Office of Research and 

Development 

Washington, DC 20590 

Federal Railroad

Administration

U.S. Department

of Transportation

Impact Performance of Draft Gears 

in 263,000 Pound Gross Rail Load and 

286,000 Pound Gross Rail Load 

Tank Car Service 

This document is available to the

U.S. public through the National

Technical Information Service

Springfield, Virginia 22161

DOT/FRA/ORD-06/16 June 2006 
Notice

The United States Government does not endorse products or 

manufacturers. Trade or manufacturers’ names appear herein 

solely because they are considered essential to the objective of 

this report. 

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS 

 Impact Performance of Draft Gears in 263,000 Pound Gross 

Rail Load and 286,000 Pound Gross Rail Load Tank Car 

Service 

6. AUTHOR(S) 

Anand Prabhakaran, Robert Trent, Vinaya Sharma 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION 

REPORT NUMBERS

 Sharma & Associates, Inc. 

 29 W. Plainfield Road 

 Countryside, IL 60525 

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

REPORT NUMBER 

 U.S. Department of Transportation 

 Federal Railroad Administration 

 Office of Research and Development 

 1120 Vermont Avenue, NW, MS-20 

 Washington, DC 20590 

DOT/FRA/ORD-06/16

11. SUPPLEMENTARY NOTES

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

This document is available through National Technical 

Information Service, Springfield, VA 22161 

13. ABSTRACT

This project quantified the impact performance of draft gears on tank cars for both the 263,000 and 286,000 gross rail load (GRL) conditions 

and the corresponding effect on the structural integrity of stub sills. Full-scale physical impact testing with an instrumented tank car for the 

263,000 GRL case using 6 different draft gear combinations of prime, average, and soft draft gear conditions were performed. Impact speeds 

of 2 to 9 mph were tested. Loss in draft gear performance with age/use along with performance comparisons of draft gears qualified under M901G versus M-901E were obtained. Test results from the 263,000 GRL cars are presented and used to validate an finite element analysis 

model with scaled up car mass to predict draft gear performance for the 286,000 GRL case. 

 This study showed that draft gears in prime condition are the most effective at reducing car impact forces, especially at higher speeds where 

the most damage occurs. Draft gears in the soft condition provided the least protection. M-901G gears offered better performance at the 

higher speeds of interest than the M-901E gears. The average setup, a combination of soft and prime gears, performed better than soft gear 

setup. 

14. SUBJECT TERMS 15. NUMBER OF 

PAGES

41 

16. PRICE CODE

Draft gear, tank car safety, tank car impacts, stub sill stresses 

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

i
METRIC/ENGLISH CONVERSION FACTORS 

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

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 34

Inches

Centimeters 01 3 26 1 4 5 7 1 1098 1 12

5

3

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

ii
TABLE OF CONTENTS 

Acknowledgments ..................................................................................... vii 

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

1.0 Introduction..................................................................................... 5 

1.1 Background............................................................................... 5 

1.2 Objectives ................................................................................. 6 

2.0 Impact Testing ................................................................................. 7 

2.1 Test Car Setup............................................................................. 7 

2.2 Impact Test Setup......................................................................... 12 

2.3 Draft Gear Configurations.............................................................. 12 

 3.0 Test Results.................................................................................... 17 

3.1 Coupler Force Comparisons............................................................ 19 

3.2 Stresses at Critical Locations........................................................... 20 

3.3 Summary................................................................................... 22 

 4.0 Impact Modeling for 286,000 Lb GRL Loading...................................... 23 

4.1 Model Development...................................................................... 23 

4.2 Model Validation......................................................................... 24 

4.3 286,000 Lb GRL Tank Cars.............................................................. 27 

4.4 Summary.................................................................................. 29 

5.0 Conclusions & Recommendations.......................................................... 33 

References................................................................................................ 35 

Acronyms................................................................................................ 37 

iii
iv
LIST OF FIGURES 

Figure 1. Test tank car............................................................................... 7 

Figure 2. Schematic of test tank car................................................................ 8 

Figure 3. Gage locations on test carBView 1..................................................... 9 

Figure 4. Gage locations on test carBView 2...................................................... 10 

Figure 5. Schematic of impact test setup.......................................................... 11 

Figure 6. Cars on impact test track................................................................. 13 

Figure 7. Hammer car on impact ramp............................................................ 13 

Figure 8. Critical locationsBElevation............................................................ 18 

Figure 9. Critical locationsBIsometric view...................................................... 18 

Figure 10. Peak coupler forces...................................................................... 19 

Figure 11. Principal stresses on the tank head (location A)..................................... 20 

Figure 12. Principal stresses on the reinforcing pad (location B)................................ 21 

Figure 13. Principal stresses at the head brace (location C)...................................... 21 

Figure 14. Finite element model of tank car structure............................................. 23 

Figure 15. Finite element model of tank car including suspension.............................. 24 

Figure 16. Schematic of coupler force impact model............................................. 25 

Figure 17. Loading and unloading characteristics for primary draft gear springsBG gear... 26 

