5: 1 of 21 COPYRIGHT © AREMA 2008 Module 6: Train-Track Dynamics.

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Module 6: Train-Track Dynamics

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 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

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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

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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

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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

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

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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 Flange Marks

Bounce & Pitch Result of Surface Variations

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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

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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

[email protected]

Contributors:

Robert Kimicata, P.E.

Kimicata Rail Consulting

(847) 394-4105

[email protected]