Railway Track & Structures - July 2008 - (Page 17)

TTCI R&D Performance evaluation of mechanical rail joints TTCI and NIEMEYER & ASSOCIATES team up to evaluate performance of noninsulated rail joints. T ransportation Technology Center, Inc., teamed up with NIEMEYER & ASSOCIATES, P.C., to evaluate the performance of rail mechanical, i.e., noninsulated, joints in revenue service main lines. This study will assist the industry in a better understanding of the failure rates and failure modes of rail joints, which will allow the industry to better allocate resources towards improving the performance of rail joints. Improving inspection capabilities, improving the design of the joint and improving the performance of rail joint materials are some of the efforts under way. Although the rail joint-related accident rate has been falling in terms of number per ton mile, rail joints have received much attention in recent years due to the following issues: • Lack of an automated inspection procedure • Improvements in other track components • Changes in the applications of rail joints Figure 1, left, shows joint bar failures by joint type. Figure 2 shows rail joint defects vs. month (2007). Mechanical rail joint The bolted rail joint has a discontinuity in the rail and creates conditions that can accelerate track degradation around the joint. At a minimum, the gap at the rail ends within the joint is a source of impact loading. Left unchecked, these impact loads increase with time as the rail ends batter, thereby increasing the impact forces generated by the passing wheels. Impact forces accelerate track degradation leading to car rocking (lateral roll of the car). The standard bolted joint in service in continuous welded rail territory is essentially the same joint that was designed early in the past century to provide vertical and horizontal rail alignment, while allowing for longitudinal movement to offset rail expansion and contraction due to temperature change. While the shape of the bars has changed over time to better match the heavier rails now in service, the joint is still designed to minimize the contact area between the joint bar and the rail web in order to accommodate longitudinal rail movement. When used in CWR territory, this design feature may be of no value and can lead to excessive stresses under today’s heavy-axle-loads and higher thermal loading conditions. by Muhammad N. Akhtar, TTCI senior engineer, David D. Davis, TTCI senior scientist, and William S. Riehl III, NIEMEYER & ASSOCIATES, P.C. Railway Track & Structures July 2008 17 www.rtands.com http://www.aar.com http://www.rtands.com

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Railway Track & Structures - July 2008 On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Products and Literature People Calendar Sales Representatives Website Directory Advertisers Index Professional Directory Classified Advertising Chicago Perspective Extending Service Life for Costly Special Trackwork Rail Welding Gets Act Together Premium Fasteners, Rail Steels Help Meet Strain of Heavy Haul

Railway Track & Structures - July 2008

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