Analysis of Rail Pad Assemblies Responses
Thiago B. do Carmo, Brent Williams, Riley Edwards, Ryan Kernes,
Bassem Andrawes, Christopher Barkan
Joint Rail Conference – JRC 2014
Colorado Springs, CO
3 April 2014
Slide 2Analysis of Rail Pad Assemblies Responses
Outline
• Background
• Load Path in the Fastening System
• Mechanistic Design Framework
• Research Project Objectives
• Field Setup and Experimental Results
• Conclusions
• Future Work
Slide 3Analysis of Rail Pad Assemblies Responses
Background
• Industry Trends:
– Increasing heavy axle loads (HAL) and traffic volumes
– Many variations in fastening system design, performance, and life cycle
– Some fastening system components are failing earlier than their intended
design life
• Challenge: develop more efficient concrete crosstie and fastening system
designs that withstand increasingly demanding loading conditions
• Over 25 million concrete crossties are in use on North American heavy
haul freight railroads
Examples of Failure Modes in the Fastening System Components
Tearing, crushing, and cracking observed in deteriorated components
Slide 4Analysis of Rail Pad Assemblies Responses
Defining the Load Path
Vertical Wheel Load
Lateral Wheel Load
Bearing Forces
Frictional Forces
Rail
Clip
Shoulder
Insulator
Concrete Crosstie
Rail Pad Assembly
Slide 5Analysis of Rail Pad Assemblies Responses
Mechanistic Design Framework
Loads
Rail
Fastening
System
Crosstie
Ballast
Subgrade
• Representative input loads and loading distribution
factors are not a clear part of the current design
methodology, particularly in the lateral direction
• Mechanistic design is an approach based on loads
measured in track structure and properties of materials
that will withstand or transfer them
• Uses responses (e.g. contact pressure, relative
displacements) to optimize component geometry and
materials requirements
• Based on measured and predicted response to load
inputs
• Can be supplemented with practical experience
• Used in other engineering applications (e.g. pavement
design, concrete design, structural steel design)
Distribution
Slide 6Analysis of Rail Pad Assemblies Responses
Research Project Objectives
• Provide a framework for a mechanistic design approach for
concrete crossties and fastening systems
• Quantify displacements of rail pad assemblies relative to
crossties in the field and investigate relationship with wheel
loads and fastening system lateral stiffness
• Develop recommendations for rail pad assembly design
based on the analysis of vertical and lateral load path
Slide 7Analysis of Rail Pad Assemblies Responses
Field Experiment Program• Objective: Analyze the distribution of forces through the fastening system and
impact on components relative displacements
• Location: Transportation Technology Center
(TTC) in Pueblo, CO
• High Tonnage Loop (HTL): 2 degree curve
section with Safelok I fasteners
• Railroad Test Track (RTT): tangent section
with Safelok I fasteners
• Instrumentation:
- Linear potentiometers were used to
measure the lateral displacement of the
rail base and rail pads
- Strain gauges placed on the rail were
used to measure the vertical and lateral
wheel loads
• Loading: Track Loading Vehicle (TLV) and
train consists (passenger and freight) were
used to apply loads
Transportation Technology Center (TTC)
High Tonnage Loop (HTL)
HT
L
RTT
Slide 8Analysis of Rail Pad Assemblies Responses
Field Instrumentation
Low
Rail
High
Rail
Potentiometer measuring pad lateral
displacement
Lateral Load Evaluation Device
(LLED) – Williams 2013
Pad Displacement
Rail Displacement
LLED
Slide 9Analysis of Rail Pad Assemblies Responses
0
2,500
5,000
7,500
10,000
12,500
15,000
17,500
20,000
22,500
25,000
0 5 10 15 20 25 30 35 40 45
Fo
rce (
lbf)
Speed (mph)
315K_LAT_WHEEL PASSENGER_LAT_WHEEL
315K_LLED PASSENGER_LLED
Maximum Lateral Wheel Loads and Lateral LLED
Forces at Rail Seat U for Increasing Speed
B C E G