Figure 18. Comparison of model and test dataBG gear............................................ 26 

Figure 19. Coupler forces under 286,000 lb GRL loading........................................ 27 

Figure 20. Comparison of coupler forcesBprime E gears versus G 

 gearsB286,000 lb GRL loading ........................................................ 28 

Figure 21. Coupler force comparisonsBPrime gears ............................................. 30 

Figure 22. Coupler force comparisonsBAverage gears ........................................... 31 

Figure 23. Coupler force comparisonsBSoft gears ................................................ 32 

LIST OF TABLES 

Table 1. Draft Gear Configurations............................................................... 15 

v
vi
ACKNOWLEDGEMENTS 

The authors wish to thank the Office of Research & Development of the Federal Railroad 

Administration, in particular Ms. Claire Orth and Mr. Jose S. Pe1⁄2a, for funding this research 

effort. We also wish to thank Mr. Jim Rader of the Office of Safety of the Federal Railroad 

Administration for his valuable input into the program. Our sincere thanks are also due to 

GATX, especially Mr. William Garfield and Mr. Doug Mullins, for providing the test car. 

vii
viii
EXECUTIVE SUMMARY

The stub sill on a tank car is one of the failure prone sections of the overall tank car, and 

failures can lead to stub sill separation, loss of lading, or even derailment. Such safety 

concerns are heightened in the case of hazardous material transport. With an increasing 

number of tank cars being introduced into 286,000 lb gross rail load (GRL) service, the stub 

sill tank car interface requires further scrutiny. 

The stub sill is subjected to considerable stress levels because of loads that are induced under 

typical revenue service operations. Draft gear systems are designed to reduce the force levels 

seen by tank cars. Therefore, draft gear performance has a significant effect on the structural 

integrity of tank car stub sills. Draft gears with higher capacities can generally absorb more 

energy and offer better protection. Typically, draft gears reach their peak capacity after being 

broken-in. Towards the end of their operating lives, they tend to become softer and lose some 

of their capacity. 

Under a 286,000 lb GRL load environment, longitudinal forces are expected to be much 

higher. The capacity of draft gears to protect tank cars in that severe environment will have a 

significant effect on the safety of hazmat transportation using tank cars in 286,000 lb GRL 

service. The safety of tank cars in 286,000 lb GRL service, therefore, cannot be adequately 

addressed without considering the performance of draft gears used on the tank cars. It has 

generally been believed in the tank car industry that draft gears qualified under M-901G 

specifications offer superior performance compared to draft gears specified under M-901E 

specifications. However, specific differences in draft gear performance between E gears and 

G gears have not been previously quantified even for 263,000 lb GRL tank cars. Apparent 

loss in draft gear performance with age/use has not been quantified either. Hence, a need to 

quantify these differences existed, so that their effect on the safety of 286,000 lb GRL cars 

could be addressed. 

The primary objective of this project is to quantify the benefits of using M-901G specification 

draft gears as compared to M-901E specification draft gears on tank cars in 286,000 lb GRL 

service. An additional objective is to quantify the benefits of using draft gears in prime 

condition as compared to draft gears in soft condition. 

As part of this project, a test tank car was instrumented, loaded to simulate 263,000 lb GRL 

service and tested on an impact ramp. Six different draft gear combinations were tested as 

part of this program. The scenarios included testing with soft gears on the anvil car (tank car) 

only and soft gears on the hammer car and the anvil car. 

To better present the results from the six different cases tested, the results are condensed from 

the various cases into three different impact conditions: 

1. Prime condition: This condition represents the cases where the impact involved draft 

gears in prime condition at struck and striking ends. 

1
2. Average condition: This condition represents the cases where the impact involved a 

soft draft gear at the struck end and a prime condition draft gear at the striking end. 

3. Soft condition: This condition represents the cases where the impact involved soft 

draft gears at the struck and striking ends. 

In addition, finite element models that simulated the impact behavior of tank cars were 

developed. These models were validated using the test data and used to simulate draft gear 

behavior under 286,000 lb GRL loading. The following conclusions were reached from the 

testing and simulations: 

1. Prime gears (M-901G gears and M-901E gears in prime condition) induced the lowest 

coupler forces, especially at higher impact speeds where the potential for damage is 

the highest. Impacts in the soft condition (draft gears at the struck and striking ends in 

used condition) produced the highest coupler forces at all speeds. 

2. A comparison of the stresses developed at critical locations indicated that gears in 

prime condition offered the best protection. Soft gears produce the highest stress in the 

tank car at all speeds, with the differences increasing substantially at higher speeds. 

At speeds less than 6 mph, prime gears induce slightly higher stresses than the average 

gears. This small disadvantage at lower speeds, however, is not enough to offset the 

significant advantage offered by the prime gears at higher speeds. At these high 

impact speeds (where the likelihood of damage is the highest), prime gears induce 

considerably lower stresses. 

