Precast Prestressed Concrete Structure Provides Solution For
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PCI DESIGN AWARD WINNER Precast Prestressed Concrete Structure Provides Solution for Getty Center Tram Guideway Mark G. Josten, RE. To solve the problem of transporting visitors Senior Project Manager from an underground parking structure up a A. T. Curd Constructors Glendale, California steep hillside to the new J. Paul Getty Museum (near Los Angeles, California), a people-mover system was devised. The design and construction of the guide way structure supporting this people-mover system posed several unique challenges to the designers and builders of the project. The answers to these challenges came in the innovative use of precast/prestressed concrete components combined with Wilfred L. Painter, Jr. post-tensioning. This article presents the P. E. design features, precast concrete fabrication, Senior Vice President and construction highlights of the project. Precast Operations A. T. Curd Constructors Glendale, California The Niobrara River Company recast and prestressed concrete played a prominent Rialto, California role in the design-construction of a 1080 m (3535 ft) p long, curved, U-shaped tram guideway near the city of Los Angeles, California. This guideway structure sup ports a people-mover system, which rapidly transports visi tors from an underground parking structure next to the San Diego Freeway to the main plaza outside the new I. Paul Getty Museum. Fig. 1 shows an aerial view of the tramway project alongside the San Diego Freeway (Interstate 405). The Getty Center is a cultural complex dedicated to the visual arts and humanities. The facility will feature the new J. Paul Getty Museum, a scholarly research library, scien James S. Guarre, RE. tific laboratories for conservation of cultural property, and headquarters for the programs and administration of The J. Vice President BERGER/ABAM Engineers Inc. Paul Getty Trust. The Center lies alongside Interstate 405 Federal Way, Washington in the Sepulveda Pass between the San Fernando Valley 24 PCI JOURNAL , r’ fr. % - - 4 Fig. 1. The Getty Center Tram guideway winds up the Southern California hillside along the San Diego Freeway, and blends in beautifully with the site. and the Los Angeles basin in Los An activities and on people-mover system contract with the project contractor, geles, California (see Fig. 2). configurations. With these problems Dinwiddie Construction Company The new museum will complement confronting them, the Getty Trust de (DCCo). Otis was to provide the vehi the existing museum at the Villa lo cided that a people-mover system cles, subsystems, and guideway design cated on the Pacific Coast Highway in would be needed to shuttle Center vis to DCCo; DCCo would then subcon Malibu. The location of the Getty itors from the parking garage to the tract the guideway construction to a Center presented the logistical chal museum on a dedicated guideway. select shortlist of qualified bidders. lenge of moving a large number of With the added responsibility of people from an entry point at an un guideway design, Otis contracted with derground parking SYSTEM PROCUREMENT structure next to BERGER/ABAM Engineers Inc. of the San Diego Freeway to the arrival After a competition among vehicle Federal Way, Washington, to design plaza of the Getty Center and to the system suppliers that included pricing, the guideway structure. new museum atop an adjacent hillside guideway aesthetics, vehicle and train overlooking the Los Angeles basin. appearance, pollution-free operating The site has limited access — only conditions, and low noise, Otis Transit THE PEOPLE-MOVER one service road and a fire road with Systems Inc. of Farmington, Connecti SYSTEM extremely steep grades. The site is cut, was chosen as the vehicle system The tram system guideway is single also located in a secluded, quiet resi supplier. The Otis system uses cable- lane with a double-lane off-center by dential area of West Los Angeles. This driven, air-cushion supported vehicles. pass section. Two separate trains will resulted in restrictions construction on The Otis contract was a design-build operate in a shuttle configuration on May-June 1995 25 (7 ft 4 in.) wide and 2.90 m (9 ft 6 in.) high. Vehicle capacity will be 14 seated and 17 standing per vehicle or 93 per three-vehicle train. THE GUIDEWAY DESIGN Site Conditions Site conditions imposed unique challenges on the guideway configura tion and design. The Getty Trust dic tated that guideway construction not scar the natural vegetation on the hill side. It was also important to position the guideway parallel to the access Miles road that wound up the hillside to fa 0 4 cilitate construction and minimize the visual impact of the guideway on views from the hillside on the opposite North side of the San Diego Freeway. These conditions produced a guideway align ment