1. 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

2. 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

3. 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#

4. 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

5. All-Granular
Traditional Track structure

6. Asphalt
Underlayment

7. Combination
Contains an asphalt layer and a granular subballast layer

8. Kentrack Theory
Superposition of Loads

9. Kentrack Theory Finite Element Method
Used to calculate the stress and strain in the rail and tie

10. Kentrack Theory Multilayered System
Used to calculate the stress and strain in each layer

11. 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

12. Kentrack Theory Ballast Subgrade
In new trackbeds the ballast behaves non-linearly
In aged trackbeds the ballast behaves linearly
Subgrade
Behaves as a linear elastic material

13. 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

14. Kentrack Theory Damage Analysis
Based on minor linear damage analysis criteria
Performance is based on periods
For Kentrack this is four seasons

15. Kentrack Theory Predicted number of repetitions
Each car equals one repetition

16. Kentrack Theory Predicted number of repetitions
Wheel Load = lb/wheel
For one car the total weight = 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

17. 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

18. 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

19. Failure Criteria All-Granular Trackbed
Vertical Compressive Stress on Subgrade

20. Failure Criteria Asphalt Trackbed
Vertical Compressive Stress on Subgrade, Tensile Strain at Bottom of Asphalt

21. Kentrack Theory Combination Trackbed
Vertical Compressive Stress on Subgrade, Tensile Strain at Bottom of Asphalt

22. Typical cross section All-Granular Trackbed Sub. Mod. = 15,000 psi
28.6 MGT/yr

23. Typical cross section Asphalt Trackbed Sub. Mod. = 15,000 psi
28.6 MGT/yr

24. Typical cross section Combination Trackbed Sub. Mod. = 15,000 psi
28.6 MGT/yr

25. Critical Outputs* Variable All-Granular Trackbed Asphalt Combination
Subgrade Vertical Compressive Stress (psi)
14.47
11.69
10.49
Asphalt Strain (in/in)
N/A
Service life of Subgrade (yrs)
10.27
25.56
38.38
Service life of Asphalt (yrs)
24.89
39.80
*Axle Load = 36 tons, Sub. Mod. = 15,000 psi, 28.6 MGT/yr

26. 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

27. Effect of Subgrade Modulus on Subgrade Compressive Stress

28. Effect of Subgrade Modulus on Subgrade Design Life
36 Ton Axle Load
28.6 MGT/yr

29. Effect of Subgrade Modulus on Asphalt Tensile Strain

30. Effect of Subgrade Modulus on Asphalt Design Life
36 Ton Axle Load
28.6 MGT/yr

31. 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

32. 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

33. Asphalt Trackbed Tutorial
Start the program
Select the trackbed to be analyzed