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Environment Study–Phase I
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13. ABSTRACT

This report documents the results of controlled testing conducted during the first phase of a tank car 

operating environment program involving the Association of American Railroads, the Railway 

Supply Institute (formerly the Railway Progress Institute), the Federal Railroad Administration, and 

Transport Canada. Strain gages, accelerometers, and an instrumented coupler were installed on a 

stub sill tank car during this phase of testing. This car was then subjected to a series of tests applying 

a range of forces to the coupler. These included the application of controlled vertical forces, car-tocar impact tests, and a short duration over-the-road test. Results showed that significant correlation 

could be established between strain gage output and output from the instrumented coupler. This 

indicates the strong possibility that longitudinal and vertical coupler forces can be inferred only from 

the output from four strain gages installed on the stub sill. Results also showed a correlation between 

accelerometer output (in the form of a shock response spectrum (SRS)) and peak longitudinal coupler 

forces, especially for impact forces above 400,000 pounds. This indicates a possibility that SRS 

values from only two accelerometers can be used to infer the magnitude of peak coupler forces that 

occur during yard impacts. During Phase II of this investigation, this transducer system will be 

tested under standard in-service conditions to further prove the concept and usefulness towards 

establishing tank car coupler force operating environment profiles.

14. SUBJECT TERMS 15. NO. OF PAGES

77 Tank car coupler forces, railcar impact test, correlation of accelerometer data with 16. PRICE CODE coupler forces

17. SECURITY 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF 

CLASSIFICATION OF THIS PAGE OF ABSTRACT ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED 

Standard Form 298 (Rec. 2-89) 

Prescribed by ANSI/NISO Std. NSN 7540-01-280-5500 239.18 

298-102
ii 
iii 

Table of Contents 

List of Figures................................................................................................................................. v 

List of Tables ................................................................................................................................. vi 

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

1.0 

 

Introduction......................................................................................................................... 3 

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

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

1.3 Approach..................................................................................................................... 4 

1.4 Scope........................................................................................................................... 4 

2.0 Test Description.................................................................................................................. 7 

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

2.2 Test Method ................................................................................................................ 7 

2.3 Instrumentation ......................................................................................................... 11 

2.4 Data Analysis............................................................................................................ 14 

2.5 Summary of Results.................................................................................................. 17 

2.6 Conclusions............................................................................................................... 35 

3.0 Recommendations............................................................................................................. 37 

References..................................................................................................................................... 39 

Appendix. Plots 1 through 22 ...................................................................................................... 41 

Acronyms...................................................................................................................................... 77 
iv 

 
v 

List of Figures 

Figure 1. VICX 1725 Tank Car Setup for Impact Test.......................................................... 7 

Figure 2. Force versus Time Trace......................................................................................... 8 

Figure 3. FAST-High Tonnage Loop................................................................................... 10

Figure 4. VICX Tank Car in FAST Train ............................................................................. 7 

Figure 5. Accelerometer Locations–Overall Layout............................................................ 11 

Figure 6. Accelerometer Locations–Details......................................................................... 12 

Figure 7. Strain Gage Locations........................................................................................... 12 

Figure 8. Strain Gage Rosette 11, 12, and 13 and Strain Gage 19....................................... 13 

Figure 9. Data Acquisition Bricks Used During Impact Test .............................................. 13 

Figure 10. Examples of SRS Plot for Accelerometer 6.......................................................... 15 

Figure 11. Measured (top) and Calculated LCF versus Time, April 15-16, 2003, 

Test Car Near Front of Train ................................................................................ 27 

Figure 12. Measured LCF (top) and Calculated VCF versus Time, April 15-16, 2003, 

Test Car Near Front of Train ................................................................................ 28 

Figure 13. Measured (top) and Calculated LCF versus Time, April 14-15, 2003, 

Test Car Near Rear of Train.................................................................................. 29 

Figure 14. Measured (top) and Calculated LCF versus Time During a 41-Second Time 

Period, April 14-15, 2003, Test Car Near Rear of Train ...................................... 29 

Figure 15. Measured LCF (top) and Calculated VCF versus Time During a 

41-Second Time Period, April 14-15, 2003, Test Car Near Rear of Train........... 30 

Figure 16. Measured LCF and Associated Longitudinal Acceleration at Location 6, 

April 14-15, 2003.................................................................................................. 30 

Figure 17. Measured LCF and Associated Longitudinal Acceleration at Location 18, 

April 14-15, 2003.................................................................................................. 31 

Figure 18. Typical Accelerometer Data Recorded April 20-22, 2003 ................................... 31 

Figure 19. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, 

April 14-15, 2003.................................................................................................. 33 

Figure 20. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, 

April 16-17, 2003.................................................................................................. 33 

Figure 21. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, 

April 20-21, 2003.................................................................................................. 34 

Figure 22. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, 

April 21-22, 2003.................................................................................................. 34 
vi 

List of Tables 

Table 1. Amplitude and Duration of Applied Vertical Force, Car Empty.................................. 8 

Table 2. Amplitude and Duration of Applied Vertical Force, Car Loaded ................................ 8 

Table 3. Summary of FAST Test.............................................................................................. 11 

Table 4. Peak LCF and VCF for Impact Sequence 1................................................................ 19 

Table 5. Peak LCF and VCF for Impact Sequence 2................................................................ 20 

Table 6. Peak LCF and VCF for Impact Sequence 3................................................................ 20 

Table 7. Peak LCF and VCF for Impact Sequence 4................................................................ 21 

Table 8. Estimated Linear Relationships, SRS Response versus Peak LCF– 

Accelerometer Number 6............................................................................................ 24 

Table 9. Sample of Predicted Peak LCF Values Using SRS Data– 

Accelerometer Number 6............................................................................................ 25 

Table 10. Estimated Linear Relationships, SRS Response versus Peak VCF– 

Accelerometer Number 6............................................................................................ 26 
1 

EXECUTIVE SUMMARY 

The Association of American Railroads (AAR), the Railway Supply Institute (formerly the 

Railway Progress Institute), the Federal Railroad Administration (FRA), and Transport Canada 

(TC) participated in a cooperative investigation of the operating environment of tank cars. Two 

technical groups cooperated on this project. 

One of the groups, known as the Tank Car Operating Environment Task Force (TCOE-TF), 

evaluated a possible inverse relationship between the costs associated with the 

design/construction of tank cars and handling/operation of those cars. TCOE-TF would like to 

establish the credibility of a reasonably priced device that would collect reliable data for use in 

investigating the magnitude and direction of the largest forces encountered by tank cars during 

over-the-road service. The second group, the Stub Sill Working Group (SSWG), investigated the 

use of failure analysis to predict the proper inspection interval for stub sill tank cars. SSWG has 

a need to verify the full range of forces that tank cars experience in the railroad operating 

environment. 

This investigation is part of an ongoing assessment of necessary components for a complete 

system optimization (i.e., to assure safety while minimizing total cost). Since the research needs 

are so closely related, the two groups agreed to work together to achieve both objectives. 

The test program, designed with the requirements of these two groups in mind, was initially 

divided into three phases. Phase I, completed in April 2003, addressed the development and 

proof of a methodology to infer peak longitudinal coupler forces (LCF) and vertical coupler 

forces (VCF) from data collected using a relatively inexpensive set of transducers. Phase I also 

included the development of the inexpensive transducer and data collection package. Phase II is 

designed to follow Phase I and provide further data collection system development and further 

validation of a correlation process by eventually subjecting as many as five cars with the 

minimal transducer package to an uncontrolled over-the-road service environment. If Phases I 

and II are successful, Phase III will implement the installation of the inexpensive transducer 

packages on a larger number of tank cars to collect a more comprehensive set of environment 

data. This report addresses the results of the following testing that was completed under Phase I: 

1. A series of controlled, car-to-car impact tests while recording acceleration versus time 

and strain versus time data from transducers mounted at numerous locations on the tank 

car. LCF was also recorded during each impact. The data from these tests was processed 

in an effort to determine if, under controlled impact conditions, a sufficient degree of 

correlation could be established between measured acceleration response and peak 

coupler forces (both longitudinal and vertical) or between strain output and peak coupler 

forces. The acceleration response versus coupler force correlation was analyzed using 

two methods: 

• Coupler force (longitudinal and vertical) versus peak acceleration values. 

• LCF and VCF versus shock response spectrum (SRS) curves generated from the 

peak acceleration values. 
2 

2. A series of tests applying upward vertical forces to the end of the tank car while 

recording the acceleration and strain output from the set of transducers. The vertical 

forces were designed to simulate the VCFs produced during over-the- road operations. 

Again, the data from these tests was processed in an effort to determine if, under 

controlled conditions, a degree of correlation could be established between measured 

vertical acceleration response and peak coupler forces (both longitudinal and vertical) or 

between strain output and peak coupler forces. 

3. The final task of Phase I was to operate the test car in a train to record similar 

accelerometer and strain gage responses while the instrumented tank car was used in 

conditions more closely approximating over-the-road service. It was intended that 

completion of this task would meet the following objectives: 

• Confirm that relationships between strain gage or accelerometer output and peak 

coupler force can also be established for the lower magnitude coupler forces produced 

by normal train action. The results of the impact tests had allowed the study of these 

relationships for peak compressive forces greater than 250,000-300,000 pounds. It 

had also established the validity of such relationships for both tensile and 

compressive forces with magnitudes from near zero to 250,000-300,000 pounds. 

• Develop and prove the reliability of a power generation system (in a relatively 

controlled environment) that can provide consistent, long-term power for the onboard 

data acquisition hardware while being hidden from casual observation. 

The results of Phase I testing have shown that strain values from gages strategically mounted to 

the stub sill can be used to calculate the magnitude of VCFs and LCFs during standard over-theroad operations, as well as during yard impact events. The results also indicate this as the 

preferred method for calculating coupler forces to be used in fatigue life predictions or damage 

tolerance analysis. The results also show that it is definitely possible to use SRS data to calculate 

or predict peak LCFs and VCFs occurring as a result of car-to-car impacts. This method, 

however, is most effectively used for impact events resulting in LCFs above 400,000-500,000 

pounds. The preferred location for accelerometers to be used in this prediction process is near 

the longitudinal center of the car attached to the top of the tank structure. Accelerometers alone, 

however, are not suitable for the prediction of LCFs and VCFs that result from normal over-theroad operations. 
3 

1.0 Introduction 

1.1 Background 

AAR, the Railway Supply Institute (formerly the Railway Progress Institute), FRA, and TC 

funded a cooperative investigation of the operating environment of tank cars. AAR subsidiary 

Transportation Technology Center, Inc. (TTCI) conducted this evaluation at FRA’s 

Transportation Technology Center (TTC), Pueblo, CO. 

Two technical groups cooperated on this project. One of the groups, known as TCOE-TF, 

evaluated a possible inverse relationship between the costs associated with the design/ 

construction of tank cars and handling/operation of those cars. The TCOE-TF would like to 

establish the credibility of a reasonably priced device that would collect reliable data that could 

be used to investigate the frequency and magnitude of the largest forces encountered by tank cars 

during over-the-road service. The second group, SSWG, investigated the use of failure or 

durability analysis to predict the proper inspection interval for stub sill tank cars. SSWG has a 

need to verify the full range of forces that tank cars experience in the railroad operating 

environment. 

This investigation is part of an ongoing assessment of what is necessary for a complete system 

optimization (i.e., to assure safety while minimizing total cost). Since the research needs are so 

closely related, the two groups have agreed to work together to achieve both objectives. 

1.2 Objectives 

This report addresses the results of Phase I of a possible three-phase program. The testing in 

Phase I had the following objectives: 

1. Study, through controlled, on-track testing, the feasibility of estimating or calculating 

coupler force using only car-mounted accelerometer or strain readings. The body of data 

must show that such a correlation is possible with an acceptable degree of accuracy. The 

acceleration versus coupler force correlation will be tested using a minimum of two 

methods: 

• Coupler force (longitudinal and vertical) versus peak acceleration values. 

