Railway Track & Structures - March 2009 - (Page 17)

TTCI R&D Rail joint installation and maintenance recommended practices Table 1, left, shows the effects of component changes on maximum IJ epoxy stresses. Figure 1 shows the installation of IJs on track panels. TTCI gathers best practices to significantly extend rail joint service life. T he effects of installation, maintenance and rail longitudinal stress management on rail joint service life can be significant. Transportation Technology Center, Inc., observed current operations on two major railroads and supplemented the findings with analysis and controlled experiments to compile a list of best practices as described. Joint installation For all joint designs, a supported foundation is superior to a suspended foundation for purposes of maximizing service life in heavy-axle-load service.1 www.rtands.com A supported foundation is one that has a crosstie under the rail ends of the joint. Traditionally, suspended joints (with rail ends over a ballast crib) are used to ensure that a) tie plates will not cause an electrical short on insulated joints (IJ) and b) a thermite weld can be made to eliminate the joint in the future. With the advent of better insulator materials and application technologies, a reliable insulating bearing plate can now be used with supported foundation insulated joints. The most significant advantage of a supported foundation is the reduced maximum shear stresses in the joint. 2 For epoxied joints, the reduction is in the epoxy layer, near the end post. For non-epoxied joints, the reduction is in the compression (contact) surfaces of the joint and rail-bar fasteners. Table 1 shows the relative effects of various components on IJ epoxy stresses. Note that a supported foundation provides a larger benefit (up to 30 percent reduction in shear stress) as compared to other design changes. Contrary to expectations, increasing joint bar section modulus, while keeping all other design elements the same, will increase epoxy shear stresses. The joint will have less deflection, but the stresses in the weakest component, the epoxy, will be higher. If the intent is to replace a temporary mechanical joint with a thermite weld, then a suspended foundation is preferable. The base of a thermite weld would have to be ground flush with the rail to accept a David D. Davis, TTCI senior scientist, Muhammad N. Akhtar, TTCI senior engineer, and David M. Read, TTCI principal investigator Railway Track & Structures March 2009 17 http://www.aar.com http://www.rtands.com

Table of Contents Feed for the Digital Edition of Railway Track & Structures - March 2009

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.