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.
Post on 15-Dec-2015
224 Views
Preview:
Transcript
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
S4
S4
S2
S4
S4
S4
S3 S2
S2
S4
S3 S2 S1
S2S1 S3
7
S3
S1
S2
S2
P1
1 2 3
S4
S1 S2
S3
S3
4 5
P2
6
S3 S2 S1 S2 S3
P
108
P3
9
P4
S4
Kentrack Theory• Superposition of Loads
P
PS
P
PSS 2
41
2'1
w(P)
y(My)
z
y
xji
l
l
w(P) z
x(Mx)i
x
jy
RAIL:
TIE:
w(P)
i
j
SPRING:
Kentrack Theory• Finite Element Method– Used to calculate the stress and strain in the rail
and tie
En-1 n-1
a
En n
E2
E1
Hzn-2
z2
z
z1
a
qr
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
n
i da
p
orNN
NL
1
1
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
top related