3. Data from simulations of 286,000 lb GRL service impacts using validated models 

indicated that prime gears would continue to offer superior protection, especially at 

higher speeds. At lower speeds, no significant differences existed in performance 

between 286,000 lb GRL service and 263,000 lb GRL service. The speed at which 

coupler forces started to increase under 286,000 lb GRL service was higher for the 

prime gears, indicating additional reserve capacity in the friction packs of the draft 

gears. 

4. Comparisons of E gears in prime condition and G gears indicated that the E gears 

offered marginally better performance at lower speeds, while the G gears offered 

better performance as speeds increased. 

5. Overall, prime gears offer better protection under both 263,000 lb GRL service and 

286,000 lb GRL service. However, in the prime conditions that were tested/simulated, 

draft gears at the struck and striking ends were in good condition. Generally, tank car 

owners have no control over placement of their cars in a train and subsequently over 

the draft gear conditions of adjacent cars. While a given tank car may be equipped 

with a prime gear, it may impact against a car with soft gears while over-the-road. 

The average setup that was tested represents this scenario. In such scenarios, the 

protection benefits offered by the prime gears may not be fully realized. Even in such 

scenarios, a prime gear will protect the car better, as evidenced by the performance of 

the average setup compared to the soft setup. In the 263,000 lb GRL and 286,000 lb 

2
GRL service, the average gear setup performed better than the soft gear setup at 

almost all speeds. 

6. An overview of the test and simulation data indicates that different gears are at their 

best at different speed ranges. Given the large number of variables involved, it is a 

difficult task to design draft gears to perform well at all speeds. However, it would be 

a worthwhile effort to try and tune draft gear performance in the design process to 

maximize the protection offered by draft gears. 

3
4
1.0 Introduction 

1.1 Background

Tank cars in revenue service are subject to occasional cracking and failures at the stub sill 

tank interface. The structural integrity of a tank car is highly dependent on the strength of its 

stub sill tank car interface. This interface is a very failure prone section of the overall tank 

car, and failures can lead to stub sill separation, loss of lading, or even derailment. Such 

safety concerns are heightened in the case of hazardous material transport. With the number 

of tank cars being introduced into 286,000 lb GRL service, the stub sill tank car interface 

requires further scrutiny. 

The stub sill is subjected to considerable stress levels under typical revenue service 

operations. When cars are over-the-road (OTR), in-train forces are generated due to run-ins 

and run-outs, which induce stresses in the stub sill region. Run-in and run-out events 

typically result in impact speeds of about 1B2 mph between cars. Train makeup operations in 

railway yards generally involve higher impact speeds and high longitudinal forces, leading to 

higher stresses. Draft gear systems at the end of each car are designed to absorb some of the 

impacting energy and reduce the force levels seen by tank cars in impact yard and OTR 

conditions. The effectiveness of these draft gear systems governs how much energy is 

absorbed by the draft gears and consequently the level of impact protection offered. Draft 

gear performance, therefore, has a significant effect on the structural integrity of tank car stub 

sills. 

Draft gears for freight cars are certified under either section M-901E or section M-901G of 

the Association of American Railroads (AAR) Manual. Most of the draft gears out in the 

market today are certified under M-901E, which requires drop hammer tests. M-901E gears 

must have a minimum official capacity of 36,000 ft-lb, when tested under the standard 27,000 

lb drop hammer. They must also have a capacity of at least 6,000 ft-lb at 1-5/16 in. travel. 

While M-901G specifications were established in 1964, common usage of these gears is 

relatively recent. These gears are certified using impact tests and must have a minimum 

rating impact velocity of 5 mph. Rating impact velocity is the velocity that produces a 

reaction of 500,000 lb. The impacts are to be conducted using 70-ton cars. This report will 

refer to the M-901E draft gears as E gears and the M-901G draft gears as G gears. 

Draft gears typically use friction wedges in series with springs (steel, rubber, or elastomer) to 

absorb impact energy. Draft gears with higher capacities can generally absorb more energy 

and therefore offer better protection. Typically, draft gears reach their peak capacity after 

being broken-in. Towards the end of their operating lives, they tend to become softer and lose 

some of their capacity. 

Under a 286,000 lb GRL load environment, longitudinal forces during yard impact and OTR 

conditions will be much higher. The capacity of draft gears to protect tank cars in that severe 

environment will have a significant effect on the safety of hazmat transportation using tank 

cars in 286,000 lb GRL service. Therefore, the safety of tank cars in 286,000 lb GRL service 

5
cannot be adequately addressed without considering the performance of draft gears used on 

the tank cars. It has generally been believed in the tank car industry that G gears offer 

superior performance to E gears in revenue service. However, specific differences in draft 

gear performance between E gears and G gears has not been previously quantified. Apparent 

loss in draft gear performance with age/use has not been quantified either. Hence, a need to 

quantify these differences existed, so that their effect on the safety of 286,000 lb GRL cars 

could be addressed. 

A previous project done by Sharma & Associates, Inc. (SA), for the Federal Railroad 

Administration (FRA) evaluated the effects of coupler height mismatch on tank car stub sill 

integrity of 263,000 lb GRL tank cars. Part of that project conducted full scale impact testing 

of a 263,000 lb GRL GATX tank car using E gears in prime condition and G gears in new 

condition. Since the majority of tank cars in service use regular (softer) E gears, additional 

testing is required to quantify gear performance. This will assist in quantifying the benefits of 

using premium gears in tank cars transporting hazardous material (HM) and 286,000 lb GRL 

service. 

