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 Computer Tekscan Sensor Predicts Measures
Tekscan Sensor Tekscan Sensor Tekscan Sensor Wooden Tie Ballast Geokon Pressure Geokon Pressure Cell Cell Subballast/HMA Pressure Cell Geokon Pressure Cell Subgrade
• Geokon Model 3500-2 • 9 in. Diameter Pressure Cell • Strain Gage • Snap-Master • Thermistor Cell Placement on Asphalt
Junction Box Pressure Cell Battery Pressure Cell Measurement Configuration
• Matrix-based array of force sensitive cells • Silver conductive electrodes • Pressure sensitive ink – Conductivity varies • Crossing of ink – strain gauge View of Tekscan Sensors Tekscan Measurement Configuration
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 Using Paver Installation of HMA Underlayment by Back-Dumping
350 ft 350 ft 10 ft 8 in. ballast 12 in. 8 in. 4 in. HMA 4 in. 4 in. subballast clay subgrade Pueblo, Colorado Longitudinal Section Existing Conditions at Transportation Technology Center, Pueblo, Colorado
1000 ft 1000 ft 9 in. 9 in. ballast 5 in. HMA 8 in. clay subgrade Conway, Kentucky Longitudinal View Existing Conditions at Conway, Kentucky
Calibration Test Configuration Using the Satec Universal Testing Machine.
25 Representative Dynamic Four 6-Axle Locos 8 in. ballast HMA Compressive Stress (psi) 5 in. HMA 20 Compressive Stress on Initial 5 Cars HMA Layer Measured for 15 Empty Coal Train on CSX 10 Transportation Mainline at Conway, KY 5 0 7 8 9 10 11 12 13 14 15 16 17 Time (s) 20 Four 6-Axle Locos 8 in. ballast 8 in. HMA HMA Compressive Stress (psi) 15 Initial 5 Cars 10 5 0 4 5 6 7 8 9 10 11 12 13 14 15 Time (s)
subgrade surface 20 HMA surface Compressive Stress (psi) 15 10 5 0 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 Time (s) Dynamic Compressive Pressures Measured on TTCI Test Track
Vertical Vertical Vertical Thickness Compressive Stress Compressive Stress Compressive Stress Ballast/HMA on Ballast on HMA on Subgrade inches KPV/ITD, psi KPV/ITD, psi KPV/ITD, psi 47.9 / 21 / 16 13.6 / - 10 / 5 48.7 / 22 / 15 11.7 / - 10 / 8 Comparison of the KENTRACK Predictive Values (KPV) Versus In-Track Data (ITD) for the CSX Mainline at Conway, Kentucky Vertical Vertical Vertical Thickness Compressive Stress Compressive Stress Compressive Stress Ballast/HMA on Ballast on HMA on Subgrade inches KPV/ITD, psi KPV/ITD, psi KPV/ITD, kPa 43.5 / - 11.7 / 14.9 8.3 / 8.0 12 / 4 47 / - 21.9 / 14.9 8.2 / 7.7 8 / 8 Comparison of the KENTRACK Predictive Values (KPV) Versus In-Track Data (ITD) at TTCI in Pueblo, Colorado
286,000 62,000 180 lb lb lb 13 - 17 2 - 4 6 100 - 200+ psi psi psi psi Vertical Pressure on Asphalt Surfaces for Various Loadings
In Track Placement During First Test Typical Pressure Distribution Plot from Tekscan System Scale in PSI
Scale in PSI This represents a typical pressure distribution between a steel tie plate and the rail .
Rubber Bladder Rail Mylar Teflon Tekscan Sensor Teflon Mylar 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.
500 450 Positioning of Lead Wheel Average Pressure (psi) 400 350 with Respect to Sensor 300 250 200 150 100 50 0 Directly Above Sensor 1 Ties Past Sensor 2 Ties Past Sensor 3 Ties Past Sensor 4 Ties Past Sensor 5 Ties Past Sensor 5 Ties Before Sensor 4 Ties Before Sensor 3 Ties Before Sensor 2 Ties Before Sensor 1 Tie Before Sensor Lead Wheel Position Snapshot of the Lead Wheel Lead Wheel Over Directly above the Sensor Sensor F = 20985 lbf, P = 437 psi
700 600 Average Pressure (psi) Positioning of Lead Wheel 500 with Respect to Sensor 400 300 200 100 0 10 Ties Before Sensor 8 Ties Before Sensor 6 Tie Before Sensor 4 Ties Before Sensor 2 Ties Before Sensor Directly Above Sensor 2 Ties Past Sensor 4 Ties Past Sensor 6 Ties Past Sensor 8 Ties Past Sensor 10 Ties Past Sensor Lead Wheel Position Lead Wheel Over Snapshot of the Lead Wheel Sensor Directly above the 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 135 psi 72.93 in^2
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
Tire Tread Mylar Teflon Tekscan Teflon Sensor Mylar 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
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