U.S. Department of 

Transportation

Federal Railroad 

Administration

Torsional Stiffness of

Railroad Coupler Connections

Office of Railroad

Policy and Development

Washington, DC 20590

DOT/FRA/ORD-10/13 Final Report

November 2010
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November 2010 Technical Report

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Torsional Stiffness of Railroad Coupler Connections

6. AUTHOR(S)

Robert Trent, Anand Prabhakaran, and Vinaya Sharma

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Sharma & Associates, Inc.

5810 S. Grant Street

Hinsdale, IL 60521

8. PERFORMING ORGANIZATION 

REPORT NUMBERS

9. SPONSORING/MONITORING AGENGY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

U.S. Department of Transportation

Federal Railroad Administration

1200 New Jersey Ave., SE

Washington, DC 20590

DOT/FRA/ORD-10/13

11. SUPPLEMENTARY NOTES

Program Manager: Francisco Gonzalez III

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

This document is available to the public through the FRA Web site at 

http://www.fra.dot.gov.

13. ABSTRACT

Tank cars are required to use double shelf couplers to prevent the coupler of an adjacent car from puncturing the tank head in the 

case of overrides or accidents. However, the added torsional stiffness of such coupler connections might lead to tank cars „taking 

down‟ adjacent coupled cars in rollover derailments. This project investigated the torsional behavior of freight car coupler 

connections through analysis and test. Tests included the following coupler combinations: no-shelf to no-shelf, shelf to no-shelf,

and shelf to shelf combinations in both clockwise to counterclockwise directions. Coupler specimens of each test run were mounted 

in a test fixture with one coupler receiving a torque application. Results show a greater torsional stiffness for coupler connections 

that have couplers with the shelf feature over those that do not. The more shelves that are present in a coupler connection, the 

greater the transmission of torque, implying that the presence of a shelf coupler or couplers adds to the torsional stiffness of the 

coupler connection. What is still not clear is whether this stiffness will contribute to, or help prevent, rollovers of adjacent coupled 

cars. We recommend further study into the potential of stiff coupler connections for propagating car rollovers, specifically through 

the use of vehicle dynamics models that incorporate the effects car suspension and car structure, in addition to the stiffness of 

coupler connections.

14. SUBJECT TERMS 15. NUMBER OF PAGES

coupler torque, coupler stiffness, rollover, shelf coupler, tank car, tank car safety 45

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 

OF THIS PAGE

19. SECURITY 

CLASSIFICATION OF 

ABSTRACT

20. LIMITATION OF ABSTRACT

Unclassified Unclassified Unclassified

NSN 7540-01-280-5500 Standard Form 298 (Rec. 2-89)

Prescribed by ANSI/NISO Std. 239.18

298-102
ii

METRIC/ENGLISH CONVERSION FACTORS 

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 7 8 9 10 11 12 13

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSION

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0 ° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters 

(cm2)

1 square centimeter (cm2) = 0.16 square inch (sq in, in2)

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, 

yd2)

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2)

1 square mile (sq mi, mi2) = 2.6 square kilometers 

(km2)

10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 

pounds (lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] F = y C [(9/5) y + 32] C = x F
iii

Contents 

Executive Summary ........................................................................................................................ 1

1 Introduction ............................................................................................................................. 3

1.1 Background ...................................................................................................................... 3

1.2 Objectives ......................................................................................................................... 3

1.3 Project Plan ...................................................................................................................... 3

2 Analytical Model ................................................................................................................. 5

2.1 Finite Element Analysis Model ........................................................................................ 5

2.2 Finite Element Analysis Results ...................................................................................... 8

3 Physical Testing .................................................................................................................... 11

3.1 Introduction and Objective ............................................................................................. 11

3.2 Test Apparatus................................................................................................................ 11

3.3 Test Specimens ............................................................................................................... 16

3.4 Test Procedure ................................................................................................................ 17

3.5 Results – Physical Testing.............................................................................................. 18

