Kentrack

• Kentrack is a computer program designed to analyze a railroad track segment as a structure

• Uses Bousinessq’s Elastic Theory• Uses Burmister’s

Multi-Layer System and Finite Element Analysis to perform calculations

Introduction

• Critical Stresses and Strains are Calculated• Design Lives are Predicted• Based on Fatigue Effects (Cumulative Damage

Criteria) of Repeated Loadings• Uses DAMA Program – Developed for Highway

Pavements

Background

• Originally Kentrack was written in FORTRAN for DOS operation

• Since been upgraded to a Windows Platform• 3.0 was written in Visual Studio using a .Net

Framework in C#

Background

• The original development goal was to analyze traditional All-Granular trackbeds and Asphalt Underlayment trackbeds

• 3.0 has the option for• All-Granular• Asphalt Underlayment• Combination – Granular & Asphalt

All-Granular• Traditional Track structure

Asphalt• Underlayment

Combination• Contains an asphalt layer and a granular

subballast layer

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Kentrack Theory• Superposition of Loads

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Kentrack Theory• Finite Element Method– Used to calculate the stress and strain in the rail

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Kentrack Theory• Multilayered System– Used to calculate the stress and strain in each layer

Kentrack Theory• Each type of trackbed is composed of different

materials– All-Granular trackbed layers include Ballast,

Subballast, and Subgrade– Asphalt trackbed layers include Ballast, Asphalt

and Subgrade– Combination trackbed layers include Ballast,

Asphalt, Subballast, and Subgrade• Different equations are used to describe the

properties of each material

Kentrack Theory

• Ballast– In new trackbeds the ballast behaves non-linearly– In aged trackbeds the ballast behaves linearly

• Subgrade – Behaves as a linear elastic material

21

KKE )21( 0321 Kz

Kentrack Theory• Asphalt is a visco-elastic material• The dynamic modulus depends on the

following:– Temperature– Aggregate passing the No. 200 sieve in %– Volume of bitumen %– Volume of air voids %– Asphalt viscosity– Load frequency

Kentrack Theory

• Damage Analysis– Based on minor linear damage analysis criteria– Performance is based on periods• For Kentrack this is four seasons

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Kentrack Theory

• Predicted number of repetitions

•Each car equals one repetition

Kentrack Theory• Predicted number of repetitions

Wheel Load = 36000 lb/wheel

For one car the total weight = 36000 lb/wheel x 8 = 286,000 lb/rep / 2000

= 143 ton/rep

The number of repetitions assumed per year = 200,000 rep/yr

The traffic per year = 200,000 rep/yr x 143 ton/rep

= 28,600,000 GT/yr / 1 x 106

= 28.6 MGT/yr

Subgrade Damage Analysis• Excessive permanent deformation controls

failure• Deformation is governed by the vertical

compressive stress on the top of the subgrade• Based on Highway experience• The number of allowable repetitions before

failure

583.3734.3510837.4 scd EN

Asphalt Damage Analysis• Fatigue cracking controls failure• Fatigue cracking is governed by the tensile

strain in the bottom of the asphalt• Based on highway experience• The number of allowable repetitions before

failure

853.0291.30795.0 ata EN

Failure Criteria• All-Granular Trackbed • Vertical Compressive Stress on Subgrade

Failure Criteria• Asphalt Trackbed• Vertical Compressive Stress on Subgrade,

Tensile Strain at Bottom of Asphalt

Kentrack Theory• Combination Trackbed• Vertical Compressive Stress on Subgrade,

Tensile Strain at Bottom of Asphalt

Typical cross section• All-Granular Trackbed

Sub. Mod. = 15,000 psi28.6 MGT/yr

Typical cross section• Asphalt Trackbed

Sub. Mod. = 15,000 psi28.6 MGT/yr

Typical cross section• Combination Trackbed

Sub. Mod. = 15,000 psi28.6 MGT/yr

Critical Outputs*

Variable All-GranularTrackbed

AsphaltTrackbed

CombinationTrackbed

Subgrade Vertical Compressive Stress (psi) 14.47 11.69 10.49

Asphalt Strain (in/in) N/A 0.000134 0.000116

Service life of Subgrade (yrs) 10.27 25.56 38.38

Service life of Asphalt (yrs) N/A 24.89 39.80

*Axle Load = 36 tons, Sub. Mod. = 15,000 psi, 28.6 MGT/yr

Material Properties

• Properties to be inputted are often industry standards or specified by the railroad

• Several properties are set as defaults as noted in the tutorial

• The majority of default values can be changed by the user

Effect of Subgrade Modulus on Subgrade Compressive Stress

Effect of Subgrade Modulus on Subgrade Design Life

36 Ton Axle Load28.6 MGT/yr

6000 12000 18000 210000

10

20

30

40

50

60

70

80

90

Subgrade life in All Granular-Trackbed

Subgrade life in Asphalt Trackbed

Subgrade life in Combination Trackbed

Subgrade Modulus (psi)

Subg

rade

Des

ign

Life

(yea

rs)

Effect of Subgrade Modulus on Asphalt Tensile Strain

6000 12000 18000 210000

10

20

30

40

50

60

70

Asphalt Life in Asphalt Trackbed

Asphalt Life in Combination Trackbed

Subgrade Modulus (psi)

Asph

alt D

esig

n Lif

e (y

ears

)Effect of Subgrade Modulus on Asphalt Design Life

36 Ton Axle Load28.6 MGT/yr

Kentrack• The output values are stored automatically in

a text file that is over written in each new analysis

• The text file can be saved by the user after the analysis

• Through the input process the program validates inputs

• Results can be used for performance-based structural design and analysis

Summary• Kentrack is a versatile program for the design and

analysis of All-Granular, Asphalt Underlayment, and Combination Trackbeds

• Subgrade compressive stress, asphalt tensile strain, and associated design lives are computed

• Design lives are considered conservative since they are based on highway failure criteria

• The relative effects of varying input parameters can be assessed

Asphalt Trackbed Tutorial • Start the program• Select the

trackbed to be analyzed