• LCF and VCF versus SRS curves generated from the peak acceleration values. 

2. If the initial testing conducted in Phase I indicated a good possibility that reliable 

relationships can be defined, effort would then be directed toward the assembly and 

demonstration of an acquisition system that could be used to efficiently and reliably 

record and broadcast, or download, such data from one or more cars placed in extended 

over-the-road service. 
4 

1.3 Approach 

The test program, designed with the requirements of these two groups in mind, was initially 

divided into three phases. Phase I, completed in April 2003, addressed the development and 

proof of a methodology to infer peak LCFs and VCFs from data collected using a relatively 

inexpensive set of transducers. Phase I also included the development of the inexpensive 

transducer and data collection package. This report discusses the results of Phase I. Phase II is 

designed to provide further data collection system development and further validation of a 

correlation process by eventually subjecting as many as five cars with the minimal transducer 

package to an uncontrolled over-the-road service environment. If Phases I and II are successful, 

Phase III will implement the installation of the inexpensive transducer packages on a possibly 

much larger number of tank cars to collect a more comprehensive set of environment data. The 

objectives of Phase I to successfully relate accelerometer or strain gage output to coupler force 

were attempted using the following methods: 

• Peak coupler force (longitudinal and vertical) versus peak output from accelerometers. 

• Peak LCF and VCF versus SRS curves generated from the peak acceleration values. 

• LCF and VCF versus output from a small number of strategically placed strain gages. 

Before a large-scale test program was undertaken, an initial or exploratory test was conducted in 

an effort to better establish some of the important parameters to be used in the subsequent Phase 

I testing, as well as gain more confidence in the validity of the correlation between acceleration 

data and coupler force or strain data and coupler force. During the initial testing, a large number 

of accelerometers and strain gages were placed at widespread locations on the tank car. This was 

done because of the uncertainty of which locations would provide the best correlation with 

coupler force. The primary focus, therefore, was to eventually eliminate most of the transducers 

and establish only a small number of accelerometer or strain measurement locations that could 

provide the best correlation. This step was vital if system complexity and expense were to be 

minimized. 

1.4 Scope 

Phase I testing included the controlled application of vertical force pulses to the end of the stub 

sill with the tank car empty and fully loaded, as well as the following impact sequences: 

• Sequence 1: Empty, instrumented tank car rolling into loaded stationary 3-car anvil 

string at velocities of 2, 4, 6, and 8 mph. The hand and air brakes were set on the two 

stationary cars farthest from the impact. 

• Sequence 2: Loaded, instrumented tank car rolling into loaded stationary 3-car anvil 

string at velocities of 2, 4, 6, and 8 mph. The hand and air brakes were set on the two 

stationary cars farthest from the impact. 

• Sequence 3: Loaded, hopper car rolling into instrumented, loaded stationary tank car at 

velocities of 2, 4, 6, and 7 mph. The tank car was not coupled to any other cars. The 

hand and air brakes were set on the stationary tank car. 

• Sequence 4: Loaded, hopper car rolling into instrumented, loaded stationary tank car at 

velocities of 2, 4, 6, and 6.5 mph. The tank car was the lead car in a loaded five-car anvil 

string. The hand and air brakes were set on all of the stationary cars. 
5 

The final task of Phase I was to record similar accelerometer and strain gage responses while the 

instrumented tank car was used in over-the-road conditions. The completion of this would meet 

the following objectives: 

• Confirm that relationships between strain gage or accelerometer output and peak coupler 

force can also be established for the lower magnitude coupler forces produced by normal 

train action. The results of the impact tests have allowed the study of these relationships 

for peak compressive forces greater than about 250,000-300,000 pounds. It is important 

to establish the validity of such relationships for both tensile and compressive forces with 

magnitudes from near zero to 250,000-300,000 pounds. 

• Develop and prove the reliability of a power generation system (again in a controlled 

environment) that can provide consistent, long-term power for the onboard data 

acquisition hardware while being hidden from casual observation. 
6 
7 

2.0 Test Description 

2.1 Test Car 

The tank car used in this study had the following characteristics: 

• Manufacturer: American Car and Foundry (pictured in Figure 1) 

• Car number: VICX 1725 (Certificate of Construction No. 21826) 

• Empty weight: 75,400 pounds 

• Maximum weight with payload of water: 262,272 pounds 

• Tank design: ACF 4-B-7188, 22,500-gallon capacity 

• Underframe design: ACF 4-B-7190 stub sill 

• Coupler design: 6 1/4x8 Type E, Top and Bottom Shelf 

• Draft gear design: Cardwell Westinghouse Mark 50 all-steel design (friction wedges plus 

springs) 

Figure 1. VICX 1725 Tank Car Setup for Impact Test 

2.2 Test Method 

2.2.1 Low Frequency Vertical Forces Applied to Sill, Simulating In-Train Forces 

A vertical force pulse was applied to the end of the sill in the upward direction. This test was 

conducted with the car both empty and loaded with water. A hydraulic cylinder created the force 

pulse, and the shape of this pulse was essentially one-half of a sine wave. Tables 1 and 2 provide 

the duration of the half-sine wave shapes, as well as the peak amplitude of the vertical force 

applied. Figure 2 shows an illustration of a typical force versus time trace and the term “t/2.” 

Each test condition was repeated at least three times. 
8 

Table 1. Amplitude and Duration of Applied Vertical Force, Car Empty 

Peak Force (pounds) t/2 (seconds) 

10,000 .25

10,000 .50

10,000 1.0

15,000 .25

15,000 .50

15,000 1.0

20,000 .25

20,000 .50

20,000 1.0

Table 2. Amplitude and Duration of Applied Vertical Force, Car Loaded 

Peak Force (pounds) t/2 (seconds) 

21,800 .25

30,900 .50

35,800 .25

51,600 .50

Figure 2. Force versus Time Trace 

2.2.2 Controlled Impact Testing 

The following summarizes the conditions for impact sequences 1 through 4. For all sequences, 

the impacts occurred at the A-end of the instrumented tank car. 

• Impact Sequence 1: Empty, instrumented tank car rolling into stationary, loaded 3-car 

anvil string at velocities of 2, 4, 6, and 8 mph. The air and hand brakes were set on the 

two anvil string cars farthest from impact. The anvil group of cars remained essentially 

stationary for all but the 8-mph impacts. During the 8-mph tests, 3 to 5 inches of 
9 

movement upon impact occurred. The height of the tank car coupler was approximately 

1.5 inches higher than that of the mating stationary cars. 

• Impact Sequence 2: Loaded, instrumented tank car rolling into loaded stationary 3-car 

anvil string at velocities of 2, 4, 6, and 8 mph. The air and hand brakes were set on the 

two anvil string cars farthest from impact. Movement of the anvil string after impact 

ranged from about 12 inches at 2 mph to over 40 inches at 8 mph. The heights of the 

couplers on the tank car and the mating anvil car were within .25 inch of each other. 

• Impact Sequence 3: Loaded, hopper car rolling into instrumented, loaded stationary tank 

car at velocities of 2, 4, 6, and 7 mph. The tank car was not coupled with any other cars. 

The gross weight of the hammer car was 261,764 pounds. The air and hand brakes were 

set on the tank car. Tank car movement after impact ranged from about 2 feet at 2 mph to 

about 20 feet at 7 mph. A maximum impact velocity of 7 mph was used in order to limit 

the maximum LCF to around 1.25 million pounds. Coupler height again matched to 

within 0.25 inch. 

• Impact Sequence 4: Loaded, hopper car rolling into instrumented, loaded stationary tank 

car at velocities of 2, 4, 6, and 6.5 mph. This was the same hopper car used in sequence 

3. The tank car was the lead car in a loaded five-car anvil string. The air and hand 

brakes were set on all cars in the anvil string. Tank car movement after impact ranged 

from about 2 inches at 2 mph to about 17 inches at 6.5 mph. A maximum impact of 

velocity of 6.5 mph was used to limit the maximum LCF to around 1.25 million pounds. 

Coupler height again matched to within .25 inch.

2.2.3 Testing at TTC’s Facility for Accelerated Service Testing (FAST) 

The High Tonnage Loop (HTL) at FAST is a 2.7-mile closed track consisting of a main loop and 

a bypass loop (see Figure 3). This track is used primarily for heavy axle load and bridge testing 

and research. The loaded instrumented tank car was included in the FAST train as it proceeded 

with its normal operating schedule. Some of the basic parameters of this loop include the 

following: 

• Each lap includes up to four 5-degree curved sections (Sections 3, 7, 31, or 38) and one 

6-degree curve (Section 25).

• During each main loop lap, the train travels over three turnouts (Sections 25, 27, and 35). 

During each bypass loop lap, the train travels through two turnouts (Sections 27 and 35), 

over one turnout (Section 23), and over three more turnout frogs in Section 36.

• Normal operating speed is approximately 40 mph.

• A number of minor grades are included in the HTL, ranging from 0.4 to 0.9 percent.

• During the test period, the train included 75-78 cars with the travel direction of both 

clockwise and counterclockwise (see Table A-1 in the appendix). 
10 

Bypass Loop

Figure 3. HTL at FAST 

The loaded instrumented tank car was allowed to run in the FAST train for 13 nights from March 

23, 2003, to April 22, 2003. The tank car was near the front of the train for part of the test period 

and near the rear of the train for the remainder (Figure 4). Table 3 briefly summarizes the 

completed testing. Table A-1 in the appendix provides additional details. 

Figure 4. VICX Tank Car in Test Train at FAST 
11 

Table 3. Summary of Test Results at FAST 

Dates Laps 

Completed 

Hours of 

Running 

Approximate Miles 

Traveled 

3/23/03–3/24/03 129 8.7 398 

3/24/03–3/25/03 86 6.0 232 

3/25/03–3/26/03 124 8.6 335 

3/26/03–3/27/03 134 8.9 362 

3/30/03–3/31/03 127 8.9 343 

3/31/03–4/1/03 130 8.8 351 

4/7/03–4/8/03 135 9.3 365 

4/13/03–4/14/03 122 8.7 329 

4/14/03–4/15/03 135 8.8 365 

4/15/03–4/16/03 129 8.9 348 

4/16/03–4/17/03 90 6.3 243 

4/20/03–4/21/03 71 5.0 192 

4/21/03–4/22/03 130 8.9 351 

Totals 1,542 159.8 4,169 

2.3 Instrumentation 

Originally, 38 single accelerometers and 22 strain gages were installed on the car. Figures 5, 6, 

and 7 show the locations of these transducers. Figure 8 shows strain gage locations 11, 12, and 

13. Figure 9 shows the installation of the data acquisition hardware on the tank car. For each 

accelerometer location shown, except for numbers 11 and 12, one vertical axis and one 

longitudinal axis accelerometer are installed. At locations 11 and 12, only longitudinal 

accelerometers were installed. The accelerometers used at the center and impact end (A-end) of 

the car had a capacity of ±100 g, while those used on the end of the car opposite the impact had a 

capacity ±50 g. An instrumented coupler was also installed at the car’s impact end to record the 

LCF. 