4 Conclusions ........................................................................................................................... 25

5 Recommendations ................................................................................................................. 26

Appendix A – Fixture Assembly Drawings .................................................................................. 27

Appendix B – Test Data ................................................................................................................ 31
iv

Illustrations 

Figure 1. F-Type Coupler Model ................................................................................................... 6

Figure 2. Coupled F-Type Couplers .............................................................................................. 6

Figure 3. Constraints ...................................................................................................................... 7

Figure 4. Mesh – Single Coupler ................................................................................................... 7

Figure 5. Analytical Model Data ....................................................................................................9 

Figure 6. Total Displacement – Virtual Model ............................................................................ 10 

Figure 7. von Mises Stress – Virtual Model ................................................................................ 10

Figure 8. Test Apparatus .............................................................................................................. 12

Figure 9. Test Apparatus .............................................................................................................. 12

Figure 10. Test Apparatus Motion ............................................................................................... 14 

Figure 11. Rear Bearing ................................................................................................................15 

Figure 12. Front Bearing .............................................................................................................. 15

Figure 13. Load Cell and Clevis .................................................................................................. 16 

Figure 14. Results Comparison – Counterclockwise ....................................................................19 

Figure 15. Comparison of Results – Clockwise............................................................................20 

Figure 16. Upper Shelf to Upper Shelf Contact ........................................................................... 23

Figure 17. Typical Contact (No-Shelf Mated to No-Shelf) ......................................................... 23

Figure 18. Shelf to Shelf Test Run............................................................................................... 24

Figure 19. No-Shelf to No-Shelf Test Run .................................................................................. 24
v

Tables 

Table 1. Combinations ................................................................................................................. 11

Table 2. Results Comparison – Counterclockwise ...................................................................... 20

Table 3. Results Comparison – Clockwise .................................................................................. 21
1

Executive Summary

Tank cars are required to use couplers with top and bottom shelves to prevent the coupler of an 

adjacent car from puncturing the tank head in the case of an undesired uncoupling, coupler 

override or accident. However, the added torsional stiffness of such coupler connections might 

be detrimental in certain other cases, especially where cars have leaned over and derailed, for 

example, low-speed derailments in classification yards. In such a scenario, a car that has 

derailed might “take down” an adjacent car with it, because of a stiff coupler connection. 

Similarly, the transmission of torque from a rail car to the next coupled car as a result of a 

disturbing force such as high winds could result in “chain” derailments. In revenue service, 

strings of stationary, coupled tank cars equipped with double-shelf couplers have been reported 

rolling over on more than one occasion in a chain reaction as a result of wind force. This 

phenomenon propagated up to the point in the consist where no-shelf couplers were located. 

In contrast, it is possible that in some scenarios, a mated shelf coupler may help resist and inhibit 

an adjacent car from rolling over. It is possible that for every “domino” effect multicar rollover, 

there are also some potential rollovers that are eliminated because of the shelf-type coupler. 

This study evaluated the behavior of freight car coupler connections in regard to the connections 

tendency to transmit torque from car to car. The goal of this study was to determine the torsional 

stiffness characteristics of the coupler connections based on the presence of coupler shelves 

considering multiple combinations of coupler types. These combinations would include all those 

possible with no-shelf, shelf, and a combination of shelf and no-shelf couplers connected. Both 

clockwise and counterclockwise rotations were performed to ensure contact at both top and 

bottom shelves. 

An analytical model was developed from a coupler connection using two F-type couplers and 

analyzed using the Finite Element Method. The torque-deflection results of this model were 

used as a comparator to controlled laboratory testing using actual couplers. 

A physical test bed was designed and constructed for mounting two connected coupler test 

specimens and for actuating one with an applied and controllable torque. A vertical offset of 5 

inches was provided between mating couplers to simulate the drop of a derailed car. Appropriate 

instrumentation was used to record the torque and the resulting angular displacement. 

