ASPIRE Spring 11 - Aspire - The Concrete Bridge Magazine

Phoenix Sky Harbortransit guideway bridgeby David A. Burrows, Gannett FlemingThe evolution ofthe PHX Sky Train’scrossing of Taxiway“Romeo”At one of the 10 busiest airports inthe United States, cast-in-place, posttensionedconcrete was used to providesuperior value, meet an aggressiveconstruction schedule, squeeze intoa tight construction corridor, andaccomplish the world’s first transitcrossing of an active aircraft taxiway.Taxiway “R” looking north showing removal of end span falsework. Photo Rights:Hensel Phelps Construction Co.; Photo Credit: Visions in Photography.The Phoenix Sky Harbor InternationalAirport is constructing the PHX SkyTrain, a 5-mile-long automatedtransit system that will run throughand connect key existing and futureairport facilities with strategically locatedstations at terminals, parking areas,ground transportation centers, MetroLight Rail, and the Rental Car Center.The development of this system requiresseveral very unique design features.The lead designers and the AviationDepartment developed a predominantlyelevated train alignment that offeredthe most economical facilities andthe best level of service for stationconnections to airport facilities.The construction of the PHX Sky Trainwill be implemented in two stages tospread the overall capital costs. Stage1 is currently under construction with aplanned opening in early 2013. Stage 2is still in conceptual design developmentand is scheduled for opening in 2020.Stage 1 consists of three stations and12,000 linear ft of guideway, of which9000 ft will be elevated. One of thebiggest challenges to Stage 1 was thecrossing of Taxiway Romeo (Taxiway“R”), the first time in the world that atransit system would cross over an activetaxiway. In fact, the taxiway itself crossesover Sky Harbor Boulevard, therebyputting planes, trains, and automobilesall within close proximity.Design ConstraintsThe main span of the bridge is 340 ftlong and 75 ft above the taxiway inorder to provide the clearance requiredfor Group V Aircraft. Additionally, tostay below the ceiling established bythe Federal Aviation Administration forsafe aircraft operations, the height ofthe bridge was limited. Thus, a narrowvertical band approximately 40 ft deepremained within which the bridgecould be built. Equally daunting to thegeometric constraints was the task ofconstructing the bridge above an activetaxiway, which could only be shut downfor a short period of 2 months.In 2007, a selection process was begunto determine the structure type thatwould best meet project objectives,while minimizing impacts to airportoperations, facilities, and security andmeeting or exceeding establisheddesign criteria. Because of advantagesin constructability, maintenance,serviceability, inspection, and total lifecyclecost, a precast concrete segmentalbox girder was recommended. Evidentfrom a drive on metro-Phoenix’sfreeway system, concrete box girdersare a popular choice. They requirelittle maintenance and only routineinspection and thus have a reducedlife-cycle cost. Aesthetically, the boxgirder was the most streamlined andleast obtrusive choice, fitting nicely withsurrounding concrete structures andadjacent guideway.Cast-in-PlaceBox Girder SelectedAfter preliminary design of the precastconcrete segmental box girder wascompleted, the contract for constructionmanager at risk was awarded. Thenbegan an investigation into reducingthe projected $10.5 million constructionprofiletaxiway “r” bridge/ PHOENIX SKY HARBOR INTERNATIONAL AIRPORT, PHOENIX,ARIZONAbridge design Engineer: Gannett Fleming, Phoenix, Ariz.construction manager at risk: Hensel Phelps Construction Company, Phoenix, Ariz.subcontractor, piers and superstructure: Austin Bridge & Road, Phoenix, Ariz.Subcontractor, drilled shafts: Case Foundation Company, Tempe, Ariz.concrete supplier: CEMEX, Phoenix, Ariz.34 | ASPIRE, Spring 2011