U.S. Department of 

Transportation

Federal Railroad 

Administration

Alternative Occupied Volume Integrity (OVI) 

Tests and Analyses

Office of Research

and Development

Washington, DC 20590

DOT/FRA/ORD-13/46 Final Report

October 2013
NOTICE

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i

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4. TITLE AND SUBTITLE

Alternative Occupied Volume Integrity (OVI) Testing and Analyses

5. FUNDING NUMBERS

RR28A1/JG343 

RR28A2/JL649

RR28A2/KL649 6. AUTHOR(S) and FRA COTR

Authors: Michael Carolan, Benjamin Perlman, David Tyrell

COTR: Melissa Shurland, Jeff Gordon

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

John A. Volpe National Transportation Systems Center

55 Broadway

Cambridge, MA 02142

8. PERFORMING ORGANIZATION 

REPORT NUMBER

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

U.S. Department of Transportation 

Federal Railroad Administration

Office of Research and Development

1200 New Jersey Avenue, SE

Washington, DC 20590

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AGENCY REPORT NUMBER

DOT/FRA/ORD – 13/46

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12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

FRA, supported by the Volpe Center, conducted research on alternative methods of evaluating occupied volume integrity (OVI) in 

passenger railcars. Guided by this research, an alternative methodology for evaluating OVI that ensures an equivalent or greater 

level of safety than that provided by the current Federal regulations was developed. The alternative methodology moves the 

evaluation loads to the collision load path and includes three sets of load magnitudes and pass-fail criteria. This methodology also 

permits a combination of elastic testing and finite element (FE) analysis to be used. This research program applied the alternative 

methodology to a passenger railcar. Three tests were performed in concert with FE analyses. The first test was a conventional 

800,000-pound buff strength test. The results of this test were used to validate an FE model of the car. The FE model was used to 

estimate the ultimate, or crippling, load of the car. Two destructive crippling tests were then performed. The crippling FE 

analysis results were compared with the crippling test results and found to describe the general behavior of the tested cars. The FE 

analysis estimated a crippling load of 1.19 million pounds, and the two test cars had crippling loads of 1.15 and 1.19 million 

pounds. The results of this program provide a technical basis for the alternative OVI methodology. The load magnitudes in the 

new methodology have been shown to be reasonable descriptions of the OVI capacity of conventionally designed passenger 

railcars.

14. SUBJECT TERMS

Occupant volume integrity, testing, finite element analysis, passenger equipment, 

crashworthiness

15. NUMBER OF PAGES

143

16. PRICE CODE

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OF REPORT

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OF ABSTRACT

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i

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

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

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

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

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

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

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

(cm2

)

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

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

yd2

)

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

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

(km2

)

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

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

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

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

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

1 short ton = 2,000 

pounds (lb)

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

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

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

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

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

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

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

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

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

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

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

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

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

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

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

 

°F

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

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and Measures. Price $2.50 

SD Catalog No. C13 10286 Updated 6/17/98
ii

Contents

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

1. Introduction ................................................................................................................. 2

1.1 Background ................................................................................................................. 2

1.2 Objectives.................................................................................................................... 8

1.3 Organization of the report ........................................................................................... 9

2. 800-kip Validation Test and Analysis....................................................................... 11

2.1 Description of Test Article ........................................................................................ 11

2.2 Elastic Test Setup ...................................................................................................... 13

2.3 Instrumentation.......................................................................................................... 15

2.4 FE Modeling of 800-kip Verification Test................................................................ 19

2.5 Elastic Test Results and FE Model Validation.......................................................... 23

3. Crippling Test Setup.................................................................................................. 37

3.1 Crippling Test Description ........................................................................................ 37

3.2 Description of Test Articles ...................................................................................... 39

3.3 Instrumentation.......................................................................................................... 41

3.4 FE Modeling of Crippling Tests................................................................................ 46

4. Crippling Test and Analysis Results......................................................................... 49

4.1 Car 248 Shakedown Crippling Test Results.............................................................. 49

4.2 Car 244 Fully-instrumented Crippling Test Results.................................................. 56

4.3 FE Model Results...................................................................................................... 65

5. Conclusions............................................................................................................... 82

6. References ................................................................................................................. 85

Appendix A. Estimated Car Stiffness.......................................................................................... 87

Appendix B. Estimated Frame Stiffness...................................................................................... 89

Appendix C. Car 244 Strain Data and FE Results....................................................................... 91

Appendix D. Car 244 Displacement Data and FE Results........................................................ 117

Abbreviations and Acronyms ..................................................................................................... 134
iii

Illustrations

Figure 1. Line of Draft Illustrated on Generic Conventional Passenger Railcar............................ 3

Figure 2. Summary of ETF OVI Procedures................................................................................. 8

Figure 3. Car 244 in Original Condition...................................................................................... 11

Figure 4. Car 248 with CEM System........................................................................................... 12

Figure 5. Car 248 Energy Absorber Support Locations .............................................................. 12

Figure 6. Patch Installed on Car 244 Side Sill............................................................................. 14

Figure 7. Car 244 in Test Frame, 800-kip Verification Test ....................................................... 14

Figure 8. Load Cell in 800-kip Verification Test ........................................................................ 15

Figure 9. VLL Array of String Pots............................................................................................. 16

Figure 10. String Pot Arrays in 800-kip Verification Test (Underside View)............................. 17

Figure 11. Strain Gage and String Pot Locations in 800-kip Verification Test........................... 17

Figure 12. Strain Gage Placement on Cross-Section of Car........................................................ 18

Figure 13. Half-symmetric FE Model used for Buff Strength Analysis...................................... 19

Figure 14. Example Bi-linear Stress-strain Behavior .................................................................. 20

Figure 15. Vertical Spring Assembly, 800-kip FE Model........................................................... 21

Figure 16. Loading Location on Live End Buff Stop, 800-kip FE Model................................... 22

Figure 17. Live Load and Reaction Load with +/-5% Envelope, 800-kip Elastic FEA .............. 24

Figure 18. Live Load and Reaction Load with +/-40 kip Envelope, 800-kip Elastic FEA ......... 24

Figure 19. Ratio of Kinetic to Internal Energies, 800-kip Elastic Model.................................... 25

Figure 20. Load-displacement Data for 800-kip Test and FE Analysis, Car 244........................ 26

Figure 21. Vertical Displacements along Length of Car, 800-kip Test (L) and FEA (R) ........... 27

Figure 22. Vertical Deflection of Center Sill at A-end of Car, 800-kip Test .............................. 28

Figure 23. Vertical Deflection of Center Sill at Center of Car, 800-kip Test.............................. 28

Figure 24. Vertical Deflection of Center Sill at B-end of Car, 800-kip Test............................... 29

Figure 25. Strain in Bottom (Left) and Top (Right) of Center Sill at 800 kips, 800-kip Test and 

FEA....................................................................................................................................... 30

Figure 26. Strain in Side Sills at 800 kips, 800-kip Test and FEA.............................................. 31

Figure 27. Strain in Purlin at 800 kips, 800-kip Test and FEA ................................................... 32

Figure 28. Strain Results in Belt Rail at 800 kips, 800-kip Test and FEA.................................. 32

Figure 29. Strain Results in Roof Rail at 800 kips, 800-kip test and FEA .................................. 33

Figure 30. FE Strain Data Compared with Test Strain Results, All Gages in 800-kip Test........ 34
iv

Figure 31. FE Strain Data Compared with Test Strain Results, Limited Gages in 800-kip Test 35

Figure 32. Car 248 in Test Frame, Crippling Test....................................................................... 37

Figure 33. Restraint End Roof Setup in Crippling Tests............................................................. 38

Figure 34. Pretest Damage to Occupied Volume in Car 248....................................................... 39

Figure 35. Live End Floor Load Setup ........................................................................................ 42

Figure 36. Typical Longitudinal String Potentiometer Setup, Car 244 ....................................... 43

Figure 37. String Pot VLL Arrays on Car 244 (Underside View)............................................... 43

Figure 38. Strain Gages at Floor-level Energy Absorber Support............................................... 44

Figure 39. Strain Gage at Roof-level Energy Absorber Support................................................. 45

Figure 40. FE Model Used in Crippling Analysis ....................................................................... 46

Figure 41. Load and Reaction Nodes, Crippling test FE Model.................................................. 47

Figure 42. Live End Loads versus Time, Car 248 Crippling Test............................................... 49

Figure 43. Live End Loads and Displacements, Car 248 ............................................................ 50

Figure 44. Restraint End Loads and Displacements, Car 248 ..................................................... 51

Figure 45. Total End Loads for Car 248 Shakedown Test .......................................................... 51

Figure 46. Annotated Underframe for Pioneer Cars.................................................................... 52

Figure 47. Damage to Underframe of Car 248 ............................................................................ 53

Figure 48. Buckle and Failed Welds in Center Sill at Cross-bearer 5, Car 248 .......................... 53

Figure 49. Damage to Sides Sills of Car 248............................................................................... 54

Figure 50. Damage to Right Sidewall, Car 248........................................................................... 54

Figure 51. Damage to Left Sidewall, Car 248 ............................................................................. 55

Figure 52. Fractured Left Belt Rail, Car 248............................................................................... 55

Figure 53. Buckled Roof, Car 248............................................................................................... 56

Figure 54. Live End Loads, Car 244 Crippling Test.................................................................... 57

Figure 55. Live End Loads and Displacements (Car 244 Crippling Test)................................... 57

Figure 56. Restraint End Loads and Displacements (Car 244 Crippling Test) ........................... 58

Figure 57. Total End Loads for Car 244 Crippling Test.............................................................. 58

Figure 58. Load-displacement Behavior for Car 248 and Car 244.............................................. 59

Figure 59. Damage to Car 244 Center Sill (1)............................................................................. 60

Figure 60. Damage to Car 244 Center Sill (2)............................................................................. 60

Figure 61. Damage to Car 244 Side Sills..................................................................................... 61

Figure 62. Damage to Right Side of Car 244............................................................................... 62

Figure 63. Damage to Right Side Interior of Car 244.................................................................. 62
v

Figure 64. Damage to Left Side of Car 244................................................................................. 63

Figure 65. Damage to Left Side Interior of Car 244.................................................................... 63

Figure 66. Roof Buckle in Car 244.............................................................................................. 64

Figure 67. Live End Loads by Location (Crippling FEA)........................................................... 65

Figure 68. Restraint End Loads by Location (Crippling FEA).................................................... 66

Figure 69. Live Load and Reaction Load for Crippling Analysis ............................................... 67

Figure 70. Ratio of Kinetic Energy to Internal Energy for Crippling Analysis........................... 68

Figure 71. Live Load at Floor for Test of Car 248 and FE Model .............................................. 69

Figure 72. Live Load at Roof for Test of Car 248 and FE Model ............................................... 69

Figure 73. Total Live Loads for Test of Car 248 and FE Model................................................. 70

Figure 74. Live Load at Floor for Test of Car 244 and FEA....................................................... 71

Figure 75. Live Load at Roof for Test of Car 244 and FEA........................................................ 72

Figure 76. Total Live Loads for Test of Car 244 and FE Model................................................. 72

Figure 77. Load-displacement Behavior for Both Tests and Analyses ....................................... 73

Figure 78. Deformed Shape of Crippled Car in FEA .................................................................. 74

Figure 79. Detail Showing Buckled Center Sill and Side Sill in FEA ........................................ 74

Figure 80. Center Sill Upper Flange Buckle in Car 244, Car 248, and FEA Result ................... 75

Figure 81. Longitudinal Displacement at Center Point of Car, Car 244 Test and FEA .............. 76

Figure 82. Lateral Displacement at Center Point of Car, Car 244 Test and FEA........................ 76

Figure 83. Vertical Displacement along Length of Car 244 in Crippling Test............................ 77

Figure 84. Vertical Displacement along Length of FE Model in Crippling Simulation.............. 78

Figure 85. Longitudinal Strain in Center Sill at 830 kips, Crippling Test................................... 79

Figure 86. Longitudinal Strain in Center Sill at 1180 kips, Crippling Test................................. 80

Figure 87. Crippling Locations for Strain Comparison, FEA (right) and Car 244 (left)............. 81

Figure 88. Strain vs. Load Behavior at Center Sill Buckling Locations, Test (left) and FEA 

(right) .................................................................................................................................... 81
vi

Tables

Table 1. ETF OVI Criteria ............................................................................................................. 7

Table 2. Descriptions of Tests in FRA Research Program............................................................ 9

Table 3. Instrumentation Summary for 800-kip Verification Test .............................................. 15

Table 4. Strain Gages Outside of +/-20% Threshold, 800-kip Test ............................................ 35

Table 5. Instrumentation Summary for Shakedown Test of Car 248 .......................................... 41

Table 6. Instrumentation Summary for Fully-instrumented Crippling Test of Car 244.............. 41

Table 7. Load Cell Names and Locations, Crippling Tests......................................................... 42
1

Executive Summary

The Federal Railroad Administration (FRA), with the assistance of the John A. Volpe National 

Transportation Systems Center (Volpe Center), has been conducting research on alternative 

methods of evaluating occupied volume integrity (OVI) in passenger rail equipment. As a result 

of this research, an alternative methodology for evaluating OVI has been developed that ensures 

an equivalent or greater level of safety than that provided by the current Federal regulations. The 

alternative methodology moves the applied load away from the line of draft to the collision load 

path, more closely representing the type of loading the occupant volume would experience 

during a collision. This methodology permits application of one of three sets of evaluation load 

magnitudes and corresponding pass-fail criteria. Additionally, this methodology permits a 

combination of elastic testing and finite element (FE) analysis to be used in the evaluation of a 

car design, whereas the conventional methodology only permits the use of testing. The new 

methodology requires that an elastic test be used to validate an FE model of the car undergoing 

evaluation. Once validated with elastic test data, the model can be used to demonstrate that the 

car’s OVI satisfies one of the three pass-fail criteria.

This research program sought to establish confidence in the alternative methodology as a means 

of evaluating OVI. The research methodology was applied to a Budd Pioneer passenger railcar. 

A pair of destructive crippling tests was performed to confirm that analysis performed according 

to the new methodology could reliably estimate the crippling behavior of a passenger railcar. 

The testing program applied the new methodology by first performing a conventional 800,000-

pound line of draft buff strength test. The results of this test were used to validate an FE model

of the car to which the test loading conditions were applied. The now-validated FE model was 

then used to estimate the ultimate, or crippling, load for this type of car. 