1616 1717

1313 1111 77 Stub

Sill

Stub

Sill

99 55 1010 88 1212

33

1,1a 1,1a

1515 44

66

1414

2,2a 2,2a

2a2a

22

1818

Figure 5. Accelerometer Locations—Overall Layout
12 

1a1a

33

11

1313

1111

1515

77

Figure 6. Accelerometer Locations—Details 

Strain Gage Locations Strain Gage Locations

66

1010

55

1717

1818

11

55

21,(22 on

other side on

neutral axis)

21 (22 on

other side on

neutral axis)

Gages 6 – 10

On other side

Of sill 11, 12, & 13

(14, 15, & 16

On other side)

11, 12, & 13

(14, 15, & 16

on other side)

19, (20

On other side

on neutral axis)

2, 3, & 4 2, 3, & 4

Rear

Draft 

Lugs

on other side 

of sill 

Gages 6–10

19 (20 on other 

side on neutral 

axis)

Figure 7. Strain Gage Locations 
13 

Figure 8. Strain Gage Rosette 11, 12, and 13 and Strain Gage 19 

Figure 9. Data Acquisition Bricks Used During Impact Test 

Before any testing began, a quasi-static calibration procedure was performed to relate strain gage 

response to LCF and VCF. This calibration procedure involved two tasks. During the first, 

compressive and tensile loads of up to 300,000 pounds were applied to the instrumented coupler. 

Response from all of the strain gages was recorded, and relationships of coupler force versus strain 

were established for each gage. For the second task, vertical forces of up to 20,000 pounds upward 

(positive) to 20,000 pounds downward (negative) were applied to the end of the stub sill on the Aend of the car. A calibrated load cell, installed between a hydraulic cylinder and the sill, measured 

these forces. Again, the response from each strain gage was recorded as the forces were applied, 

and relationships of coupler forces versus strain were established for each gage. 

During the controlled, dynamic vertical force test, data was recorded for all strain gages but only 

for the following accelerometers: 1 vertical and longitudinal, 1A vertical and longitudinal, 11 

longitudinal, 13 longitudinal, 3 vertical and longitudinal, 15 vertical and longitudinal, 5 vertical 

and longitudinal, and 6 vertical and longitudinal. 
14 

During the first impact test (Sequence 1), the output from all transducers was recorded, and the 

data was processed. Decisions about which longitudinal and vertical accelerometer locations to 

study in detail were based on the shape of the acceleration versus time curve and the 

characteristics of the associated Fast Fourier Transfer (FFT) plots. If an acceleration versus time 

plot showed a distinct low frequency displacement, the associated FFT plot also indicated very 

little high frequency response. Longitudinal accelerometer locations 2, 2A, 5, 6, 8, 9, 12, 11, 13, 

14, 16, 17, and 18 and vertical accelerometer locations 1, 1A, 2, 2A, 5, 6, 14, and 18 generally 

exhibited this type of response. Of the transducers listed above, the output of locations 18, 9, 6, 

and 5 demonstrated the best correlation between peak longitudinal acceleration and peak LCF. 

As a result, for all subsequent impact tests, data was recorded for all transducers, but that data 

was processed only for this most significant subset. The following lists those transducers: 

• Strain Gages: Numbers 21-22, 8, 19, and 20 

• Vertical Accelerometers: Numbers 1, 1A, 2, 2A, 5, 6, 9, 10, and 18 

• Longitudinal Accelerometers: Numbers 1, 1A, 2, 2A, 5, 6, 9, 10, and 18

During testing at FAST, data was recorded and stored for 10 accelerometers, 4 strain gages, 

and 1 instrumented coupler. Examination of the data from all of the previous impact 

sequences revealed which transducers provided responses that could best be correlated to 

LCF and VCF. This analysis helped determine which of the transducers would be used for 

the FAST test. These transducers are listed below: 

• Strain Gages: Numbers 21-22, 19, and 20 

• Vertical Accelerometers: Numbers 5, 6, 9, 10, and 18 

• Longitudinal Accelerometers: Numbers 5, 6, 9, 10, and 18

Data was reduced and examined only for the accelerometer locations of primary interest. Those 

locations were Number 6 vertical and longitudinal and Number 18 vertical and longitudinal, as 

well as the strain gages and instrumented coupler. These four accelerometers are near the center 

of the car and were proven by impact test data to be the most useful for the estimation of peak 

VCFs and LCFs. The strain gages used (8, 19, 20, and 21-22) are all located on the A-end stub 

sill (Figure 7). 

2.4 Data Analysis 

2.4.1 Impact and Controlled Vertical Force Test 

• Data for all tests was collected at a rate of 5,000 samples per second. The data collection 

system was activated approximately 0.5 seconds before impact and collected data for a 

duration of 3 seconds. 

• The data collected from the transducers listed above was in the form of acceleration 

versus time and strain versus time. 

• VCF was calculated using the strain output from strain gages 21 and 22 that were 

mounted on the neutral axis of the stub sill. These two shear gages were connected in a 

half-bridge circuit so that they were sensitive primarily to vertical force applied to the 

stub sill. The relationship between the output from strain gages 21 and 22 and vertical 

force had been established during static and dynamic calibration tests performed before 

any impact tests and is shown in the following equation: 

Calculated VCF (kip) = -0.16 × (Gage 21/22 microstrain + 0.5 × Coupler Force) 
15 

Where gage 21/22 microstrain is the output from strain gages 21/22 and coupler force is 

the longitudinal force output from the instrumented coupler. 

Since the available instrumented couplers only measure longitudinal force, vertical force 

must be derived in this manner.

• The data from the transducers listed above was used to evaluate correlations between the 

following measurements: 

- Peak strain from strain gages 19 and 20 versus peak LCF 

- Peak longitudinal acceleration versus peak LCF 

- Peak vertical acceleration versus peak VCF 

- Maximum longitudinal SRS versus peak LCF 

- Maximum vertical SRS versus peak VCF 

- Average longitudinal SRS values over 5-50 Hz versus peak LCF 

- Average vertical SRS values over 5-50 Hz versus peak VCF 

- Average longitudinal SRS values over 10-100 Hz versus peak LCF 

- Average vertical SRS values over 10-100 Hz versus peak VCF 

The correlation of average SRS values and peak LCF and VCF values has proven to be the best 

one for the estimation of coupler forces using accelerometer output. This is in large part due to 

the considerable amount of high frequency content in the acceleration versus time traces 

produced by the impact forces. SRS analysis does not describe the shock itself but its influence 

on a set of idealized, single-degree of freedom (SDOF) mechanical systems. To convert 

acceleration versus time data to SRS, the actual acceleration response (acceleration at each time 

step T) is applied to a number of SDOF systems. Each SDOF system has a unique natural 

frequency. A maximum response value is obtained for each of these SDOF systems. A SRS plot 

is then created when these maximum response values are plotted against frequency. An average 

SRS value over the frequency range 5 to 50 Hz would just be the average of all of the individual 

response values between 5 and 50 Hz. Figures 10(a) and 10(b) are examples of SRS plots for 

accelerometer 6 at impact velocities of 2 and 7 mph, respectively. 

5 10 20 50 100 200 500

1

2

5

10

20

50

100

200

500

Frequency (Hz)

Abs.Value Max. SRS

2C-5 ACCEL 6 Lng

5 10 20 50 100 200 500

1

2

5

10

20

50

100

200

500

Frequency (Hz)

Abs.Value Max. SRS

7A-5 ACCEL 6 Lng

10(a) 10(b) 

Figure 10. Examples of SRS Plot for Accelerometer 6 
16 

2.4.2 Testing at FAST 

Data was recorded from transducers and one instrumented coupler on the VICX 1725 tank car 

during 13 nights of operation on the track at FAST between March 23, 2003, and April 22, 2003. 

The FAST train operated 4 nights a week during this time period, but problems with the data 

acquisition system limited the nights during which data could be recorded. The problems 

encountered during the first 8 nights of testing were as follows:

• Frequent computer shutdown and reboot due to vibration and data throughput limitations. 

The device that allows the computer to automatically reboot did not provide enough time 

for a scan disk operation.

• Excessive signal noise and spikes due primarily to poor analogue-to-digital card 

connection.

• Large zero load and electronic offsets in the signal due to a software problem.

Of the 13 nights in which attempts were made to record data, useful information was obtained 

from 9 nights. For 5 of these nights, the test car was located 6 cars from the end of the train. For 

the remainder of the nights, the test car was located four to eight cars from the last locomotive. 

Three to eight hours of data were recorded each night.

All data channels were sampled at either 4,096 samples per second (for 9 nights) or 2,048 

samples per second. The sample rate was reduced by half for 4 of the nights in an effort to 

determine if that rate was the cause of problems with the data acquisition computer.

The data was processed using the following steps:

• The full night of data for each channel was inspected to determine if any of the specified 

thresholds had been exceeded. The MatlabTM signal processing toolbox was used to 

perform this task. The thresholds were set as follows:

- Accelerometer 5 longitudinal, accelerometer 6 longitudinal, or accelerometer 18 

longitudinal: > 5 g or < -5 g. 

- Strain gages 21/22: > 100 microstrain or < -100 microstrain. 

- Instrumented coupler: > 80,000 pounds positive (buff) or < 140,000 pounds negative 

(draft). 

These values were chosen as a first cut to allow the isolation of the most meaningful data 

and to somewhat reduce the size of the data analysis task for this short test. 

• Data files were created and stored in 45-second increments. Using a Matlab macro, all of 

the 45-second files that demonstrated values exceeding any of the thresholds were tagged 

for subsequent inspection. Again using a Matlab macro, these files were then 

concatenated in a way that allowed the data to be combined into one large file. This 

allowed inspection of all data at one time. 

• Based primarily on the longitudinal coupler values observed in this set of data, a subset of 

files was then selected for further, closer examination. The result was that data recorded 

over the entire night had been reduced to the 1 to 2 hours of data that was of the most 

interest. 

• Initially, the data receiving this closer examination was from the following channels: 

instrumented coupler, strain gage 21/22, strain gage 19, and strain gage 20. This reduced set 
17 

of data was converted to a format that could be used with computer software developed by 

nCode International called FatimasTM. During the conversion process, the coupler force and 

strain gage data was decimated from the original sample rate (either 4,096 or 2,048 

samples/second) to 256 samples per second. nCode Fatimas is a fatigue analysis software but 

also has significant capabilities to process, condition, and evaluate large amounts of data. 

This software can be used to digitally filter data, remove obvious spikes, concatenate short 

files into longer files, and perform mathematical operations using the data from separate files. 

• Within Fatimas, the selected strain gage and coupler force files were subjected to spike 

removal if required and filtered with a 30 Hz low pass filter. The strain gage and coupler 

force data was then used in the following sequence to compute LCF and VCF: 

Calculated VCF (kip) = -0.16 × (Gage 21/22 Microstrain + 0.5 × Coupler Force) 

Calculated LCF (kip) = -1.24 × (Gages 19 and 20 Microstrain – 1.36 × Calculated VCF) 

Where gage 21/22 microstrain is the output from strain gages 21/22, coupler force is the 

output from the instrumented coupler (in thousands of pounds or kips), and gages 19 and 

20 microstrain is the average of the output from gages 19 and 20. 

Positive LCF values are compressive, and positive VCF values are upward. These 

relationships were established using the data collected during the static load calibration 

tests conducted in September 2000 (before the initial impact testing). 

• Finally, acceleration versus time data collected during the nights of April 14-15, April 

15-16, and April 20-21 was inspected. This set of data was chosen based on the 

magnitude of the coupler forces recorded during these time periods. Only the data from 

accelerometers 18 longitudinal, 18 vertical, 6 longitudinal, and 6 vertical were inspected. 

SRS analysis was performed for a total of 9 events where either compressive or tensile 

coupler forces of over 150,000 pounds were measured. The average SRS response over 

frequencies of 5-50 Hz and 10-100 Hz were then compared to peak LCF values recorded 

during the same event. 

2.5 Summary of Results 

2.5.1 Controlled Vertical Force Test 

2.5.1.1 Strain Gage Response

• Strain gages 8 and 21-22 were not the most responsive to vertical force input, but they 

were the most responsive gages that were least affected by longitudinal force input. The 

sensitivity of gage 8 was approximately 0.00431 microstrain per pound of vertical force. 

