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5: 1 of 21 COPYRIGHT © AREMA 2008 Module 6: Train-Track Dynamics
5: 2 of 21 COPYRIGHT © AREMA 2008 Module Objectives Understanding the Rail/Wheel Interface Identifying Force Generators Understanding Force Effects
5: 3 of 21 COPYRIGHT © AREMA 2008 Train-Track Dynamics Definition Interaction of forces occurring as train moves over the track structure –Lateral Forces –Vertical Forces –Vehicle Dynamics –Rail & Wheel Profile Many factors affect these forces –Train Speed & Handling –Train Consist & Placement of Cars, etc.
5: 4 of 21 COPYRIGHT © AREMA 2008 L/V Ratio L/V Definition Effect on Stability Lateral Forces Vertical Forces Wheel/Rail Profile
5: 5 of 21 COPYRIGHT © AREMA 2008 Lateral Forces Flanging Force Centrifugal Force Frictional Curving Force Coupler Force Buff & Draft Force Truck Hunting Track Geometry Force
5: 6 of 21 COPYRIGHT © AREMA 2008 Frictional Curving Force Difference in Distance Outside Vs. Inside Wheel Rolls in Curve Effect of Conical Wheel Tread Generation of Creep Forces –Cause Truck to Steer to Curve Outside –Magnitude of Forces Vs. Wide Gage, Corrugations & Geometry Problems Importance of Lubrication
5: 7 of 21 COPYRIGHT © AREMA 2008 Coupler Forces Position of Coupler Faces in Curves Long Car Coupled to Short Car Longitudinal Force Effect Angularity of Couplers Torque Applied at Wheel-Rail Interface
5: 8 of 21 COPYRIGHT © AREMA 2008 Buff & Draft Forces Longitudinal Train Forces Result of Changes in Gradient, Curvature & Speed Buff - Run-in = Train in Compression - Produces Outward Force on Curve, Increases Vertical Load on Outside Draft - Run-Out = Train in Tension Produces Inward Force on Curve, Increases Vertical Load on Inside Train in Simultaneous Buff & Draft -Torque Produced - Force Applied at Coupler Resisted at the Rail Slack 6"/Car 50' Slack/6000' Train
5: 9 of 21 COPYRIGHT © AREMA 2008 Hunting Caused by: Empty or lightly loaded cars (though heavy cars can also hunt). Train speeds above 45 mph. Dry rail. Three piece freight car truck. Roller side bearings. Tangent track or curvature of 1 degree. Roller bearing wheelsets. Worn wheel treads having a hollow appearance over good quality track. Poor vertical snubbing. s v
5: 10 of 21 COPYRIGHT © AREMA 2008 Track Geometry Forces Lateral Force Result of Changes in Alignment & Gage –Wide Gage > Truck Hunting at High Speeds –Tight Gage > Truck Hunting at Low Speeds Vertical Force Result of Changes in Cross-level/Superelevation & Profile –Vehicle Rocks About CG –Produces Horizontal Component at Rail because of Shift in CG
5: 11 of 21 COPYRIGHT © AREMA 2008 Vertical Forces Vehicle Weight Unbalanced Elevation in Curves Car/Locomotive Dynamics Track Geometry Input Coupler Forces
5: 12 of 21 COPYRIGHT © AREMA 2008 Effects of Centrifugal Force UNDERBALANCE Superelevation Centrifugal Force Gravity Resultant Center of Gravity EQUILIBRIUM Superelevation Gravity Resultant OVERBALANCE Superelevation Gravity Resultant D E V a max = Maximum allowable operating speed (mph). = Average elevation of the outside rail (inches). = Degree of curvature (degrees). D E V a max Amount of Underbalance Centrifugal Force Center of Gravity Center of Gravity Centrifugal Force
5: 13 of 21 COPYRIGHT © AREMA 2008 Car & Locomotive Dynamics Bounce Increase & Decrease Vertical Loading Speeds > 40 MPH Change in Track Modulus Pitch Varying Vertical Load Transfers End to End Square Joints Wheel Climb & Short Flange Marks Bounce & Pitch Result of Surface Variations
5: 14 of 21 COPYRIGHT © AREMA 2008 Track Geometry Deviations in Geometry Accentuate Pitch & Bounce –Deviation in Uniform Profile –Mismatched, Bent or Battered Joints –Worn Points/Battered Frogs & Crossing Diamonds –Poor Cross-level Rock & Roll –Spirals Warp Forces Suspension Diagonally to Limits –Bind Side Bearings - Trucks Can't Turn
5: 15 of 21 COPYRIGHT © AREMA 2008 Harmonic Oscillation Rock & Roll High Center of Gravity Cars & Low Joints at Truck Spacing Rocking Magnifies Alternate Rocking on Other Rail –Wheel Lift on Successive Joints –Especially Dangerous on Curves Resonance Occurs at Critical Speed Critical Speeds Occurs at Multiples of Frequency & Wavelength
5: 16 of 21 COPYRIGHT © AREMA 2008 Center of Gravity & Oscillation
5: 17 of 21 COPYRIGHT © AREMA 2008 Longitudinal Coupler Forces Loaded car coupled to empty car (difference in compression of springs). Differences in wheel wear, especially with multi-wear wheels. Inequality of track surface, or sharp vertical curvature. Vehicle bounce or pitch. Effects of slack run-in or run-out.
5: 18 of 21 COPYRIGHT © AREMA 2008 Coupler Forces & Derailments Time duration of coupler forces Train consist and makeup Train handling by crew Terrain Geometry of coupled cars
5: 19 of 21 COPYRIGHT © AREMA 2008 Rail-Wheel Profile New Wheel & New Rail New Wheel & Worn Rail Worn Wheel & Worn Rail Worn Wheel & New Rail
5: 20 of 21 COPYRIGHT © AREMA 2008 Critical L/V Ratio L/V = 1.29 wheel may climb new rail. L/V =.82 wheel lift impending. L/V =.75 wheel may climb worn rail. L/V =.64 rail overturn force starts (unrestrained rail may overturn: rail rollover).
5: 21 of 21 COPYRIGHT © AREMA 2008 QUESTIONS? Author: Joseph E. Riley, P.E. Federal Railroad Administration (202) Contributors: Robert Kimicata, P.E. Kimicata Rail Consulting (847)
5: 22 of 21 COPYRIGHT © AREMA 2008 REVISION HISTORY
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