kentrack - university of kentucky college of engineeringjrose/ce533_html/powerpoint/kentrack/... ·...
TRANSCRIPT
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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
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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
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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#
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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
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All-Granular • Traditional Track structure
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Asphalt • Underlayment
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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 and tie
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Kentrack Theory • Multilayered System
– Used to calculate the stress and strain in each layer
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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
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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
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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
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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
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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
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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
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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
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Failure Criteria • All-Granular Trackbed
• Vertical Compressive Stress on Subgrade
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Failure Criteria • Asphalt Trackbed
• Vertical Compressive Stress on Subgrade, Tensile Strain at Bottom of Asphalt
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Kentrack Theory
• Combination Trackbed
• Vertical Compressive Stress on Subgrade, Tensile Strain at Bottom of Asphalt
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Typical cross section • All-Granular Trackbed
Sub. Mod. = 15,000 psi 28.6 MGT/yr
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Typical cross section • Asphalt Trackbed
Sub. Mod. = 15,000 psi 28.6 MGT/yr
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Typical cross section • Combination Trackbed
Sub. Mod. = 15,000 psi 28.6 MGT/yr
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Critical Outputs*
Variable All-Granular
Trackbed Asphalt
Trackbed Combination
Trackbed
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
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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
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Effect of Subgrade Modulus on Subgrade Compressive Stress
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Effect of Subgrade Modulus on Subgrade Design Life
36 Ton Axle Load 28.6 MGT/yr
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Subgrade life in All Granular-Trackbed
Subgrade life in Asphalt Trackbed
Subgrade life in CombinationTrackbed
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Effect of Subgrade Modulus on Asphalt Tensile Strain
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Asphalt Life in Combination Trackbed
Effect of Subgrade Modulus on Asphalt Design Life
36 Ton Axle Load 28.6 MGT/yr
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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
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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
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Asphalt Trackbed Tutorial • Start the program
• Select the trackbed to be analyzed
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