The second test performed as part of this research program was a limited-instrumentation 

“shakedown” test that loaded a Pioneer car to its crippling load along its collision load path. The 

third test performed was a fully instrumented crippling test of a second Pioneer car along its 

collision load path.

Data collected during the tests include the incremental load versus displacement behavior of each 

car, the longitudinal strains in major structural members, and the vertical, lateral, and 

longitudinal displacements of the underframe. The elastic FE analysis results were compared 

with the results of the elastic test and found to be in reasonable agreement. The crippling FE 

analysis results were compared with the crippling test results and were found to describe the 

general load versus displacement behavior of the two tested cars. The crippling FE analysis 

estimated a crippling load of 1.19 million pounds. The first tested car crippled after reaching a 

load of 1.15 million pounds, and the second car slightly exceeded 1.19 million pounds before it 

crippled. 

The results of this testing and analysis program have provided a technical basis for the 

alternative OVI evaluation methodology. The load magnitudes adopted as a part of the new 

methodology have been shown to be reasonable descriptions of the capacity of the OVI of 

conventionally designed passenger railcars.
2

1. Introduction

1.1 Background

The FRA Office of Research and Development supports the safety rulemaking and enforcement 

programs of the FRA Office of Railroad Safety. The Volpe Center provides engineering support 

to the Office of R&D. 

Presently, FRA’s Passenger Equipment Safety Standards are located within the Code of Federal 

Regulations at 49 CFR 238. These standards provide design and performance requirements for 

ensuring an appropriate level of safety for various locations and components of passenger 

railcars. The purpose of these standards is described in 49 CFR 238.1(a) as follows:

The purpose of this part is to prevent collisions, derailments, and other 

occurrences involving railroad passenger equipment that cause injury or death to 

railroad employees, railroad passengers, or the general public; and to mitigate 

the consequences of such occurrences to the extent they cannot be prevented.

One of the techniques employed in mitigating the consequences of accidents is the use of 

structural standards to establish a baseline level of performance for various structures that make 

up the car body. Among the structural requirements given in 49 CFR 238 are the compressive

strength of the car body (§238.203), the collision posts (§238.211), the corner posts (§238.213), 

the rollover strength (§238.215), and the side structure (§238.217). These structures are intended 

to prevent loss of occupied volume in the event of an accident that is not prevented through other 

measures.

The Passenger Equipment Safety Standards are applied to all passenger equipment that operates 

over the general railroad system of the United States. Because different structural standards are

applied to railroad vehicles built for service in other parts of the world, FRA has received several 

requests for waivers of the domestic structural requirements [1, 2, 3, 4]. These waiver requests 

seek to permit rail vehicles built to different structural standards to operate on the general 

railroad system of the United States. The entity seeking the waiver must generally demonstrate

that the subject vehicle provides an equivalent level of safety as a vehicle that complies with the 

requirements of the CFR.

To help facilitate the waiver application process, in 2009 FRA’s Railroad Safety Advisory 

Committee (RSAC) established its Engineering Task Force (ETF). The ETF was responsible for

generating a set of technical criteria and procedures to demonstrate that trainsets developed to 

meet alternative standards provide a level of safety equal to the domestic standard. Compliance 

with the criteria and procedures may be demonstrated when a waiver is sought to permit an 

alternatively designed trainset to operate in the United States [5]. ETF members included rail 

vehicle manufacturers, railroad operators, industry consultants, and FRA and Volpe Center staff. 

The recommendations proposed by the ETF were published as a report, “Technical Criteria and 

Procedures for Evaluating the Crashworthiness and Occupant Protection Performance of 

Alternatively Designed Passenger Rail Equipment for Use in Tier I Service” [6]. The final 

version of this report was posted on FRA’s Web site in October 2011.
3

One of the structural requirements addressed in the ETF’s report is used to demonstrate that an 

equivalent level of safety for the occupant volume integrity (OVI) exists between the vehicle in 

question and a conventional vehicle meeting the requirements of the CFR. The existing CFR 

requirement places an 800,000-pound compressive load along the line of draft of the car, and the 

car is required to experience no permanent deformation under this load. The ETF alternative 

offers the choice of one of three optional load magnitudes, applied along the collision load path 

of the car, each with a corresponding pass-fail criterion. The existing OVI requirement and the 

proposed ETF methodology for ensuring OVI are discussed in this section. 

1.1.1 Existing OVI Requirement

The current OVI requirement for all passenger equipment traveling on the general railroad 

system is contained in the CFR at 49 CFR 238.203 and reads, in part, as follows:

(a)(1) Except as further specified in this paragraph or in paragraph (d), on or after November 8, 

1999 all passenger equipment shall resist a minimum static end load of 800,000 pounds applied 

on the line of draft without permanent deformation of the body structure.

(2) For a passenger car or a locomotive, the static end strength of unoccupied volumes may be 

less than 800,000 pounds if:

 (i) Energy absorbing structures are used as part of a crash energy management design of the 

passenger car or locomotive, and

 (ii) The passenger car or locomotive resists a minimum static end load of 800,000 pounds 

applied on the line of draft at the ends of its occupied volume without permanent deformation of 

the body structure.

The line of draft is an imaginary line that runs from the structure of the car just inboard of 

the coupler at one end to just inboard of the coupler at the opposite end. This line 

represents the line-of-action of the tensile (draft) and compressive (buff) forces 

introduced into a railcar through its couplers by the adjacent cars. Based on the specific 

design of a passenger car, an actual structure may or may not exist along the line of draft. 

The line of draft is illustrated schematically in Figure 1 for a generic, conventionally

designed passenger railcar.

Figure 1. Line of Draft Illustrated on Generic Conventional Passenger Railcar

A large compressive load applied to the line of draft of a passenger railcar has been in place as a 

standard or recommended practice since the first half of the twentieth century [7], and was 

codified in 1999 as a Federal regulation applicable to all passenger equipment on the general 

railroad system [8]. Historically, this loading requirement was used to ensure a baseline 

resistance to loss of occupant volume through longitudinal crush.

The 800,000-pound requirement has several positive attributes that have contributed to its

continued use. Because the OVI requirement has traditionally been evaluated through the use of 
4

a quasi-static test, verification of a railcar’s success in meeting the requirement is 

straightforward. The criterion for “no permanent deformation” may be verified through visual 

inspection of the car, as well as through the use of strain gages installed on the structural 

members of the car. For a car that has been designed and constructed to meet the 800,000-pound 

requirement, a successful test is nondestructive. If a car structure succeeds in resisting 800,000 

pounds without permanent deformation, that structure may then have its assembly completed and 

be delivered to the customer as a functional rail vehicle. This ability to utilize a structure as both 

test article and deliverable product gives this test an economic advantage over destructive testing.

However, there are several disadvantages associated with the existing OVI requirement. The 

regulation places the full 800,000-pound load along the line of draft for all vehicles, regardless of 

the design of the body structure. While a conventionally designed railcar may have the ability to 

support that load at the line of draft, vehicles with a partial low-floor section, an articulation at 

one or both ends, an alternative load path, or an otherwise nonconventional design may not. 

A modern development in railcar crashworthiness design is the use of sacrificial unoccupied 

areas designed to permanently deform and absorb collision energy in a controlled manner. This 

approach to design, known as crash energy management (CEM), is more frequently being 

included in the design of passenger railcars as a means to increase safety in the event of a 

collision. In order to function as intended in a collision, the CEM system must crush at a lower 

force than it takes to crush the occupant volume. The car’s OVI must be sufficient to prevent 

crush of the occupied areas before the CEM system has fully exhausted.

The current CFR requirement makes allowance for CEM designs, permitting the evaluation load 

to be applied to the car inboard of the designated energy absorbing structures. However, the 

800,000-pound load must still be applied along the line of draft. In a CEM-equipped railcar, the 

normal service loads may still be transmitted along the line of draft. Nevertheless, in a collision 

with sufficient severity to activate the CEM system, the load path into the occupant volume will 

be altered. During crush of the CEM components, the collision forces will travel through the 

energy absorbing elements and into the occupant volume where these elements are attached to it. 

Because these elements may not be attached to the car along its line of draft, the collision load 

path for a CEM car may differ significantly from its normal service load path. Therefore, 

although applying 800,000 pounds along the line of draft determines some level of resistance to 

loss of occupant volume, it does not evaluate the car in the manner in which it was designed to 

be loaded in a collision.

1.1.2 Previous FRA Research on OVI

For several years, FRA, in support of the advancement of improved safety standards for passenger 

rail vehicles, has sponsored work at the Volpe Center investigating alternative ways of evaluating 

OVI. This research was intended to identify an alternative manner of evaluating the OVI that 

would ensure a level of safety equivalent to that provided by the conventional requirement. Such 

an alternative would permit nonconventional passenger car designs to be introduced into service 

in the United States. 

This research first set out to investigate the behavior of a conventionally designed passenger 

railcar when subject to the conventional 800,000-pound (800 kip) line of draft load [9]. Using a 

simplified FE model, the 800-kip load was applied to a generic representation of a conventional 
5

passenger car. The effect of this loading was to impart to the railcar a large bending moment as 

well as a significant compressive load.

The next step in this research program was to determine whether a conventionally designed 

passenger railcar could be loaded in an alternative manner and develop a similar state of stress as 

a conventionally loaded railcar subjected to the 800-kip compressive line of draft load. Again 

using a simplified FE model, alternative loading schemes were evaluated on a generic singlelevel passenger railcar of conventional construction. Because the line of draft may be difficult to 

define for some rail cars, or may be easily defined but not descriptive of the path traveled by 

collision loads through the structure, alternative loading locations that were easily definable and 

descriptive of the collision load path were examined. The alternate loading scheme examined a 1

million-pound load applied across the floor of the endframe of the car in concert with a 200,000-

pound load applied across the roof of the endframe of the car. The combined 1.2 million-pound 

load, distributed across the floor and roof of the endframe, resulted in a state of stress in the car’s 

structural members that was more severe than the stress state developed by the conventional 

800,000-pound load along the line of draft. 

By moving the load away from the line of draft and onto the end structure of the car, the previous 

research program sought to make the compressive strength requirement applicable to a wider 

range of passenger car designs than could readily be evaluated with the conventional test. The 

suggested approach to alternative loading also sought to provide an equivalent level of occupant 

protection as the existing 800,000-pound requirement by selecting loads that placed an equal or 

greater demand on the car’s structure. These preliminary results indicated that a conventional

car’s structure was capable of supporting compression loads above the conventional 800,000-

pound load, if the loads were introduced into the structure at a location other than the line of

draft.

A general strategy for evaluating passenger cars of an alternative design was developed; it

employed a combination of elastic analysis, elastic testing, and plastic analysis. Because placing 

large compressive loads in several locations on a car may be difficult to accomplish during a test, 

FE analysis was considered a possible method of evaluating an occupant volume’s response to 

loads at several locations. Any FE model will have certain assumptions, simplifications, and 

approximations built in; therefore, it is essential that a model be validated by comparing a 

modeled load case with the results of a test under the same conditions. If the model is capable of 

closely estimating the results of an elastic load test, there is greater confidence in the model’s

results for a load case that is not also tested. If simulating the response of the carbody to loads 

that induce plastic behavior, the FE model may be validated with test data obtained for loads 

producing elastic behavior. The plastic response for greater load magnitudes may then be 

extrapolated using the model alone. With this methodology, the test article is not subjected to 

loads that would cause plastic deformation.

A 2009 technical paper outlined the general strategy of using a combination of elastic analysis, 

elastic testing, and plastic analysis to estimate the crippling behavior of a passenger car loaded in 

an alternative manner [10]. Following the development of this alternative approach to loading 

the passenger car structure, the next objective of the research program was to apply these 

alternative loads to an exemplar railcar in a quasi-static test. A preliminary testing strategy was 

developed that placed alternative loads along the collision load path of a passenger railcar 

equipped with CEM.
6

1.1.3 Adopted ETF OVI Methodology

In 2009, the ETF was tasked with developing a set of technical criteria and procedures that 

would help determine whether an alternatively designed rail vehicle would perform as well as a 

vehicle designed to meet the Passenger Equipment Safety Standards. The ETF examined current 

requirements for OVI as detailed by 49 CFR 238.203. FRA and the Volpe Center were active 

participants in the ETF and presented information on the ongoing OVI research program as well 

as future testing plans. Additionally, railcar manufacturers provided technical information on 

OVI requirements in other parts of the world as well as test and simulation results for 

alternatively designed passenger railcars. The ETF adopted a set of technical criteria and 

procedures for evaluating the OVI of alternatively designed passenger equipment, in lieu of

applying the requirements of 49 CFR 238.203 [6].

In the ETF’s report, the criteria are defined as the loading conditions to be applied and the 

acceptable behavior of the vehicle under those conditions. The procedures are the required tests 

and/or analyses that are employed to demonstrate compliance with the criteria. The ETF’s 

criteria and procedures are intended to allow for flexibility with respect to car design 

methodology and evaluation procedure while maintaining an equivalent level of safety as 

equipment designed to meet and be evaluated against the existing 800,000-pound buff strength 

requirement.

In developing alternative criteria and procedures for evaluating OVI, the ETF examined some of 

the reasons waivers are sought for alternatively designed equipment. In recognition of a variety 

of passenger car designs that could be the subject of potential waiver applications, the ETF 

adopted three loading options consisting of pairs of load magnitudes and corresponding pass-fail 

criteria. To meet the alternative OVI requirement, a passenger railcar design must satisfy one of 

the three options. The three options for demonstrating a vehicle’s OVI are provided in Table 1.
7

Table 1. ETF OVI Criteria

ETF Option Criteria for Each Option

Option A

Passenger equipment shall resist a minimum quasi-static end load of 800,000 

pounds applied on the collision load path without permanent deformation of 

the occupied volume.

Option B

Passenger equipment shall resist a minimum quasi-static end load of 1 million

pounds applied on the collision load path with limited permanent deformation 

of the occupied volume. Limited permanent deformation means that local 

plastic strains must be less than 5 percent and vehicle shortening must not 

exceed 1 percent over any 15 feet of occupied volume.

Option C

Passenger equipment shall resist a minimum quasi-static end load of 1.2 

million pounds applied on the collision load path without crippling the body 

structure.

