Track Buckling Hazard Detection and Rail Stress Management

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Challenge C: Increasing Freight capacity and services Figure 3 – Five Years of RSM Data on the Union Pacific 50 40 Neutral Temperature (°F) RB1 A RB2 B 30 20 Neutral Temperature (°C) 2°(875m) Curve Low Rail 10 High Rail 0 Calendar Days Figure 4 – RNT Behavior in Rail Breaks 4.0 Rail Break Mechanics, Repair and Restressing A major reason for the reduced and possibly unsafe neutral temperatures is the difficulty in resetting the RNT to the desired target value after a rail break or after a rail defect removal. The fundamentals of rail break mechanics are discussed in [4, 5], while Figure 5 illustrates the basics. It is a well known that when the rail is broken or cut for defect removal the RNT drops to the temperature of the rail when the break/cut occurs. For example, in Figure 5 when the rail breaks at 40°F(4°C) its RNT is 40°F (4°C) at that location. Additionally in this case, the rail break/cut influence is experienced for a track length exceeding 635 ft (194m) on either side of the break/cut as indicated by L d . As shown in [4, 5], these L d ’s can be on the 4
Challenge C: Increasing Freight capacity and services order of 200–1200 ft (60–365 m) depending on the tensile force in the rail and on the rail/fastener’s longitudinal resistance. Rail Break/Cut RNT Profile T Break =40°F(4°C); SFT PreBreak =100°F (38°C); Gap=3in (7.6cm) RNT(°F) Pre-Break RNT = 100°F (38°C) RNT Locked in After Joint Closes 100 80 Add 3 in Rail 60 T BR = 40°F 3 in 136#Rail Timber Ties 40 20 RNT Profile Just After The Break/Cut L d =635 ft (194m) 900 800 700 600 500 400 300 200 100 0 Distance from break (ft) 100 200 300 400 500 600 700 800 900 Figure 5 – Rail Break/Cut RNT Profiles The resulting rail gaps require closure by “adding rail” through a rail-plug insertion. Note that as shown in [4] closing the gap by pulling rail together is generally not an effective procedure since it might only restore the RNT to what it was in the rail prior to the break/cut, which may be much lower than the required target RNT. Adding rail through a plug insertion, however, does result in locking in the reduced RNT as indicated by the green RNT profile. It is this reduced RNT profile that is required to be readjusted before the onset of warm temperatures to avoid buckling prone conditions. The usual readjustment is made by cutting rail out and unfastening a prescribed length of rail at warmer temperatures. As indicated in [4, 5], the basic difficulty with this procedure is that the “correct” amount of rail to cut out and the “correct” unfastening lengths required are not known because the reduced RNT profile requiring adjustment is not known. The Salient RSM-StressNet TM System can be applied to provide this knowledge, thus promoting a more effective management of rail break/defect removal repairs in terms of RNT readjustment. Specifically, the RSM-StressNet TM System: Determines and monitors the RNT after plug/joint interim repair Alerts on when to return for the final repair/RNT readjustment to avoid a buckling prone condition (see Buckling Hazard description in next Section) Provides information on how to readjust to the desired RNT Provides information on effectiveness of the RNT readjustment One such application is shown in Figure 6 where the RSM data shows the specifics of rail break (RB3 shown in Figure 3) repair on the Union Pacific test site. The RSM measured RNT data clearly shows the interim joint’s RNT of 60°F (16°C) to be readjusted. Without RSM/RNT measurement this would not be known, hence the amount of rail to cut out and unfasten would also be not known. RSM data also shows the effectiveness of the readjustment procedure and tracks the subsequent RNT condition. UP South Morrill Sub Rail Break on 2/8/06 , Joint Repair and RNT Readjustment As Monitored By Rail Stress Module (RSM) 5 RNT Readjustment 50 40 Rail Break 30 emp (° F) Joint Repair RNT 40°F (4°C) Joint RNT 60°F (16°C) 20 RNT and
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Track Buckling Hazard Detection and Rail Stress Management

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