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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

[email protected]

Contributors:

Robert Kimicata, P.E.

Kimicata Rail Consulting(847) 394-4105

[email protected]