The ETF adopted a two-stage procedure as the general approach to demonstrating OVI. The first 

stage consists of simulating an elastic compression test with an FE model. An elastic test is then 

performed and the data collected during the test is used to validate the FE model. In the second 

stage, the now-validated FE model is used to demonstrate that the modeled car satisfies one of 

the three options. The ETF’s report discusses the procedures that may be used to evaluate any of 

the three options, as well as particular procedures unique to each option. The ETF’s general 

approach to ensuring OVI is the same as that employed for conventional cars, that is, a large 

compressive load is applied to the occupant volume. However, the ETF’s procedures include

two major changes from the current OVI evaluation methodology. 

The first major difference is the placement of the load. The CFR requires the load to be placed 

along the line of draft for all equipment under evaluation. Recognizing that collision loads pose 

a greater threat to the integrity of the occupant volume than service loads and that a vehicle may 

be designed to transmit collision loads at a location other than the line of draft, the applied

evaluation load was moved to the ends of the collision load path. 

Placing the load along the collision load path offers a better approximation of the type of loading 

the car will actually experience during a collision. This change also permits CEM-equipped cars 

to be evaluated in the manner in which they were designed to be loaded during a collision. By

removing the specific language of “line of draft” and allowing loads to be applied along the 

collision load path specific to the vehicle undergoing evaluation, the ETF’s procedures represent 

a design-neutral approach to evaluating OVI.

The second major change to procedures adopted by the ETF involves allowing a combination of 

testing and analysis to be used to demonstrate a vehicle’s OVI. The 800,000-pound buff strength 

requirement has been demonstrated using a quasi-static test. Although analysis may be used 

during the development of a design, testing has traditionally been used to demonstrate the ability 

of the vehicle to support the 800,000-pound load without permanent deformation. Because two 

of the ETF’s options permit some permanent deformation to occur in a successful demonstration 

of OVI, the use of analysis is necessary to avoid performing a destructive test. Although the 
8

ETF’s procedures do not prevent a destructive test from being used to demonstrate compliance, it 

was envisioned that a combination of nondestructive (elastic) testing and analysis would more 

typically be applied.

Permitting the combined use of nondestructive (elastic) testing and analysis (as a surrogate for 

potentially destructive testing) is a significant step away from the conventional approach of 

permitting only testing to be used to demonstrate compliance. Because of the uncertainties 

introduced in an analysis, it is important to verify that the model being analyzed is capable of 

producing reasonably accurate results. The ETF procedures do not permit a total abandonment 

of testing, but contain a methodology where testing and analysis are both utilized to increase the 

confidence in the analytical results. 

Under the ETF procedures, model results may be used to demonstrate that a vehicle complies 

with Option A, Option B, or Option C only if the model has been previously validated with 

elastic test data. Specifically, the vehicle being evaluated must be tested under a longitudinal 

load that meets a recognized national or international testing standard. The applied load must be 

no less than 337,000 pounds, regardless of the standard being applied. A model should be used 

to analyze the behavior of the car in this test. If the strain and displacement results from the 

model and the data from the test are within the tolerances adopted by the ETF, the model is 

considered validated and may be used to demonstrate compliance with any of the three OVI 

options. A flowchart of the ETF’s procedures is shown in Figure 2.

Figure 2. Summary of ETF OVI Procedures

1.2 Objectives

The ETF criteria and procedures represent a departure from the existing 800,000-pound buff 

strength requirement. This alternative methodology for demonstrating OVI permits a wider 

variety of equipment designs to be evaluated through a waiver process using criteria that place 

loads on the equipment in the manner in which it was designed to support load. This alternative 

methodology permits the use of modern engineering analysis techniques to demonstrate a rail 

vehicle’s OVI. However, as this procedure is relatively new, additional progress needs to be 

made in applying the methodology to evaluate the OVI of a passenger railcar. FRA, with the 

support of the Volpe Center, has conducted a series of full-scale, quasi-static compression tests 

of passenger rail equipment in concert with FEA of each test. The goal of this testing program 

was to develop confidence in using the elastic test and crippling analysis methodology adopted 

by the ETF to estimate the crippling behavior of passenger rail equipment. The results of the 

research program could verify the load magnitudes adopted by the ETF as representative of the 

performance of conventionally designed equipment. Application of the research findings would 

also provide confidence that the methodology of elastic analysis, elastic testing, and plastic 
9

extrapolation analysis is capable of describing the behavior of a passenger railcar when loaded 

up to its crippling load.

The series of tests undertaken in this research program consisted of a conventional 800-kip line 

of draft elastic test and two collision load path crippling tests. Two Budd Pioneer cars were used 

in this program. The three tests are summarized in Table 2. An FE model was used to simulate 

the elastic line of draft test, and a second model was used to simulate the crippling test. The 

results of the testing and analyses were compared using the ETF’s criteria to evaluate whether 

the modeling provided a reasonable estimate of the behaviors of the cars under the given test 

conditions. 

Table 2. Descriptions of Tests in FRA Research Program

Test Test Date Test Article Description

800,000-pound 

line of draft 

January 2011 Pioneer 244 Elastic test used to verify structural integrity of 

Car 244 and provide data for FE validation.

“Shakedown” 

crippling test

May 2011 Pioneer 248 Verify performance of newly constructed test 

frame and newly installed hydraulic control 

system.

Fully instrumented 

crippling test

May 2011 Pioneer 244 Establish whether the loading options 

considered in the ETF’s methodology 

reasonably reflect the OVI of a conventionally

designed passenger railcar.

1.3 Organization of the report

The body of this report contains five sections that are as follows. 

This section, section one, includes the introduction, background information on OVI, and a 

description of the objectives of this research program. 

Section two discusses the first test, the 800-kip elastic verification test, which was conducted in 

this series. The general test setup and the instrumentation used to collect data are presented. A 

detailed description of the test article, Pioneer 244, used in the elastic test and one crippling test 

is also provided in this section of the report. In addition, section two presents the FE model that 

was used to simulate the 800-kip elastic test. Discussion of the FE model includes the history of 

the model’s development, the boundary conditions placed on the model, and the loading 

mechanism used to simulate the elastic test. Validation of the FE model using strain and 

displacement data from the 800-kip elastic test is discussed in this section of the report.

Section three examines the crippling tests that were performed in this research program. Both 

the limited-instrumentation crippling test of Car 248 and the fully instrumented crippling test of 

Car 244 are considered. This section also provides a discussion of the test setup, a description of 

the physical condition of the two test cars, and a listing of the instrumentation that was installed 

on both cars during their crippling tests. The FE model that was used to simulate the crippling 

tests is presented. The discussion in this section touches on the modifications made to the elastic 

model to create the crippling model, the boundary conditions placed on the model, and the 

loading mechanism used in the crippling simulation. 
10

In section four, the results of the two crippling tests are compared with one another, as well as 

with the results obtained from the FE model. This section includes a detailed discussion of the 

damage observed in each test. For both tests, the load-versus-displacement measurements are 

compared with the load-versus-displacement calculations made by the FE model. For the fully

instrumented crippling test, the vertical mode of deformation and the strain results on key 

longitudinal members of the body structure are also discussed. These results are compared with 

the results calculated by the FE model. 

Section five contains concluding remarks. The major results of the research program are 

summarized. This section also touches on the relevance of the results to the criteria and 

procedures that were adopted by the ETF.
11

2. 800-kip Validation Test and Analysis

The first test performed in this research program was a conventional 800,000-pound line of draft 

loading. This test was performed to verify the structural integrity of Budd Pioneer Car 244 and

to validate the FE model of the car. The car was instrumented during this test to measure the 

applied load, strains in the major longitudinal members, and displacements of the underframe 

along its length.

2.1 Description of Test Article

The test article selected for this program was the Budd Pioneer car. Two Pioneer cars were used: 

Car 244 and Car 248. These two cars were used in commuter rail service for approximately 30 

years before being retired. The cars were donated to FRA by the Southeastern Pennsylvania 

Transportation Authority (SEPTA). The Pioneer was originally designed to comply with the 

800-kip line of draft load requirement. Cars of this design utilized a conventional draft sill and 

underframe arrangement featuring a center sill and two side sills capable of meeting the 800-kip 

requirement. The Pioneer design made extensive use of high-strength stainless steels for the 

structural members as a means of ensuring a lightweight vehicle. Budd Pioneer Car 244 is 

shown in Figure 3 in its original condition.

Figure 3. Car 244 in Original Condition

Prior to their use in the OVI testing program, both cars were used in a previous FRA research 

program. This previous program used the cars in a series of dynamic impact tests [11]. 

Following the collision tests, each car was repaired and retrofitted with a CEM system designed 

to dissipate collision energy through controlled permanent deformation. The CEM system 

featured energy absorbing elements at both the floor level and roof level of the car. The CEMequipped cars were then subjected to a second series of impact tests designed to evaluate the 
12

performance of the CEM systems. Pioneer 248 is shown in Figure 32 with its CEM system 

highlighted. 

Figure 4. Car 248 with CEM System

The design of this particular CEM system provides two paths for longitudinal loads through the 

occupant volume. During normal operations, the service loads are transmitted on the 

conventional load path along the line of draft. In the event of a collision, trigger elements are 

activated and the energy absorbing components begin to crush. Once the energy absorbing 

elements begin crushing, the collision loads are transmitted through these elements and into the 

occupant volume at the energy absorber support structures. Figure 5 shows Car 248 with its 

CEM components removed. The energy absorber supports at one end of the occupant volume 

are indicated in this figure. 

Figure 5. Car 248 Energy Absorber Support Locations
13

2.2 Elastic Test Setup

Because Car 244 had previously been involved in a series of high-energy dynamic impacts [11],

a test was needed to ensure the structural integrity of the car and verify its suitability for further 

OVI testing. Additionally, the ETF procedures require that an elastic test be used to validate the 

FE model used to simulate the crippling behavior of the car. The 800-kip line of draft test was 

chosen to accomplish both of these tasks. Because the Pioneer Cars were originally designed to 

meet the 800-kip line of draft load requirement, their ability to support this load would verify 

their structural integrity. The 800-kip magnitude of load applied also exceeds the minimum load 

of 337,000 pounds required by the ETF procedures for an elastic validation test. Therefore, the 

results of this test can also be used to validate the FE model of the car. The validated model 

would then be modified slightly to simulate loading up to crippling.

The 800-kip elastic verification test was performed on January 19, 2011, at Transportation 

Technology Center (TTC) in Pueblo, CO. A previous 800-kip elastic verification test had been 

performed on this car on January 10, 2010 [11]; however, during review of the test results,

several anomalies were discovered. These anomalies included indication of a lateral shift of the 

test frame that was not captured by any instrumentation. This behavior caused difficulty in 

comparing the test results and the results of the corresponding FE analysis. Additionally, posttest examination of the car revealed several small cracks in one side sill. The decision was made 

to perform a second buff test on the car. A doubler plate was installed over the side sill cracks, 

with a second patch placed on the other side sill to maintain symmetry. Figure 6 shows a 

photograph of one of the crack patches that was added to the side sill of Car 244. Following the 

addition, the test frame was better restrained against unintended lateral motion. Finally, 

additional string potentiometers were installed on the underframe of the car so that motion in the 

vertical, lateral, and longitudinal directions could be resolved into its components.
14

Figure 6. Patch Installed on Car 244 Side Sill

During the test, Car 244 remained on its trucks. Because the line of draft represents the service 

load path taken by normal operational loads, the CEM endframes of the car were left intact for 

this test. Load was applied to the A-end buff stops through a hydraulic actuator with a capacity 

of 1 million pounds. The car was restrained at the B-end buff stops by the test frame’s cross 

member. The test frame itself was composed of two longitudinal beams running the length of 

the car connected by two large lateral cross members. These longitudinal beams are themselves 

supported by a series of sawhorses, preventing the beams from moving downward but offering 

no resistance to uplift. The lateral cross member is attached to the ground at the live end but is 

free to move longitudinally at the restraint end. Figure 7 shows Car 244 in the test frame during 

the January 2011 test. The CEM endframes are indicated in this figure at both ends of the car.

Figure 7. Car 244 in Test Frame, 800-kip Verification Test
15

2.3 Instrumentation

In the 800-kip verification test, Car 244 was instrumented with uniaxial strain gages installed on 

the longitudinal members and string potentiometers (string pots) having vertical, lateral, and 

longitudinal orientations. A single load cell with a capacity of 1,000 kips was installed in-line 

with the hydraulic actuator at the live end of the car. A summary of the instrumentation used in 

this test is provided in Table 3.

Table 3. Instrumentation Summary for 800-kip Verification Test

Type of Instrumentation Number of Channels

Uniaxial Strain Gages 64

String Potentiometer 27

1,000 kip Load Cell 1

Total 92

2.3.1 Load Cell

A single load cell with a 1,000-kip capacity was used in the 800-kip elastic verification test. The 

load cell was installed in series between the hydraulic actuator and a column used to transmit 

load to the buff stops within the draft sill of the car. The single load cell used in this test is 

shown in Figure 8.

Figure 8. Load Cell in 800-kip Verification Test
16

2.3.2 String Potentiometers

Each string pot reports the change in string length between its grounded end and its attachment

point on the car. Because the point on the car can experience simultaneous motion in all three 

directions, the change in length reported by any one string could include components in all 

directions. Vertical, lateral, and longitudinal (VLL) arrays of string pots were installed at each 

instrumented point on the underframe of the car in the 800-kip test. By attaching three string 

pots to a single point on the car, the reported change in length of each string can be used to 

resolve the VLL motion of the point on the car. The procedures for resolving the motion of a 

single point into its components are discussed in Appendix D. An exemplar VLL array is shown 

in Figure 9. 

Figure 9. VLL Array of String Pots

In the elastic verification test of Car 244, a total of nine VLL arrays were installed on the 

underframe of the car. At both ends of the car, arrays were placed on the side sills and the lateral 

member at the end of the occupant volume. Between the two body bolsters, VLL arrays were 

attached to the center sill of the car. Figure 10 shows the nine locations and the names of the

VLL arrays used in the elastic verification test of Car 244. This image shows an inverted view 

of the car, taken from the FE model.
17

Figure 10. String Pot Arrays in 800-kip Verification Test (Underside View)

2.3.3 Strain Gages

Uniaxial strain gages were installed on Car 244 at six cross-sections, as shown in Figure 11

below. This figure also indicates the locations on Car 244’s underframe where string pot arrays

were installed during the elastic verification test.