1.2 Objectives

The primary objective of this project was to quantify the benefits of using G spec draft gears 

as compared to E spec draft gears on tank cars under 286,000 lb GRL service. An additional 

objective was to quantify the benefits of using draft gears in prime condition as compared to 

draft gears in soft condition. As part of the project, full-scale impact testing was conducted 

on a test GATX tank car at various impact speeds with different gears on the tank car. The 

impact test series included testing with soft gears on the anvil car (tank car) only and soft 

gears on the hammer car and the anvil car. The results from the tests were combined with 

modeling of tank car impacts to quantify draft gear performance. 

6
2.0 Impact Testing 

The outline of the test plan was similar to the testing done as part of the earlier project [1]. A 

test tank car (Figure 1), generously donated by GATX, was instrumented for monitoring 

strains at critical locations. This was followed by a series of specifically designed impact 

tests to evaluate tank car response to different draft gear types and configurations. 

Figure 1. Test tank car 

 

2.1 Test Car Setup 

The test tank car (GATX 15693) is a DOT 111A100W1 non-insulated car with a built date of 

January 1981. It has a capacity of 26,791 gallons, with a light weight of 70,200 lb and a load 

limit of 192,800 lb. The stub sill consists of two channels and a top plate. The sill connects 

to the tank through a head brace near the bolster (Figure 2). The head brace is connected to 

the tank shell through a reinforcement pad (head pad extension). The front draft lugs and the 

striker are a single casting that is welded onto the web of the sill. The rear draft lugs and the 

center bowl are a single casting that is bolted on to the web of the sill. The material of tank 

head, tank shell, and head pad extension is American Society for Testing and Materials 

(ASTM) A515, Gr. 70 LR (yield point (yp): 38,000 psi). The head brace material is ASTM 

A36 (yp: 36,000 psi), and the draft sill material is ASTM A572, Gr. 50 (yp: 50,000 psi). 

7
Bolster

Tank Head

Head PadExtension

Head Brace

Center Plate

Top Flange 

of Sill

Sill Web

Bottom Flange

of Sill

Figure 2. Schematic of test tank car 

8
9

Figure 3. Gage locations on test carBView 1 
Figure 4. Gage locations on test car–View 2 

 

10
11

HAMMER CAR

HOPPER CAR

ME-6503

GRL: 263,000 lb.

TEST CAR

TANK CAR

GATX-15693

GRL: 266,200 lb.

BACK UP CAR 1

HOPPER CAR

ME-7601

GRL: 177,000 lb.

BACK UP CAR 2

HOPPER CAR

ME-6502

GRL: 220,000 lb.

Figure 5. Schematic of impact test setup 
The test car was loaded with water to weigh 266,200 lb GRL. The A end of the car was 

instrumented with strain gages at critical locations on the stub sill, tank head, 

reinforcement pad, and head brace. Gage locations were determined based on preliminary 

finite element analysis, consultations with industry experts, and an industry survey of fatigue 

crack locations on cars of similar design. Care was taken to place strain gages away from 

stress concentrations, so that the strains in the parent material would be measured. As a part 

of the instrumentation, 30 single element and 4 rectangular rosette strain gages, 42 channels 

total, were applied. Based on results from initial static tests, data from 28 channels was 

collected for the impact tests. Figures 3 and 4 represent the gage locations (listed in table 1). 

Miner Enterprises, Inc. (Geneva, IL) conducted the instrumentation and testing. Miner and 

SA completed the data acquisition during impact testing. 

2.2 Impact Test Setup 

The impact tests were conducted using an inclined test track (impact ramp). Desired impact 

speeds were obtained by releasing a hammer car from different heights on the impact ramp. 

A hopper car loaded to weigh 263,000 lb GRL served as the hammer car. Two backup cars 

were behind the tank car, weighing a total of 397,000 lb, with hand-brakes applied on the last 

car (Figures 5, 6, and 7). The tank car, hammer car, and backup cars were all equipped with 

E couplers. The A end of the tank car (instrumented end) was the struck end. The tank car 

and the backup cars were bunched together after each impact. 

In addition to the strain channels, coupler force at the impacting end (using a dynamometer 

coupler in the hammer car), draft gear travel (struck end of the tank car) and impact velocity 

were also measured. For some of the impacts, coupler force at the B end of the tank car was 

measured. 

2.3 Draft Gear Configurations

Part of SA=s earlier work included two series of impact tests. The first series used E gears in 

prime condition (model A) at either end (struck end and non-struck end) of the tank car 

(impact set #1). These gears were provided with the test car. The second series used G gears 

in new condition, at either end of the tank car (impact set #2). For these test series, the 

striking end of the hammer car was equipped with a draft gear in prime condition, which was 

supplied by Miner as part of the test setup. Reference [1] presents the results from these tests. 

