Railway Track & Structures - March 2009 - (Page 20)

TTCI R&D Table 2 shows the effect of rail longitudinal force on maximum epoxy stress. electric flash butt welder is being used. A conservative rule-ofthumb for track buckling strength is 60 degrees Fahrenheit above the neutral temperature. This value can be used to establish an optimal neutral temperature condition that minimizes tension to the extent possible without compromising the lateral stability of the track. Longitudinal restraint of the rail at joint locations is another important consideration. A bonded IJ that is structurally sound is basically no different than a weld. In this case, once the rail is fully constrained against thermal expansion, as is normally provided with a standard rail anchor pattern (every other tie box anchored or every tie fastened with elastic fasteners), additional anchoring will not change; i.e., additional anchors will not reduce the longitudinal thermal forces that develop at the joint. However, when the bonding material of the joint begins to fail, additional anchors will resist slippage of the rail within the joint and can prolong its service life. If the joint fails completely and the rail ends pull apart, additional rail anchors will obviously minimize the gap size compared to the standard pattern. Additional anchoring is also necessary to control the longitudinal rail movement, or rail creep, that is caused by train traction and braking forces in addition to temperature changes. This train-induced rail movement can significantly reposition one IJ relative to the IJ on the other rail, causing the allowable stagger distance to be exceeded. Box anchoring every wood tie 200 to 300 feet each side of the IJ is a fairly typical, but not universal, practice for main line track. Some railroads also selectively add rail anchors to ties with elastic fasteners to increase the longitudinal restraint. References 1. Davis, D, M. Akhtar, J. Bosshart, E. Kohake, and T. O’Connor. July 2007. “Evaluation of Improved Designs for Bonded Insulated Joints in HAL Service.” Technology Digest TD-07-020, Association of American Railroads, Transportation Technology Center, Inc., Pueblo, Colo. 2. Himebaugh, A. K., R. H. Plaut, and D. A. Dillard. January 2007. “Finite Element Analysis of Bonded Insulated Rail Joints.” Project Summary Report to the Association of American Railroads, Transportation Technology Center, Inc., Pueblo, Colo. 20 Railway Track & Structures March 2009 www.rtands.com http://www.transalert.com http://www.aar.com http://www.rtands.com

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Railway Track & Structures - March 2009 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D NRC Smashes Attendance Bridge Inspection Battling Bugs Ballast Fundamentals Vital to Keeping Track in Shape Products and Literature People Calendar Sales Representatives Advertisers Index Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - March 2009

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