Figure 11. Strain Gage and String Pot Locations in 800-kip Verification Test
18

At cross-sections 1–5, strain gages were installed on the center sill, side sills, belt rails, roof rails, 

and purlins on both the left and right sides of the car. At cross-section 6, strain gages were 

installed on the side sills and belt rails. Figure 12 shows the locations on each longitudinal 

member where the strain gages were placed.

Figure 12. Strain Gage Placement on Cross-Section of Car
19

2.4 FE Modeling of 800-kip Verification Test

In the ETF’s procedures, analysis used to demonstrate the OVI of a passenger car must first be 

validated with elastic test data. Accordingly, FE analysis was used to simulate the 800-kip 

elastic verification test. The ETF’s report provides guidelines for acceptable tolerances between 

test measurements and analysis results for successful validation of the model.

The ETF’s guidance procedures were followed in this research program. Because the 800-kip 

test being performed to verify the structural integrity of Car 244 met the ETF requirement of an 

elastic test with a load greater than 337 kips, this test was also used to validate an FE model. The 

FE model used in this research program was derived from models used in several previous tests. 

This FE model was first constructed to simulate the impact tests of unmodified Pioneer cars [12]. 

The FE model was then modified to include CEM components when the Pioneer cars themselves 

had CEM components installed [13]. Finally, the model was modified in this OVI research 

program to accommodate the quasi-static loading that would take place during the elastic test. 

The model used to simulate the CEM system only featured the occupied volume directly behind 

one CEM end of the car. The full-length of the car was modeled for the 800-kip test load case. 

The doublers that were installed on the side sills of Car 244 were also included in the model. 

Finally, the energy absorbing components that were removed from the test cars following the 

dynamic impact testing program were removed from the model used to simulate the 800-kip test.

The FE model represented the full-length of the car and half of its width. A symmetry boundary 

condition was applied along the vertical-longitudinal midplane of the car to account for the halfwidth condition. The model featured a total of 223,888 elements and 220,986 nodes. The model 

had a characteristic element length of 1.37 inches. The car structure was modeled almost 

entirely with shell elements. A small number of solid (brick) elements were used around the 

window frames and in the endframes to represent geometry too thick to be effectively modeled 

using shell elements. Other element types used in the model included rigid elements to represent 

the ground and spring elements to represent the suspension. Figure 13 shows the FE model as it 

existed during simulation of the buff strength test.

Figure 13. Half-Symmetric FE Model used for Buff Strength Analysis

Because the 800-kip test and the corresponding FE analysis were performed with the goal of 

validating the FE model to be used to simulate crippling, certain aspects of the buff strength 
20

analysis were performed with this objective in mind. Although the 800-kip test is intended to be 

a nondestructive elastic test, the materials that were used in the model included elastic and plastic 

stress-strain behavior. The plastic behavior was included so that the same material models could 

be used for the buff strength simulation and the crippling simulation. 

Because the 800-kip model was derived from models previously used to simulate dynamic 

impacts, elastic-plastic material models were already defined for the materials in the car [12, 13]. 

These existing material properties were defined in the models used to simulate the 800-kip test 

and the subsequent crippling test. The majority of the structural members of the car were made 

of steel. Steel material properties featuring different yield and ultimate strengths were included 

in this model. The simplest representation of elastic-plastic material properties was a bilinear 

characteristic. The first part of this characteristic represents the stress-strain behavior in the 

elastic range with a line of one slope. The second part of this characteristic represents the plastic 

behavior from the yield strength up to the ultimate strength of the material. The model did not 

employ any damage initiation, damage progression, or element removal techniques. A simple 

bilinear stress-strain characteristic is shown in Figure 14.

Figure 14. Example Bilinear Stress-Strain Behavior

Although the buff strength test was initially to be performed quasi-statically, an explicit FE 

solver (Abaqus/Explicit) [14] was used in anticipation of the follow-on crippling simulation. An 

explicit solver was intended to simulate the crippling behavior of the car due to the expectation 

of nonlinear geometric and material behaviors. Because one goal of the elastic test was 

validation of the FE model that would be used to estimate crippling, it was important to ensure 

that the elastic model used was substantially representative of the crippling model. An explicit 

solver was expected to simulate the crippling test to capture the plastic and crippling behaviors 

of the car; therefore, this solver was also chosen to execute the buff strength model. 
21

2.4.1 Boundary Conditions

Boundary conditions were applied to the FE model of Car 244 to simulate the support conditions 

of the test car within its frame. A lateral symmetry condition was applied along the longitudinalvertical midplane of the model. This boundary condition prevented any lateral motion of nodes 

along this plane. Because the boundary condition extends along the length of the car, it also 

serves to prevent gross lateral motion of the entire car.

Vertical support to the model was provided by nonlinear springs at the body bolsters where the 

secondary suspension attaches to the carbody. The nonlinear spring characteristic used in the 

model has a stiffness of 1x106 pounds/inch in compression and 1/1000 pounds/inch in tension. 

This prevents the car from moving downward, but offers only a small resistance to upward 

motion. In the physical car, the body is resting on the trucks. Thus, contact of the car body and 

the truck prevents downward motion of the car body, but the truck does not impede upward 

motion of the body. The car’s own weight serves to impede vertical uplift.

The spring at each body bolster is attached to the ground. The ground is represented by a rigid 

plate beneath each body bolster. This plate is free to move in the longitudinal direction, 

simulating the truck’s ability to roll down the track in response to the applied buff load. The 

ground is prevented from moving in either the lateral or vertical direction. An inverted view of 

the car, the suspension spring, and the ground plate at one body bolster location is shown in 

Figure 15.

Figure 15. Vertical Spring Assembly, 800-kip FE Model

Additional vertical constraint was provided at the back end buff lugs. Upon review of the test 

data it was apparent that the rear end of the car was limited in its ability to move downward but 

free to lift upward. As an approximation of this limitation, a vertical nonlinear spring was 
22

attached to the buff stop at the rear end of the car; this attachment offered a high resistance to 

downward motion of the buff stop but a very small resistance to upward motion. No such spring 

was used on the live end of the model.

In both the model and the test, longitudinal restraint was accomplished through the buff stops on 

the reaction end of the car. In the model, a zero-displacement boundary condition was applied to 

nodes on the rear buff stop to prevent longitudinal motion. Because the buff stops were not

prevented from pivoting during the test, the nodes used in the boundary condition were permitted 

to rotate in response to the applied load. The FE solver calculated the restraint force necessary to 

maintain zero longitudinal displacement at each of the nodes in this boundary condition.

On the live end of the car, a corresponding set of nodes on the buff stop was used to apply the 

load to the car. The nodes were given a prescribed displacement-time behavior. The FE solver 

calculated the longitudinal force needed to achieve the prescribed displacement. The analysis 

was run until the applied load reached 800 kips. The displacement boundary condition was only 

applied to the longitudinal degree-of-freedom on these nodes. The nodes were free to pivot as 

the structure responded to the applied load. The loading location on the live end buff stop of the 

FE model is shown in Figure 16. 

Figure 16. Loading Location on Live End Buff Stop, 800-kip FE Model 
23

2.5 Elastic Test Results and FE Model Validation

The elastic verification test of Car 244 was used both to verify the car’s structural integrity and 

to validate the FE model that would be used to estimate the crippling behavior of the car. The 

ETF procedures report provides target tolerances for validating a model with test data; those 

tolerances were used in comparing the results of the test with the results of the FE model. 

The key results that were compared between the test and the FE model are the longitudinal load 

versus displacement behavior, the vertical deformation shape, and the strains in key longitudinal 

members. There is very good agreement between the measured and modeled longitudinal load 

versus displacement behavior. The model results also indicate good agreement with the vertical 

mode of deformation of the tested car. The strain results for the center sill, side sills, and purlins 

have good agreement between test and analysis. The strain results from the roof rail and belt rail 

do not agree with the model as well as the results in the other longitudinal members. These two 

members are fairly lightly loaded members with thin cross-sections. In general, the FE results 

effectively captured the behavior of the tested car. The model has been determined to be suitable 

for use in simulating the crippling tests. 

2.5.1 Verification of Quasi-Static Behavior in FEA

Because the line-of-draft testing and modeling effort was meant to validate the FE model that 

would be used to simulate crippling, the same explicit solver was used to execute both models. 

It was important to verify that the line-of-draft model was sufficiently free of dynamic effects to 

be considered quasi-static before comparing test results with analysis calculations. The ETF 

report provides two procedures for determining if a model may be considered quasi-static. 

Although only one method needs to be used as a part of the ETF’s procedures, both methods 

were used in this research program. The following two conditions are taken directly from the 

ETF’s report:

ETF Condition One

For a given simulated load rate, the load at the live end of the model should be the same 

as the load at the fixed end. Load at the reaction end may vary by up to +/-5 percent of 

the load at the live end of the model for the analysis to be considered quasi-static.

ETF Condition Two

The ratio of kinetic energy-to-strain energy within the structure should be small (< 5

percent). The ratio of kinetic energy-to-strain energy may exceed 5 percent during the 

first 10 percent of the total simulation time without invalidating the analysis as quasistatic.

Evaluation of Condition One

Loading in the 800-kip model was accomplished by applying a prescribed displacement-time 

boundary condition to a row of nodes on the live end buff stops. The FE solver calculated the 

force that was applied to each node to achieve the desired displacement. Similarly to the loading 

on the live end, a row of nodes on the rear end buff stops was prevented from moving 

longitudinally. The solver calculated the force that was applied to each node to prevent it from 
24

moving. The total live end load and total restraint load are plotted alongside a +/-5 percent

envelope in Figure 17.

Figure 17. Live Load and Reaction Load with +/-5 % Envelope, 800-kip Elastic FEA

This figure shows that at loads above approximately 200 kips the live load and reaction load are 

very close and well within the 5 percent envelope on the live end force. Because the envelope 

gets larger as the applied load is increased, at low loads the reaction end load may be outside the 

envelope. Both the live and reaction end loads are noisier at the beginning of the analysis but 

stabilize as the load magnitude increases. One possible alternative to applying a 5 percent

envelope to the live load that varies in magnitude over the course of the simulation is to apply a 

constant-width envelope of 5 percent of the target load. In the case of the 800,000-pound load,

this means a constant width envelope of +/-40 kips. The live and reaction loads are plotted 

against this envelope in Figure 18. The simulation is deemed to be quasi-static using ETF 

Condition One.

Figure 18. Live Load and Reaction Load with +/-40 kip Envelope, 800-kip Elastic FEA
25

Evaluation of Condition Two

Because the load applied to the car was dynamic, the FE solver calculated the total kinetic 

energy in the model. The solver also calculated the total internal energy, which is the total strain 

energy in the model. The ratio of kinetic energy to internal energy in the model of the 800-kip 

buff simulation is plotted in Figure 19 against the normalized time of the analysis. The energy is 

plotted on a logarithmic scale because it decreases by multiple orders of magnitude as loading 

progresses.

Figure 19. Ratio of Kinetic to Internal Energies, 800-kip Elastic Model

The car was loaded in two steps. In the first step, gravity was applied and the car responded by 

settling. In the second step, the longitudinal load was applied. In both steps, the energy ratio 

quickly drops below the 5 percent limit. This behavior indicates that the model quickly stabilizes 

and the dynamic effects are minimal, especially at the critical load of 800 kips. The simulation is 

deemed to be quasi-static using ETF Condition Two.
26

2.5.2 Load-Displacement Results

The applied load is plotted against the change in the car’s length in Figure 20 for both the 800-

kip test and the corresponding FE analysis. A +/-10 percent envelope on the test load magnitude 

is also plotted in this figure. This figure shows good agreement between the overall longitudinal 

load-displacement behavior measured during the test and calculated during the analysis.

Figure 20. Load-Displacement Data for 800-kip Test and FE Analysis, Car 244

2.5.3 Vertical Displacement Results

Vertical displacement of the underframe of the car was measured during the test by a series of 

string pots. The locations and channel names of the string potentiometers used in this test are 

shown in Figure 10. The vertical displacement along the length of the car is plotted in Figure 21

at a series of load increments. In these two plots, the horizontal axis has its datum at the end of 

the side sill at the live end of the car. The distance between each instrumented location and the 

live end datum is given as the initial distance between these points and is not updated to reflect 

any longitudinal travel by the instrumented point of the car. The data points correspond to the 

instrumented locations, and the lines have been interpolated between adjacent locations. The left 

side plot shows the data measured during the 800-kip test, and the right side plot shows the 

calculated vertical displacement at the corresponding locations in the FE model. Each plot 

marks the location of the live and restraint end body bolsters where the car is supported in both 

the test and the model. 
27

Figure 21. Vertical Displacements along Length of Car, 800-kip Test (L) and FEA (R)

Figure 21 indicates a strong similarity between the global vertical behaviors of the car in both the 

test and the analysis at a given load. At the live end, the car moves downward in both test and 

analysis. At the live end truck, the displacement crosses from downward to upward in both sets 

of results. This indicates the live end truck is acting like a pivot for the car body. At the rear 

end, the truck does not act as a pivot. Figure 21 demonstrates that the FE model is capturing the 

global bending behavior of the car under line-of-draft loading conditions. 

The vertical displacement measurement from each string pot in the 800-kip test was compared 

with the calculated vertical deflection at the corresponding location in the FE analysis and, for 

most locations, good agreement was observed between the two results. The full set of 

comparison plots is provided in Appendix D. The vertical displacement measurements at the 

three locations on the center sill between the trucks of the car are plotted against the FE results in

Figure 22, Figure 23, and Figure 24. At all three locations, the FE results are within +/-10

percent of the test data when the load is greater than approximately 200 kips. Similar to the +/-

10 percent envelope applied to the longitudinal force-displacement results, the envelope applied 

to the vertical displacement data increases in width as the displacement value increases. The FE 

results are outside the +/-10 percent envelope at low loads because of the small displacement 

magnitude measured and the correspondingly small envelope.
28

Figure 22. Vertical Deflection of Center Sill at A-end of Car, 800-kip Test

Figure 23. Vertical Deflection of Center Sill at Center of Car, 800-kip Test
29

 Figure 24. Vertical Deflection of Center Sill at B-end of Car, 800-kip Test
30

2.5.4 Longitudinal Strain Results

A total of 64 longitudinal strain gages were installed on Car 244 for the 800-kip test. These 

gages were installed on nine longitudinal members (Figure 12) at six cross-sections along the 

length of the car (Figure 11). The complete set of strain gage results is provided in Appendix C. 

