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
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 ties
o
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
4
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
5
Current Simplifications
Fasteners are not modeled
Vertical load is applied as direct rail seat
pressure
Lateral load is not applied
6
Directionality in Wood Material
L: parallel to fiber
T: perpendicular to fiber and tangent to growth rings
R: normal to growth rings
L
R
T
7
Orthotropic Elasticity
RT
LT
LR
TT
RR
LL
RT
LT
LR
T
R
RT
L
LT
T
TR
R
L
LR
T
TL
R
RL
L
RT
LT
LR
TT
RR
LL
G
G
G
E
E
E
E
E
E
E
E
E
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
8
Orthotropic Strength Limits
Symbol
Description
X
Lt
Tensile
strength
in
the
fiber
direction
L
X
Lc
Compressive
strength
in
the
fiber
direction
L
X
Rt
Tensile
strength
in
the
radial
direction
R
X
Rc
Compressive
strength
in
the
radial
direction
R
X
Tt
Tensile
strength
in
the
tangential
direction
T
X
Tc
Compressive
strength
in
the
tangential
direction
T
S
LR
Shear
strength
in
the
L

R
plane
S
LT
Shear
strength
in
the
L

T
plane
S
RT
Shear
strength
in
the
R

T
plane
9
Representative Wood Properties
E
L
(psi)
E
R
(psi)
E
T
(psi)
1,958,000
319,154
140,976
LR
LT
RT
0.369
0.428
0.618
G
LR
(psi)
G
LT
(psi)
G
RT
(psi)
168,388
158,598
41,118
X
Lt
(psi)
X
Lc
(psi)
X
Rt
,
X
Tt
(psi
)
X
Rc
,
X
Tc
(psi
)
S
LR
,
S
LT
(psi
)
15,200
7,440
800
1,070
2,000
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.
10
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
11
Quarter Symmetric FE Models of 8

Strand and 24

Wire Concrete Crossties
12
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
d
t
–
tensile damage variable
d
c
–
compressive damage
variable
d
–
stiffness degradation
variable (a function of
d
t
and
d
c
)
13
Cohesive Interface Elements
n
–
normal direction
s, t
–
shear directions
Normal traction
t
n
Shear tractions
t
s
,
t
t
bracket
Macaulay
the
is
where
,
1
2
0
t
t
2
0
s
s
2
0
n
n
t
t
t
t
t
t
Quadratic nominal stress criterion for damage initiation
14
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
15
Material Parameters
All material parameters are obtained from
open literature
There is insufficient data on the bond

slip
properties of steel tendon

concrete interfaces
16
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)
17
Deformed
Concrete Tie
Shape After
Pretension Release
18
Compressive Stress State in Concrete
After Pretension Release
19
Ratio of Pretension Retention
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
8strand tie
24wire tie
Average ratio of pretension retention
Relative distance to tie center (1=tie end)
20
Predicted Failure Mode Under Rail
Seat Pressure
Wood tie
–
compressive rail seat failure
21
Predicted Failure Mode Under Rail
Seat Pressure
Concrete tie
–
tensile cracking at tie base
22
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
8strand concrete tie
24wire concrete tie
Wood tie
Rail seat force (kip)
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
Rail seat force (kip)
Relative rail seat displacement (inch)
(b)
23
Partition of Tie

Ballast Interface
Fifty

one
sub

surfaces on lower surface of
wood tie
Contact
force
calculated on each
sub

surface
24
Contact Force Distribution on the
Lower Surface of Wood Tie
25
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
26
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
27
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.
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