1. KENTRACK 4.0: A Railway Structural Design Program -- Tutorial
Shushu Liu
Graduate Research Assistant
Department of Civil Engineering
University of Kentucky
Lexington, KY 40506
Dr. Jerry G. Rose, P.E.
Professor of Civil Engineering
261 Raymond Building
University of Kentucky
Lexington, KY 40506
2013

2. Kentrack
Kentrack is a computer program designed to analyze a railroad track segment as a structure
Uses Burmister’s Multi-Layer System and Finite Element Analysis to perform calculations

3. Introduction
Critical Stresses and Strains are Calculated at Various Interfaces within the Track Structure
Design Lives are Predicted
Based on Fatigue Effects (Cumulative Damage Criteria) of Repeated Loadings
Uses DAMA Program – Developed for Highway Pavements (Applicability for RR Trackbeds?)

4. Background
Originally Kentrack was written in FORTRAN for DOS operation
Since been upgraded to a Windows Platform
Witczak E* Predictive Model was incorporated
Unit system in 4.0 was expanded to
English Unit System
SI Unit System

5. Background
The previous version included properties of asphalt cements.
4.0 has incorporated properties of performance graded asphalt binders,
and has the option for
AC System
PG System

7. Kentrack Theory
Superposition of Loads

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

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

10. 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

11. 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

12. Kentrack Theory Asphalt is a visco-elastic material
Viscosity is determined by A-VTS relationship.
log log = A + VTS log TR
= binder viscosity, cP;
A, VTS = regression parameters;
TR= temperature, Rankine.
The dynamic modulus depends on the following:
Aggregate passing the No. 200 sieve in %
Aggregate retained on the No.3/4, No.3/8, No.4 Sieve in %
Volume of bitumen %
Volume of air voids %
Asphalt viscosity
Load frequency

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

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

15. 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

16. 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

17. 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

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

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

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

22. Kentrack 4.0
Step-by-Step Procedure for All-Granular Trackbed
1. Enter project title.
2. Select unit system.
3. Select trackbed type.
4. Click “Submit”.

23. 5. Select rail type.
6. Click Next.

24. 7. Select type of tie.
8. Select Number of Seasons.
10. Select cross section for out put.
9. Select Seasons for output.
11. Click “Next”.

25. 12. Select number of axle loads.
13. Click “Next”.

26. 14. Select number of track layers.
15. Select number of layers for vertical compression.
14. Select number of track layers.
16. Select layers to compute compression.
17. Click “Next”.

27. 18. Click “Result”.

29. Kentrack 4.0
Step-by-Step Procedure for Asphalt Underlayment Trackbed
1. Enter project title.
2. Select unit system.
3. Select trackbed type.
4. Click “Submit”.

30. 5. Select rail type.
6. Click “Next”.

31. 7. Select type of tie.
8. Select Number of Seasons.
10. Select cross section for out put.
9. Select Seasons for output.
11. Click “Next”.

32. 12. Select number of axle loads.
13. Click “Next”.

33. 21. Click “Next”. 14. Select number of track layers.
17. Select number of layers for vertical compression.
15. Select asphalt layers.
18. Select layers to compute compression.
16. Select asphalt binder grade.
19. Select number of layers for horizontal tension.
20. Select layers to compute tension.
21. Click “Next”.

34. 22. Click “Result”.

36. Kentrack 4.0
Step-by-Step Procedure for Combination Trackbed
1. Enter project title.
2. Select unit system.
3. Select trackbed type.
4. Click “Submit”.

37. 5. Select rail type.
6. Click Next.

38. 7. Select type of tie.
8. Select Number of Seasons.
10. Select cross section for out put.
9. Select Seasons for output.
11. Click “Next”.

39. 12. Select number of axle loads.
13. Click “Next”.

40. 21. Click “Next”. 14. Select number of track layers.
17. Select number of layers for vertical compression.
15. Select asphalt layers.
18. Select layers to compute compression.
16. Select asphalt binder grade.
19. Select number of layers for horizontal tension.
20. Select layers to compute tension.
21. Click “Next”.

41. 22. Click “Result”.

43. Subgrade Compressive Stress
Table 1 Critical Outputs for All-Granular, Asphalt Underlayment, and Combination Trackbeds with Wood Ties
Trackbed Type
Subgrade Compressive Stress
(psi)
Subgrade Service Life
(years)
Asphalt Tensile Strain
Asphalt Service Life
All-Granular Trackbed
13.37
6.2
n/a
Asphalt Underlayment Trackbed
10.75
22.0
25.8
Combination Trackbed
9.75
29.2
35.1