For this project, two 2 sets of draft gears (model B & model C) from two different 

manufacturers in used condition were selected. The selected gears were subjected to standard 

hammer tests to ascertain that their capacities satisfied AAR (M-901E) specifications (36,000 

ft-lb). Four different impact series were conducted with these gears (impact sets 3 through 6). 

12
13

Figure 6. Car on impact test track

Figure 7. Hammer car on impact ramp
The first series was conducted with draft gears of model B at either end of the tank car 

(impact set #3). The Miner-supplied E gear was maintained on the striking end of the 

hammer car from the previous tests. 

The second series used draft gears of model C at either end of the tank car (impact set #4). 

The Miner-supplied E gear was maintained on the hammer car. 

The third series used model B draft gears at the struck end of the tank car and the striking end 

of the hammer car (impact set #5). One of the model C draft gears was used at the non-struck 

end of the tank car. 

The fourth series used model C draft gears at the struck end of the tank car and the striking 

end of the hammer car (impact set #6). One of the model B draft gears was used at the nonstruck end of the tank car. Table 1 illustrates the various configurations. This table also 

shows the impact series names used and the impact conditions referred to in this report. 

For each test series, the impact tests started with an impact velocity of about 2 mph. For 

impact sets 3 and 4, impacts were continued with increasing impact speed until the draft gears 

on the tank car bottomed out. For impact sets 5 and 6, impacts were continued until a coupler 

force of 950,000 lb was reached. 

14
Impact 

Prime Condition Average Condition Soft Condition 

Notes 1. MSBMiner supplied gears on hammer car, which were E gears in their prime. 2. Model A gears used in series 1 were supplied with the test car by GATX and were in prime condition. 3. Models B and C were used E gears from two different manufacturers. They were within M-901E specifications. 

Tank Car 

Non-Struck End

Model A2

New G Model B3Model C3Model C3Model B3

NON-STRUCK END STRIKING END

 STRUCK END

STRUCK CAR HAMMER CAR

Table 1. Draft Gear Configurations 

Tank Car 

Struck End

Model A2New G Model B3

Model C3Model B3Model C3

Hammer Car 

Striking End

MS1

MS1MS1MS1Model B3

Model C3 

Prime A G Average B Average C Soft B Soft C 

Impact Set No. and Name

1 2 3 4 5 6 

15
16
3.0 Test Results 

The raw data collected during the impact tests was further processed using some data 

processing software routines that were developed in-house. These routines filter the data as 

needed and convert it into a useful and readable format, while also converting the measured 

strain data into stress data, including the calculation of principal stresses wherever rosettes 

were used. Zero balancing of the data is also done during this process. 

To compare the relative performance of the draft gears tested, coupler force histories (at the 

impacting end) and stress histories at three critical locations on the car structure were studied. 

The locations studied were the tank head (shell), the head pad extension, and the head brace. 

The locations picked are also generic (i.e., the results at these locations would be applicable at 

corresponding locations on most tank car designs). Figures 8 and 9 marked the three 

locations as A, B, and C, respectively. 

To better present the results from the six different cases tested, the results were condensed 

from the various cases into three different impact conditions: 

1. Prime condition: The results from impact sets 1 and 2 (see Table 1) were combined 

into this condition. This condition represents the cases where the impact involved 

draft gears in prime condition at struck and striking ends. As reported in the previous 

work [1], the performances of the prime E gear was comparable to the performance of 

the G gears at most speeds. It was reasonable, therefore, to combine the results from 

the two test sets for this discussion. As noted in [1], the G gear had a slight advantage 

at higher (greater than 8 mph) speeds; the ramifications of which a subsequent section 

will discuss. 

2. Average condition: The results from impact sets 3 and 4 (see Table 1) were combined 

into this condition. This condition represents the cases where the impact involved a 

soft draft gear at the struck end and a good draft gear at the striking end. A 

comparison of the specific performance differences between sets 3 and 4 is not very 

relevant to this project. However, the appendix presents these results. 

3. Soft condition: The results from impact sets 5 and 6 (see Table 1) were combined into 

this condition. This condition represents the cases where the impact involved soft 

draft gears at the struck and striking ends. As in the previous case, comparison of the 

specific performance differences between these sets is not very relevant to this project. 

However, the appendix presents these results. 

17
 

A

B

C

Rear Draft Lugs

Vertical Force

Gages

Figure 8. Critical locations–Elevation 

 

Figure 9. Critical locations–Isometric view 

18
3.1 Coupler Force Comparisons

Figure 10 presents peak coupler force data from various impact runs. It is seen that the 

coupler forces using prime gears at impact speeds between 3 mph and 6 mph is slightly higher 

but significantly lower at higher speeds (where most chance for damage exists). For example, 

at an impact speed of 7 mph, the prime gears have a peak coupler force of 557,000 lb, 

whereas the average gears have a force of 705,000 lb (27 percent higher), and the soft gears 

have a peak coupler force of 959,000 lb (72 percent higher). It is also observed that, at speeds 

less than 3 mph (typical OTR run-in/run-out speeds), the prime gears are not any higher than 

the other gears. While tank cars must be switched at impact speeds lower than 4 mph, impact 

speeds of 8 mph or more are not uncommon. If such an impact were to occur at an average or 

soft condition, it is quite likely that the resulting coupler force would be over a million pounds 

or even over the 1.25 million pound design limit of tank cars, even under 263,000 lb GRL 

loading. 