Q S U W
315 K Lateral Wheel Load Passenger Lateral Wheel Load
Passenger LLED315 K LLED
Slide 10Analysis of Rail Pad Assemblies Responses
Comparison of Fastening System Lateral Stiffness (Freight Consist on HTL)
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050
LL
ED
La
tera
l F
orc
e (
lbf)
Rail Base Lateral Displacement (in)
Rail Seat S
Rail Seat U
B C E G
Q S U W
294,810 lbf/in
163,514 lbf/in
Slide 11Analysis of Rail Pad Assemblies Responses
Rail Base Lateral Translation (Freight Consist on HTL)
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0.022
7 9 11 13 15 17 19 21
Rail
Base L
ate
ral
Dis
pla
cem
en
t (i
n)
Lateral Wheel Load (Kips)
Rail Base S
Rail Base U
B C E G
Q S U W
Slide 12Analysis of Rail Pad Assemblies Responses
Rail Pad Lateral Displacement (Freight Consist on HTL)
0.0020
0.0022
0.0024
0.0026
0.0028
0.0030
0.0032
0.0034
0.0036
0.0038
0.0040
7 9 11 13 15 17 19 21
Rail
Pad
Late
ral
Dis
pla
cem
en
t (i
n)
Lateral Wheel Load (Kips)
Rail Pad S
Rail Pad U
B C E G
Q S U W
Slide 13Analysis of Rail Pad Assemblies Responses
Rail Base and Rail Pad Lateral Displacement (Track Loading Vehicle on RTT)
0.000
0.003
0.006
0.009
0.012
0.015
0.018
0.021
0.024
0.027
0.030
0.033
0.036
0.039
0.042
0 5 10 15 20 25
Dis
pla
cem
en
t (i
n)
Lateral Force (kips)
Rail Base S
Rail Base E
Pad E
Rail Base W
Pad S
Pad U
Pad W
Rail Base U
40 kips Vertical
Load
Slide 14Analysis of Rail Pad Assemblies Responses
Relative Lateral Displacement Between Rail Base
and Rail Pad Assembly (40 kips Vertical Load)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.1 0.2 0.3 0.4 0.5
Dis
pla
cem
en
t (i
n)
Rail Pad
Rail Base
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.1 0.2 0.3 0.4 0.5
Dis
pla
cem
en
t (i
n) S
Rail Pad
Rail Base
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.1 0.2 0.3 0.4 0.5
Dis
pla
cem
en
t (i
n)
Rail Pad
Rail Base
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.1 0.2 0.3 0.4 0.5
Dis
pla
cem
en
t (i
n)
Rail Pad
Rail Base
Slide 15Analysis of Rail Pad Assemblies Responses
Conclusions• Relative displacements of the rail pad assembly and rail base with respect
to the concrete crosstie were successfully measured in the field
• The lateral displacement of the rail pad and rail base is directly related to
the lateral wheel loads applied to the track
• Depending on the location of the load application, the lateral displacement
of the rail base is able to reach a value six times higher than the lateral
displacement of the rail pad
• Rail seats with higher lateral stiffness resulted in a higher percentage of
lateral load bearing on the insulator post and shoulder face
• Adjacent rail seats can have considerable
differences in lateral stiffness and resultant
magnitudes of lateral forces
• Lateral displacement of rail and rail pad
assembly should be considered in
fastening system design and material
selection
Slide 16Analysis of Rail Pad Assemblies Responses
Future Work: RailTEC’s Research and
Innovation Laboratory (RaIL)
Slide 17Analysis of Rail Pad Assemblies Responses
Acknowledgements
• Funding for this research has been provided by
– Federal Railroad Administration (FRA)
– National University Rail Center - NURail
• Industry Partnership and support has been provided by
– Union Pacific Railroad
– BNSF Railway
– National Railway Passenger Corporation (Amtrak)
– Amsted RPS / Amsted Rail, Inc.
– GIC Ingeniería y Construcción
– Hanson Professional Services, Inc.
– CXT Concrete Ties, Inc., LB Foster Company
– TTX Company
– Transportation Technology Center, Inc (TTCI)
• For assisting with research and experimentation
– Marcus Dersch, George Chen, Brandon Van Dyk
FRA Tie and Fastener BAA
Industry Partners:
Slide 18Analysis of Rail Pad Assemblies Responses
Thank you!
Questions or Comments?
Thiago Bizarria do Carmo
University of Illinois at Urbana-Champaign
Department of Civil and Environmental Engineering
Email: [email protected]