The sensitivity of gages 21-22 was approximately 0.00633 microstrain per pound of 

vertical force (see Plot A-1 in the appendix).

• Strain response for all gages was essentially linear with increasing vertical force. 

• The rate at which load was applied made little significant difference in the relationship 

between strain and applied peak load for a particular gage.

• Standard deviation values were calculated based on the three repetitions at each test 

condition. These values indicated that the repeatability of the response of all strain gages 

was essentially equivalent. 
18 

2.5.1.2 Accelerometer Response 

• No detectable output existed from any of the accelerometers until a peak load of at least 

13,000-15,000 pounds was applied. 

• At a pulse duration of 2 seconds, a peak force amplitude of at least 20,000 pounds was 

required to generate any detectible acceleration response. Plots A-2 and A-3 in the 

appendix show estimated linear relationships between peak acceleration and vertical 

force amplitude for vertical accelerometers 1 and 1A. Using these plots, the peak vertical 

force can be roughly estimated:

- From accelerometer 1: 

-8,354.3 × (peak accel.) + 11,977 for a 0.5-second pulse duration 

-11,162 × (peak accel.) + 11,940 for a 1.0-second pulse duration 

- From accelerometer 1A: 

-12,984 × (peak accel.) + 10,894 for a 0.5-second pulse duration 

-29,583 × (peak accel.) + 7,433.8 for a 1.0-second pulse duration 

As an example, at a force pulse duration of 0.5 second, a peak 0.5 g output from 

Accelerometer 1 would predict a peak vertical force of about 16,200 pounds while a similar 

output value from accelerometer 1A would yield a peak vertical force of 17,400 pounds. If 

the same 0.5 g output came during an event of about 1.0 second in duration, the 

accelerometer 1 relationship would yield a peak vertical force of about 17,500 pounds while 

the accelerometer 1A relationship would result in an estimate of about 22,200 pounds. 

• Due to the scatter of this data, these are only rough estimations. At a pulse duration of 2 

seconds, a peak force amplitude of at least 20,000 pounds was required to generate any 

detectable acceleration response. 

• Responses were recorded for both longitudinal and vertical accelerometers. The most 

responsive vertical accelerometers were at the 1 and 1A positions while the most 

responsive longitudinal accelerometer was at the 3 position. 

2.5.2 Controlled Impact Tests 

2.5.2.1 Peak Coupler Forces versus Impact Velocity

Plot A-6 in the appendix shows two very significant relationships between impact velocity and 

peak LCF. For all loaded car impacts (Sequences 2 through 4), the peak LCF versus impact 

velocity relationship is essentially horizontal for impact velocities between 2 and 4 mph. Peak 

LCF only varies between about 350,000 and 500,000 pounds for impact events in this velocity 

range. As impact velocities increase to 6 and 8 mph, however, suddenly a very steep slope with 

peak LCF values increasing significantly exists. This is likely an indication that the draft gear is 

performing as designed. At velocities up to about 5 mph, movement occurs within the draft gear, 

and the friction wedges and internal springs produce the required reaction forces. At velocities 

above 5 mph, however, the draft gear has likely reached its deflection capacity, resulting in a 

sudden rise in the force transmitted from the gear to the car structure. The data indicates that for 

this loaded car, impact velocity could be used to estimate peak LCF in the following manner: 

• For velocities from 2-5 mph, peak LCF = 350,000 to 500,000 pounds 

• For velocities above 5 mph, peak LCF = 440,000 × (velocity - 5) + 440,000 
19 

The last 440,000 value in this equation is the point on the y-(force) axis at which the function 

intersects the 5-mph x value. 

Plot A-6 also shows that the peak LCF versus impact velocity relationship for Sequence 1 

(empty car) again is significantly different from the loaded car relationships. The Sequence 1 

data indicates a more constant relationship between velocity and peak LCF with no significant 

change in slope between 5 and 6 mph. This could indicate that the characteristics of the draft 

gear changed between the Sequence 1 and Sequence 2 impacts or that due to the lower kinetic 

energy levels during Sequence 1, the draft gear never reached its deflection limits.

Plots A-7 through A-10 in the appendix show that throughout all of the impact sequences, a 

relatively good relationship exists between measured peak LCF and calculated peak VCF. The 

weakest correlation was observed from the data recorded during Impact Sequence 3 (single carto-single car). Generally, the peak VCF can be estimated by using the following function:

Peak VCF = (0.11 to 0.12) × (Peak LCF) 

In all impact cases, the peak VCF was in the upward (away from track) direction. 

Tables 4-7 give a summary of the recorded peak LCF and calculated peak VCF values for all 

four impact sequences. These tables illustrate that the coupler forces at a given impact velocity 

were about 30 to 40 percent greater during the loaded car impacts (Sequences 2-4) than during 

the empty car tests. They also reveal that Sequence 4 generally produced the highest coupler 

forces per mph of impact velocity.

Table 4. Peak LCF and VCF for Impact Sequence 1 

Velocity at Impact Measured Peak LCF Calculated Peak VCF 

(mph) (lbs) (lbs) 

2.5 374,743 51,320

2.0 254,972 38,060

3.0 242,145 34,790

4.5 444,059 52,900

5.0 541,853 70,230

3.8 593,849 63,700

5.9 618,556 55,920

6.1 582,814 59,960

6.2 808,052 98,490

8.0 1,051,530 116,680

7.8 970,455 105,310

7.9 1,003,544 126,950
20 

Table 5. Peak LCF and VCF for Impact Sequence 2 

Velocity at Impact 

(mph) 

Measured Peak LCF 

(lbs) 

Calculated Peak VCF 

(lbs) 

3.0 469,000 44,600

2.9 495,000 53,500

2.6 500,000 50,600

2.4 445,500 39,600

2.4 408,000 52,500

3.3 479,600 36,800

4.2 495,000 58,200

4.1 442,000 55,340

4.1 485,700 44,810

4.2 404,400 44,700

6.1 1,108,000 118,080

6.1 1,057,000 115,040

6.1 1,050,000 113,790

7.4 1,346,600 149,400

7.2 1,275,900 142,600

7.5 1,374,600 149,400

Table 6. Peak LCF and VCF for Impact Sequence 3 

Velocity at Impact 

(mph) 

Measured Peak LCF 

(lbs) 

Calculated Peak VCF 

(lbs) 

3.0 338,880 46,300 

2.8 408,110 52,000 

2.7 419,870 53,900 

2.4 420,070 71,000 

2.2 377,970 32,200 

2.3 373,140 64,600 

4.2 380,720 59,000 

4.1 396,580 57,000 

4.2 350,260 71,700 

4.2 344,510 54,700 

5.1 405,620 44,400 

6.0 836,660 133,000 

6.0 843,660 85,000 

6.1 793,490 72,000 

7.1 1,242,740 137,800 

7.1 1,175,090 141,700 

7.1 1,168,440 127,100 
21 

Table 7. Peak LCF and VCF for Impact Sequence 4 

Velocity at Impact 

(mph) 

Measured Peak LCF 

(lbs) 

Calculated Peak VCF 

(lbs) 

2.4 399,520 399,000

2.2 369,360 379,000

2.2 418,040 451,000

2.2 392,030 485,000

4.1 529,760 699,000

4.0 396,480 521,000

4.1 415,790 527,000

5.0 443,980 619,000

6.0 1,134,080 132,400

6.1 1,111,210 128,400

6.0 1,091,080 128,600

6.4 1,235,730 155,400

6.9 1,333,100 159,900

5.8 1,023,790 122,300

6.3 1,185,110 144,600

2.5.2.2 Strain Gage Response 

Strain gages at locations 15, 16, 19, and 20 proved to be the most consistent and most sensitive 

indicators of peak LCF. Of these four gages, the output of gage 20 proved to be the most 

consistent and sensitive. 

The relationship between peak LCF and maximum strain from gage 20 was not a continuous 

linear relationship during Impact Sequence 1. Plot A-11 in the appendix shows that whether the 

strain versus peak LCF relationship is treated as a continuous or discontinuous function, an 

obvious change occurs in that relationship at coupler forces above about 600,000 pounds. Still, 

the relationship between peak strain and peak LCF at strain gage location 19 remains relatively 

consistent as peak LCF reaches maximum levels. 

The fact that a significant difference existed between the strain response of gages at similar 

locations on either side of the sill (gage 19 versus gage 20) may indicate that, as the peak coupler 

forces reached levels above 600,000 pounds, the longitudinal forces into the rear draft lugs were 

not the same on one side of the sill as the other. This could result from slight misalignment of 

the coupler and draft gear or manufacturing tolerances locating the rear draft lugs. A 

contributing factor could also be that the point of application of the force is offset from the center 

of the sill’s side plate. This could introduce out-of-plane, localized stresses on the plate surface 

that are difficult to predict. Plot A-11 shows that the strain versus peak LCF relationships for 

gages 20 and 19 actually diverge significantly at peak forces above about 600,000 pounds. One 

way to combat these effects could be to use an average of the outputs from gages 19 and 20 to 

predict or calculate LCF. Plot A-11 also shows a set of points created by averaging the output 

from gages 19 and 20.
22 

Even though the data from gages 19 and 20 recorded during the loaded car impacts (Sequences 2 

through 4) did not show the tendency to diverge at larger LCF values, averaging the output from 

these two gages still provided the best correlation between strain and peak LCF.

2.5.2.3 Accelerometer Response 

Accelerometers 18, 9, 6, and 5 provided the best correlation between peak longitudinal 

acceleration and peak LCF. Plots A-12 and A-13 in the appendix show examples of these 

relationships. This trend was discovered as a result of the analysis of the Sequence 1 impact 

data. In all cases for Impact Sequence 1, discontinuous linear relationships appeared to provide 

the best fit for the data. As an example, for accelerometer 18, when output values were between 

0 and about -2.5 g, the peak LCF could be estimated as:

-183,590 × peak acceleration 

However, for accelerations greater than -2.5 g, the peak LCF could be estimated as: 

-20,561 × (peak acceleration) + 430,000 

Even though the relationships above could be estimated using peak acceleration versus coupler 

force data from Impact Sequence 1, further analysis demonstrated that a significantly better 

correlation between acceleration response and peak coupler force values could be obtained if 

calculated SRS values rather than peak acceleration values were used. As a result, for the 

remaining impact tests, emphasis was placed on the SRS versus coupler force relationships.

SRS calculations were performed on the Impact Sequence 1 output from the following 

longitudinal accelerometers: 1, 1A, 2, 2A, 5, 6, 8, 9, 11, 12, 13, 14, and 18. Shock response 

values were calculated for natural frequencies ranging from 5 to 500 Hz. The result was an SRS 

plot of response versus frequency for each accelerometer and each impact (see Figure 10 for 

examples).

Relationships were studied relating peak LCF with the following values from the Impact 

Sequence 1 SRS data:

• Peak SRS value over the 5-500 Hz range versus peak LCF. 

• The average SRS value over the 5-500 Hz range versus peak LCF. 

• The average SRS value over a restricted frequency range of 5-50.4 Hz versus peak LCF. 

• The average SRS value over a restricted frequency range of 10-100.8 Hz versus peak LCF.