Results of the physical testing show that a significant difference exists in the torsional stiffness 

of the coupler connections depending on the combination of coupler types used in the 

connection. Generally, the more shelves that are present in a coupler connection, the greater the 

transmission of torque. In other words, a coupler connection between two couplers equipped 

with top shelves was the stiffest, torsionally. Conversely, a coupler connection between two 

nonshelf couplers was the most torsionally flexible. The combinations that included only one 

shelf coupler also showed less deflection than the combination without any shelves. This reveals 

that the presence of a shelf coupler or couplers will add to the torsional stiffness of the coupler 

connection. 
2

The question as to whether shelf couplers add to the torsional stiffness of coupled connections 

has been answered in this study. What is still not clear is whether this stiffness will contribute to, 

or help prevent, rollovers of adjacent coupled cars. Therefore, we recommend further study into 

the characteristics of the coupler connection and its propensity of propagating car rollovers. 

Through the use of the torque-displacement relationships established in this study, vehicle 

dynamics simulations should be performed using the appropriate dynamics software, such as 

Vampire. Such analyses can capture more variables likely to affect the outcome such as those in 

the car suspension and car structure. Analytical models of multiple rail cars coupled together

can be constructed and analyzed to determine the actual propensity of one car to rollover, based 

on the types of couplers used.
3

1. Introduction

1.1 Background

Tank cars are required to use couplers with top and bottom shelves to prevent the coupler of an 

adjacent car from puncturing the tank head in the case of an undesired uncoupling, coupler 

override or accident. A tank head puncture could result in uncontrolled lading release leading to 

serious consequences, especially in the case of hazardous materials (hazmat). Certain hazmat 

commodities also require the use of head shields in addition to shelf couplers. 

Although such shelf couplers are beneficial in cases where potential uncoupling and coupler 

override might occur, the added torsional stiffness of such coupler connections might be 

detrimental in certain other cases, especially where cars have leaned over and derailed, for 

example low-speed derailments in classification yards. In such a scenario, a car that has derailed 

might take down an adjacent car with it, because of a stiff coupler connection. 

Similarly, the transmission of torque from a rail car to the next coupled car as a result of a 

disturbing force such as high winds could result in “chain” derailments. In revenue service, 

strings of stationary, coupled tank cars equipped with double shelf couplers have been reported 

rolling over in chain reaction as a result of wind force, on more than one occasion. This 

phenomenon can propagate up to the point in the consist where no shelf couplers were located. 

Thus, examining the torsional behavior of shelf couplers is necessary to evaluate whether there is 

an increased potential for derailment (if any) of cars that use shelf couplers as compared with 

cars that use nonshelf couplers.

1.2 Objectives

The effect of shelf coupler torsional rigidity on the derailment potential of hazmat tank cars was 

investigated (i.e., to investigate whether a derailed tank car could take down an adjacent car). 

The first step in the process was to establish whether shelf couplers were significantly stiffer than 

nonshelf couplers, and if so, by how much. The stiffness would be studied by using appropriate 

analytical models and controlled laboratory testing of actual coupler designs, as appropriate. The 

results of this study will help the tank car industry evaluate the risks and benefits associated with 

using shelf couplers on hazmat tank cars. 

1.3 Project Plan 

The overall plan of action for the study was as follows: 

1. Develop analytical models to study and evaluate the relative torsional rigidity of shelf 

couplers. The modeling and analysis would quantify the extent to which shelf 

coupler designs could contribute to increased derailment potential. 

2. Evaluate the torsional stiffness of shelf couplers in controlled laboratory tests using 

actual couplers. A suitable test bed for the test effort would be designed and 

implemented, including suitable instrumentation to measure the torque applied and 

the corresponding rotations. 

3. Compare the analytical results against the laboratory tests to verify reasonableness. 
4

4. Prepare a suitable test/evaluation plan for additional work, if the analytical or 

physical evaluations indicate a safety implication. 