The ETF report provides a target tolerance of +/-20 percent for validating an FE model using 

strain data. That value is used for comparing the strain data with the calculated strains in the FE 

model. 

The strain results discussed in this section are organized by structural member. For each 

member, the strain measurement at each location on that member is plotted against the 

longitudinal location of the corresponding strain gage. For strain data, the longitudinal datum in 

the elastic test of Car 244 is the center of the restraint end body bolster. Because of the 

orientation of the car within the test frame, the following strain-versus-distance graphs have the 

restraint end of the car at the left (i.e., small distances) and the live end of the car at the right 

(i.e., at the large distances). The strain measurements plotted in this section have all been 

recorded at an applied load of 800 kips. In each plot, the longitudinal strain along the length of a 

given member has also been calculated in the FE model and plotted alongside the measured data. 

The test data appear as a series of discrete points and the FE model data as a continuous line.

Figure 25 is a plot of the longitudinal strain in the center sill under a load of 800 kips. At each 

cross-section, the center sill was instrumented with 4 strain gages: top left, top right, bottom left, 

and bottom right. Each plot in the figure contains three data series: test data from the left side of 

the member, test data from the right side, and the calculated strain along the length of the 

member in the FE analysis. The error bars plotted for each point of test data represent the ETF’s 

adopted tolerance of +/-20 percent.

Figure 25. Strain in Bottom (Left) and Top (Right) of Center Sill at 800 kips, 800-kip Test 

and FEA 

The longitudinal strains obtained from the FE analysis agree well with the strains measured in 

the test. At all locations on the center sill, the FE results are within the 20 percent envelope on 

the test data. Additionally, both the test measurements and the FEA results indicate a fairly 

stable state of strain in the center sill under a load of 800 kips. The FE results indicate a steep 

strain gradient at the ends of the center sill. The center sill ends at the body bolster at each end 

of the car. Although the strain results are within the tolerance at these locations, the presence of 

such a steep gradient underscores the need for careful strain gage placement in a test article. In 
31

areas of high gradient, moving the strain gage by only a few inches could result in a large

difference in measured value.

Figure 26 is a plot of the longitudinal strain in the side sills under a load of 800 kips. The solid 

line represents the FE results along the length of the side sill, and the points represent the 

measurements recorded at the strain gages at each location during the test. Although the FE 

result exhibits more peaks and valleys than the calculation for the center sill, the strain level is 

roughly constant in the side sill under a load of 800 kips. This “noise” is likely seen in the model 

due to the presence of many vertical wall supports and floor members that are attached to the 

side sill. The test data indicate good agreement with the model predictions. As was observed in 

the center sill strain results, the side sill test data show similar levels of strain in the left and right 

sides of the car, indicating that both side sills are carrying roughly equal loads. The decrease in 

strain that occurs at distances between 400 and 450 inches, as seen in the model results,

corresponds to the location where a doubler plate had been added to the side sill to act as a patch 

over two small cracks that were discovered during inspection of the car prior to the test. 

Figure 26. Strain in Side Sills at 800 kips, 800-kip Test and FEA

Figure 27 is a plot of the longitudinal strain in the purlin under a load of 800 kips. The FEA and 

test both exhibit the same arched shape. Because the 800-kip compressive load is applied along 

the line of draft, the car experiences both compression and bending. The underframe of the car is 

placed in compression, while the bending stresses that develop in the roof result in tensile 

stresses. However, the FEA results indicate a higher tensile strain than the strains measured in 

the test, which suggests that the tested car develops lower bending stresses in the roof than were 

developed in the model. Overall, however, the model is capturing the behavior of the tested car. 

The test results show very good agreement between the measurements on the left purlin and the 

right purlin of the car, indicating that the load is being shared equally between the left and right 

sides of the car. The left and right side measurements are nearly the same at each location, 

leading the two data points to overlay one another.
32

Figure 27. Strain in Purlin at 800 kips, 800-kip Test and FEA

Figure 28 is a plot of the longitudinal strain in the belt rail under a load of 800 kips. In this 

particular car, the belt rail is a relatively thin z-shaped member located just below the window 

line (see Figure 12). The belt rail carries relatively little load compared to the members making 

up the underframe. The FE results indicate a relatively constant level of strain along the length 

of the member, with intermittent peaks corresponding to locations where wall supports are 

attached to the belt rail. The test results indicate more variation in the strains measured in the 

belt rails than the model. The test results also indicate differing levels of strain in the test car’s 

left and right side belt rails. 

Figure 28. Strain Results in Belt Rail at 800 kips, 800-kip Test and FEA

Figure 29 is a plot of the strains along the length of the roof rail from the test and from the 

analysis under a longitudinal load of 800 kips. The roof rail is a fairly thin L-shaped member 
33

located above the window line in this car’s design (see Figure 12). In both the test and the 

analysis, the roof rail indicates a low state of stress (for steel, +/-100 microstrain is 

approximately equal to +/-3 ksi). In the FE model, the roof rail is under a fairly constant low

level of tensile strain. The intermittent peaks correspond to the locations of roof stiffeners. In 

the test data, the strain state ranges from slightly compressive to slightly tensile. The left and 

right sides of the test car exhibit slight differences in strain level at each location.

Figure 29. Strain Results in Roof Rail at 800 kips, 800-kip test and FEA

A total of 64 longitudinal strain gages were installed on the major structural members of Car 244 

during the 800-kip buff strength test. Of these, eight strain gages reported strains that 

corresponded to stresses less than 2200 psi. This measurement is less than 4 percent of the yield 

strength for the materials to which they are attached. These eight gages were all located on the 

belt or roof rails. Because of the low stress reported by these gages, they are omitted from the 

statistical assessment performed in this section.

For the remaining 56 strain gages used in the test, the stress measured in the test was compared 

with the stress at the corresponding location in the FE model. The difference between the two 

values was normalized by the measured stress. The resulting percentage differences between the 

test data and the FE results for the strain data are plotted in Figure 30.
34

Figure 30. FE Strain Data Compared with Test Strain Results, All Gages in 800-kip Test 

The ETF has established a threshold of +/-20 percent for comparing strain gage data with strain 

results in an FE model. As seen in the figure above, 37 out of 56 gages fall within the threshold. 

The majority of the gages that fall outside of this range were installed on the roof rail and the belt 

rail, which indicated poor agreement with the FE model in this test and low stress/strain. 

If the strain gages considered in the comparison between test and model are limited to the 

longitudinal members with the largest load-carrying capacity (i.e., the center sill, side sills, and 

purlin), a total of 42 gaged locations remain. The histogram in Figure 31 shows the distribution 

of strain levels at these 42 locations in the test and in the analysis. The same 37 gages included 

in the previous figure fall within the +/-20 percent threshold. Only five gages fall outside the +/-

20 percent threshold when the comparison is limited to the center sill, side sills, and purlins.
35

Figure 31. FE Strain Data Compared with Test Strain Results, Limited Gages in 800-kip 

Test

Details on the five gages that are outside the +/-20 percent range are shown below, in Table 4.

Three of the five gages that are outside the +/-20 percent range reported strains that are less than 

22 percent different from the model’s estimates at the corresponding locations. Although the 

differences are outside the +/-20 percent envelope, the exceedance is very small. These values 

may be within the uncertainty introduced into the measurement either through the precision of 

the instrumentation or the precision of the model. The remaining two gages provided 

measurements that are different from the model’s calculations by 30 percent or more. These 

gages are located on the left and right side sills at cross-section 6, the cross-section nearest to the 

live end of the car. These data points can be seen at the far right of Figure 26. As shown in this 

figure, the model reports a very high strain gradient in this region, owing to a change in crosssection of the side sill. 

Table 4. Strain Gages Outside of +/-20 % Threshold, 800-kip Test

Channel 

Name

Location Delta Strain

(FEA-Test)/(Test)

Comments

S1PR Cross-Section 1, Right Purlin 20.1 % Slightly outside +/-20 %

S2PL Cross-Section 2, Left Purlin 20.2 % Slightly outside +/-20 %

S5PL Cross-Section 5, Left Purlin 21.7 % Slightly outside +/-20 %

S6SSL Cross-Section 6, Left Side Sill 31.5 % High strain gradient area (see 

Figure 26)

S6SSR Cross-Section 6, Right Side Sill 30.0 % High strain gradient area (see 

Figure 26)
36

The stress/strain measurements made during the 800-kip test were compared with the 

stress/strain calculations made during the simulation of the 800-kip test. With the exception of 

the roof rail and belt rail, which experienced fairly low levels of stress in the test, the remaining 

locations on the center sill, side sills, and purlins exhibited good agreement between test and 

analysis. The FE model appears capable of capturing both the global deformation behaviors of 

the tested car and the stress states of the major longitudinal load-carrying members.
37

3. Crippling Test Setup

Two crippling tests were performed in this research program. A limited-instrumentation 

“shakedown” test of Pioneer 248 was conducted at TTC on June 15, 2011. The purpose of this 

test was to evaluate the operation of a newly installed hydraulic loading system, determine that 

the test frame was capable of loading and restraining a car simultaneously at the floor and roof 

levels, assess the procedures that had been developed for performing a crippling test, and 

examine the response of a passenger car under crippling conditions. Because Car 248 had 

structural damage likely caused by a previous dynamic testing program, this car was chosen for 

the limited-instrumentation test. The test frame was instrumented to measure the applied load 

and the stroke length of the hydraulic actuators introducing that load.

A fully instrumented crippling test was conducted on June 21, 2011, at TTC. This second test 

used Pioneer 244 as the test article. This car was fully instrumented with string potentiometers 

and strain gages, and the test frame was instrumented with load cells and displacement 

transducers. 

3.1 Crippling Test Description

In both crippling tests, the desired load scheme was to introduce compression loads into the car 

at the ends of the collision load path. Because each Pioneer car was equipped with a CEM 

system, the points where the CEM elements attached to the occupied volume were chosen as the 

load and restraint locations. For this particular CEM system design, these elements included two 

floor-level energy absorbers and two roof-level energy absorbers at each end of the car. Pioneer 

248, with its CEM system indicated, is shown in Figure 4.

Each car was installed into a test frame and remained on its trucks during the test. The test frame 

was designed to enable simultaneous loading of a structure at two different heights. In the case 

of the Pioneer cars, these heights correspond to the roof and floor of the car. Car 248 is shown 

within the test frame in Figure 32. 

Figure 32. Car 248 in Test Frame, Crippling Test
38

The energy absorbing components and endframes at each end of each car were removed to allow 

for loads to be applied directly to the energy absorber support structures at the ends of the 

occupied volume. The support structures are the locations where collision loads would be 

introduced into the occupied volume and are therefore the end points along the collision load 

path. The roof and floor loading locations are shown on one end of the car in Figure 5.

In both crippling tests, the car was loaded simultaneously at the floor energy absorber supports 

and the roof energy absorber supports. Four independent hydraulic actuators were used to apply 

load at the four locations. A displacement control scheme was used so that the four hydraulic 

actuators maintained equal displacements during the loading of the car. The amount of force 

exerted by each actuator was dependent on the stiffness of the car’s structure and was allowed to 

vary from actuator to actuator.

Because of the need to simultaneously load the car at the floor and roof levels, the load frame 

used in the crippling tests is significantly different from the load frame used in the 800-kip buff 

strength test. The crippling load frame consisted of four longitudinal beams, two at the floorlevel and two at the roof-level of the car, as seen in Figure 32. At the floor-level and the rooflevel, a lateral restraint block was installed between the two longitudinal beams. This lateral 

block provided a support for the hydraulic actuators on the live end of the car and a bearing 

surface for the load cells at the restraint end of the car. The roof-level arrangement at the 

restraint end of the car is shown in Figure 33. A similar setup is used at the floor level of the 

restraint end, with 1,000 kip capacity load cells used in place of the 500 kip capacity load cells 

used at the roof.

Figure 33. Restraint End Roof Setup in Crippling Tests
39

3.2 Description of Test Articles

3.2.1 Pioneer Car 248

Pioneer Car 248 has a testing history similar to that of Car 244. Car 248 was previously used in 

a series of impact tests, was retrofitted with a CEM system, and was then used in a second series 

of impact tests. However, Car 248 experienced more structural damage to its occupant volume 

during this series of impact tests than Car 244 did. Because of its existing damage, Car 248 was 

considered structurally compromised for use in a fully instrumented crippling test, as the 

damaged area could affect the crippling behavior of the car. However, Car 248 was used in the 

“shakedown” test to verify the performance of testing frame and hydraulic control system. 

Both Car 244 and Car 248 were inspected prior to the beginning of this test program. Damage 

was found in several longitudinal members in Car 248. Damage to the two floor longerons was 

readily apparent during a walkthrough of the car and is noted on the left side of Figure 34. These 

two channels run the length of the occupant volume and both have an observable dent caused by 

high longitudinal loading in the previous impact tests. The floor damage is located in the 

vicinity of the sixth window from the live end of Car 248. 

Figure 34. Pretest Damage to Occupied Volume in Car 248

In the same area as the deformed longerons, the belt rail on the left side of the car had an 

observable wrinkle in it adjacent to the seventh window from the live end of the car. This 

damage was also likely caused by high longitudinal loading during the previous impact testing 

program. This damage is shown on the right side of Figure 34.

Because the testing methodology called for applying loads directly to the energy absorber 

support locations on the ends of the occupant volume, some of the CEM components of the car 

needed to be removed to provide access to these locations. At each end of the car, the endframe 

components were removed from the car. The primary energy absorbers were removed from the 

floor level of each end of the car, and the energy absorber supports had any remaining weld 

material ground down to provide a flat bearing surface for the load to be introduced into the car. 
40

Figure 4 shows the car with its energy absorbers and endframes intact, and Figure 5 shows Car 

248 in its crippling test configuration. 

3.2.2 Pioneer Car 244

Following the successful 800-kip elastic verification test of Car 244, the car was deemed 

structurally sufficient for use in the crippling test. The endframes of the car and the primary 

energy absorbing components were removed from the ends of the car to provide access to the 

loading locations at the ends of the occupant volume. A more detailed discussion of Pioneer Car 

244’s history is provided in Section 2.1.
41

3.3 Instrumentation

The shakedown test of Car 248 was intended to verify the capabilities of the newly installed load 

frame and hydraulic control system in supporting the car. It was also performed to verify the 

ability of the testing setup to successfully load a car to crippling and assess the test procedures to 

be followed. Because this was a preliminary test, only a limited number of instrumentation 

channels were used. The primary data recorded in this test were the applied load and stroke 

length of each live end hydraulic actuator and the restraint load at each restraint location. 

