a steel-plate girder bridge,BergerABAM used precast, prestressedconcrete girders, 83 in. deep withan 8-in.-thick, cast-in-place concretedeck. The large, flat surfaces providedlandscaping and trail amenities toenhance aesthetics.BNSF Railway mainline tracks in Tacoma,Wash. The bridge supports an elevatedsingle-point urban interchange (SPUI),the first elevated SPUI designed in thestate of Washington and one of the firstin the country. The superstructure is acast-in-place, post-tensioned concretebox girder with superelevation, variabledepthwebs, and complex geometry. Itshows the material’s ability to be formedinto almost any shape.The SR 509 Bridge created acombination of needs for long spans toclear railroad tracks, vertical clearancesover the railroad, and freewayrestricted design options, Spry says.Cast-in-place concrete girders withcurved exterior webs were used, withthe overall bridge measuring 340 ftwide and 320 ft long with scallopedcutouts. “We had to completely rethinkhow we prepare design drawings inorder to communicate the complexreinforcement requirements to thecontractor on this project,” he explains.“In retrospect, this was really an earlyexample of using computers to createthree-dimensional models of thestructure in order to build it.”Speed Becomes a FocusIn all types of projects, the designersare seeing more emphasis on speed ofconstruction to minimize user costs andtraffic congestion. The firm’s focus onconstructability aids this process.BergerABAM is taking that focus furtherthrough a grant from the FederalHighway Administration’s Highwaysfor LIFE Technology PartnershipsProgram. The grant is being used todevelop a precast pier system foraccelerated bridge construction (ABC)in high-seismic areas. Dr. Lee Marsh,seismic specialist with BergerABAM,is managing the project, with a teamcomprising WSDOT, the University ofWashington, Concrete TechnologyCorp., and TriState Construction.A demonstration project for the piersystem will be constructed for WSDOTin 2011.Marsh is also leading a team that isdeveloping a synthesis of practice forthe National Cooperative HighwayResearch Program in Washington,D.C. The synthesis will summarize theinnovative techniques for applying ABCconcepts in moderate to high-seismicareas and will recommend the nextsteps the bridge industry should take tomake ABC a reality in these areas.The firm recently completed a notableproject in Redmond, Wash., in whichThe ways that longand heavy componentsare shipped have reallychanged.additional attention was paid toaccelerating construction while creatinga dramatic design. BergerABAM deviseda unique design for a roadway thatcrossed SR 520 at a skew of 70 degrees.Offset spans allowed the structuralframing to be skewed at 30 degreesand provided additional surface areafor landscaping and park-like amenities.The resulting design was a cost-effectivesolution that ideally suited the goal ofthe project, which was to connect theMicrosoft campuses on both sides of SR520.To speed construction, precast concretecolumns were used, minimizingconstruction time for an intermediatepier in the medians. “High-seismicforces require close attention to theconnections,” says Spry. Meeting thoserequirements, while also incorporatingABC concepts, necessitates the properbalance to ensure all needs are met.8 | ASPIRE, Spring 2011