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Rail Breaks Department of Transit Infrastructure and Engineering Services April 2015
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Overview of Problem Rail Break (2015) Heat Kink (2012)
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Running Rail at WMATA Type: 115 lbs / yard Durability: Head Hardened (>370BH) Cross Section: 11.25 sq in Strength: 120/170 ksi yield/ultimate -Older Rail: 75/135 ksi yield/ultimate Age: Various throughout system Milling Report HEAD WEB FOOT (BASE)
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Axial Stresses in Rail 115 lb / yard Rail
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Setting the Neutral Temperature -2°F Ambient -12°F Rail ΔT = 107°F 105°F Ambient 140°F Rail T N Neutral Temp (95°F) ΔT = 45°F Rail Temp Lower Than T N Rail Temp Higher Than T N
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Axial Stresses: Temperature Low: -10°F High: 135°F Typical Cold Break: -100°F → 200 KIPS → 15-20 KSI TENSION Stress Independent of Length of CWR 200 KIPS → 15-20 KSI TENSION ΔT = (T N - T Rail )
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Bending Stresses in Rail Max tension stress in HEAD from bending: 1.65 ksi Rail Truck Wheelset = 88 inch Max tension stress in BASE from bending: 2.75 ksi
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Contact Stresses in the Rail Correct Contact Irregular Contact
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Defects in the Rail Thermal StressResidual Stress COMPRESSION TENSION Thermal stress is tensile when rail temperature is below neutral or stress-free temperature Residual stresses develop from heat treatment, roller straightening, and accumulation of traffic Calculations assume a detail fracture in the head of a 132 RE rail. Internal Defect
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20 50 40 30 60 70 80 De f e c t S iz e at F a il u r e ( % Head A r ea) Temperature Affects Critical Defect Size 10 -20 -30-40-50-60-70-80-90-100 Δ T from Neutral (°F) 10 Colder 45% Defect at 30°F ΔT 15% Defect at 90°F ΔT
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Cause of Breaks
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Rail Break Examples K05 East Falls Church), 1/27/2015: 1982 Rail 20°F, but 50% Defect K05 446+ 2/20/2015: -6°F
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Grosvenor 65°F (2013): Heavy Squats, Defects Dupont Circle (2013) 65°F Tunnel: Head Defect Rail Break Examples
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EXTRA SLIDES References – Fracture Mechanics of Pull-Apart Failures (Jeong) Fracture Mechanics of Pull-Apart Failures – Investigation on CWR, Summer Destressing (Kish) Investigation on CWR, Summer Destressing (Kish) – The Art and Science of Rail Grinding. (Zarembski) – Milling Report for 115 RE (Dulles) Milling Report for 115 RE (Dulles) – Track Maintenance Manual (Rev 6 2015) Track Maintenance Manual (Rev 6 2015) – List of Rail Breaks List of Rail Breaks
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Rail Breaks, Winter 2015
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2013: Not Temperature Related
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115 RE Rail Rail Type AREMA 115 RE, head- hardened Cross Sectional Area11.25 in Minimum Tensile Strength170 ksi (AcelorMittal 2013) Minimum Yield Strength120 ksi (AcelorMittal 2013) Moment of Inertia S xx65.852 Moment of Inertia S yy10.738 Steel Modulus of Elasticity 2,100,000 kgf/cm^2 (30,000,000 lb/in^2) Coefficient of Linear Thermal Expansion 0.0000115 1 ∘ C
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