Laterally mounted string potentiometers were installed to monitor any lateral shift that may have 

occurred in the carbody during the test. The instrumentation used in this test is summarized in

Table 5.

Table 5. Instrumentation Summary for Shakedown Test of Car 248

Type of Instrumentation Number of Channels

500 kip Load Cell 4

1000 kip Load Cell 4

Displacement Transducer (within hydraulic actuator) 4

Pressure Transducer (within hydraulic actuator) 4

Lateral String Potentiometers 2

Total 18

In the crippling test of Car 244, instrumentation was used to measure the load-displacement 

behavior of the live end of the car, strains in key longitudinal structural members, and the 

vertical, lateral, and longitudinal displacements of several points on the underframe of the car. 

String potentiometers were installed at the rear end of the car to measure the stretching of the 

frame in response to the applied loads. A summary of the instrumentation used in the crippling 

test of Car 244 is provided in Table 6.

Table 6. Instrumentation Summary for Fully Instrumented Crippling Test of Car 244

Type of Instrumentation Number of Channels

500 kip Load Cell 4

1000 kip Load Cell 4

Displacement Transducers (within hydraulic actuators) 4

Pressure Transducer (within hydraulic actuators) 4

String Potentiometers 41

Uniaxial Strain Gages 76

Temperature Sensor 1

Total 134

A total of eight load cells were used in each crippling test. One load cell was placed in-line with 

each load application or restraint location so that the total load on both ends of the occupied 

volume could be measured. The names and locations for the eight load cells are listed in 

Table 7. 
42

Table 7. Load Cell Names and Locations, Crippling Tests

Channel Name Capacity Car End Side Height

Load Cell 1 1000 kips Live Left Floor

Load Cell 2 1000 kips Live Right Floor

Load Cell 3 500 kips Live Left Roof

Load Cell 4 500 kips Live Right Roof

Load Cell 5 1000 kips Restraint Left Floor

Load Cell 6 1000 kips Restraint Right Floor

Load Cell 7 500 kips Restraint Left Roof

Load Cell 8 500 kips Restraint Right Roof

The live end floor loading setup used in both crippling tests is shown in Figure 35. There are 

two hydraulic actuators installed at the floor-level with a load cell installed between each 

actuator and the energy absorber support on the car. A similar arrangement of hydraulic 

actuators and load cells is installed at the roof-level of the car. At the restraint end of the car,

load cells are installed between the roof and floor reaction points and the load frame. This 

arrangement allows the load through each load or reaction point to be measured independently. 

This load measurement arrangement was designed to help measure the load path traveled 

through the structure, as well as to ensure that the load introduced at the live end was only 

exiting the car structure through the designated reaction locations on the back end.

Figure 35. Live End Floor Load Setup

3.3.1 String Potentiometers in Car 244 Crippling Test

String potentiometers were used to measure the displacements of various points on Car 244. 

Two arrangements of string pots were used in this test. A single, longitudinally oriented string 

pot was installed between each loading or reaction point on the car and a ground point. These 
43

string pots were used to measure the longitudinal displacement of each load and reaction 

location. Exemplar longitudinal string pots are shown in Figure 36.

Figure 36. Typical Longitudinal String Potentiometer Setup, Car 244

The second string pot arrangement used in this test was a VLL array of string pots attached to a 

single point on the underframe of the car. In the crippling test of Car 244, a total of 11 VLL 

arrays were installed on the underframe of the car. At both ends of the car, arrays were placed 

on the side sills and the lateral member at the end of the car. Between the two body bolsters, 

VLL arrays were attached to the center sill of the car. Figure 37 shows the 11 locations 

instrumented with VLL arrays, as well as the names of the arrays in the crippling test of Car 244. 

This image shows an inverted view of the car taken from the FE model.

Figure 37. String Pot VLL Arrays on Car 244 (Underside View)
44

3.3.2 Strain Gages in Car 244 Crippling Test

Uniaxial strain gages were installed on Car 244 prior to the 800-kip elastic test. These gages 

were placed on the major longitudinal structural members of the car at six cross-sections. The 

six cross-sections are shown in Figure 11, and the instrumented members at each cross-section 

are shown in Figure 12. These same locations were instrumented during the crippling test of Car 

244. In addition to these locations, gages were added in the vicinity of the floor and roof energy

absorber supports at the live and restraint ends of the car. These gages were added to measure 

the local strains at the ends of the collision load path, where load is introduced or reacted through 

the occupant volume.

At the floor-level, two strain gages were added to each of the four energy absorber supports, for 

a total of eight floor-level strain gages. The first location instrumented at each support is on the 

longitudinal channel supporting the lateral face where the load was applied. The second location 

instrumented with a strain gage at each floor-level support was on the longitudinal channel 

inboard of the first lateral member of the car. The strain gages at a floor-level energy absorber 

support are shown in Figure 38. 

Outboard Floor EA Strain Gage

Inboard Floor EA Strain Gage

Figure 38. Strain Gages at Floor-Level Energy Absorber Support

Strain gages were also placed at the roof energy absorber support location. The roof support 

consists of a longitudinal tube that passes through the bulkhead of the car and is attached to the 

roof structure within the occupant volume of the car. One additional strain gage was placed on 

the interior of the car’s roof just inboard of the bulkhead at each roof loading or restraint 

location. A typical location is shown in Figure 39.
45

Figure 39. Strain Gage at Roof-Level Energy Absorber Support
46

3.4 FE Modeling of Crippling Tests

FE modeling of the crippling tests was performed as a part of this research program. One goal of 

this research program was to demonstrate the efficacy of the proposed ETF methodology of 

validating an FE model with elastic test data, then using the FE model to simulate loading

conditions that include plastic deformation and crippling of the structure. The FE model was 

executed prior to conducting the crippling tests and was used to help design the tests. 

The FE model for the 800-kip buff strength test was used as a starting point for the crippling 

model. Because the endframes and CEM components were removed from the Pioneer cars prior 

to the crippling tests, these structures were removed from the FE model as well. The section 

thickness and plastic stress-strain behavior assigned to the center sill and the plastic stress-strain 

behavior assigned to the side sills were adjusted to reflect the properties used in the original 

Pioneer car FE model. Additionally, because the lateral-vertical symmetry used in the 800-kip 

model could suppress a potential lateral buckling mode in the crippling model, the existing 

structure was mirrored to create a full-car model. The full-car model contained a total of 

381,700 elements. This model is shown in Figure 40. 

Figure 40. FE Model Used in Crippling Analysis

The crippling analysis was executed using the commercial FE software Abaqus/Explicit. An 

explicit finite-element solver was chosen for the analysis because of the expectation of large 

deflections and of plastic deformation. The load was slowly applied dynamically as an 

approximation of the quasi-static test condition.

3.4.1 Boundary Conditions

Suspension springs were placed at each of the four body bolster locations where the trucks would 

interface with the physical car body to support the car vertically. The springs had the same 

nonlinear characteristics and ground attachment as were used in the 800-kip FE analysis. The 

car-spring-ground attachment is shown in Figure 15.

Four locations on the live end of the car were used as loading locations. The corresponding 

locations on the back end of the car were used to restrain the car. The car was loaded at the 

floor-level energy absorber supports and at the inboard end of the roof energy absorber tubes. At 

each of the four load locations, a single row of nodes was selected and given a prescribed 2 

inch/second longitudinal velocity. Because only the longitudinal motion was controlled and only 
47

a single row of nodes at each load area was selected, each load application or restraint location

was free to rotate as a result of this boundary condition. At the rear end of the car, corresponding 

rows of nodes were selected at each restraint location and were restricted from longitudinal 

motion. The nodes to which the boundary condition was applied are shown in Figure 41 for one 

end of the FE model.

Figure 41. Load and Reaction Nodes, Crippling test FE Model

Using this loading technique, the FE solver calculated the force necessary to maintain the 

prescribed displacement at each node on the live end. In this way, the applied (live) load is 

calculated independently for each load application location, thus replicating the test condition. 

Similarly, the software calculated the force necessary to maintain zero longitudinal displacement 

at the back end of the car for the reaction locations. Because only a single row of nodes was 

subject to the longitudinal boundary condition at each location, each load or restraint location 

was able to move laterally, vertically, and rotate in response to the loads that developed.

Because the loading technique used in the FE model does not allow the rear end of the car to 

displace in the longitudinal direction, the displacement measurements on the front end will be 

equal to the overall shortening of the car. Because the test frame in the physical test stretches in 

response to the loads applied to the car, the rear end of the test car has a nonzero longitudinal 

displacement. The FE results for load-displacement obtained using this approach can be directly 

compared with the test data only if longitudinal displacement data is collected at the rear of the 

car. Because longitudinal displacement was only measured at the live end of the car during the 

shakedown test of Car 248, the displacements measured in this test include the change in length 

of both the car and the test frame that was restraining it. To compare the load-displacement 

results from the FE model with the test data, the stretching of the frame must be incorporated 
48

into the model results. The longitudinal stiffness of each frame beam is estimated in Appendix B 

of this report.
49

4. Crippling Test and Analysis Results

Results are presented in this section for the crippling tests of Cars 248 and 244 as well as the FE 

analysis of the crippling load cases. These results include the load versus displacement behavior 

and discussion of the observed damage to both tested cars. Additional results from the test of 

Car 244 include strain measurements and displacements of the underframe. Results are 

compared, as necessary, between the two tested cars and the FE calculations.

4.1 Car 248 Shakedown Crippling Test Results

The limited-instrumentation shakedown test of car 248 was performed at TTC on June 15, 2011. 

An initial longitudinal load was used to settle the car within the test frame. The car was then 

loaded in 200-kip increments, with a return to a nominal load of approximately 20 kips between 

increments. Once a load of 800 kips was reached, the load was not actively removed between 

loading increments. The load was paused at 800 kips to permit the data recorded up to that point 

to be reviewed. Loading increased beyond 800 kips until the roof buckled, at which point the 

test was paused to permit inspection of the data collected and photographs of the car to be taken. 

Loading then resumed until crippling was reached. The load versus time data from the four live 

end load cells are plotted in Figure 42 for the final load increment, from the nominal load to 800 

kips, and then up to crippling. This figure also includes the sum of the four load cell 

measurements plotted against time.

Figure 42. Live End Loads versus Time, Car 248 Crippling Test

The load from each individual load cell is plotted against the corresponding actuator 

displacement in Figure 43 for the load cells at the live end of the car. As seen in this figure, the 

two load cells at the roof recorded very similar load-displacement characteristics. The roof’s

stiffness was approximately the same for both the left and right sides, and both sides reached 

nearly identical peak loads. The right load cell recorded a peak load of 185 kips, and the left 

load cell recorded a peak load of 183 kips.
50

Figure 43. Live End Loads and Displacements, Car 248

At the floor-level, both load cells recorded similar load-displacement characteristics. There is a

larger variance in peak load between the floor-level load cells than was seen at the roof-level. 

The right load cell recorded a peak load of 554 kips, and the left recorded a peak load of 607 

kips. The left side load begins to decrease at a smaller displacement than the load on the right 

side. This behavior may be an indication of the left side sill crippling before the right side sill. 

Because of the limited instrumentation employed in the test of Car 248, additional information 

on the progression of damage to the carbody is not available.

The loads in the individual load cells at the restraint end of the car are plotted in Figure 44

against the displacement of the corresponding actuator on the live end. The roof-level data are

nearly identical for the left- and right-side load cells, as it was at the front end of the car. At the 

floor-level, the left and right side data have more variance than at the front end. The left-side 

load cell records a higher load at zero displacement than the load cell at the right. However, 

even with this offset taken into account, the right side load does not reach the same level as the 

left side load at the floor. 
51

Figure 44. Restraint End Loads and Displacements, Car 248

The total applied load and total restraining load are obtained by summing the four load cell

measurements at each respective end of the car. The total applied load and total restraint load are 

plotted against the average live end actuator displacement in Figure 45. These two values are in 

excellent agreement with each other. This indicates that the test is being conducted in a quasistatic manner, free from dynamic effects, and that the full load applied to the front end of the car 

is exiting the structure through the rear restraints. The load does not appear to be exiting the car 

through any uninstrumented locations or “short-circuits” in the load path. 

Figure 45. Total End Loads for Car 248 Shakedown Test

The load-displacement response is approximately linear to above 800 kips. At a total load of 

approximately 950 kips, the roof structure begins to buckle and the total load decreases. Because 
52

the underframe has not yet exhausted its load-carrying capacity, the total applied load begins to 

climb again. At a global maximum of 1150 kips, the underframe begins to buckle, and the car 

has reached its crippling load.

4.1.1 Post-test Examination of Car 248

The car’s structure was examined following the test. The center sill, side sills, sidewalls, and 

roof structure had all experienced buckling in at least one location. 

Underframe Damage

The underframe of the car consists of three major longitudinal structural members: the center sill 

and the left and right side sills. These three members are attached by two types of lateral 

members: the body bolsters and cross-bearers. The body bolsters are located at the ends of the 

occupied volume and attach the trucks to the car body. A total of six cross-bearers are located at 

irregular intervals between the two bolsters. An underframe view of Pioneer 248, taken from the 

FE model of the car, is shown in Figure 46 with these structural members indicated.

Figure 46. Annotated Underframe for Pioneer Cars

Damage occurred on the center sill and both side sills of Car 248. Because of the limitedinstrumentation applied to this car during the shakedown test, it is unclear in what sequence the 

damage occurred. On the center sill, buckling was found to have occurred in two locations. The 

first location was approximately 44 inches toward the live end from the centerline of cross-bearer 

5. This buckle occurred in the top half of the web of the center sill. A second buckle was found 

approximately 29 inches toward the restraint end, measured from the centerline of cross-bearer 5. 

This buckle was in the lower flange of the center sill. Both of these buckles are shown in Figure 

47. 
53

Figure 47. Damage to Underframe of Car 248

A third area of damage was observed on the center sill of car 248. A small buckle and failed 

welds were observed at the intersection of the center sill and cross-bearer 5. This area of damage 

is shown in Figure 48.

