1 Volpe The National Transportation Systems Center Finite Element Analysis of Wood and Concrete Crossties Subjected to Direct Rail Seat Pressure U.S. Department of Transportation Research and Innovative Technology Administration John A. Volpe National Transportation Systems Center Volpe The National Transportation Systems Center Advancing transportation innovation for the public good Hailing Yu and David Jeong Structures and Dynamics Division
Transcript
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Volpe The National Transportation Systems Center
Finite Element Analysis of Wood and Concrete Crossties Subjected to Direct Rail Seat Pressure
U.S. Department of Transportation
Research and Innovative Technology Administration
John A. Volpe National Transportation Systems Center
Volpe The National Transportation Systems Center
Advancing transportation innovation for the public good
Hailing Yu and David JeongStructures and Dynamics Division
2
Overview
Background Finite element analyses Results Conclusions Future work Acknowledgements
3
Background Rail seat failure in ties can
cause rail rollover derailments Plate cutting in wood ties Rail seat deterioration in
concrete tieso Probable cause for two Amtrak
derailment accidents in Washington in 2005 and 2006
o Recently observed on the Northeast Corridor
Correlation of rail seat failure with rail seat load is needed
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Objectives
Develop finite element (FE) models for wood and concrete ties in a ballasted track
Study failure mechanisms of railroad ties subjected to rail seat loading using the FE models
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Current Simplifications
Fasteners are not modeled Vertical load is applied as direct rail seat
pressure Lateral load is not applied
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Directionality in Wood Material
L: parallel to fiberT: perpendicular to fiber and tangent to growth ringsR: normal to growth rings
L
R
T
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Orthotropic Elasticity
RT
LT
LR
TT
RR
LL
RT
LT
LR
TR
RT
L
LT
T
TR
RL
LR
T
TL
R
RL
L
RT
LT
LR
TT
RR
LL
G
G
G
EEE
EEE
EEE
100000
01
0000
001
000
0001
0001
0001
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Orthotropic Strength Limits
Symbol DescriptionXLt Tensile strength in the fiber direction LXLc Compressive strength in the fiber direction LXRt Tensile strength in the radial direction RXRc Compressive strength in the radial direction RXTt Tensile strength in the tangential direction TXTc Compressive strength in the tangential direction TSLR Shear strength in the L-R planeSLT Shear strength in the L-T planeSRT Shear strength in the R-T plane
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Representative Wood PropertiesEL (psi) ER (psi) ET (psi)
Based on properties of the white oak species described in Bergman, R., et al., “Wood handbook - Wood as an engineering material,” General Technical Report FPL-GTR-190, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory: 508 p. 2010.
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Macroscopic Heterogeneity and Material Nonlinearity in Concrete Ties Steel strands/wires
Linear elasticity with perfectly plastic yield strength
Concrete Linear elasticity followed by
damaged plasticity Interfaces
Bond-slip depicted in linear elasticity followed by initiation and evolution of damage to bond
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Quarter Symmetric FE Models of 8-Strand and 24-Wire Concrete Crossties
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Concrete Material Models Concrete damaged plasticity Uniaxial tension: linear
elasticity followed by tension stiffening
Uniaxial compression: linear elasticity followed first by strain hardening and then by strain softening
Multi-axial yield function dt – tensile damage variable
dc – compressive damage variabled – stiffness degradation variable (a function of dt and dc)
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Cohesive Interface Elements
n – normal directions, t – shear directions
Normal traction tn
Shear tractions ts, tt
bracketMacaulay theis where,12
0t
t
2
0s
s
2
0n
n
t
t
t
t
t
t
Quadratic nominal stress criterion for damage initiation
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Support to the Ties Ballast
Extended Drucker-Prager model for granular, frictional materials
Subgrade Modeled as an elastic
half space using infinite elements
Transitional layers can be modeled if geometric and material properties are known
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Material Parameters
All material parameters are obtained from open literature
There is insufficient data on the bond-slip properties of steel tendon-concrete interfaces
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Analysis Steps Initial condition
Steel tendons pretensioned to requirements (concrete tie) First step (static analysis)
Pretension released in the tendons (concrete tie) Second step (dynamic analysis)
Uniformly distributed pressure loads applied on rail seats (wood and concrete ties)
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Deformed Concrete Tie Shape After Pretension Release
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Compressive Stress State in Concrete After Pretension Release
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Ratio of Pretension Retention
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
8-strand tie24-wire tie
Av
erag
e ra
tio
of
pre
ten
sio
n r
ete
nti
on
Relative distance to tie center (1=tie end)
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Predicted Failure Mode Under Rail Seat Pressure
Wood tie – compressive rail seat failure
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Predicted Failure Mode Under Rail Seat Pressure
Concrete tie – tensile cracking at tie base
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Rail Seat Force vs. Displacement Up To Predicted Failure
Absolute rail seat displacement
0
5
10
15
20
25
30
35
40
0 0.05 0.1 0.15 0.2 0.25 0.3
8-strand concrete tie24-wire concrete tieWood tie
Ra
il s
eat
forc
e (k
ip)
Rail seat displacement (inch)
(a)
Rail seat displacement relative to tie base
0
5
10
15
20
25
30
35
40
0 0.005 0.01 0.015 0.02 0.025 0.03
Rai
l sea
t fo
rce
(kip
)
Relative rail seat displacement (inch)
(b)
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Partition of Tie-Ballast Interface
Fifty-one sub-surfaces on lower surface of wood tie
Contact force calculated on each sub-surface
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Contact Force Distribution on the Lower Surface of Wood Tie
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Conclusions
FE analyses predict that under a uniform rail seat pressure load, The wood tie fails at the rail seats due to excessive
compressive stresses Tensile cracks form at the base of the concrete ties
The simplified loading application predicts rail seat failure in the wood tie but not in the concrete ties
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Future Work
Calibrate bond-slip relations in the steel tendon-concrete interfaces from tensioned or untensioned pullout tests
Incorporate fasteners and rails, and apply both vertical and lateral loading
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Acknowledgements
The Track Research Division in the Office of Research and Development of Federal Railroad Administration sponsored this research.
Technical discussions with Mr. Michael Coltman, Dr. Ted Sussmann and Mr. John Choros are gratefully acknowledged.