0

100

200

300

400

500

600

700

800

900

1000

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Impact Speed (mph)

Coupler Force (kips)

Prime

Average

Soft

Figure 10. Peak coupler forces 

19
3.2 Stresses at Critical Locations

An analysis of stresses at critical locations also emphasizes that high stresses result from 

using soft gears on tank cars, especially at higher speeds. Figure 11 displays the stresses on 

the tank shell (location A). It is seen that the soft gears produce the highest stress in the tank 

car at all speeds, with the differences increasing substantially at higher speeds. At speeds less 

than 6 mph, prime gears induce slightly higher stresses than the average gears. At higher 

impact speeds (where the likelihood of damage is the highest), however the prime gears 

induce considerably lower stresses. 

0

5

10

15

20

25

30

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Impact Speed (mph)

Tank Stress - Location A (ksi)

Prime

Average

Soft

Figure 11. Principal stresses on the tank head (location A)

The stresses at the pad follow a similar trend (Figure 12). Soft gears provide the least 

protection at almost all speeds. Average gears provide good protection at low impact speeds, 

but the level of protection drops as impact speeds increase. The prime gears provide 

reasonable protection at low speeds and excellent protection as impact speeds increase. 

Stresses in the head brace could only be compared between the average and soft gear sets 

(Figure 13) resulting from change in gage location and orientation after the first set of tests 

(with the prime gears). As seen, soft gears provide significantly less protection when 

compared to the average gears, just as observed at the other locations. Given these 

observations about coupler forces and stresses at the other locations, it would be reasonable to 

expect that the prime gears would have offered superior protection at this location also. 

20
0

10

20

30

40

50

60

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Impact Speed (mph)

Pad Stress - Location B (ksi)

Prime

Average

Soft

Figure 12. Principal stresses on the reinforcing pad (location B)

 

 

0

10

20

30

40

50

60

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Impact Speed (mph)

Brace Stress - Location C (ksi)

Average

Soft

Figure 13. Principal stresses at the head brace (location C)

 

21
3.3 Summary 

The impact test series evaluated the performance of different draft gear types and conditions 

as applied to tank cars with 263,000 lb GRL loading. In summary, from the test results, prime 

gears provide the best protection from overload impacts, with their advantage over the soft 

gears being significant at all impact speeds. Average gear setups provide reasonable 

protection at lower speeds, but their performance at higher speeds is lacking when compared 

to the prime gears. However, average gear setups do provide better protection than soft gear 

setups at all speeds. 

Generally, tank car owners have no control over placement of their cars in a train and 

subsequently over the draft gear conditions of adjacent cars. While a given tank car may be 

equipped with a prime gear, it may impact against a car with soft gears while OTR. The 

average setup that was tested represents this scenario. In such scenarios, the protection 

benefits offered by the prime gears may not be fully realized. Even in such scenarios a prime 

gear will protect the car better, as evidenced by the performance of the average setup 

compared to the soft setup. 

22
4.0 Impact Modeling for 286,000 lb GRL Loading 

One of the main objectives of this project was to evaluate the effects of gear type and gear 

condition on the protection offered to tank cars in 286,000 lb GRL service. Such an 

evaluation for cars in 263,000 lb GRL service was done as part of the impact test series. 

Since a similar test program for 286,000 lb GRL cars was outside this project=s scope, an 

alternate approach was chosen. A finite element model to simulate tank car impacts was 

developed for 263,000 lb GRL cars. This model was validated using data from the tests. 

Upon proper validation, the model was up rated to 286,000 lb GRL cars, and the resulting 

coupler forces were evaluated for various impact speeds. 

4.1 Model Development

First, a detailed finite element model suitable for dynamic analysis was developed paying 

close attention to all the relevant details, including the complex shape of the stub sill tank car 

connection, the weldments between different components, the bolted draft lugs, and the center 

plate (Figure 14). The model also accounts for complete draft gear/coupler characteristics, 

coupler shank-to-striker contact parameters, detailed truck suspension characteristics (Figure 

15), and the masses and stiffnesses of the hammer car and backup cars. The model uses LSDYNA, an explicit finite element solver for modeling impact. 

Figure 14. Finite element model of tank car structure 

 

 

23
Figure 15. Finite element model of tank car including suspension 

 

In addition, a coupler force model was developed which modeled the cars and their lading 

through a series of springs, dampers, and masses. The sloshing of water inside the tank car 

was modeled using a series of springs and masses. Draft gear characteristics at all the car 

interfaces was also modeled in detail (Figure 16). Non-linear characteristics for the various 

springs and dampers used (especially in the draft gear systems) was modeled to represent the 

behavior observed during the impact tests. This model was also created in LS-DYNA and 

used for most of the subsequent work. 

