Rail Breaks Department of Transit Infrastructure and Engineering Services April 2015.

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Presentation transcript:

Rail Breaks Department of Transit Infrastructure and Engineering Services April 2015

Overview of Problem Rail Break (2015) Heat Kink (2012)

Running Rail at WMATA Type: 115 lbs / yard Durability: Head Hardened (>370BH) Cross Section: 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)

Axial Stresses in Rail 115 lb / yard Rail

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

Axial Stresses: Temperature Low: -10°F High: 135°F Typical Cold Break: -100°F → 200 KIPS → KSI TENSION Stress Independent of Length of CWR 200 KIPS → KSI TENSION ΔT = (T N - T Rail )

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

Contact Stresses in the Rail Correct Contact Irregular Contact

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

De f e c t S iz e at F a il u r e ( % Head A r ea) Temperature Affects Critical Defect Size Δ T from Neutral (°F) 10 Colder 45% Defect at 30°F ΔT 15% Defect at 90°F ΔT

Cause of Breaks

Rail Break Examples K05 East Falls Church), 1/27/2015: 1982 Rail 20°F, but 50% Defect K /20/2015: -6°F

Grosvenor 65°F (2013): Heavy Squats, Defects Dupont Circle (2013) 65°F Tunnel: Head Defect Rail Break Examples

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 ) Track Maintenance Manual (Rev ) – List of Rail Breaks List of Rail Breaks

Rail Breaks, Winter 2015

2013: Not Temperature Related

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 xx Moment of Inertia S yy Steel Modulus of Elasticity 2,100,000 kgf/cm^2 (30,000,000 lb/in^2) Coefficient of Linear Thermal Expansion ∘ C