Concrete Ties for Transit Track-An Update


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Title: Concrete Ties for Transit Track-An Update

Author(s): A. N. Hanna

Publication: Special Publication

Volume: 93


Appears on pages(s): 343-360

Keywords: ballast; electrical properties; fasteners; insulation; performance; prestressed concrete; production methods; railroad ties; rapid transit railways; reinforced concrete; specifications; tests

Date: 9/1/1986

Today, at least ten transit properties in the United States and Canada use pretensioned monoblock or reinforced two-block concrete ties. Pretensioned monoblock concrete ties have been manufactured by the long-line method. Reinforced two-block ties have been manufactured in individual forms using the "instant demolding" method. High strength concrete and pre-stressing tendons, and reinforcing and structural steel conform-ing to current standards have been specified for the production of concrete ties. Quality control programs that address material properties, production operations, and tolerances are required to assure consistency in quality and performance. In a concrete tie rack, the fastening system maintains gage, maintains alignment, restrains longitudinal rail movement, provides resilience, and assures electrical insulation. The ballast provides supporting strength and resistance to the loads imposed on track, resil-ience, stability, and drainage capabilities. The ability of the ties and fasteners to provide their intended functions is evalu-ated by laboratory tests. The tests evaluate tie strength at rail seat and at tie center, the bond between the concrete and prestressing tendons or reinforcing steel, the ability of the fastener to provide adequate longitudinal and lateral restraint and to resist uplift forces, the serviceability of the tie and fastener components under service-simulated loads, and the ability of the tie-fastener system to provide adequate electrical resistance and impedance. A concrete tie track provides techni-cal, economical, and environmental advantages by using improved fastening systems and eliminating components with high mainten-ance requirements. A concrete tie track would generally yield a lower life-cycle cost than a wood tie track and provide better service operation and increased safety.