This report describes the evaluations conducted and the results derived.
5

2. Analytical Model 

2.1 Finite Element Analysis Model 

In the early stages of this investigation, a virtual three-dimensional model was developed using 

an F-type coupler geometry, because at the time, this was the only detailed geometry available 

for modeling purposes. A model of two coupled F-type couplers was created. The basic 

geometry was developed using Pro/E software (see Figure 1 and Figure 2). This model was 

exported to Ansysfor meshing. The model was constructed using structural solid elements 

with contact surfaces defined at all possible contacting surfaces between the mated couplers. The 

contact elements chosen were three-dimensional surface-to-surface type. The shank end of one 

coupler was constrained, whereas the shank end of the mating coupler had varying torques 

applied. These torques were produced by applying a predefined angular displacement on the 

actuated coupler shank (see Figure 3 and Figure 4).

The development of this model and its successful convergence to produce meaningful results 

was a very lengthy process. The first attempts utilized a mesh of tetrahedron elements that 

produced too large of a model if an acceptable mesh refinement was used. A solid mesh of brick 

(six sided, eight nodes) elements was then constructed for the complex shape of the F-type 

coupler. This process necessitated the manual construction of many elements individually. 

Many trials were required in refining the mesh on the complex contoured surfaces of coupler 

knuckles and mating surfaces before successful runs were possible with the contact elements 

used. The double convex–concave surfaces at the knuckle interfaces contributed to the 

complexity of this model. 
6

Figure 1. F-Type Coupler Model 

Figure 2. Coupled F-Type Couplers
7

Figure 3. Constraints 

Figure 4. Mesh – Single Coupler 

4 Nodes 

constrained

6 DOF

4 nodes given 

UY and UZ displacement to produce 11.6 degree rotation
8

2.2 Finite Element Analysis Results

A relationship between angle of coupler deflection (at the rear end of the actuated coupler shank) 

and torque was obtained and shown in Figure 5. The plot reveals a mostly linear relationship 

with a slope of 12,337 pounds per feet (lb-ft)/degree by using liner regression along the inclined 

linear portion of the curve and about 4.8 degrees of rotation at 40,000 lb-ft of torque. The 

actuated coupler was displaced in the counterclockwise direction. The displacement contour plot 

and the von Mises stress contours are displayed for a single coupler in Figure 6 and Figure 7. 
9

Figure 5. Analytical Model Data
10

Figure 6. Total Displacement – Virtual Model

Figure 7. von Mises Stress – Virtual Model 
11

3. Physical Testing 

3.1 Introduction and Objective

Physical testing was performed to obtain torsional transmission stiffness data for four basic 

coupler combinations in both the clockwise and counterclockwise directions. Table 1 below 

summarizes these combinations: 

Table 1. Combinations 

ACTUATED To REACTION COMBINATION 

No-Shelf (NS2) Shelf (S2)

No-Shelf (NS2) No-Shelf (NS1)

Shelf (S1) No-Shelf (NS1)

Shelf (S1) Shelf (S2)

Resulting torque–displacement data from these test combinations should indicate whether any 

combination produces a stiffer torsional connection and possibly a greater tendency for 

overturning an adjacent coupled car. Use of both the clockwise and counterclockwise directions 

ensures that any contact at both the upper and lower shelves is taken into account. 

3.2 Test Apparatus

A test apparatus was designed and fabricated consisting of two coupler support fixtures and a 

method of applying torque to one of the couplers. A welded steel actuation fixture and a reaction 

fixture were developed (see Figure 8 and Figure 9 and manufacturing drawings in Appendix B). 

The two fixtures face each other and can be moved relative to each other to allow the installation 

of the couplers into the fixtures and to allow the couplers to be mated and coupled together. The 

actuation fixture consists of a lower support frame and two upstanding stiffened webs, which 

locate and support bearings that accept the coupler shank of the actuated coupler. Provisions are 

made to attach a hydraulic cylinder to either the right or the left side of the fixture. A separate 

fabricated arm is provided. It grips the coupler shank of the actuated coupler and is given a force 

at its outer end by the hydraulic cylinder (see Figure 9 and Figure 10).