4.2 Model Validation

The coupler force model was validated for the six different impact scenarios, as presented in 

Table 1. During the validation process, the characteristics of the model that pertained to car 

and lading (i.e., the car body stiffnesses and masses), were kept constant for all six scenarios. 

Draft gear characteristics, however, were tuned to best represent the performance observed 

during the tests. At the end of validation, six different models represented the six scenarios, 

with the models differing between each other only in draft gear characteristics. The draft gear 

characteristics for each scenario were kept constant for the range of impact speeds (2B8.5 

mph) that the simulations were run. 

Draft gear characteristics were modeled using appropriate springs and dampers. The main 

draft gear spring was modeled using appropriate loading and unloading curves that were 

derived from the coupler force versus draft gear travel plots from the impact tests. Figure 17 

shows the derived loading/unloading curves for the M-901G gear. The characteristics of the 

dampers were picked to represent the observed behavior at all speeds. 

24
 

BACKUP CAR 1 BACKUP CAR 2 HAMMER CAR

Lading (Water)

Car Body 

Stiffness

TANK CAR Damper to Simulate Hand Brakes Being Set 

on BACKUP CAR 2

Damper 1

Damper 2

Spring 1

DRAFT GEAR MODEL (DG)

TANK CAR IMPACT MODEL

Spring 2

DG DG DG DG DG DG

Figure 16. Schematic of coupler force impact model 

 

25
0

100

200

300

400

500

600

700

800

900

1000

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25

Draft Gear Travel (in.)

Coupler Force (kips)

Loading

Unloading

Figure 17. Loading and unloading characteristics for primary draft gear springs–G gear 

200

300

400

500

600

700

800

900

1000

1100

23456789

Impact Speed (mph)

Coupler Force (kips)

Model

Test

Figure 18. Comparison of model and test data–G gear 

26
Figure 18 shows the measured data for scenario 2 (G gearBsee Table 1) as compared to model 

data. As seen, the model tracks the measured data very well. Similar comparisons were seen 

for all five scenarios. The performance of draft gears is well represented by these models, 

especially at speeds greater than 4 mph. In some cases, however, the low speed performance 

was not duplicated exactly. 

4.3 286,000 Lb GRL Tank Cars

The above-mentioned models that were validated using test data were then scaled to represent 

impact scenarios using 286,000 lb GRL cars. Essentially, all parameters were retained except 

the car masses which were scaled up. The simulations were then run for impact speeds 

between 2 and 9 mph for all six scenarios. Certain key observations may be made by 

studying the results: 

1. Figure 19 shows the coupler forces resulting from various impact speeds for the three 

gear conditions. As seen in the previous chapter, prime gears continue to offer 

superior protection even in 286,000 lb GRL service, especially at speeds higher than 5 

mph. Soft gears provide the least protection at most speeds. Average gears provide 

reasonable protection at lower speeds, but as speeds increase the levels of protection 

offered drop. 

200

400

600

800

1000

1200

1400

1600

3456789

Impact Speed (mph)

Coupler Force

Prime

Average

Soft

Figure 19. Coupler forces under 286,000 lb GRL loading 

 

27
2. Figure 20 shows the performance of the two prime gears, the G gear and the E gear in 

prime condition (model A). It is seen that the G gears offer better performance at 

higher speeds (greater than 6.5 mph). At lower speeds, the E gear offers slightly better 

performance 

3. Figures 21, 22 and 23 show the coupler forces for 263,000 lb GRL cars (model), 

286,000 lb GRL cars (model) and the measured test data (for 263,000 lb GRL cars). It 

can be seen from these charts that, at lower speeds, no significant differences exist in 

coupler forces between 263,000 lb GRL cars and 286,000 lb GRL cars for a given set 

of draft gears. The lack of variation in coupler forces at these speeds indicates that the 

friction packs in the gears have sufficient capacity to absorb the additional impact 

energy arising from the increased mass. However, at a certain speed, 286,000 lb GRL 

cars start producing higher coupler forces. The impact speed at which this separation 

occurs varies from gear type to gear type and is one measure of the draft gears 

capacity to protect tank cars. The separation speed is highest for the prime gears 

(approximately 6.5 mph) and lower for the soft gears (about 4mph), once again 

underlining the superior protection offered by the prime gears. In other words, prime 

gears offer 286,000 lb GRL cars the same protection as 263,000 lb GRL cars over a 

larger range of speeds, as compared to the soft gears. 

200

400

600

800

1000

1200

1400

3456789

Impact Speed (mph)

Coupler Force

G Gear

Prime E

Figure 20. Comparison of coupler forces–Prime E gears versus G gears–286,000 lb GRL loading

28
4.4 Summary

As part of the modeling effort, validated finite element models that represent draft gear 

behavior in the six different scenarios were developed. The models were then scaled for 

simulating impact of 286,000 lb GRL cars. It was seen from these simulations that prime 

gears provided the best protection for tank cars, especially as speeds increased. 

