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Module 6: Train-Track
Dynamics
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Module Objectives
Understanding the Rail/Wheel Interface
Identifying Force Generators Understanding Force Effects
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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.
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L/V Ratio
L/V Definition
Effect on Stability
Lateral Forces Vertical Forces
Wheel/Rail Profile
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Lateral Forces
Flanging Force
Centrifugal Force
Frictional Curving Force Coupler Force
Buff & Draft Force
Truck Hunting Track Geometry Force
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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
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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
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Buff & Draft Forces
Longitudinal Train Forces Result ofChanges in Gradient, Curvature &Speed
Buff - Run-in = Train inCompression - Produces Outward
Force on Curve, Increases VerticalLoad on Outside
Draft - Run-Out = Train in TensionProduces Inward Force on Curve,Increases Vertical Load on Inside
Train in Simultaneous Buff & Draft-Torque Produced - Force Appliedat Coupler Resisted at the Rail
Slack 6"/Car
50' Slack/6000' Train
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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 hollowappearance over good quality track.
Poor vertical snubbing. s
v
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Track Geometry Forces
Lateral Force Result of Changes inAlignment & Gage
Wide Gage > Truck Hunting at HighSpeeds
Tight Gage > Truck Hunting at Low Speeds
Vertical Force Result of Changes inCross-level/Superelevation & Profile
Vehicle Rocks About CG Produces Horizontal Component at Rail
because of Shift in CG
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Vertical Forces
Vehicle Weight
Unbalanced Elevation in Curves
Car/Locomotive Dynamics Track Geometry Input
Coupler Forces
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Effects of Centrifugal ForceUNDERBALANCE
Superelevation
Centrifugal
Force
GravityResultant
Centerof
Gravity
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
E
V
a
max
Amount of
Underbalance
Centrifugal
ForceCenterof
Gravity
Centerof
Gravity
Centrifugal
Force
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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 FlangeMarks
Bounce & PitchResult of SurfaceVariations
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Track Geometry
Deviations in GeometryAccentuate Pitch & Bounce
Deviation in Uniform Profile
Mismatched, Bent or Battered Joints
Worn Points/Battered Frogs & CrossingDiamonds
Poor Cross-level
Rock & RollSpirals
Warp Forces Suspension Diagonally to Limits Bind Side Bearings - Trucks Can't Turn
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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
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Center of Gravity & Oscillation
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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.
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Coupler Forces & Derailments
Time duration of coupler forces
Train consist and makeup
Train handling by crew Terrain
Geometry of coupled cars
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Rail-Wheel Profile
New Wheel & New Rail New Wheel & Worn Rail
Worn Wheel & Worn Rail Worn Wheel & New Rail
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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).
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QUESTIONS?
Author:Joseph E. Riley, P.E.Federal Railroad Administration
(202) 493-6357
Contributors:
Robert Kimicata, P.E.
Kimicata Rail Consulting(847) 394-4105