Clockwise or counterclockwise motion is possible by way of the cylinder supports at both sides 

of the fixture. Two cylindrical coupler shank adapters provided with tapered square holes and 

adjustable set screws allow the coupler shank to fit into the fixture at the bearing locations. The 

plain bearings are machined from Nylon 6 and fit between the adapters and the steel tubes that
12

Figure 8. Test Apparatus 

Figure 9. Test Apparatus 
13

make up part of the fixture weldment. These bearings allow the actuated coupler to freely 

and easily rotate in the fixture with only hand force and remove any vertical moment out of 

the mated couplers upon actuation (see Figure 11 and Figure 12).

A theoretical range of motion of 23 degrees is possible by the use of an Enerpac model RC1014 single acting 14-inch extension hydraulic cylinder capable of providing 20,000 lb of 

force. In line with the cylinder is an Interface model 1220 load cell with a 50,000-pound 

capacity. An Interface model 9320 handheld load cell indicator is used to obtain force 

readings from the load cell. The cylinder, load cell, and two threaded adapters that connected

the load cell to the cylinder and to a clevis pivot at the clevis on the mounting point of the 

fixture are shown in Figure 13.
14
15

Figure 12. Front Bearing 

Nylon

Bearing

Shank

Adapter

Actuation

Arm Figure 11. Rear Bearing
16

Figure 13. Load Cell and Clevis 

An Enerpac model P391 hydraulic hand pump is used in conjunction with a model V66 valve to 

actuate the cylinder and to provide the fine extensions of the cylinder plunger to obtain the 

angular displacement of the actuation arm. 

The reaction fixture supports the nonactuated coupler and secures it by fastening a steel-hat 

section over the shank. The reaction fixture positions the coupler at a level 5 in above that of the 

actuated coupler to simulate the drop of one car relative to its mated neighbor in a derailment 

condition. Both fixtures were analyzed for acceptable stresses and deflections using the Finite 

Element Method with Ansys. The actuation fixture is designed to slide into the reaction fixture 

and is bolted to the reaction fixture at the base. 

3.3 Test Specimens

Four couplers were acquired for the test: two E68 and two SE68 types. All four couplers met 

AAR dimensional service standards and then had their shanks cut off near the rear at their 

narrowest point before the widening of the shank to allow them to fit into the fixture. The two 

E68 couplers were identified and labeled as S1 and S2. The two SE68s were identified and 

labeled NS1 and NS2.
17

3.4 Test Procedure 

Four basic combinations of couplers were tested. 

1. No-shelf with no-shelf (NS2 to NS1), NS2 actuated 

2. Shelf with shelf (S1 to S2), S1 actuated 

3. No-shelf with shelf (NS2 to S2), NS2 actuated 

4. Shelf with no-shelf (S1 to NS1), S1 actuated 

For each of these basic combinations, a clockwise and counterclockwise actuation was 

performed. Three runs of each direction were made for all four basic combinations. Force and 

angular displacement data were recorded typically at about 2,000-pound intervals. A KellStrom

Pro 360 digital protractor with magnetic base attachment was used for determining the 

angular displacement. 

Shimming was used to remove any gaps or motion between the actuation arm and the coupler 

shanks and between the reaction-hold-down fixture and the coupler shanks. Before each run, 

initial data consisting of initial angle of coupler, initial force reading, and initial angles of the 

heads and shanks of both couplers were recorded. Similar readings were taken after stabilizing 

the maximum load and after unloading the system. 

After each appropriate combination of coupler specimens were installed in the fixtures and the 

arm/cylinder assembly was securely attached and shimmed, the fixtures were moved together, 

and the couplers were coupled and the frames bolted together. The hydraulic hand pump was 

then carefully operated until the target force increment was approximately attained. The V66 

valve was then closed, and a reading of the load cell was recorded along with the corresponding 

displacement. The valve was then opened, and the next increment of displacement was attained 

and so on. A maximum force reading of about 15,000 lb, equivalent to about 43,000 lb-ft of 

torque, was set as the limit for the test. 

