Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Comparisons of Railroad Track
and Substructure Computer
Model Predictive Stress Values
and In-Situ Stress Measurements
By: Dr. Jerry G. Rose, Ph.D., PE
Bei Su, MSCE and
Frank Twehues, EIT
Earth Pressure Cell
Measures Predicts Tekscan Sensor
Computer
Geokon Pressure
Cell
Ballast
Subballast/HMA
Wooden Tie
Subgrade
Geokon Pressure
Cell
Tekscan Sensor
Tekscan Sensor
Geokon Pressure Cell
Pressure Cell
Tekscan Sensor
• Geokon Model 3500-2
• 9 in. Diameter
• Strain Gage
• Snap-Master
• Thermistor
Pressure Cell
Cell
Placement
on Asphalt
Pressure Cell
Junction Box
Battery
Pressure Cell Measurement Configuration
View of Tekscan Sensors
Tekscan Measurement
Configuration
•Matrix-based array of
force sensitive cells
•Silver conductive electrodes
•Pressure sensitive ink –
Conductivity varies
•Crossing of ink – strain gauge
Traditional Track Structure
Track Structure With Asphalt Underlayment
– 5-10 feet beyond crossing
– Typical highway dense-graded
base mix
– 0.5% higher asphalt content
Installation of HMA Underlayment by Back-Dumping
Installation of HMA Underlayment Using Paver
HMA
ballast
subballast4 in.
4 in.
12 in.
4 in.
8 in.
8 in.
clay subgrade
10 ft350 ft350 ft
Pueblo, Colorado Longitudinal Section
Existing Conditions at Transportation Technology Center, Pueblo, Colorado
Conway, Kentucky Longitudinal View
Existing Conditions at Conway, Kentucky
clay subgrade
9 in.
8 in.
9 in.
5 in.HMA
ballast
1000 ft 1000 ft
Calibration Test Configuration Using the
Satec Universal Testing Machine.
0
5
10
15
20
25
7 8 9 10 11 12 13 14 15 16 17
Time (s)
HM
A C
om
pre
ssiv
e S
tress (
psi)
Four 6-Axle Locos
Initial 5 Cars
8 in. ballast
5 in. HMA
0
5
10
15
20
4 5 6 7 8 9 10 11 12 13 14 15
Time (s)
HM
A C
om
pre
ssi
ve
Str
ess (
psi
)Four 6-Axle Locos
Initial 5 Cars
8 in. ballast
8 in. HMA
Representative Dynamic
Compressive Stress on
HMA Layer Measured for
Empty Coal Train on CSX
Transportation Mainline
at Conway, KY
0
5
10
15
20
2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5
Time (s)
Co
mpre
ssiv
e S
tre
ss (
ps
i)
subgrade surfaceHMA surface
Dynamic Compressive Pressures Measured on TTCI Test Track
Comparison of the KENTRACK Predictive Values (KPV)
Versus In-Track Data (ITD) for the CSX Mainline at Conway, Kentucky
Thickness
Ballast/HMA
inches
Vertical
Compressive Stress
on Ballast
KPV/ITD, psi
Vertical
Compressive Stress
on HMA
KPV/ITD, psi
Vertical
Compressive Stress
on Subgrade
KPV/ITD, psi
10 / 5 47.9 / 21 / 16 13.6 / -
10 / 8 48.7 / 22 / 15 11.7 / -
Comparison of the KENTRACK Predictive Values (KPV)
Versus In-Track Data (ITD) at TTCI in Pueblo, Colorado
Thickness
Ballast/HMA
inches
Vertical
Compressive Stress
on Ballast
KPV/ITD, psi
Vertical
Compressive Stress
on HMA
KPV/ITD, psi
Vertical
Compressive Stress
on Subgrade
KPV/ITD, kPa
12 / 4 43.5 / - 11.7 / 14.9 8.3 / 8.0
8 / 8 47 / - 21.9 / 14.9 8.2 / 7.7
286,000
lb
62,000
lb
180
lb
13 - 17
psi
2 - 4
psi
6
psi
100 - 200+
psi
Vertical Pressure on Asphalt Surfaces for Various Loadings
In Track Placement During First Test
Scale in PSI
Typical Pressure Distribution
Plot from Tekscan System
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.
Scale in PSI
This represents a typical pressure distribution
between a steel tie plate and the rail.