The last two relationships were studied because the response versus frequency plots were 

generally more linear within these frequency ranges. Attempts were made to apply continuous, 

as well as discontinuous, function relationships, but, again, it appeared that the discontinuous 

linear functions provide the best correlation of SRS response to peak LCF. 
23 

The output from accelerometer locations 1A, 2A, 5, 6, 18, 9, and 12 recorded during Impact 

Sequence 1 provide credible correlation between SRS response and peak LCF. The best 

correlation is generally provided by locations 12, 6, and 18. Plots A-14 and A-15 in the 

appendix show examples. As an example, using the average SRS response from accelerometer 6 

over the 10-100.8 Hz range peak LCF could be estimated as follows:

LCF = 231,620 × (average SRS response) for average response values from 0 to 2.4, or 

LCF = 30,097 × (average response) + 460,000 for response values greater than 2.4 

Plot A-17 in the appendix shows that a very distinct difference exists in the SRS versus LCF 

relationships between Sequence 1 (empty car) and Sequences 2 through 4 (loaded case). This 

difference could be due to the condition of the draft gear or to the significant change in the car’s 

mass. The factors contributing to this difference are not fully understood at this point. It is 

therefore important to know the state of as many of the contributing factors as possible. Since 

car mass could be one of these important contributing factors, it remains important to be able to 

determine the car’s mass during an impact. It is also important to recognize that a discontinuous 

or dual function appears to be the best approximation for the SRS versus peak LCF data from 

Sequence 1. One linear function fits the data fairly well at coupler forces below about 550,000 

pounds. It is at these impacts that the draft gear is still effective and has not bottomed. 

However, a different linear function exists at coupler forces greater than 550,000 pounds. At 

coupler forces higher than 550,000 pounds, the draft gear does apparently go through its full 

range of travel, resulting in a distinctly different transfer function. 

The data shows that for these impact conditions, the SRS versus peak LCF relationship may be 

represented reasonably well by a simple linear function of the form:

Peak LCF = m × (Average SRS Response) + b 

Where A is the slope, and B is the intercept constant. 

Plots A-18 through A-21 in the appendix and Table 8 summarize some proposed linear SRS 

versus peak LCF relationships for a loaded, instrumented tank car during three different impact 

conditions (Impact Sequences 2 through 4). Plot A-21 also illustrates, however, that when all of 

the loaded tank car impact data is considered, the SRS versus peak LCF relationship might be 

best approximated by more than one function. For this car/draft gear combination, the change in 

relationship or function generally occurred at peak LCF values of about 400,000 to 500,000 

pounds and again at about 1.0- to 1.1-million pounds, indicating the possibility of three functions 

to completely define the SRS versus peak LCF relationship. 
24 

Table 8. Estimated Linear Relationships, SRS Response versus Peak LCF— 

Accelerometer Number 6 

Impact 

Sequence 

Frequency Over 

Which SRS 

Values Averaged

Function 

Slope 

(m) 

Function 

Intercept 

(b) 

Coefficient of 

Determination 

(R2

)

2 5-50 Hz 97,046 125,834 .925

3 5-50 Hz 136,612 13,476 .894

4 5-50 Hz 128,634 40,716 .926

2, 3, and 4 5-50 Hz 110,904 101,369 .882 

 

2 10-100 Hz 74,905 109,071 .904 

3 10-100 Hz 96,763 -3,486 .840 

4 10-100 Hz 91,009 40,896 .880 

2, 3, and 4 10-100 Hz 83,731 70,821 .865 

Plots A-18 through A-21 of the appendix show the results of linear regression analysis of the 

SRS data produced from the output of accelerometer 6 during Impact Sequences 2, 3, and 4. 

Plots A-18 through A-20 show the results if the data from each impact sequence is considered 

separately, and Plot A-21 shows the results if the data from all three sequences is considered 

together. Each plot contains a scatter band (bounded by the dashed lines), illustrating the range 

of peak LCF values that could be expected to be calculated from a given SRS value with a 95 

percent confidence level. Table 9 lists a sample of calculated peak LCF values using given SRS 

values of 4 g and 10 g for the 5-50 Hz data, and 6 g and 14 g for the 10-100 Hz data. 

The information contained in Tables 8 and 9 show the following significant results: 

• The Coefficient of Determination data in Table 8 indicates that a linear approximation is 

a better fit for the SRS data averaged over 5 to 50 Hz than that averaged over 10 to 100 

Hz. This would also imply that the bands of scatter on each side of the best-fit, mean line 

are somewhat smaller for the 5 to 50 Hz data than for the 10 to 100 Hz data. 

• For any measured SRS value, the estimated or calculated peak LCF value should fall 

within the ranges shown in the last column of Table 9 with a 95 percent confidence level. 

These ranges of peak LCF values could be significant, ranging from about ±45 to 50 

percent at the lower LCF values to ±20 to 25 percent at the higher LCF values. 

• Considering the range of estimated LCF values that are calculated for a given SRS value, 

the data from all impact sequences yield similar results. The implication is that, other 

than payload condition, knowledge of the details of an impact situation may not be 

required for this method of estimating peak LCF. 
25 

Table 9. Sample of Predicted Peak LCF Values Using SRS Data— 

Accelerometer Number 6 

Impact 

Sequence 

Frequency Over Which 

SRS Values Averaged

SRS Value Used to 

Calculate Peak LCF 

Range of Calculated 

LCF Values 

(lb) 

2 5-50 Hz 4 272,260 to 755,684 

3 5-50 Hz 4 306,747 to 813,098 

4 5-50 Hz 4 304,787 to 805,718 

2, 3, and 4 5-50 Hz 4 285,276 to 804,719 

 

2 5-50 Hz 10 843,304 to 1,349,246 

3 5-50 Hz 10 1,102,023 to 1,657,160 

4 5-50 Hz 10 1,070,675 to 1,583,438 

2, 3, and 4 5-50 Hz 10 1,164,740 to 1,699,919 

 

2 10-100 Hz 6 283,604 to 833,938 

3 10-100 Hz 6 264,251 to 889,944 

4 10-100 Hz 6 266,713 to 907,193 

2, 3, and 4 10-100 Hz 6 295,743 to 851,355 

 

2 10-100 Hz 14 872,452 to 1,443,030 

3 10-100 Hz 14 1,016,915 to 1,685,504 

4 10-100 Hz 14 991,449 to 1,638,609 

2, 3, and 4 10-100 Hz 14 960,783 to 1,525,771 

As shown in Plot A-22 in the appendix, considerable scatter exists in the peak vertical 

acceleration versus peak VCF data. As a result, even though a general trend of increasing peak 

vertical acceleration with increasing peak VCF exists, it is difficult to identify a function that 

satisfactorily defines a relationship between the two parameters from the data currently available.

Shock response calculations were performed on the output from the following vertical 

accelerometers: 1, 1A, 2, 2A, 5, 6, 14, and 18. Shock response values were calculated for 

natural frequencies ranging from 5 to 500 Hz. The result was an SRS plot of response versus 

frequency for each accelerometer and each impact. Relationships were studied relating peak 

VCF with the following values from the SRS data:

• Peak SRS value over the 5-500 Hz range versus peak VCF. 

• The average SRS value over the 5-500 Hz range versus peak VCF. 

• The average SRS value over a restricted frequency range of 5-50.4 Hz versus peak VCF. 

• The average SRS value over a restricted frequency range of 10-100.8 Hz versus peak VCF. 

The last two relationships were studied because the response versus frequency plots were 

generally more linear within these frequency ranges. 
26 

Table 10. Estimated Linear Relationships, SRS Response versus Peak VCF— 

Accelerometer 6 

Impact 

Sequence 

Frequency Over Which 

SRS Values Averaged 

Function 

Slope 

(m) 

Function 

Intercept 

(b) 

Coefficient of 

Determination 

(R2

)

2 5-50 Hz 5,542 20,235 .930

3 5-50 Hz 5,782 36,821 .753

4 5-50 Hz 9,997 15,087 .918

2, 3, and 4 5-50 Hz 5,905 32,661 .732 

 

2 10-100 Hz 4,282 12,651 .901

3 10-100 Hz 4,420 31,070 .761

4 10-100 Hz 7,152 5,761 .919

2, 3, and 4 10-100 Hz 4,535 25,031 .741 

The last two types of relationships studied provided the best correlation between SRS response 

and peak VCF. Plots A-23 through A-26 in the appendix indicate that some fairly well-defined 

trends relating SRS data from vertical accelerometer 6 to peak VCF also exist. The SRS versus 

peak VCF relationships for accelerometer 5 are similar. As shown in Table 10, however, these 

relationships tend to be somewhat less defined than those established for the LCF response. As a 

result, for a given SRS value generated using data from either accelerometer 5 or 6, the predicted 

peak VCF would have a range of possible values larger than for the similar peak LCF 

predictions. 

Engineers at the Volpe National Transportation Center performed additional analysis of the 

acceleration versus time data. A power spectral density (PSD) analysis was performed on each 

tank car acceleration history to determine the dominant frequencies in the response of the tank 

car structure. Accelerations in the vertical and longitudinal directions, with the tank empty as 

well as filled, were examined. The results of this analysis indicated that for an empty tank, the 

dominant excited frequencies for the tank structure were 0 Hz (rigid body motion) in the 

longitudinal axis and 13 Hz in the vertical direction. A vertical axis frequency of 100 Hz, likely 

excited by the stick-slip action of the draft gear, was also prominent in the empty car data 

collected during events when the stick-slip coupler forces were observed. PSD results from the 

full tank tests exhibit dominant peaks at 0 Hz in the longitudinal direction and at both 5 Hz and 

23 Hz in the vertical direction [1][2]. 

2.5.3 Testing at FAST 

2.5.3.1 Coupler Forces 

Table A-1 in the appendix summarizes the test conditions and resulting coupler force 

measurements (LCF from coupler and VCF calculated) during the FAST test. In general terms, 

when the car was near the locomotives (near the front of the train), the LCF values were 

primarily tensile and varied from near 0 to 170,000-250,000 pounds. The mean value was about 

60,000-70,000 pounds. The calculated VCF values were similar in character and varied from 

about 20,000-40,000 pounds upward to 6,000-13,000 pounds downward (negative values). 

Figure 11 shows typical measured LCF (top plot) and calculated LCF (lower plot) versus time 
27 

data for this car location. This data was recorded on the night of April 15-16, 2003, over a time 

period of approximately 45 minutes. Figure 12 shows the measured LCF and calculated VCF 

values for the same time period as the data in Figure 11. This plot demonstrates the relationship 

between LCF and calculated VCF for this operating environment. Output from accelerometers 

6L, 6V, 18L, and 18V was insignificant during this time period. This 45-minute segment is 

indicative of the data recorded for the entire night with the car near the front of the train. 

Figure 11. Measured (top) and Calculated LCF versus Time, April 15-16, 2003, 

Test Car Near Front of Train
28 

Figure 12. Measured LCF (top) and Calculated VCF versus Time, April 15-16, 2003, Test 

Car Near Front of Train 

By contrast, when the test car was near the end of the train, enough slack action existed to 

produce numerous events characterized by short duration buff and draft LCF. As shown in Table 

A-1 in the appendix, the values of the measured LCF were in order of magnitude from 160,000- 

to 263,000-pound compression to 150,000- to 270,000-pound tension. Figures 13 through 15 

illustrate this. Figure 13 shows about 45 minutes of measured and calculated LCF data from the 

night of April 14-15, 2003. Figures 14 and 15 show a 41-second segment from the same time 

period. 

2.5.3.2 Accelerometer Response 

Tables A-2 and A-3 in the appendix and Figures 16 and 17 show some of the data from 

accelerometers 6L and 18L recorded during the night of April 14-15, 2003. This acceleration 

data was processed for the nine most significant LCF events recorded during the night. The peak 

acceleration values were less than 7 g, and SRS values were generally in the 2-3 g range.
29 

Figure 13. Measured (top) and Calculated LCF versus Time, April 14-15, 2003, 

Test Car Near Rear of Train 

. 

