International Concrete Abstracts Portal

The Vancouver SkyTrain guideway structures employ concrete beams precast in full-span lengths, with vertical and horizontal curvature and variable superelevation to follow the precise track trajectory. Tangent and curved structures, special structures, and structures containing spans of up to 45 m utilize the same trapezoidal beam. Approximately 300 inserts were placed in the deck and sidewalls of each beam during concreting operations. The trackwork, the linear induc-tion motor, and other subsystems were attached directly to the precast beams through these inserts without a second concrete pour. Construction of the Vancouver SkyTrain was preceded by simul-taneous development of vehicle and guideway technologies and the construction of a 1.1-km elevated guideway section that was used to demonstrate the operational characteristics of the system and confirm its constructability. This paper describes the guideway structure, reviews its design and construction, and presents an overview of the construction schedule and costs.

This paper describes the manufacture of 1040 prestressed concrete trapezoidal box girder guideway beams for the 14.8 km long dual-lane aerial guideway for the Vancouver Advanced Light Rapid Transit Project. The guideway beams are up to 36 m in length and weigh up to 100 t. In order to achieve the extremely tight tolerances dictatedbythe direct fixation ofrunning and linear induction motor railstotheprecastbeams, a sophisticated forming system was utilized to produce b ea ms with continuously varying vertical and horizontal alignment and super-elevation. Ahigh-precision jigging system was developed to cast in threaded inserts for attachment of the track hardware, and a thorough quality control program for dimensional and material control was instituted to ensure compliance with the construction specifications. Thedesignofthe first pumped concrete placing system to be used in a North American precast plant is described, as well as details of the plant layout, movable shelters, hoisting equipment and steam curing system utilized. Stripping, storageandtransportationoftheserrassivebeamstothe siteovercity streets at night is described. Details of the plant and field post-tensioning operations which were included inthebeamsupplycantract are also provided.

The Long Island Rail Road (LIRR) in conjunction with New York State Department of Transportation (NYSDOT) in December 1980, completed a grade crossing eli.mination project in Long Island. To provide a solution to problems of costly track maintenance, two parallel, 1.13 mile (1.82 km) long slab tracks were constructed. Unl ike convent ional track with cross ties ancl ballast, this slab track consists of a continuously reinforced concrete slab supported on an asphalt-treated subbase and compacted subgrade to help determine adequacy of design and suitability of this type of construction for other projects, a field testing program was developed and implemented by contracting with Construction Technology Labora-t o r i e s . The paper describes advantages of slab track systems, design details, construct i on t echni ques and sequence, inst rument at i on, test results and findings.

In 1985 Metropolitan Dade County, Florida, completed its first stage of Metrorail. This 22.5 miles of rapid transit system includes 21.5 miles of aerial guideways . The standard aerial structures used for the guideways are prestressed concrete doubletee girders, each 80 feet long, 12 feet wide, 5 feet deep, and weighing 94 tons. The double-tee design concept was the first of such a structure to be used in a U.S. transit system. It was recommended for reasons of aesthetics as well as economy. As compared to the traditional box sections, the double-tee girders were estimated to have resulted in savings of up to $10 million. Extensive technical studies were conducted to examine the various aspects of design and performance of thee structure. including the testing of two 2/3-scale models and three full scale cale girders. . Special attention has been given to shear and torsional design, since large torsional moments were produced by wind load on vehicles and structures , b y the horizontal nosing /lurching action of the vehicles, and by the centrifugal forces on curved tracks. Vlosov's elastic torsion analysis has been made which considers both the St. Venant tosrsion and the warping torsion. This is the theory that accurately predicted the behavior of the girders before cracking. Based on this theory, torsional rotatoin at service load stage was controlled to provide riding comfort for the passengers. Vlasov's theory based on uncracked section was found to be very uneconomical for the design of shear and torsional reinforcement. Considerable savings were achieved by extending Vlasov's theory to the post-cracking ultimate loads stage using a reduced torsional characteristic number. Recommended design value fork is 30% of the torsional characteristic number for an uncracked beam.

Three f u l l -s c a l e , precast, prestressed doub le-tee girders measuring 80 ft (24.4 m) long by 5 ft (1.5 m) deep by 12 ft (3.7 m) wide were con-stru cted. One girder was used to monitor long-term deformations under site conditions. Two girders were tested to demonstrate the adequacy of the girder design, to check construction and reinforcement details, and to verify fatigue performance. Static tests of uncracked and deliberately precracked girders showed that torsional rotations due to service loads were in close agreement with the analysis and were smal 1 enough to ensure rider comfort. Fatigue resis-tance of the girders was verified using two separate test spectra involving 5- and 6-million cycles of loading. The loading represented the cumulative fati gue damage of sixty years of operational llife . Over load tests of the girders showed adequate strength and ductility . A strength of at least 1.6 times the required factored severe derailment load including 100% impact was obtained. The excellent behavior of the girders from serviceability and strength viewpoints substantiated the design methods and construction details used.