Figure 48. Buckle and Failed Welds in Center Sill at Cross-Bearer 5, Car 248

Damage was observed on both the left and right side sills of Car 248. On both side sills, the 

damage was located longitudinally between cross-bearers 4 and 5. On both sides, the damage 
54

was in the form of a buckle to the lower portion of the side sill. Also, on both sides, the damage 

was proximate to observed damage in the sidewall structure of the car. The side sill damage is 

shown below in Figure 49.

Figure 49. Damage to Sides Sills of Car 248

Right Side Damage

Structural damage was observed to the right sidewall of car 248 following the crippling test. On 

the exterior of the car, the sidewall of the car buckled inward at approximately the midpoint of 

the seventh window from the live end of the car. This location corresponds with the buckle 

observed on the right side sill. The buckled sidewall is shown in Figure 50.

Figure 50. Damage to Right Sidewall, Car 248
55

Left Side Damage

The left sidewall of Car 248 also had a visible buckle on the outside of the car. The sidewall 

buckled outward at the seventh window from the live end and buckled inward above the eighth 

window. The outward buckle of the sidewall is in approximately the same area as the buckle in 

the side sill on this side of car 248. The sidewall buckle is shown in Figure 51. 

Figure 51. Damage to Left Sidewall, Car 248

The buckled area of the left sidewall was also examined from within the car. Because the 

interior finish and fittings had been removed, the structural members making up the skeleton of 

the superstructure were clearly visible in this area. On the left side of the car, the belt rail had 

fractured in two locations. The fractured belt rail is shown in Figure 52. These fractures 

occurred in an area of the car known to have had pre-existing damage. The pretest damage is

shown in Figure 34.

Figure 52. Fractured Left Belt Rail, Car 248
56

Roof Damage

The roof and sidewalls of Car 248 buckled during the test at a total applied load of slightly less 

than 1 million pounds. The roof buckled outward on both the left and right sides of the car. The 

roof buckle does not extend laterally across the car in a straight line, but follows a zigzag pattern 

from left to right. The roof buckle on each side of the car connects with the sidewall buckle on 

each side. The roof buckle is shown from above in Figure 53.

Figure 53. Buckled Roof, Car 248

4.2 Car 244 Fully Instrumented Crippling Test Results

The fully instrumented crippling test of Car 244 was conducted at TTC on June 28, 2011. In 

addition to measuring the live and restraint end loads and live end displacements as was done in 

the test of Car 248, this test included strain gages along key structural members and arrays of 

string potentiometers designed to measure VLL deflections in the underframe of the car. 

Additional displacement transducers measured the longitudinal motion of the live and restraint 

ends of the car, permitting the overall change in car length to be calculated.

The loading procedures used in the test of Car 244 were similar to the procedures used on Car 

248. In both tests, the car was secured within the frame by a small longitudinal load. The car 

was then loaded in 200-kip increments, with a return to a nominal load of approximately 20 kips 

between increments. Once a load of 800 kips was reached, the load was not actively reduced 

between increments. The actuators were pushed forward in 0.25-inch increments and then 

paused to allow the structure to settle. This approach was followed until crippling occurred. The 

individual live end loads and the total live end load are plotted against time in Figure 54 for the 

full sequence of loads.
57

Figure 54. Live End Loads, Car 244 Crippling Test

The loads measured by each of the four live end load cells are plotted against the displacement of 

each hydraulic actuator in Figure 55. The load cell names and locations for the test of Car 244

are the same as were used for Car 248, as shown in Table 7. Both of the floor-level load cells 

recorded approximately the same load-displacement characteristic, with the left-side load cell 

measuring a slightly higher peak load than the right-side. The two roof load cells also recorded 

very similar load levels. The right load cell measured a slightly higher peak load than the left.

Figure 55. Live End Loads and Displacements (Car 244 Crippling Test)

The load at each restraint location is plotted against actuator displacement for the corresponding 

location on the live end for the four restraint end load cells in Figure 56. At both the floor and 

roof restraint locations, the left and right side loads are roughly equal. Comparing the loads at a 
58

given displacement between the restraint end (Figure 56) and the live end (Figure 55), it is 

apparent that some portion of the load that is introduced to the car through the floor at the live 

end is being reacted through the roof at the restraint end of the car. The peak load in each floor 

location on the live end is approximately 600 kips, while the peak load in each floor location on 

the restraint end is slightly greater than 500 kips.

Figure 56. Restraint End Loads and Displacements (Car 244 Crippling Test)

In Figure 57, the total applied load on the live end of the car and the total reaction load from the 

restraint end of the car are plotted against the average displacement of the actuators on the live 

end. The live end and restraint end loads are approximately equal throughout the entire test. 

This verifies that the test is being run in a quasi-static manner, free from dynamic effects. 

Additionally, this result indicates that the longitudinal load is entering and exiting the car 

through the load cells without experiencing losses through any noninstrumented load paths.

Figure 57. Total End Loads for Car 244 Crippling Test
59

The results from the crippling test of Car 244 are similar to the results from Car 248. The live 

end load versus actuator displacement from each car is plotted in Figure 58. In both cars, the 

roof structure buckles at a load of approximately 1 million pounds. In Car 248, the actual 

buckling load is slightly below 1 million pounds and in Car 244 this load is slightly above 1

million pounds. Because the underframe structure has not been compromised at the roof 

buckling load in either car, as the displacement continues to increase, the load is able to increase 

as well. Car 248 had a crippling load of 1.15 million pounds and Car 244 had a crippling load of 

more than 1.19 million pounds. 

Figure 58. Load-Displacement Behavior for Car 248 and Car 244

4.2.1 Post-Test Examination of Car 244

Following the crippling test of Car 244, the structure of the car was inspected for damage. 

Damage was observed on the center sill, the side sills, and both sidewalls of the car. The damage 

to Car 244 occurred primarily between the live end of the car and the lateral-vertical midplane of 

the car. The conventions used in reference to “left” and “right” are the same as were used in the 

discussion of the damage to Car 248 and are shown in Figure 46.

Underframe Damage

The center sill buckled in multiple locations. One buckle occurred approximately 24 inches

toward the live end from the first cross-member on the underframe. The bottom flange of the 

center sill folded into a “z” at this location. Figure 59 shows two photographs of the damaged 

center sill at this location, as well as the location on the underframe where the damage occurred. 

The figures also show the proximity of the cross-section 5 strain gages to the buckled flange. 
60

Figure 59. Damage to Car 244 Center Sill (1)

The bottom flange of the center sill experiences a change in geometry at this point, decreasing 

from three built-up sections to two. The three layers of the center sill flange can be seen in both 

photographs of Figure 59. The third layer of material is not connected to the other two by a 

continuous weld, but through a series of spot welds. This discontinuous connection allows two 

layers to fold and deform while the third layer remains straight.

A second buckle occurred on the center sill approximately 44 inches toward the restraint end 

from the first cross-bearer. This location experienced buckling primarily in the top flanges of the 

center sill. Two photographs of the damage, as well as the damaged location on the underframe 

of the car, are shown together in Figure 60. The photographs in this figure also show the 

proximity of the cross-section 4 strain gages to the damaged area of the center sill. A second, 

similar buckle in the top flange of the center sill was observed approximately 29 inches toward 

the A-end from the second cross-member.

Figure 60. Damage to Car 244 Center Sill (2)
61

Figure 61 shows the damage to the side sills of Car 244. On the left side, the side sill buckled at 

a point approximately 13 inches toward the restraint end from the first cross-bearer. On the right 

side, the side sill buckled at approximately 68 inches toward the live end from the first cross 

bearer. Both side sills buckled laterally.

Figure 61. Damage to Car 244 Side Sills

Right Side Damage

Following the crippling test, large-scale buckles in the sidewall of Car 244 were visible on the 

right side. The main sidewall buckle occurred between window 4 and window 5 on this side. A 

second buckle was observed in the vicinity of window 2. In this area, a rectangular cutout in the 

outer skin of the car had been made to permit material testing during a previous testing program. 

The skin of the car buckled in the area around this cutout. The large buckle and this second 

buckle are both shown in Figure 62.
62

Figure 62. Damage to Right Side of Car 244

The damage to the right side of Car 244 was also inspected from the interior of the car. The 

sidewall between windows 4 and 5 protruded into the interior of the car by several inches. The 

belt rail in this region exhibited a gradual deformation without any sharp kinks or buckles. The 

right-side interior of the car is shown in Figure 63.

Figure 63. Damage to Right Side Interior of Car 244
63

Left Side Damage

The sidewall on the left side of Car 244 buckled over a large region of the car. At window 3, the 

sidewall buckle is outward and at window 5 the sidewall buckle is inward. The damage to the 

right side of the car was more localized than the damage to the left side of the car. The left side 

damage is shown in Figure 64.

Figure 64. Damage to Left Side of Car 244

This damaged area was inspected from the interior of the car as well as the exterior. The belt rail 

on the left side of the car was buckled beneath window 3. The vertical supports below this 

window were also buckled. This damage can be seen in Figure 65. 

Figure 65. Damage to Left Side Interior of Car 244
64

Roof Damage

The roof buckled during the test of Car 244 in a manner similar to the roof of Car 248’s 

buckling. In both cars the roof buckled at a load of approximately 1 million pounds. As was the 

case with Car 248, the roof on Car 244 did not buckle laterally across the car, but buckled in a 

zigzag pattern across the width of the car. An overhead view of the roof buckle is shown in 

Figure 66.

Figure 66. Roof Buckle in Car 244
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4.3 FE Model Results

The FE model of the crippling test case was executed before the shakedown test of Car 248 and 

its results were used to prepare and execute both crippling tests. A single analysis was used to 

simulate both crippling tests. The model represented Car 244 and included the crack patches that 

had been installed prior to the elastic verification test. The results of this analysis are compared 

with the results from both the crippling test of Car 248 and the crippling test of Car 244.

4.3.1 Load-Displacement Results

Load versus displacement data were obtained independently for each loaded location on the live 

end of the car in the crippling analysis. Figure 67 shows the load-displacement behavior 

calculated by the FE analysis for each of the four live end load locations. In this figure, the 

horizontal axis represents the total shortening of the car.

Figure 67. Live End Loads by Location (Crippling FEA)

A corresponding set of load versus displacement characteristics were generated for the restraint 

end of the car. These four characteristics are shown in Figure 68. Figure 67 and Figure 68

indicate that the load being reacted and the load being introduced into the car at the 

corresponding live end location are approximately the same. These results show the same 

qualitative behavior as was seen in the crippling tests of Cars 248 and 244.
66

Figure 68. Restraint End Loads by Location (Crippling FEA)

4.3.2 Verification of Quasi-Static Behavior

In the ETF’s report, two criteria are established for determining whether a slow, dynamic 

analysis is sufficiently free from dynamic effects to be considered quasi-static. While an 

analysis that meets only one of the two criteria qualifies as quasi-static, both methods of 

evaluation were used to examine the FE model in this study. The following two conditions are 

taken directly from the ETF’s Report:

ETF Condition One

For a given simulated load rate, the load at the live end of the model should be the same 

as the load at the fixed end. Load at the reaction end may vary by up to +/-5 percent of 

the load at the live end of the model for the analysis to be considered quasi-static.

Evaluation of Condition One

A displacement boundary condition was used to apply loads to the four live end locations in the 

FE model. The FE solver calculates the force that must be applied at each location to maintain 

the prescribed displacement. In this way, the load and displacement behavior at each live end 

location is calculated. 

Similarly, at the back end of the car a zero-displacement boundary condition is enforced at each 

reaction location. The software calculates the force that must be applied to maintain zero 

displacement at the selected locations. The reaction load can then be determined for each of the 

restraint locations in the model. 

For the purpose of applying the quasi-static condition, the four loads applied to the live end are 

added together and plotted versus the displacement of the live end. The four loads at the back 

end are also summed and plotted against the displacement of the live end. Because the restraint 
67

end in the model cannot move, the live end displacement is the same measurement as the 

shortening of the car. A +/-5 percent envelope on the live end force is plotted alongside the two 

load-displacement characteristics in Figure 69.

Figure 69. Live Load and Reaction Load for Crippling Analysis

ETF Condition Two

The ratio of kinetic energy to strain energy within the structure should be small (< 5%). 

The ratio of kinetic energy-to-strain energy may exceed 5 percent during the first 10

percent of the total simulation time without invalidating the analysis as quasi-static.

Evaluation of Condition Two

Because an explicit FE solver was used to estimate the crippling load, the load that is applied is 

dynamic. The solver calculates the total amount of kinetic energy in the system, as well as the 

internal (strain) energy. Because the model initially experiences very little deformation, the ratio 

of kinetic energy to internal energy may exceed 5 percent for the first 10 percent of the 

simulation time. 

The ratio of kinetic energy to internal energy for the crippling simulation is plotted in Figure 70. 

The simulation consisted of two steps: a gravity step and a compression load step. The 

transition between the two steps is indicated by a dashed vertical line in this figure. The energy 

ratio is plotted on a logarithmic scale because this quantity varies over several orders of 

magnitude during the course of the simulation.
68

Figure 70. Ratio of Kinetic Energy to Internal Energy for Crippling Analysis 

Figure 70 shows that the ratio of kinetic energy to internal energy is well below 5 percent for 

nearly the entire length of the simulation, except for the initial portion of each step. Based upon 

either of the ETF criteria, the crippling analysis can be considered quasi-static.

4.3.3 Comparison of Car 248 Test Results with FE Results

The longitudinal load-displacement behavior was the primary output data collected in the 

shakedown test of Car 248. This data is compared with the FE analysis results to determine if 

the FE model is providing a reasonable estimation of the car behavior as observed in the test. 

Because longitudinal displacement data were only measured on the live end actuators during the 

shakedown test, the behavior of the test frame must be incorporated into the FE results before the 

test and analysis results may be compared with one another. Each longitudinal frame beam is 

treated as an axially loaded member and its stiffness is calculated in Appendix B. For a given 

load magnitude, this stiffness is used to calculate the deflection of each frame member. The 

overall actuator displacement is the sum of the change in car length (directly calculated by the 

FE analysis) and the deflection of the test frame obtained through this approximation. 