Figure 14. Measured (top) and Calculated LCF versus Time During a 41-Second Time 

Period, April 14-15, 2003, Test Car Near Rear of Train 
30 

Figure 15. Measured LCF (top) and Calculated VCF versus Time During a 41-Second 

Time Period, April 14-15, 2003, Test Car Near Rear of Train 

Figure 16. Measured LCF and Associated Longitudinal Acceleration at Location 6, 

April 14-15, 2003 
31 

Figure 17. Measured LCF and Associated Longitudinal Acceleration at Location 6, 

April 14-15, 2003 

Figure 18. Typical Accelerometer Data Recorded April 20-22, 2003 
32 

Plots A-28 and A-29 in the appendix are plots of average SRS value versus measured peak LCF 

for the same events mentioned previously. Little correlation seemed to exist between peak LCF 

and average SRS values at this coupler relatively low (less than 300,000 pounds) force level. It 

must be recognized, however, that all of the LCF values in this small comparison were of the 

same general order of magnitude.

During the first 4 to 5 nights of testing, several problems occurred with the data acquisition 

system, including premature computer shutdown and data with considerable noise, spikes, and 

zero offsets. Much of this poor quality data was not processed. Most of the problems were 

eventually solved, and the result was significantly better data quality during the last 5 nights of 

testing. The problem of spikes in the acceleration data, however, was never totally solved. This 

problem may have resulted from amplifier connections that became intermittent during train 

action impacts. The peak acceleration values indicated by these spikes are not realistic or 

consistent with data recorded and illustrated in Figure 18 during previous nights when lower 

coupler force events occurred. 

2.5.3.3 Strain Gage Response 

Figures 19 through 22 are cross plots of recorded LCF values versus those calculated using the 

data from strain gages 19 and 20. These plots cover time spans of 1.25 to 2.34 hours 

(representing over 1 million data points) and demonstrate that the correlation is close to 1-to-1 

with a relatively narrow band of scatter. This is especially true of the data recorded during the 

last 3 to 4 nights of testing. It was during this time period that the data quality was at its best. It 

is possible that the band of scatter could be reduced in width at higher LCF values (above 

300,000 pounds) or if additional filtering was used.
33 

Figure 19. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, April 14-15, 2003 

Figure 20. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, April 16-17, 2003 
34 

Figure 21. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, April 20-21, 2003 

Figure 22. Cross Plot of Calculated LCF (y-axis) versus Measured LCF, April 21-22, 2003 
35 

2.6 Conclusions 

2.6.1 Controlled Vertical Force Test 

Phase I testing measuring accelerometer response resulting from controlled, low-magnitude, 

vertical force pulses applied to the end of the stub sill revealed that such acceleration responses 

(in the form of peak acceleration values) could not effectively be used in an estimation of peak 

VCF resulting from such low magnitude inputs. Plots A-4 and A-5 in the appendix illustrate two 

problems with this method. In both plots, T/2 represents one-half of the time period of the 

vertical force pulse. The first area of concern is that as the rate of force input decreased (T/2 

increased), accelerometer response (in terms of the resulting peak vertical acceleration) became 

less sensitive to changes in magnitude of the maximum amplitude of the vertical force pulse. 

This is illustrated by observing the difference in the slopes of the curves estimated for the T/2 = 

0.25 and T/2 = 0.5 tests in Plot A-5. The second and more serious problem with this method is 

that different peak force versus peak acceleration curves could develop depending on the 

duration of the vertical force pulse. As a result, if all that is known is the amplitude of the 

acceleration, two or more peak force values could be surmised. As an example using the data in 

Plot A-4, if a peak acceleration value of 0.38 g had been recorded, the calculated peak VCF 

could be estimated from 14,000 to 20,000 pounds depending on the rate at which the load was 

applied. These problems should effectively eliminate this method as a way to calculate in-train 

VCF at this time.

2.6.2 Impact Test 

The data from these tests provides the most accurate alternative to instrumented couplers for 

predicting peak LCF and the best option for predicting VCF. The strain versus peak LCF and 

VCF relationships do not appear to be significantly affected by impact severity or draft gear 

action. The variation of strain response for a given measured peak LCF appears to be 

significantly smaller than the variation of SRS response. If strain gages are used to indicate 

VCFs, it is recommended that they be placed in locations where they will be sensitive to those 

vertical forces but essentially unaffected by LCFs. 

As Plots A-14 through A-21 in the appendix show, it is possible to use SRS data to estimate peak 

LCF that occur as a result of car-to-car impacts. This method shows the most promise for the 

purposes of indicating the severity of moderate to severe impacts (impact environment 

characterization) using accelerometer response. For the purposes of such impact environment 

characterization, the range or scatter of SRS response for a given peak LCF and some changes in 

SRS versus coupler force relationships as impact severity increases may not be unacceptable 

limitations. The longitudinal accelerometer at location No. 6 in Figure 5 (top surface of the tank 

shell near the longitudinal center line) has thus far proven to provide the best data for such 

predictions. Conversely test data has shown that the use of unfiltered (as recorded) peak 

accelerometer output (either positive or negative) cannot be used to reliably predict peak LCF 

during an impact event. Peak acceleration values that result from acceleration versus time data 

filtered at either 50 or 100 HZ have also proven to be a relatively poor predictor of peak coupler 

force resulting from impacts.
36 

The data collected from Impact Sequences 1 through 4 indicates that SRS response cannot, at this 

time, be used very effectively to estimate peak VCF or LCF values for the purposes of performing 

crack growth, fatigue, or damage tolerance analysis. The reasons for this are as follows: 

• Even for the best SRS versus peak LCF relationships, enough scatter exists in the data 

(regardless of the regression function used) that the resulting range of peak LCF values 

that might be predicted with a given SRS value is too broad to be effectively used in an 

accurate crack growth or damage tolerance analysis.

• The change of the SRS versus peak LCF relationship as impact forces increase (for a 

particular type of impact) most likely results from draft gear design or condition. It must 

be recognized that among different draft gear designs or even among draft gear of the 

same design but different ages, a wide variation can exist in force versus deflection 

performance. If this is the case, the effects on the SRS versus peak LCF relationship 

cannot be generalized in a way that can be applied to all possible draft gear/car 

combinations.

Since testing thus far has only involved one car/draft gear combination, the overall form of the 

peak LCF versus SRS relationship is only known for that one combination. At this time it must 

be assumed that the form of the LCF versus SRS relationship will be significantly different for 

any other car/draft gear combination. These factors again prevent any type of practical 

generalization or expansion of the relationships established thus far to cover all significant 

car/draft gear designs.

2.6.3 Testing at FAST 

Analysis of the data revealed that at peak LCF values less than 300,000 pounds, the output from 

strain gages 20 and 19 could be used to make estimates of LCF as measured by the instrumented 

coupler. Figures 11, 13, 14, and 19 through 22 illustrate this. The response versus time traces in 

Figures 11, 13, and 14 illustrate the similar nature of the data from the instrumented coupler to 

that calculated using strain values from gages 19 and 20. Figures 19 through 22 show the similar 

data in a cross plot format and illustrate the accuracy and scatter of the LCF values calculated 

using strain gage output versus those measured by the instrumented coupler. 

The data collected during this test confirmed that accelerometer response in the form of SRS 

values does not correlate well with either vertical or longitudinal peak coupler force at peak LCF 

values below 200,000 pounds. 

Plots A-30 and A-32 in the appendix illustrate that at this coupler force level, correlation seemed 

to exist between peak LCF and SRS values averaged over frequency ranges of either 5 to 50 Hz 

or 10 to 100 Hz. 
37 

3.0 Recommendations 

Conduct extended over-the-road trials to prove that: (1) strain gage response can be used to 

accurately predict LCFs and VCFs during uncontrolled, long-term service and (2) accelerometer 

response in the form of SRS values can be used to effectively monitor the level of LCFs and 

VCFs resulting from severe yard impacts. This could be accomplished within Phase IIA by 

installing a reduced set of transducers on a single stub sill tank car that would then be subjected 

to standard over-the-road conditions for 10,000 to 13,000 miles. Mileage could be accumulated 

in 6 to 8 weeks of testing. If the data collected during this trial test continue to suggest that these 

two methods of predicting coupler forces are valid and useful, three more cars—each of a 

different design—should be similarly instrumented and placed in similar extended service. This 

last step would be required to prove that the concept has true universal application. 

The following transducers should be installed on the stub sill/tank structure: 

• Instrumented coupler at each end of car. 

• Strain gages at locations 19 and 20 on A-end of car. 

• Strain gages at locations 19 and 20 on B-end of car. 

• Strain gages at location 21/22 on A-end of car. 

• Strain gages at location 21/22 on B-end of car. 

• 100 g vertical and longitudinal accelerometers at location 6. 

• 100 g vertical and longitudinal accelerometers at location 5. 

• 100 g vertical and longitudinal accelerometers at location 18 (used as backup). 

In addition, a set of strain gages should be applied to one of the bolsters to record data on bolster 

loads that can be compared with similar data collected in the stub sill tank car research project 

DOT/FRA/ORD/95-11, often referred to as FEEST II,3

 conducted in 1995. As the coupler force 

data from the proposed Phase IIA test is evaluated and compared with that recorded during the 

FEEST II test, it will be useful to also compare bolster load history as an indication of relative 

route severity. 

Before on-track testing begins, the output of all strain gages should be re-calibrated against 

known loads, repeating the quasi-static process used before Phase I testing began. 

The recorded data during over-the-road testing should be processed in a manner similar to that 

used for the FAST test of Phase I. Thresholds should be set to control the recording of 

acceleration data, and that data should only be recorded for the time that the values exceed the 

limits. The acceleration versus time data for each event should be converted to SRS values 

averaged over 5-50 Hz by software within the data acquisition system. As a result, the data 

downloaded for each significant acceleration event would be an SRS value averaged over a range 

of 5-50 Hz and a peak coupler force value. Based on the Volpe analysis, accelerometer data 

should be recorded at about 2,000 samples per second.1, 2

Strain gage and coupler force data should be recorded continuously while car velocity is over 1.0 

mph. This data can also be recorded at 2,000 samples per second but then decimated to 256 Hz 

to save onboard file space. This data should then pass through a 30-Hz digital filter before being 

processed. The filtered strain gage data should be processed using software on the data 
38 

acquisition computer so that the information available for download is in the form of calculated 

VCFs and LCFs versus time. 

If the data recorded during this trial test continues to confirm an acceptable level of accuracy for 

the correlation of SRS response versus measured peak coupler force and coupler force calculated 

form strain data versus measured peak coupler force, a Phase IIB should be planned. In this 

phase, similar transducer/data acquisition systems would be installed on three more stub sill tank 

cars of three different contemporary designs. These 3 cars would also be subjected to 10,000 to 

13,000 miles of over-the-road testing as a final confirmation of the system effectiveness and the 

usefulness of using cars designed differently from that of the Phase IIA car. 
39 

References 

1. Lyons, M., Riddell, W., and Koch, K. “Analysis of Accelerations Measured During FullScale Tank Car Impact Tests,” Report No. DOT/FRA/ORD-07/08, U.S. Department of 

Transportation, Federal Railroad Administration, April 2007. 

2. Lyons, M., Riddell, W., and Koch, K. “Full-Scale Tank Car Impact Tests,” American 

Society of Mechanical Engineers Report IMECE2003-44062, November 2003. 

3. Cogburn, L. “Stub Sill Tank Car Research Project Results of a 15,000-Mile Over-the-Road

Test,” Report No. DOT/FRA/ORD-95/11, U.S. Department of Transportation, Federal 

Railroad Administration, September 1995. 
40 
41 

Appendix. 