Rail
Mylar Teflon
Tekscan
Sensor
Teflon
Mylar
Rubber Bladder
Tie Plate
Scale in PSI
This represents a typical pressure distribution between a machined
steel tie plate and the rail with an included rubber bladder.
Scale in PSI
This represents a typical pressure distribution between
a polyurethane plastic tie plate and the rail.
0
50
100
150
200
250
300
350
400
450
500
5 Tie
s Bef
ore
Senso
r
4 Tie
s Bef
ore
Senso
r
3 Tie
s Bef
ore
Senso
r
2 Tie
s Bef
ore
Senso
r
1 Tie
Bef
ore
Sen
sor
Dire
ctly A
bove
Sen
sor
1 Tie
s Pas
t Sen
sor
2 Tie
s Pas
t Sen
sor
3 Tie
s Pas
t Sen
sor
4 Tie
s Pas
t Sen
sor
5 Tie
s Pas
t Sen
sor
Lead Wheel Position
Avera
ge P
ressu
re (
psi) Positioning of Lead Wheel
with Respect to Sensor
Snapshot of the Lead Wheel
Directly above the Sensor Lead Wheel Over
Sensor F = 20985 lbf, P = 437 psi
0
100
200
300
400
500
600
700
10 T
ies Bef
ore
Sen
sor
8 Tie
s Bef
ore
Senso
r
6 Tie
Bef
ore
Sen
sor
4 Tie
s Bef
ore
Senso
r
2 Tie
s Bef
ore
Senso
r
Dire
ctly A
bove
Sen
sor
2 Tie
s Pas
t Sen
sor
4 Tie
s Pas
t Sen
sor
6 Tie
s Pas
t Sen
sor
8 Tie
s Pas
t Sen
sor
10 T
ies Pas
t Sen
sor
Lead Wheel Position
Avera
ge P
ressu
re (
psi)
Positioning of Lead Wheel
with Respect to Sensor
Snapshot of the Lead Wheel
Directly above the Sensor
Lead Wheel Over
Sensor F = 25372 lbf, P = 529 psi
Rear Tires of Tractor of a 151,000 lb Loaded Coal Truck on Concrete
Crossing of Kentucky Coal Terminal, Mile Post 6.6. May 25, 2004
9842 lb
72.93 in^2
135 psi
Front Tire of a CSXT Suburban on Asphalt Parking Lot in Ashland Oil
Company. May 25, 2004
1652 lb 75 PSI
22.15 in^2
Rear Tire of a CSXT Suburban on Asphalt Parking Lot in Ashland Oil Company.
May 25, 2004
2197 lb 81 PSI
27.15 in^2
Mylar Teflon
Tekscan
Sensor
Teflon
Mylar
Tire Tread
Asphalt Surface
FINDINGS
• KENTRACK -- utilized to predict stresses in the track structure and foundation
• Earth Pressure Cells -- provide direct measurement of
pressures (stresses) in the track structure and foundation
• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces
• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements
FINDINGS
• KENTRACK -- utilized to predict stresses in the track structure and foundation
• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation
• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces
• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements
FINDINGS
• KENTRACK -- utilized to predict stresses in the track structure and foundation
• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation
• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces
• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements
FINDINGS
• KENTRACK -- utilized to predict stresses in the track structure and foundation
• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation
• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces
• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements
Findings (conti.)
• Tekscan Sensors -- technology developed for using them for track pressure measurements at the rail/plate and plate/tie interfaces – Sensors are thin and non-intrusive
– Repeatability is very good - consider loads applied, loading rate, and surrounding material
– Calibration is very important consideration
– Thin rubber bladder must be used on steel tie plates
– Shim stock is necessary
– Wide range of track related applications
Findings (conti.)
• Tekscan Sensors -- technology developed for using them for track pressure measurements at the rail/plate and plate/tie interfaces
– Sensors are thin and non-intrusive
– Repeatability is very good - consider loads applied, loading rate, and surrounding material
– Calibration is very important consideration
– Thin rubber bladder must be used on steel tie plates
– Shim stock is necessary
– Wide range of track related applications
Potential Tekscan Applications
• Superelevation – Curve design
• Impact pressures – diamonds
-- bridge approaches
• Plates, Pads, Fastenings & Ties
• ? ? ? ? ?
Acknowledgements