ASPIRE Spring 11 - Aspire - The Concrete Bridge Magazine

some cases to stitch together micro-cracksthat might arise.Concrete with monofilament fibers wasused for the Wye Interchange on I-184 inBoise, Idaho, in 2000. When originallyconstructed in 1969, the interchange couldeasily carry 33,000 vehicles per day. By1998, the average daily traffic had reached92,000 vehicles. The redesign allows it tocarry about 120,000 vehicles per day, theanticipated traffic level in 2020. The projectwas constructed in two stages at a totalcost of about $80 million. Throughout theconstruction, two lanes of traffic remainedopen in all directions—the same level ofservice available before construction began.The 817-ft-long bridge features cast-inplace,single-cell concrete box girders thatwere post-tensioned both transversely andlongitudinally. The bridge consists of fourspans, with 187-ft end spans and two interior222-ft spans. The structure is 58 ft wide withjust a single-cell box. This approach, whichis more common in California, helped meeta multitude of challenges resulting from thecurvature of the roadway.ABC Concepts UsedITD has also been examining a variety of ABCmethods. One of the approaches that has proveneffective is precast concrete columns and piercaps. This technique allows the components tobe fabricated as other work progresses, speedingup installation when the site is ready.This approach was used on three interchangesor overpasses in the past 2 years, on Black CatRoad, Robinson Road, and the Vista Interchangeover I-84 in Boise. The two overpasses featureprecast, prestressed concrete girders, precastconcrete columns, and precast pier caps. TheVista Interchange uses precast, prestressedconcrete girders with precast concrete pier capsbut cast-in-place concrete columns, becausethe construction staging did not benefit fromaccelerating the column construction. The localoffices of HDR Engineering, Forsgren Engineers,On the Wye Interchange on I-184 in Boise, the 817-ft-long, fly-over bridge features cast-in-place, single-cellconcrete box girders that were post-tensioned both transversely and longitudinally.and Stanley Engineers assisted on these projects.Mixing the two types of components andtargeting those elements where acceleratedconstruction can be most effective offerssignificant benefits for future designs. Whereappropriate, ITD intends to continue to usethese concepts, while tweaking them to gainmaximum effectiveness. The experiencerepresented a fairly innovative approach andshowed us how we can utilize ABC techniques.Another project using all precast concretecomponents is on the drawing boards. The StateHighway 200 Bridge over Trestle Creek, to beconstructed in 2013, consists of a 105-ft-long,simple-span structure using entirely precastconcrete elements, including deck bulb-teebeams and precast concrete abutments. Theroad is not heavily trafficked, but it provides anopportunity to test ABC principles in practice.If this project proves successful by significantlycutting construction time, the concepts will beexpanded.These projects show the wide range of designsand construction methods being used by ITD.The state tracks its bridge conditions closely,although funding to accomplish all that shouldbe done creates a great challenge. Fortunately,the state is focusing more attention on bridgestoday as it realizes the great value in providingeffective asset management to make best use oftaxpayer dollars. No doubt, with past history as aguide for future projects, many of those bridgeswill feature innovative concrete methods._________Matthew Farrar is the state bridgeengineer with the Idaho TransportationDepartment in Boise, Idaho.For more information on Idaho’s bridges,visit www.dot.state.idaho.gov.Precast concrete bent caps and columns were used onthe Robinson Road over I-84 Bridge, one of severalrecent projects to incorporate accelerated bridgeconstruction (ABC) techniques.42 | ASPIRE, Spring 2011