Track Buckling Hazard Detection and Rail Stress Management

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Challenge C: Increasing Freight capacity and services Figure 6 – RNT Monitoring and Readjustment during a Rail Break and Repair 5.0 Track Buckling Hazard Detection With the annual buckle derailments in the US ranging from 20 - 40 at a cost of over $10M per year, the prevention of track buckle caused derailments remains a key industry goal. Railroad efforts are continuing to focus on improving buckling prevention practices and on to better identifying buckling prone conditions. To assist in these efforts Salient Systems has recently developed a “Buckling Hazard Index” which provides a warning on potential buckles in terms of a yellow, orange, or red alert. The yelloworange-red alerts are based on the track having a prescribed buckling margin of safety (BMS). The BMS is determined by the StressNet TM system and is based on the RSM measured rail and neutral temperature data coupled with the track’s buckling strength evaluations. The latter is based on the Volpe/FRA “CWR-SAFE” model [6], a part of which has been incorporated into the StressNet TM system, referred to as BUCKLE. The BMS is a numerical temperature index on how close the track is to a “critical” condition in accordance with theoretical developments in [7, 8]. For completeness, a brief review of buckling safety concepts and BMS are provided below. 5.1 Buckling Safety Concepts for BMS Applications Figure 7 shows the fundamental safety concept and criterion for buckling prevention as detailed in [9], as well as applied by the UIC in line with [10, 11]. T Bmax T Bmin Temperature increase above neutral Buckle Temperature increase above neutral Step 1 Step 2 Buckle o Deflection o Deflection 6 Temperature increase above neutral T Bmax T Bmin Step 3 Buckle Buckling regime Temperature increase above neutral T Bmax T Bmin Step 4 Buckle Buckling regime Safe temperature increase
Challenge C: Increasing Freight capacity and services Figure 7- Track Buckling Stability Response and Safe Temperature Concept Step 1 shows the track lateral deflection from an initial line defect with amplitude o with temperature increase. Step 2 exhibits the theoretically determined buckling equilibrium curve (shown in dashed) identifying the upper and lower critical temperatures ΔT Bmax and ΔT Bmin . Step 3 shows that the actual buckling occurs at a temperature in a buckling regime bounded by the upper and lower critical temperatures, and Step 4 identifies the lowest point on the buckling response curve as the safe allowable temperature increase. According to theoretical concepts [5], at temperatures below this value buckling should not occur, and the track’s deflections are confined to the growth of the initial line defects with temperature. The safety criterion on track buckling prevention is based on this safe temperature value i.e. on the ΔT Bmin on the buckling response curve. Buckling prevention safety criterion then requires that rail temperature increase above neutral to be confined to values less than ΔT Bmin. Since ΔT Bmin is an analytically determined quantity based on theory and on track condition/parameter inputs, for additional safety considerations it is customary to add a safety factor on ΔT Bmin . For most heavy-haul applications this safety factor is typically 10°F (6°C) less than ΔT Bmin [9]. For the European rail network’s safety factors refer to [10, 11]. It is important to note that the safe temperature increase value, ΔT Bmin , and the buckling regime’s upper bound, ΔT Bmax , are highly track parameter/type/condition dependent, and are referenced to the track’s neutral temperature. Hence for buckling hazard detection both the safe allowable temperature (as modified by any additional safety factors) and the track’s RNT are required in accordance with the safety criterion that: thermal load < buckling strength, where the thermal load is based on the RNT, and the track strength is based on the safe allowable temperature. In line with the above, the buckling margin of safety (BMS) is defined as the reserve “buckling strength” in terms of the additional temperature or thermal load required to produce a buckling prone condition i.e. reaching the track’s safety limit. This is graphically illustrated in Figure 8. T T Bmax T Bmin T ALL T actual Safety Factor BMS = (T ALL – T actual ) Buckle Amplitude 7
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Track Buckling Hazard Detection and Rail Stress Management

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