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5: 1 of 21COPYRIGHT © AREMA 2008
Module 6: Train-Track Dynamics
Module 6: Train-Track Dynamics
5: 2 of 21COPYRIGHT © AREMA 2008
Module Objectives
• Understanding the Rail/Wheel Interface
• Identifying Force Generators
• Understanding Force Effects
5: 3 of 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
L/V Ratio
• L/V Definition• Effect on Stability• Lateral Forces• Vertical Forces• Wheel/Rail Profile
5: 5 of 21COPYRIGHT © AREMA 2008
Lateral Forces
• Flanging Force• Centrifugal Force• Frictional Curving Force• Coupler Force• Buff & Draft Force• Truck Hunting• Track Geometry Force
5: 6 of 21COPYRIGHT © 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 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
Buff & Draft ForcesLongitudinal 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 21COPYRIGHT © AREMA 2008
HuntingHuntingCaused 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 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
Vertical Forces
• Vehicle Weight• Unbalanced Elevation in Curves• Car/Locomotive Dynamics• Track Geometry Input• Coupler Forces
5: 12 of 21COPYRIGHT © AREMA 2008
Effects of Centrifugal ForceUNDERBALANCE
Superelevation
Centrifugal Force
GravityResultant
Center ofGravity
EQUILIBRIUM
Superelevation
GravityResultant
OVERBALANCE
Superelevation
GravityResultant
D
EV a
0007.0
3max
= Maximum allowable operating speed (mph).= Average elevation of the outside rail (inches).= Degree of curvature (degrees).D
EV
a
max
Amount of Underbalance
Centrifugal ForceCenter of
GravityCenter ofGravity
Centrifugal Force
5: 13 of 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
Track GeometryDeviations in GeometryAccentuate 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 21COPYRIGHT © AREMA 2008
Harmonic OscillationRock & 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 21COPYRIGHT © AREMA 2008
Center of Gravity & Oscillation
5: 17 of 21COPYRIGHT © 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 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
Rail-Wheel Profile
New Wheel & New Rail New Wheel & Worn Rail
Worn Wheel & Worn Rail Worn Wheel & New Rail
5: 20 of 21COPYRIGHT © 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 21COPYRIGHT © AREMA 2008
QUESTIONS?Author:
Joseph E. Riley, P.E.
Federal Railroad Administration
(202) 493-6357
Contributors:
Robert Kimicata, P.E.
Kimicata Rail Consulting
(847) 394-4105