Plots A-1 through A-22 
42 

PLOT A1 - STRAIN VERSUS PEAK VERTICAL SILL FORCE - GAGES 21-22

.5 SEC PULSE DURATION

1.0 SEC PULSE 

DURATION

2.0 SEC PULSE 

DURATION

-160.0 -140.0 -120.0 -100.0 -80.0 -60.0 -40.0 

MICROSTRAIN

PEAK FORCE

.5-second pulse duration 1.0-second pulse duration 2.0-second pulse duration 

Plot A-1. Strain versus Peak Vertical Sill Force—Gages 21-22
43 

PLOT A2 - PEAK VERTICAL ACCELERATION VS MAX. VERTICAL SILL FORCE

 ACCEL. 1 VERT.

.5 SECOND PULSE 

DURATION

1.0 SEC. PULSE 

DURATION

2.0 SEC PULSE 

DURATION

.

-1.2 -1 -0.8 -0.6 -0.4 -0.

PEAK ACCELERATION G'S

MAX. VERTICAL FORCE LB.

0.5-second pulse duration 1.0-second pulse duration 2.0-second pulse duration 

MAX. VERTICAL FORCE LB 

PEAK ACCELERATION–G 

Plot A-2. Peak Vertical Acceleration versus Maximum Vertical Sill Force—Acceleration 1 V
44 

PLOT A3 - PEAK LONGITUDINAL ACCEL VS VERTICAL SILL FORCE

ACCEL. 1A VERT.

.5 SEC. PULSE 

DURATION

1.0 SEC. PULSE 

DURATION

2.0 SEC. PULSE 

DURATION

-1.5 -1.3 -1.1 -0.9 -0.7 -0.5 -0.3 

VERTICAL ACCELERATION (g)

VERTICAL FORCE AT SILL 0.5-second pulse duration 1.0-second pulse duration 2.0-second pulse duration 

VERTICAL ACCELERATION–G 

Plot A-3. Peak Longitudinal Acceleration versus Vertical Sill Force—Acceleration 1A Ver
45 

PLOT A4 AVERAGE OF PEAK VERTICAL FORCES VS AVERAGE PEAK VERT. ACCEL. #1 EMP

T/2 - .25 SECT/2 - .5 SEC.

T/2 - 1.0 SEC.

-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 

ACCELERATION - G'S

PEAK FORCE - LB. PEAK FORCE LB 

T/2 0.25 second T/2 0.5 second T/2 1.0 second 

ACCELERATION–G 

Plot A-4. Average Peak Vertical Forces versus Average Peak Vertical—Acceleration #1 Emp
46 

 PLOT A5 - AVERAGE OF PEAK VERTICAL FORCES VS AVERAGE PEAK VERTICAL ACCEL. - L

T/2 - .25, 50G ACCEL

T/2 - .5, 50G ACCEL

T/2 - .25 ACCEL 1 

VERT.(100 G ACCEL)

T/2 - .50 ACCEL 1 

VERT.(100 G ACCEL)

0

100002000030000400005000060000

0 0.511.522.5 

ACCELERATION - G'S

PEAK FORCE - LB.

T/2 .25, 50 G ACCEL T/2 .25 ACCEL 1 VERT. (100 G ACCEL) T/2 .5, 50 G ACCEL T/2 .50 ACCEL 1 VERT. (100 G ACCEL) 

PEAK FORCE LB 

ACCELERATION–G 

Plot A-5. Average of Peak Vertical Forces versus Average Peak Vertical Acceleration—Lo
47 

PLOT A6 - PEAK LCF VERSUS IMPACT VELOCITY - ALL IMPACTS

IMPACT SEQ. 2

IMPACT SEQ. 2IMPACT SEQ. 3

IMPACT SEQ. 3

IMPACT SEQ. 4

IMPACT SEQ. 4

IMPACT SEQ. 1

0

200000400000600000800000

1000000120000014000001600000

01234567

VELOCITY - MPH

PEAK LCF - LB.

IMPACT SEQUENCE 2 IMPACT SEQUENCE 2 IMPACT SEQUENCE 3 IMPACT SEQUENCE 3 IMPACT SEQUENCE 1 IMPACT SEQUENCE 4 IMPACT SEQUENCE 4

PEAK LCF LB 

VELOCITY–MPH 

Plot A-6. Peak LCF versus Impact Velocity—All Impacts 
48 

PLOT A7 - CALCULATED PEAK VCF VERSUS PEAK LCF 

 IMPACT SEQ. 1

0

20000400006000080000

100000120000140000

0 200000 400000 600000 800000 10000

PEAK LCF - LB.

CALCULATED PEAK VCF - LB CALCULATED PEAK VCF LB 

PEAK LCF–LB

Plot A-7. Calculated Peak VCF versus Peak LCF Impact Sequence 1 
49 

PLOT A8 - CALCULATED PEAK VCF VERSUS PEAK LCF 

 IMPACT SEQ. 2

0

20000400006000080000

100000120000140000160000

0 200000 400000 600000 800000 1000000 1200000 

PEAK LCF - LB.

CALCULATED PEAK VCF LB 

CALCULATED PEAK VCF - LB

PEAK LCF–LB

Plot A-8. Calculated Peak VCF versus Peak LCF Impact Sequence 2 
50 

PLOT A9 - CALCULATED PEAK VCF VERSUS PEAK LCF

 IMPACT SEQ. 3

0.0

20000.040000.060000.080000.0

100000.0120000.0140000.0160000.0

0 200000 400000 600000 800000 1000000 12

PEAK LCF - LB.

PEAK LCF - LB.

PEAK LCF–LB

PEAK LCF–LB 

Plot A-9. Calculated Peak VCF versus Peak LCF Impact Sequence 3 
51 

PLOT A10 - CALCULATED PEAK VCF VERSUS PEAK LCF

IMPACT SEQ. 4

0.0

20000.040000.060000.080000.0

100000.0120000.0140000.0160000.0180000.0

0 200000 400000 600000 800000 1000000 12

PEAK LCF–LB PEAK VCF–LB PEAK LCF - LB.PEAK VCF - LB.

Plot A-10. Calculated Peak VCF versus Peak LCF Impact Sequence 4 
52 

PLOT A11 - STRAIN FROM GAGES 19 & 20 VERSUS PEAK LCF

IMPACT SEQUENCE 1

AVERAGE OUPUT FROM 

GAGES 19 & 20

STRAIN GAGE 20STRAIN GAGE 19

-1400.0 -1200.0 -1000.0 -800.0 -600.0 -400.0 -2

PEAK STRAIN (MICROSTRAIN)

PEAK LCF (KLB)

Best fit line for 

average output

Plot A-11. Strain from Gages 19 and 20 versus Peak OCF Impact Sequence 1 
53 

PLOT A12 AVERAGE STRAIN FROM GAGES 19 & 20 VERSUS PEAK LCF

ALL LOADED IMPACTS 

-1600.0 -1400.0 -1200.0 -1000.0 -800.0 -600.0 -400.0 

PEAK STRAIN (MICROSTRAIN)

PEAK LCF (KLB)

Plot A-12. Average Strain from Gages 19 and 20 versus Peak LCF—All Loaded Impac
54 

PLOT A13 AVERAGE STRAIN FROM GAGES 19 & 20 VERSUS PEAK LCF

ALL IMPACTS 

LOADED IMPACTS

UNLOADED IMPACTS

-1600.0 -1400.0 -1200.0 -1000.0 -800.0 -600.0 -400.0 

PEAK STRAIN (MICROSTRAIN)

PEAK LCF (KLB)

Plot A-13. Average Strain from Gages 19 and 20 versus Peak LCF—All Impacts 
55 

PLOT A12 - PEAK ACCELERATION VERSUS PEAK LCF - ACCEL 6 LONG.

-50 -45 -40 -35 -30 -25 -20 -15 -10 

PEAK ACCELERATION (G'S)

PEAK LCF LB.

PEAK ACCELERATION–G 

PEAK LCF LB 

Plot A-14. Peak Acceleration versus Peak LCF—Acceleration 6 Longitudinal 
56 

PLOT A13 - PEAK ACCELERATION VERSUS PEAK LCF - ACCEL 18 LONG.

-35 -30 -25 -20 -15 -10 

PEAK ACCELERATION (G'S)

PEAK LCF LB. PEAK LCF LB 

PEAK ACCELERATION–G 

Plot A-15. Peak Acceleration versus Peak LCF—Acceleration 18 Longitudinal
57 

PLOT A14 - AVERAGE SRS RESPONSE, 10 - 100.8 HZ VS PEAK LCF

 ACC E L. 6 LON GIT UD INAL

0

200000400000600000800000

10000001200000

0 5 10 15 20 

AVERAGE SRS RESPONSE

PEAK LCF LB 

PEAK LCF LB.

Plot A-16. Average SRS Response, 10-100.8 HZ versus Peak LCF—Acceleration 6 Longitu
58 

P LO T A15 - AV E R AG E S R S R E S P O N S E , 10 -100.8 H Z V S P E AK LC F - AC C E L 18 L

0

200000400000600000800000

10000001200000

0 5 1 0 1 5 2 0 

AVERAGE SRS VALUE

PEAK LCF LB PEAK LCF LB.

Plot A-17. Average SRS Response, 10-100.8 Hz versus Peak LCF—Acceleration 18 Longitu
59 

PLOT A16 - AVERAGE LONGITUDINAL SRS RESPONSE (5 - 50 HZ) VERSUS PEAK LCF

ACCEL. 6, IMPACT SEQ, 1

0

200000400000600000800000

10000001200000

0 2 4 6 8 10 12 14 

SRS RESPONSE - G'S

PEAK LCF LB 

PEAK LCF - LB.

SRS RESPONSE–G 

Plot A-18. Average Longitudinal SRS Response (5-50 Hz) versus Peak LCF—Acceleration 6, Impa
60 

PLOT A17- AVERAGE LONG. SRS RESPONSE (5 - 50 HZ) VERSUS PEAK LCF

ALL IMPACTS - SEQ. 1, 2, 3, & 4 - ACCEL 6

IMPACT SEQ. 2

IMPACT SEQ. 

IMPACT SEQ 1

0

200000400000600000800000

10000001200000140000016000001800000

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 

SRS RESPONSE - G'S

PEAK LCF - LB.

Possible Function 

for Impact 

Sequences 2, 3, & 4

Possible Function 

for Impact 

Sequence 1

PEAK LCF LB 

IMPACT SEQUENIMPACT SEQUENIMPACT SEQUEN

SRS RESPONSE–G 

Plot A-19. Average Longitudinal SRS Response (5-50 Hz) versus Peak LCF—Acceleration 6, All Impacts—
61 

PLOT A18 - AVERAGE LONG. SRS RESPONSE (5 -50 HZ) VERSUS PEAK LCF

 ACCEL 6, IMPACT SEQ. 2 - REGRESSION ANALYSIS

0

200000400000600000800000

100000012000001400000160000018000002000000

0 2 4 6 8 10 12 

SRS RESPONSE - G'S

PEAK LCF - LB. PEAK LCF LB 

SRS RESPONSE–G 

Plot A-20. Average Longitudinal SFS Response (5-50 Hz) versus Peak LCF—Acceleration 6, Impact Sequen
62 

PLOT A19 - AVERAGE LONG. SRS RESPONSE (5 - 50 HZ) VERSUS PEAK LCF 

 ACCEL. 6, IMPACT SEQ. 3 - REGRESSION ANALYSIS

0

200000400000600000800000

100000012000001400000160000018000002000000

0 2 4 6 8

SRS RESPONSE - G'S

PEAK LCF - LB. PEAK LCF LB 

SRS RESPONSE–G 

Plot A-21. Average Longitudinal SRS Response (5-50 Hz) versus Peak LCF—Acceleration 6, Impact Sequenc
63 

PLOT A21 - AVERAGE LONG. SRS RESPONSE (5 - 50 HZ) VERSUS PEAK LCF

 SEQ. 2, 3, & 4, ACCEL 6 - REGRESSION ANALYSIS

0

500000

1000000150000020000002500000

0 2 4 6 8 10 12 

SRS RESPONSE - G'S

PEAK LCF - LB.

