Kentrack, A Performance-Based Layered Elastic Railway Trackbed Structural Design and Analysis Procedure A Tutorial

Transcription

1 Kentrack, A Performance-Based Layered Elastic Railway Trackbed Structural Design and Analysis Procedure A Tutorial Jerry G. Rose University of Kentucky Lexington, KY USA Justin D. Brown University of Kentucky Lexington, KY USA Nithin K. Agarwal University of Kentucky Lexington, KY USA Neeharika Ilavala University of Kentucky Lexington, KY USA Prepared for the 2010 Joint Rail Conference April , Urbana, IL, USA Copyright 2010 by ASME JRC

2 Introduction 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

3 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

4 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#

5 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

6 All-Granular Traditional Track structure

7 Underlayment Asphalt

8 Combination Contains an asphalt layer and a granular subballast layer

9 Kentrack Theory Superposition of Loads P P S ' S 1 S P P

10 x Kentrack Theory Finite Element Method Used to calculate the stress and strain in the rail and tie RAIL: y(my) i y l j x w(p) z TIE: x(mx) i l j y w(p) z i SPRING: w(p) j

11 Kentrack Theory Multilayered System Used to calculate the stress and strain in each layer a a q r E1 z1 z2 E2 zn-2 H En-1 n-1 En n z

12 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

13 Kentrack Theory Ballast In new trackbeds the ballast behaves nonlinearly In aged trackbeds the ballast behaves linearly E Subgrade K 1 K Behaves as a linear elastic material 2 z( 1 2K )

14 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

15 Kentrack Theory Damage Analysis Based on minor linear damage analysis criteria Performance is based on periods For Kentrack this is four seasons L n 1 N p i 1 N a orn d

16 Kentrack Theory Predicted number of repetitions Each car equals one repetition

17 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 10 6 = 28.6 MGT/yr

18 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 c s N d E 3.583

19 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 t a N a E 0.853

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

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

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

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

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

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

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

27 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

28 Effect of Subgrade Modulus on Subgrade Compressive Stress

29 Subgrade Design Life (years) Effect of Subgrade Modulus on Subgrade Design Life Ton Axle Load 28.6 MGT/yr Subgrade life in All Granular-Trackbed Subgrade life in Asphalt Trackbed Subgrade life in Combination Trackbed Subgrade Modulus (psi)

30 Effect of Subgrade Modulus on Asphalt Tensile Strain

31 Asphalt Design Life (years) Effect of Subgrade Modulus on Asphalt Design Life Ton Axle Load 28.6 MGT/yr Asphalt Life in Asphalt Trackbed Asphalt Life in Combination Trackbed Subgrade Modulus (psi)

32 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 performancebased structural design and analysis

33 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

34 Start the program Asphalt Trackbed Tutorial Select the trackbed to be analyzed

35

36

37

38

39

40

41

42

43

44 Thank You Questions?