Railway Track & Structures - July 2008 - (Page 19)

in tangent track, but this is reversed in curves with the field-side bars breaking four percent more than the gauge side. Top center cracking appears slightly less susceptible to curve location with field-side top center cracking to be 27 percent higher in tangent track and only eight percent higher in curved track. The effects of position (high rail or low rail) are indeterminate due to the limited sample size. Need for inspection method The data show almost 70 percent of the joint bar reports are service failures, i.e., the bar is broken, rather than cracked. Also, nine percent of the reports have field- and gauge-side bars that were found broken simultaneously. This is the population of defects from which derailments are most likely. This suggests better and more frequent joint bar inspections are needed to improve system safety and reliability. An ideal system would inspect the entire bar, rather than just the outward side of the bar. Figure 3 shows the location of found rail joint bar defects. Recommendations • The observed typical joint bar failure mode is not in agreement with theoretical predictions and engineering judgment. More rigorous modeling and laboratory testing are recommended to better understand the relationship between load environment and the behavior of joint bars. • A new joint bar specifically designed for CWR territory. This joint design should closely match the life expectancy of the parent rail, be capable of resisting thermal stresses in the rail, consider the effects of rail wear, and address the matter of differences in wear conditions. • A system design, which addresses more than one factor affecting performance, is needed for rail joints. The rail fabricator should work closely with the track engineer to develop an appropriate foundation for the joints. This design should include best practices for the use, installation, and maintenance of bolted joints. Acknowledgements: The findings reported here would not have been possible without the cooperation of the following individuals and their companies and their staffs: Raymond E. Snyder and Theodore M. Niemeyer, NIEMEYER & ASSOCIATES; R. Bowman, NS; A. C. Charrow, BNSF; D. Clark, UP; A. Tajaddini, Federal Railroad Administration; and R. Zenisek, CSXT. References: 1. Association of American Railroads, Railroad Facts, 2007 Edition. 2. Davis, D.D., and D.E. Staplin, “Rail Defects and Their Effects on Service Reliability,” International Heavy Haul Railway Conference, Vancouver, B.C., Canada, 1991. www.rtands.com Railway Track & Structures July 2008 19 http://www.rtands.com

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Railway Track & Structures - July 2008

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