Railway Track & Structures - May 2008 - (Page 20)

TTCI R&D Figure 3 is a sample of the input menu. Here, 136RE rail has been cut to remove a defect on wood tie track with every other tie anchored. The anchor condition is considered to be average with no missing anchors and the majority of anchors tight against the ties. The ballast is not frozen, the rail was cut at 12ºF resulting in a gap of 3-1/2 inches with one-inch additional rail removed to square the rail ends. The DRLT is 95ºF and minimum readjusted RNT is 75ºF (DRLT minus 20ºF). The output module from the Figure 3 input data is shown in Figure 4 and indicates the RNT at the time the rail was cut was 76ºF. Because the pre-break RNT is above the minimum value of 75ºF entered on the input menu, the program will provide information to readjust back to the pre-break 76ºF condition. If a higher minimum readjusted RNT had been entered, say 85ºF, the program would provide information to readjust to 85ºF instead of the pre-break value. The output module also provides the influence zone length; the recommended de-anchor length of each side of the gap and the total gap width to cut that removes the rail added, allows for movement of the unanchored rail, the estimated end movement of the anchored rail, and includes the field weld gap. To summarize the example given in Figures 3 and 4, the rail was cut at 12ºF producing a 3-1/2-inch gap. The program estimated the RNT at the time the rail was cut as 76ºF; therefore, the T was about 64ºF. The program estimated the influence zone as 698 feet each side of the cut based on the track type and anchor condition information. A distance of 349 feet each side of the cut was specified to be de-anchored during the readjustment and the total gap width to cut and close to the one-inch weld gap using a rail puller and/or heat was 6-3/4 inches. The optimal time to readjust the RNT is when the rail temperature is near but not above the desired readjusted RNT and the recommended procedure is to mark the rail and cut the total gap width before de-anchoring. The rail will be in compression near the break/cut location and much of the total gap width will be recovered as the rail runs together as it is being cut. For example, if readjustment of the conditions shown in Figures 3 and 4 is performed at a rail temperature of 65ºF, an estimated 3-3/4 to four inches of the required 5-3/4-inch movement would come from the ambient rail temperature, leaving about two inches or slightly less remaining gap to close with a rail puller or additional heat. It is important to point out that the program assumes the rail added is the same as the rail gap width (3-1/2 inches in Figure 3). Figure 2 shows a work description menu. break RNT, if the rail break temperature is known and the longitudinal resistance is estimated. • The release of tension that produces the gap also causes the RNT to drop to the rail temperature at the gap location. The difference between the pre- and post-break/cut RNT diminishes with distance away from the gap by the incremental longitudinal resistance. The distance on each side of the gap over which the RNT was affected is referred to as the influence zone (LD) and is a function of the T and longitudinal resistance. • The recommended distance to de-anchor during the readjustment process is half the LD. 5 Automation of the RNT Software has been written to automate the RNT methodology and facilitate its use as a maintenance tool that allows the readjusted RNT to be controlled and restored to a desired value. The program is menu driven, with the first menu (Figure 2) asking the user to select one of two possible work scenarios, i.e., cold weather rail break repair/defect removal, which is the readjustment of a low RNT condition due to cold weather rail repair, or hot weather de-stressing to relieve compressive forces in a hot rail. Having selected the appropriate work scenario, the next menu prompts the user for necessary input information, including: • Drop-down menus defining the track type (wood with every other tie anchored, wood with every tie anchored, concrete or wood with elastic fasteners), anchor/fastener condition (weak, average or strong) and rail size. These inputs establish the rail area and longitudinal resistance variables. • Yes/no frozen ballast query that doubles the longitudinal resistance if the ballast is frozen. • The rail break/cut gap width which is used to calculate the pre-break RNT. • The amount of additional rail removed, if any, to square the rail ends. The rail break gap width plus any additional rail removed establishes the excess rail to be recovered during the readjustment. • The rail temperature at the time of the break/cut. • The DRLT and the minimum RNT desired from the readjustment. The minimum RNT may be the same as the DRLT, or some lesser value, but the program recommends that it be no more than 20ºF lower than the DRLT. 20 Railway Track & Structures May 2008 Future program development The next step in the program development is to concentrate on user interface and implementation issues. Once finalized, TTCI intends to package the program in a handheld PDA device. References 1. Read, D., D. Li, A. Kish, W. GeMeiner, “Monitoring Rail Neutral Temperature Behavior in Revenue Service,” Railway Track and Structures, May 2006. 2. Kish, A. and G. Samavedam, 2005. “Improvements in CWR Destressing for Better Management of Rail Neutral Temperature,” Journal of the Transportation Research Board, No. 1916, pp. 56-65. 3. Read, D. and A. Kish. April 2006. “Methodology for www.rtands.com http://www.aar.com http://www.rtands.com

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