consisting of nine curves, with horizontal radii of curvature varying from 38 to 305 m (125 to 1000 ft), that follows a profile with an average ver tical grade of 7.2 percent (see Fig. 4). The total length of the tramway is 1080 m (3535 ft). The rise in elevation from the parking garage station to the museum at the station is 64 m (210 ft). The aerial structure is 800 m (2580 ft) long flanked by either at-grade or pile- supported grade beam sections ap proaching the two passenger stations. This 800 m (2580 ft) long structure is divided into 9 four- to six-span con tinuous units. The average span length is 20 m (63 ft); maximum span length is 26 m (86 ft). At some locations, the guideway is supported on columns over 13 m (42 ft) tall. At other loca Tension Weight tions, the guideway superstructure is supported directly on drilled pier caps without columns. Fig. 3. Schematic of the cable drive system. Vehicle System Interfaces The guideway supports the vehicle on a smooth “flying” surface and sup the guideway. Each train will be at just outside of the station area. ports the guide rail, sheave supports tached to drive a cable supported The shuttle operation will be con for the drive cable, power rails, and along the length of the guideway by a trolled by computerized equipment lo control subsystems. A U-shaped support sheave network. In turn, each cated in a control room next to the ma guideway with a horizontal bottom cable will be driven by an elevator- chine room. A schematic drawing of slab and vertical sidewalls was re type geared drive system located in a the cable drive system is shown in Fig. quired to interface with the Otis vehi machine room outside and under the 3. Each train will be 27.4 m (90 ft) cle system. Supports for a guidebeam Museum Station. illustrated As in Fig. long and will consist of three, two- for maintaining the lateral position of 3, a cable tension device (tension module vehicles, each with a length of trains on the guideway, brackets to weight) is located at the entry station 8.8 m (29 ft). Vehicles will be 2.24 m support the numerous rope sheaves re 26 PCI JOURNAL necessary elements to interface with the Otis vehicle system as structural elements. Added structure beneath the ( supporting slab would generally be North eliminated. In the bypass area, a struc ture to stiffen the cross section would be added beneath the supporting slab. Alternative C — Precast concrete L-beams spanning from column to column with a cast-in-place connect ing slab to form the above U-section. Precast concrete stem beams extend Road ing below the supporting slab would be used in the bypass area. Precast Fig. 4. The Getty Center site plan. concrete beam components would be designed to support the weight of the connecting slab and associated form- work and construction loads without auxiliary supports. This alternative minimized the amount of cast-in-place shoring and minimized the pick weights of precast concrete elements. Alternative C was chosen by the Getty Trust, the project architect, and the project contractor because of cost, aesthetics, and constructability factors. Design Criteria The site for the guideway Guiderail Support was within the jurisdiction of the City of Los Angeles, so the Los Angeles De Sheave Support partment of Building and Safety was the approving authority. Early discus sions with the Department of Building Air and Safety indicated that the Depart Cushion ment would be comparing the design for the guideway with the Los Angeles Rope Sheaves Uniform Building Code (LAUBC). Power Rail Post The concerns of the Department cen tered on the seismic design of the Concrete Beam or Pavement guideway structure. This review process presented a Fig. 5. The guideway/vehicle system interfaces. dilemma to the design team because the guideway structure was more like a bridge than a building. The LAUBC quired to guide the propulsion cable way cross sections included those sec grouped this type of structure into the around numerous turns, and the power tions shown in Fig. 6. category of “Other” structures. Guide- rail for supplying electric power to the Alternative A — Precast concrete way design engineers thought it was operating vehicles are secured to the double tees spanning column to col essential to introduce the latest re guideway sidewalls and supporting umn. The stems of these double tees search regarding bridge seismic be slab (see Fig. 5). would be straight; the flanges of the havior and safety into the design of double tees would be curved to make this structure. Therefore, prior to be curved guideway sections. The side- ginning the final design process, Preliminary Design a walls and flying surface would be cast- Getty Center People-Mover Guideway The guideway designer’s initial ef in-place concrete. Multiple double tees Structural Design Specification was fort was to develop alternative guide- would be used in the bypass area.