The recorded data points were of the input force through the hydraulic cylinder and the resulting 

angle of the arm. These data were reduced to obtain output torque on the coupler shank and the 

corresponding angle of the coupler shank. This was accomplished by using a spreadsheet with 

the appropriate trigonometric relationships. 
18

3.5 Results – Physical Testing

Figure 14 and Figure 15 show the second run for each of the four basic coupler combinations 

plotted on a single graph. It shows that a significant difference exists among the four basic 

combinations. Regardless of rotational direction, the no-shelf to shelf combination produced the 

greatest angular displacement for a given torque, followed by the shelf to no-shelf, then the noshelf to shelf and the shelf to shelf showing least angular displacement (see Table 2 and Table 3). 

In the counterclockwise case, the shelf-to-shelf combination exhibited contact between the 

mating upper shelves through the duration of the tests (see Figure 16). The slopes of all the 

counterclockwise runs range from about 11,000 lb-ft/degree to about 18,000 lb-ft/degree (see 

Table 2).

The clockwise results are similar to the counterclockwise results except that: 

1. The shelf-to-shelf and no-shelf-to-shelf curves show significantly more displacement for 

the clockwise direction. 

2. The clockwise runs have slopes ranging from about 12,000 lb-ft/degree to about 

15,000 lb-ft/degree (see Table 3).

The greater displacement of item 1 above is probably due to the top shelf contact, which occurs 

after a relatively small rotation in the counterclockwise direction. The top shelves do not make 

contact in the clockwise direction. Because of their shape and location, the bottom shelves 

appear to be less of a factor in effecting the couple rotation. 

Irrespective of rotational direction, the shelf-to-shelf combination shows the steepest slope and 

therefore the greatest stiffness. These slopes most likely represent a combination of the fixture 

stiffness after the relative angles between the couplers have stabilized at their maximum values 

and stiffness of the coupler itself. Slope values were obtained by performing linear regression on 

all but the first two data points of each curve. The offset between curves represents the most 

significant difference in behavior of the chosen couplers.
19

Figure 14. Results Comparison – Counterclockwise
20 Figure 15. Comparison of Results – Clockwise
21

 

 

Table 2. Results Comparison – Counterclockwise 

COUNTERCLOCKWISE (run 2)

S to S NS to NS S to NS NS to S 

Max. angle (deg) 6.9 14.2 12.7 10.4

Max. torque (lb-ft) 43,923 42,122 42,872 43,368

Slope (lb-ft/degree) 17,942 10,760 14,194 10,538

Table 3. Results Comparison – Clockwise 

CLOCKWISE (run 2)

S to S NS to NS S to NS NS to S 

Max. angle (deg) 11 14.9 13.8 13.7

Max. torque (lb-ft) 42,166 42,162 42,292 42,516

Slope (lb-ft/degree) 14,708 11,943 11,649 12,884
22

The virtual model was made of an F-type to F-type coupler connection. However, comparison of 

the physical testing with that of the virtual model will tell us whether the results of each are 

similar. Comparing the results from the physical testing with that of the virtual model of the 

F-type couplers, we can see that the test slope values agree well with the simulated 

12,337 lb-ft/degree value obtained. The actual value of angular displacement (used as reference) 

from the virtual model of 4.8 degrees at 40,000 lb-ft of torque is somewhat lower (greater 

stiffness) than that obtained in the physical test of the E-type couplers. This is most likely due to 

the presence of the interlocking aligning wing feature of the F-type coupler which will reduce the 

allowable angular displacement between couplers. 

Appendix A contains data plots for all the runs and shows comparisons of the first through third 

runs (or first and second if only two runs were made) for each direction and combination. Most 

of the curves show a distinct break-in that occurs during the first run, followed by more 

consistent results at a greater displacement for the subsequent runs.