29
200

400

600

800

1000

1200

1400

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 21a. Scenario 1–Prime A gear 

200

400

600

800

1000

1200

1400

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 21b. Scenario 2–G gear 

Figure 21. Coupler force comparisons–Prime gears 

30
200

400

600

800

1000

1200

1400

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 22a. Scenario 3–Average B gear 

200

400

600

800

1000

1200

1400

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 22b. Scenario 4–Average C gear

Figure 22. Coupler force comparisons–Average gears

31
200

400

600

800

1000

1200

1400

1600

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 23a. Scenario 5–Soft B gear

200

400

600

800

1000

1200

1400

1600

23456789

Impact Speed (mph)

Coupler Force (kips)

286K (Model)

263K (Model)

263K (Test)

Figure 23b. Scenario 6–Soft C gear 

Figure 23. Coupler force comparisons–Soft gears 

32
5.0 Conclusions and Recommendations 

As part of this project, a test tank car was instrumented, loaded to simulate 263,000 lb GRL 

service and tested on an impact ramp. Six different draft gear combinations were tested as 

part of this program. Subsequent to the testing, finite element models that simulated the 

impact behavior of tank cars was developed. These models were validated using the test data 

and used to simulate draft gear behavior under 286,000 lb GRL loading. The following 

conclusions were reached from the testing and simulations. 

1. When coupler forces from the tests were compared, it was seen that the prime gears (M901E gears in prime condition and M-901G gears) induced the lowest coupler forces, 

especially at higher impact speeds where the potential for damage is the highest. Impacts 

in the soft condition (draft gears at the struck and striking ends in used condition) 

produced the highest coupler forces at all relevant speeds. 

2. A comparison of the stresses developed at locations A, B, and C indicated that the best 

protection was offered by the gears in prime condition. Soft gears produce the highest 

stress in the tank car at all speeds, with the differences increasing substantially at higher 

speeds. At speeds less than 6 mph, prime gears induce slightly higher stresses than the 

average gears. This small disadvantage at lower speeds, however, is not enough to offset 

the significant advantage offered by the prime gears at higher speeds. At these high 

impact speeds (where the likelihood of damage is the highest), the prime gears induce 

considerably lower stresses. 

3. Simulations of 286,000 lb GRL service impacts using validated models indicated that 

prime gears would continue to offer superior protection, especially at higher speeds. At 

lower speeds, no significant differences existed in performance between 286,000 lb GRL 

service and 263,000 lb GRL service. The speed at which coupler forces started to increase 

under 286,000 lb GRL service was higher for the prime gears, indicating additional 

reserve capacity in the friction packs of the draft gears. 

4. Comparisons of E gears in prime condition and G gears indicated that the E gears offered 

marginally better performance at lower speeds, while the G gears offered better 

performance as speeds increased. 

5. It was seen that prime gears offer better protection under both 263,000 lb GRL service and 

286,000 lb GRL service. In the prime conditions that were tested/simulated, however, 

draft gears at the struck and striking ends were in good condition. Generally, tank car 

owners have no control over placement of their cars in a train and subsequently over the 

draft gear conditions of adjacent cars. While a given tank car may be equipped with a 

prime gear, it may impact against a car with soft gears while OTR. The average setup that 

was tested represented this scenario. In such scenarios, the protection benefits offered by 

the prime gears may not be fully realized. However, even in such scenarios a prime gear 

will protect the car better, as evidenced by the performance of the average setup compared 

to the soft setup. In both 263,000 lb GRL and 286,000 lb GRL service, the average gear 

setup performed better than the soft gear setup at almost all speeds. 

33
6. An overview of the test and simulation data indicates that different gears are at their best 

at different speed ranges. Given the large number of variables involved, it is a difficult 

task to design draft gears to perform well at all speeds. However, it would be a 

worthwhile effort to try and tune draft gear performance in the design process to 

maximize the protection offered by draft gears. 

34
REFERENCES 

1. Prabhakaran, A. and Sharma, V., 2001. AEffects of Coupler Height Mismatch on the 

Structural Integrity of Railroad Tank Car Stub Sills.@ Report No. DOT/FRA/ORD-01/14, 

U.S. Department of Transportation/Federal Railroad Administration, Washington, DC. 

2. Sharma, V., Sneed, W.H., and Punwani, S.K., 1984. AFreight Equipment Environmental 

Sampling Test-Description and Results.@ ASME Rail Transportation Spring Conference 

Proceedings, pp. 59-70. 

3. Cogburn, L.T., 1995. AStub Sill Tank Car Research Project–Results of a 15,000 mile 

Over-the-Road Test.@ Report No. FRA/ORD/95-11, U.S. Department of 

Transportation/Federal Railroad Administration, Washington, DC. 

4. AFatigue Design of Freight Cars.@ Specifications for design, fabrication, and construction 

of freight cars, AAR specification M-1001, Association of American Railroads. 

35
36
ACRONYMS 

AAR Association of American Railroads 

ASTM American Society of Testing and Materials 

FRA Federal Railroad Administration 

GRL gross rail load 

OTR over-the-road 

SA Sharma & Associates, Inc. 

37