ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306183
Taxiway "R" looking north showing removal of end span falsework. Photo Rights: Hensel Phelps Construction Co.; Photo Credit: Visions in Photography. The evolution of the phx Sky Train's crossing of Taxiway "Romeo" At one of the 10 busiest airports in the United States, cast-in-place, post- tensioned concrete was used to provide superior value, meet an aggressive construction schedule, squeeze into a tight construction corridor, and accomplish the world's first transit crossing of an active aircraft taxiway. The Phoenix Sky Harbor International Airport is constructing the PHX Sky Train™, a 5-mile-long automated transit system that will run through and connect key existing and future airport facilities with strategically located stations at terminals, parking areas, ground transportation centers, Metro Light Rail, and the Rental Car Center. The development of this system requires several very unique design features. The lead designers and the Aviation Department developed a predominantly elevated train alignment that offered the most economical facilities and the best level of service for station connections to airport facilities. The construction of the PHX Sky Train will be implemented in two stages to spread the overall capital costs. Stage 1 is currently under construction with a planned opening in early 2013. Stage 2 is still in conceptual design development and is scheduled for opening in 2020. Stage 1 consists of three stations and 12,000 linear ft of guideway, of which 9000 ft will be elevated. One of the biggest challenges to Stage 1 was the crossing of Taxiway Romeo (Taxiway "R"), the first time in the world that a transit system would cross over an active taxiway. In fact, the taxiway itself crosses over Sky Harbor Boulevard, thereby putting planes, trains, and automobiles all within close proximity. Design Constraints The main span of the bridge is 340 ft long and 75 ft above the taxiway in order to provide the clearance required for Group V Aircraft. Additionally, to stay below the ceiling established by the Federal Aviation Administration for safe aircraft operations, the height of the bridge was limited. Thus, a narrow vertical band approximately 40 ft deep remained within which the bridge could be built. Equally daunting to the geometric constraints was the task of constructing the bridge above an active taxiway, which could only be shut down for a short period of 2 months. In 2007, a selection process was begun to determine the structure type that would best meet project objectives, while minimizing impacts to airport operations, facilities, and security and meeting or exceeding established design criteria. Because of advantages i n c o n s t r u c t a b i l i t y, m a i n t e n a n c e , serviceability, inspection, and total life- cycle cost, a precast concrete segmental box girder was recommended. Evident f ro m a d r i v e o n m e t ro - P h o e n i x 's freeway system, concrete box girders are a popular choice. They require little maintenance and only routine inspection and thus have a reduced life-cycle cost. Aesthetically, the box girder was the most streamlined and least obtrusive choice, fitting nicely with surrounding concrete structures and adjacent guideway. Cast-in-place Box girder Selected After preliminary design of the precast concrete segmental box girder was completed, the contract for construction manager at risk was awarded. Then began an investigation into reducing the projected $10.5 million construction profile TAXIWAY "R" BRIDGE/ PHOENIX SKy HARBOR INTERNATIONAL AIRPORT, PHOENIX, ARIZONA BRIDgE 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. S UBCOnTRACTOR, DRILLED ShAFTS: Case Foundation Company, Tempe, Ariz. COnCRETE SUppLIER: CEMEX, Phoenix, Ariz. Phoenix Sky Harbor transit guideway bridge by David A. Burrows, Gannett Fleming 34 | ASPIRE , Spring 2011 Book_Spr11.indb 34 3/30/11 5:10 PM