It should be noted that visual observation during test runs revealed that the buff to draft 

relationship of the knuckles in contact tended to change as the torque was applied or released. 

See Figure 17 for a view of the typical contact between couplers. The exception to this was the 

shelf-to-shelf case where the contact of the upper shelf to upper shelf maintained the relative 

longitudinal position of the knuckles constant throughout the run after starting the test run in a 

buff position (see Figure 16). Figure 18 and Figure 19 show side views of the shelf to shelf and 

no-shelf to no-shelf test runs. 
23

Figure 16. Upper Shelf to Upper Shelf Contact 

Figure 17. Typical Contact (No-Shelf Mated to No-Shelf)

Upper Shelf to

Upper Shelf Contact
24

Figure 18. Shelf to Shelf Test Run 

Figure 19. No-Shelf to No-Shelf Test Run
25

4. Conclusions 

The results of this test clearly show less angular rotation for a given torque for couplers with 

shelves than those without. The combinations that included only one shelf coupler also showed 

less deflection than the combination without any shelves. This reveals that the presence of a 

shelf coupler or couplers will add to the torsional stiffness of the coupler connection. Therefore, 

it‟s possible that couplers with shelves are more prone to “domino” adjacent cars in a rollover 

scenario than those without. This propensity could be greater if the shelf-to-shelf couplers are in 

a generally buff condition when overturning because their upper shelves are more likely to be in 

contact in this position. 

In contrast, in some scenarios, a mated shelf coupler may help to resist and inhibit an adjacent 

car from rolling over. Possibly, for every “domino” effect type of multicar rollover, some 

potential rollovers are eliminated because of the shelf type coupler. 
26

5. Recommendations

The question as to whether shelf couplers add to the torsional stiffness of coupled connections 

has been answered in this study. What is still not clear is whether this stiffness will contribute to, 

or help prevent, rollovers of adjacent coupled cars. Therefore, we recommend further study into 

the characteristics of the coupler connection and its propensity of propagating car rollovers. 

Through the use of the torque-displacement relationships established in this study, a vehicle 

dynamics simulation should be performed using a software application such as Vampire. This 

type of analysis model can account for more variables such as those of the car suspension and car 

structure not possible in this study. A virtual model of a rail car with a coupler connection or 

multiple rail cars coupled can be constructed and analyzed to determine the actual propensity of 

one car to rollover its coupled neighbor based on the types of couplers used in the connection. 
27

Appendix A – Fixture Assembly Drawings 
28
29
30
31

Appendix B – Test Data 
32

COUPLER DEFLECTION 

NS2 (active) mated w/ S2 (fixed) 

CLOCKWISE

0.00

5000.00

10000.0015000.0020000.0025000.0030000.0035000.0040000.0045000.00

0 2 4 6 8 10 12 14

ANGLE (degrees) TORQUE (lb-ft)

RUN 2RUN 1
33

COUPLER DEFLECTION 

NS2 (active) mated w/ S2 (fixed) 

COUNTER CLOCKWISE

0.00

5000.00

10000.0015000.0020000.0025000.0030000.0035000.0040000.0045000.0050000.00

0 2 4 6 8 10 12

ANGLE (degrees) TORQUE (lb-ft)

RUN 2RUN 1
34
35

COUPLER DEFLECTION 

NS2 (active) mated w/ NS1 (fixed) 

COUNTERCLOCKWISE

0.00

5000.00

10000.0015000.0020000.0025000.0030000.0035000.0040000.0045000.00

0 2 4 6 8 10 12 14 16

ANGLE (degrees) TORQUE (lb-ft)

RUN 3RUN 2RUN 1
36

COUPLER DEFLECTION 

NS2 (active) mated w/ NS1 (fixed) 

CLOCKWISE

0.00

5000.00

10000.0015000.0020000.0025000.0030000.0035000.0040000.0045000.00

0 2 4 6 8 10 12 14 16

ANGLE (degrees) TORQUE (lb-ft)

RUN 3RUN 2RUN 1
37
38