SRS RESPONSE–G 

PEAK LCF LB 

Plot A-22. Average Longitudinal SRS Response (5-50 Hz) versus Peak LCF—Acceleration 6, Sequence 2, 3, an
64 

PLOT A22 - MAXIMUM VERTICAL ACCELERATION VS PEAK VCF 

ACCELS 5, 6, AND 18 VERT.

0

5000

10000150002000025000

0.0 10.0 20.0 30.0 40.0 50.0 6

VERTICAL ACCELERATION (G'S)

PEAK VCF LB. PEAK VCF LB 

VERTICAL ACCELERATION–G 

Plot A-23. Maximum Vertical Acceleration versus Peak LCF—Accelerations 5, 6, and 18 V
65 

PLOT A23 - AVERAGE VERTICAL SRS RESPONSE (5 TO 50 HZ) VERSUS PEAK VCF

IMPACT SEQ. 2, ACCEL 6 

0

20000400006000080000

100000120000140000160000180000200000

0.00 5.00 10.00 15.00 20.00 25.0

SRS RESPONSE - G'S

PEAK VCF - LB.

SRS RESPONSE–G 

PEAK VCF LB 

Plot A-24. Average Vertical SRS Response (5-50Hz) versus Peak VCF Impact—Acceleration 6, 
66 

PLOT A24 - AVERAGE VERTICAL SRS RESPONSE (5 - 50 HZ) VERSUS PEAK VCF

IMPACT SEQ. 3, ACCEL 6

0.0

20000.040000.060000.080000.0

100000.0120000.0140000.0160000.0

0 5 10 15 20 

SRS RESPONSE - G'S

PEAK VCF - LB.

SRS RESPONSE–G 

PEAK VCF LB 

Plot A-25. Average Vertical SRS Response (5-50 Hz) versus Peak VCF Impact—Acceleration 6, 
67 

PLOT A25 - AVERAGE VERTICAL SRS RESPONSE (5 - 50 HZ) VERSUS PEAK VCF

IMPACT SEQ. 4, ACCEL 6

0.0

20000.040000.060000.080000.0

100000.0120000.0140000.0160000.0180000.0

0 2 4 6 810 12 

SRS RESPONSE - G'S

PEAK VCF - LB.

SRS RESPONSE–G 

PEAK VCF LB 

Plot A-26. Average Vertical SRS Response (5-50 Hz) versus Peak VCF Impact—Acceleration 6, 
68 

PLOT A26 - AVERAGE VERTICAL SRS RESPONSE (5 - 50 HZ) VERSUS PEAK VCF

SEQ 2, 3, & 4, ACCEL 6

0

50000

100000150000200000250000

0.00 5.00 10.00 15.00 20.00 25.0

SRS RESPONSE - G'S

PEAK VCF - LB.

SRS RESPONSE–G 

PEAK VCF LB 

Plot A-27. Average Vertical SRS Response (5-50 Hz) versus Peak VCF—Acceleration 6, Sequenc
69 

PLOT A27 - AVERAGE VERTICAL SRS RESPONSE (5 - 50 HZ) VERSUS PEAK VCF

SEQ 1, 2, 3, & 4, ACCEL 6

2 IMPACT SEQ. 2, 3, & 4

IMPACT SEQ. 1

0

50000

100000150000200000250000

0.00 5.00 10.00 15.00 20.00 25.00 

SRS RESPONSE - G'S

PEAK VCF - LB. 

SRS RESPONSE–G 

PEAK VCF LB 

IMPACT SEQUENCE 2, 3IMPACT SEQUENCE 1 

Plot A-28. Average Vertical SRS Response (5-50 Hz) versus Peak VCF—Acceleration 6, Sequence 
70 

PLOT A30 SRS RESPONSE VERSUS PEAK LCF, ACCEL 18 LONG 

APRIL 14/15

Average over 5 to

 50 HZ

Average over 10 to 

100 HZ

0.00.51.01.52.02.53.03.54.0

-300.0 -200.0 -100.0 0.0 100.0 200.0 

PEAK LCF, NEG IS TENSION

SRS RESPONSE G'S

Average over 5 to 50 Hz Average over 10 to 100 Hz 

SRS RESPONSES–G 

PEAK LCF, NEGATIVE IS TENSION 

Plot A-29. SRS Response versus Peak LCF—Acceleration 18 Longitudinal, April 14-15, 2
71 

 APRIL 14/15

Average over 5 to

 50 HZ

Average over 10 to 

100 HZ

0.00.51.01.52.02.53.03.54.0

-25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 

PEAK VCF KLB, NEG. IS TOWARD GROUND 

SRS RESPONSE G'S SRS RESPONSES–G 

PEAK VCF, NEGATIVE IS TOWARD GROUND 

Average over 5 to 50 Hz Average over 10 to 100 Hz 

Plot A-30. SRS Response versus Peak VCF—Acceleration 18 Vertical, April 14-15, 200
72 

PLOT A32 SRS RESPONS VERSUS PEAK LCF, ACCEL 6 LONG.,

APRIL 14-15

Average over 5 to 

to 50 HZ

Average over 10 to 100 

HZ

0.01.02.03.04.05.06.07.08.09.0

10.0

-300.0 -200.0 -100.0 0.0 100.0 200.0 

PEAK LCF (KIP) - NEG. IS TENSION

SRS RESPONSE (G'S)

PEAK LCF (KIP), NEGATIVE IS TENSION 

SRS RESPONSES–G 

Average over 5 to 50 Hz Average over 10 to 100 Hz 

Plot A-31. SRS Response versus Peak LCF—Acceleration 6 Longitudinal, April 14-15, 2
73 

PLOT A33 SRS RESPONSE VERSUS PEAK VCF, ACCEL 6 VERT

APRIL 14-15

Average over 5 to

50 HZ

Average over 10 to 

100 HZ

0.02.04.06.08.0

10.012.0

-25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 

PEAK VCF (KIP) - NEG. IS TOWARD GROUND

SRS RESPONSE (G'S)

Average over 5 to 50 Hz Average over 10 to 100 Hz 

SRS RESPONSES–G 

PEAK VCF (KIP), NEGATIVE IS TOWARD GROUND 

Plot A-32. SRS Response versus Peak VCF—Acceleration 6 Vertical, April 14-15, 200
74 

DATE 

3/23/03–

3/24/03 

3/24/03– 

3/25/03 

3/25/03– 

3/26/03 

3/26/03– 

3/27/03 

3/30/03– 

3/31/03 

3/31/03– 

4/01/03 4/7/03– 

4/8/03 

4/13/03– 

4/14/03 

4/14/03– 

4/15/03 

4/15/03– 

4/16/03 

4/16/03– 

4/17/03 

4/20/03– 

4/21/03 

4/21/03– 

4/22/03 

CAR TRAIN 

LOCATION DIRECTION 

6TH from CCWfront Bypass 

6th from CCWfront Bypass 

6th from CCWend Bypass 

6th from CCWend Bypass 6th from CCW-Main 

end Loop 

6th from CCW-Main 

end Loop 

4th from CCWfront Bypass 

6th from CCWend Bypass 

6th from CCW-Main 

end Loop 

8th from CW-Main 

front Loop 

8th from CW-Main 

front Loop 

6th from CCW-Main 

end Loop 

6th from CCW-Main 

end Loop 

Table A-1. Summary of TCOE FAST Test Data 

TOTAL SAMPLE DATA MAXIMUM MINIMUM NUMBER RATE USABLE LCF LCF OF CARS 

76 4096 No 75 4096 No 76 4096 Yes 222.6 -152.4 76 4096 Yes 203.2 186.9 76 4096 Poor 166.1 -236.8 76 4096 No 78 4096 Yes 1 -185.3 77 4096 No 76 2048 Yes 263.5 -219.2 77 2048 Yes 177 -253.6 77 2048 Yes -19.9 -173.3 76 2048 Yes 164.5 -214.7 75 4096 Yes 193.8 -269.9 

MAXIMUM 

VCF 

22.5 

41.6 

21.1 

21 

20.5 41.2 

19.4 

27 

31.8 
75 

Table A-2. Peak and SRS Acceleration Response versus Peak Coupler Force, April 14-15, 2003, Accelero

FILE 

NAME 

PEAK 

LCF 

KLB 

PEAK 

VCF 

KLB 

PEAK 

POS. 

LAT. 

ACCEL. 

PEAK 

NEG. 

LAT. 

ACCEL. 

PEAK 

POS. 

VERT. 

ACCEL. 

PEAK 

NEG. 

VERT. 

ACCEL. 

LAT. 

SRS 

5-50 Hz 

LAT. 

SRS 

10-100 HZ 

18L 18L 18V 18V 18L 18L 

414225311 211.1 -17.3 4.0 -4.8 6.0 -4.1 2.9 3.7 

414225405 -169.3 13.7 4.0 -3.1 5.2 -3.4 2.1 2.7 

414225805 -186.5 15.8 2.6 -4.9 3.9 -4.4 1.9 2.5 

414230528 235.5 -18.3 4.2 -3.3 4.3 -2.5 2.2 2.8 

414230614 -180.1 15.5 3.1 -5.2 3.9 -2.7 2.2 2.9 

414230921 224.7 -19.5 4.5 -3.9 2.6 -3.4 2.5 2.9 

414232248 -205.7 16.3 3.0 -2.5 3.0 -2.3 2.3 2.6 

414232513 240.4 -18.6 6.5 -4.4 4.5 -4.4 2.6 2.7 

414235259 265.8 -18.9 4.6 -3.7 3.9 -3.4 2.4 2.6 

Table A-3. Peak and SRS Acceleration Response versus Peak Coupler Force, April 14-15, 2003, Acceler

FILE 

NAME 

PEAK 

LCF 

KLB 

PEAK 

VCF 

KLB 

PEAK 

POS. 

LAT. 

ACCEL. 

PEAK 

NEG. 

LAT. 

ACCEL. 

PEAK 

POS. 

VERT. 

ACCEL. 

PEAK 

NEG. 

VERT. 

ACCEL. 

LAT. 

SRS 

5-50 Hz 

LAT. 

SRS 

10-100 HZ 

6L 6L 6V 6V 6L 6L 

414225311 211.1 -17.3 2.2 -6.8 3.2 -7.0 4.5 6.9 

414225405 -169.3 13.7 2.4 -7.5 3.2 -8.5 4.7 7.5 

414225805 -186.5 15.8 4.7 -9.4 7.3 -8.9 4.8 7.9 

414230528 235.5 -18.3 2.9 -9.9 3.8 -7.8 5.1 8.6 

414230614 -180.1 15.5 3.2 -6.5 3.6 -7.2 3.9 6.1 

414230921 224.7 -19.5 5.2 -6.8 6.2 -7.7 3.6 6.7 

414232248 -205.7 16.3 2.6 -6.9 2.7 -7.3 4.1 6.8 

414232513 240.4 -18.6 2.7 -7.3 3.3 -7.6 3.8 6.8 

414235259 265.8 -18.9 3.0 -5.8 2.8 -5.6 3.4 5.5 
76 
77 

Acronyms 

AAR Association of American Railroads 

FAST Facility for Accelerated Service Testing 

FFT Fast Fourier Transfer 

FRA Federal Railroad Administration 

HTL High Tonnage Loop 

LCF longitudinal coupler force 

PSD power spectral density 

SDOF single-degree of freedom 

SRS SRS 

SSWG Stub Sill Working Group 

TC Transport Canada 

TCOE-TF Tank Car Operating Environment Task Force 

TTC Transportation Technology Center (the site) 

TTCI Transportation Technology Center, Inc. (the company) 

VCF vertical coupler forces 
78