Figure 71 plots the load in the floor-level energy absorber supports in the test and the loads in the 

corresponding energy absorber supports in the FE model. There is generally good agreement 

between the floor-level load data from the test and the floor-level response of the FE model. The 

FE model is slightly stiffer than Car 248. The load through the left floor energy absorber support

in the model reaches a maximum load of 525 kips, and the load on the right floor energy 

absorber reaches a maximum load of 550 kips. 
69

Figure 71. Live Load at Floor for Test of Car 248 and FE Model

The live end load-displacement responses of the roof-level energy absorber supports are plotted 

in Figure 72 for both the test of Car 248 and the analysis. In both the test and the analysis, the 

roof reaches its maximum load at an actuator displacement of approximately 1.5 inches. The 

roof in the model exhibits a softer response than the roof of the test car. Additionally, the model 

has a lower maximum load of approximately 135 kips at each roof load point, compared with 

approximately 180 kips at each roof load point in the test.

Figure 72. Live Load at Roof for Test of Car 248 and FE Model
70

The four live end load cell data channels are added together to obtain the total live end load for 

Car 248. Similarly, the four applied loads on the live end of the FE model are added together to 

obtain the total applied load. The total end load from the test of Car 248 and the FE model are 

plotted in Figure 73 against the actuator displacements. 

Figure 73. Total Live Loads for Test of Car 248 and FE Model

There is good agreement between the FE results and test data up to the point where the roof 

buckles at a total load of approximately 1 million pounds. At this point, the load reported in the 

test and calculated in the FE model both drop. Because the underframe structure has not yet 

crippled in either case, the total applied load begins to increase as the actuator displacement 

continues to increase. Following buckling of the roof structure, the FE results are greater than 

the test results. The FE results reach a global maximum load of approximately 1.2 million 

pounds and Car 248 reaches a global maximum load of approximately 1.15 million pounds. 

These maxima occur at different actuator displacements, owing to the model being stiffer than 

Car 248 actually was following buckling of the roof. Additionally, because the stiffness of the 

load frame was estimated and added to the displacement results for the FE model, the apparent 

difference in displacement at the time of crippling may be partially due to this approximation.
71

4.3.4 Comparison of Car 244 Test Results and FEA Results

Load, strain, and displacement data for Car 244 were collected during its crippling test. These 

results are compared with the results obtained by the FE analysis results to determine whether 

the FE analysis is producing a reasonable approximation of the test results.

Because displacement data were measured at both the live end and the restraint end of Car 244, 

the frame stiffness does not need to be accounted for in order to compare test results with the FE 

results. The reduction in the car’s length was calculated by subtracting the displacement at the 

restraint end (owing to extension of the frame) from the actuator displacement at the live end of 

Car 244. Because the FE model was prevented from longitudinal movement at its restraint end, 

the displacements calculated at its live end are equal to the change in car length.

The floor-level loads from the test of Car 244 and the FE model are compared with one another 

in Figure 74. All four measurements follow approximately the same initial slope. At both the 

left and right FE locations the maximum sustained load is below the maximum load recorded 

during the test.

Figure 74. Live Load at Floor for Test of Car 244 and FEA

The live end load-displacement responses of the roof-level energy absorber supports are plotted 

in Figure 75 for both the test of car 244 and the FE analysis. Both the test results and the FE 

analysis results have the same shape. The model has an apparent lower stiffness in its roof than 

the test car did. The model reaches a lower peak load than the test on both the left and right 

sides. In both the test and the analysis, the roof reaches its peak load at approximately the same 

displacement. 
72

Figure 75. Live Load at Roof for Test of Car 244 and FEA

The post-crippling behavior of the roof is different between the test and analysis. In the test, 

both the left and right side channels record a sudden drop in load, followed by a more gradual 

decrease in load. In the FE analysis results, the peak is followed by a gradual drop in load.

The four live end load cell data channels are added together to obtain the total live end load

placed on Car 244. Similarly, the four loads on the live end of the FE model are added together 

to obtain the total simulated applied load. The total end load from the test of Car 244 and the FE 

model are plotted against the reduction in car length in Figure 76.

Figure 76. Total Live Loads for Test of Car 244 and FE Model
73

There is good agreement between the FE model and Car 244’s test data prior to the point where 

the roof buckles. Both the test and the analysis experience a drop in load when the roof has 

begun to cripple at a load of approximately 1 million pounds. Since the floor structure has not 

yet crippled, the total load can begin to rise again. In both the test and the model, the second rise 

in load is along approximately the same slope. Both Car 244 and the model have a global 

crippling load of nearly 1.2 million pounds. The FE model reached its crippling load after a 

reduction in length of approximately 1.9 inches and Car 244 reached its crippling load after a 

reduction in length of approximately 2.2 inches.

The results of the crippling test of Car 244 and the FE analysis are both qualitatively and 

quantitatively similar to the results from the crippling test of Car 248. The three forcedisplacement results (two tests, one analysis) are plotted together in Figure 77. In this figure, the 

horizontal axis represents the live end (actuator) displacement for all three results. Because Car 

244 and Car 248 were both tested within the same test frame, the actuator displacements may be 

directly compared. The FE results in this figure have been adjusted to include the estimated 

expansion of the test frame. The FE model reached its crippling load after an actuator 

displacement of approximately 2.2 inches. Car 244 reached its crippling load after an actuator 

displacement of approximately 2.8 inches, and Car 248 reached its crippling load after an 

actuator displacement of approximately 2.9 inches. 

Figure 77. Load-Displacement Behavior for Both Tests and Analyses

There are slight variations in each of the results plotted in Figure 77. The analysis result exhibits 

slightly higher roof buckling and crippling loads than the test of Car 248, but a slightly lower 

roof buckling load than Car 244. Car 248’s roof buckled at a load slightly below 1 million 

pounds, while Car 244’s roof buckled at a load slightly above 1 million pounds. Car 244’s 

crippling load of nearly 1.2 million pounds is slightly larger than the 1.15 million pound 

crippling load reached by Car 248. This is likely due to the damage known to preexist in Car 

248. The two crippling load magnitudes measured in the tests vary by approximately 50 kips, 

which is approximately 4 percent of 1200 kips. 
74

The FEA displacement results appear to correlate better in Figure 76 than in Figure 77. In Figure 

76, the horizontal axis represents the reduction in car length. This quantity is derived entirely 

from the results of the FEA and from test data for Car 244. In Figure 77, the horizontal axis 

represents the displacement of the actuators at the live end of the test cars. The FE results in this

figure must be adjusted to account for the stretching of the test frame. These two figures indicate 

that this approximation represents the behavior of the car well, up to the point of roof buckling. 

Beyond this point, the frame stiffness approximation results in an overestimate, resulting in an 

underestimation of the actuator displacement at a given amount of load.

4.3.5 Deformation Modes

In the FEA results the car first experiences buckling of the roof and sidewall structures. As seen 

in Figure 78, the roof buckle is a fairly long wavelength buckle, spanning from the sixth window 

to the eighth window. While buckling initiated at the roof and sidewalls, the underframe 

continued to carry load until the center sill reached its crippling load. In the FEA, the center sill 

buckled beneath the eighth window. The center sill also experienced a fairly gradual buckling, 

as can be seen in Figure 78. 

Figure 78. Deformed Shape of Crippled Car in FEA

In the FE model, buckling occurred at both side sills and on the center sill at approximately the 

same distance from the live end. In the model, each side sill experienced an inward buckling 

mode of its lower web and flange. The center sill buckled at its upper flange and web. The 

buckled center sill and one of the two buckled side sills are shown in Figure 79. The center sill 

has been given a different color from the other members to allow it to stand out in this figure.

Figure 79. Detail Showing Buckled Center Sill and Side Sill in FEA
75

In both the test of Car 244 and the test of Car 248, the center sill experienced buckling at several 

locations along its length. The buckling mode that occurred in the FE model, where the top 

flange of the center sill buckled, was also observed in both tests. Figure 80 shows an image of 

the undamaged underframe (taken from the FE model) with photographs of damage from each of 

the three cases indicated. The approximate location of each upper flange buckle on the center 

sill is indicated on the underframe. 

Figure 80. Center Sill Upper Flange Buckle in Car 244, Car 248, and FEA Result

4.3.6 Displacement Results

Displacement measurements were made between the underframe of Car 244 and the ground 

during its crippling test. At each instrumented location, a VLL array of string pots was used to 

capture motion in three directions. Displacement data were requested at the corresponding 

locations in the FE model. The string pot locations are indicated in Figure 37. The full set of 

string pot results from the crippling test of Car 244 is provided in Appendix D of this report.

The predominant deflections occurred parallel to the applied load, in the longitudinal direction. 

There is good agreement between the FE analysis and the test of car 244. An exemplar 

comparison between test and analysis is presented in Figure 81, which shows the longitudinal 

displacement measured at the center sill at the centerline of the car. The negative displacement 

indicates motion in the direction of the applied load in both the test and the model.
76

Figure 81. Longitudinal Displacement at Center Point of Car, Car 244 Test and FEA

Lateral displacement data were also collected during both the test and analysis. The lateral 

displacements were small compared to the longitudinal displacements for both the test of Car 

244 and the analysis. The car exhibited very little lateral motion prior to the buckling of the roof. 

Lateral motion is observed from the onset of roof buckling through unloading of the car. The 

largest magnitude of lateral deflection in the test was measured at the center sill at the centerline 

of the car. This result is plotted in Figure 82 alongside the FE results for the same location. 

Although the FE model was not constrained against lateral motion, it does not exhibit very much 

lateral motion. A small amount of lateral motion occurs once buckling begins to occur, as was 

the case with the car in the test.

Figure 82. Lateral Displacement at Center Point of Car, Car 244 Test and FEA

Vertical displacement was measured at the same locations as longitudinal and lateral 

displacements in the test of Car 244. While Car 244 exhibited significant bending deflection 

during the conventional buff strength test (Figure 21), the car demonstrated a different behavior 

in the crippling test. In the 800-kip test, the load was applied and reacted at the buff stops, 
77

within the draft sills. This single point load resulted in a significant bending moment developing 

in the car body. In the crippling test, load was applied to the energy absorber supports at the 

floor and roof levels. This loading scheme resulted in a smaller bending moment developing in 

the car, causing smaller vertical deflections to occur in the underframe.

The vertical displacement measured at each instrumented location on Car 244 is plotted against 

the distance of that instrumented location from the end of the side sill on the live end of the car in 

Figure 83. Each data series in this figure represents a “snapshot” of the mode of deformation at a 

particular load level. With a total applied load of 1 million pounds (1,000 kips) and less, the car 

experiences very little vertical deflection. Above 1 million pounds, buckling has started to occur 

within the body of the car. The largest deformations are measured near the live end of the car 

where the center sill crippled.

Figure 83. Vertical Displacement along Length of Car 244 in Crippling Test

An analogous plot was created for the FE results and is shown in Figure 84. As with the tested 

car, the FE model initially experiences very little vertical deflection. The test and the analysis

both experienced different initial modes of deformation. Where Car 244 exhibited an “M” 

shaped bending mode with 2 inflection points, the FEA results indicate a shallow inverted “U” 

shaped mode. This may indicate that the FE model is underweight compared to Car 244, as the 

center of the model experiences greater vertical uplift under small bending moments. 
78

Figure 84. Vertical Displacement along Length of FE Model in Crippling Simulation

As the load increased beyond 1 million pounds, both the model and Car 244 began to exhibit 

fairly large vertical deflections. Because Car 244 and the FE model experienced center sill 

crippling at different locations along their lengths, the vertical bending modes are somewhat 

different as crippling occurs. Buckling occurs further away from the live end of the car in the 

model than was observed in the test. The model also indicates smaller downward deflections 

than were recorded during the test of Car 244. 

4.3.7 Strain Results

Longitudinal strain measurements were made on the structural members shown in Figure 12. 

Selected strain results are discussed in this section of this report; the complete set of longitudinal 

strain data is provided in Appendix C.

Strain data were collected on the center sill at five cross-sections. At each cross-section one 

gage was placed on each quadrant of the center sill’s webs (upper left, upper right, lower left, 

lower right). Figure 85 is a plot of the longitudinal strain in the center sill as measured in the 

gages on the bottom half of the member. The horizontal axis indicates the undeformed distance 

between the datum of the car (the center of the restraint end body bolster) and each strain gage. 

The strains in this figure are the result of an 830-kip total load applied to the car. The error bars 

on the test data indicate a +/-20 percent tolerance on the measured test data. The strains 

calculated along the length of the center sill in the FEA result are plotted as a continuous line in 

this figure.
79

Figure 85. Longitudinal Strain in Center Sill at 830 kips, Crippling Test

The strain data measured in the test indicate a relatively constant level of strain in the center sill 

at this load. At each cross-section, the strain measured on the left and right sides of the center 

sill of the tested car are nearly equal. The FE results also indicate a constant level of strain along 

the length of the center sill. The peaks that occur along the plot of the FE result coincide with 

locations of the six cross members that connect the center sill with the side sills. At the ends of 

the center sill, the model indicates a steep strain gradient where the center sill ends at the body 

bolster. If this high gradient is present in the physical car as well as the model, it emphasizes the 

need to place strain gages with extreme care. A small difference in placement can result in a 

large difference in the strain measurement. Although the FE results are not within +/-20 percent

of the FE results at the left-most cross-section in this figure, the test and analysis results would 

overlay one another if the strain gage were placed a few inches closer to the restraint end.

A second plot of longitudinal strain versus distance along the center sill for the strain 

measurements in the bottom half of the web is shown in Figure 85. In this figure the strain 

measurements are taken at a total applied load of approximately 1.18 million pounds. This load 

is just prior to crippling in both the test and the model. The test data at 1.18 million pounds are

similar in appearance to the test data at a load of 830 kips (Figure 84) with the exception of the 

measurement location at approximately 600 inches. Because the datum point on this car is at the 

restraint end, this cross-section is the closest to the live end of the tested car. This set of center 

sill strain gages happened to be adjacent to an area of the center sill that buckled during the test 

(Figure 59).
80

Figure 86. Longitudinal Strain in Center Sill at 1180 kips, Crippling Test

The strain gages adjacent to the buckle indicate a very high level of strain in the center sill at a 

load just prior to crippling. However, even though the crippling load is a global measurement for 

the entire car, the strain data in the previous figure indicate that the center sill’s buckling is a 

localized behavior. The center sill remains elastic at the cross-section away from this local 

buckle even at a load just below the crippling load of 1.2 million pounds.

Figure 86 also contains the strain-distance results calculated from the FE model along the entire 

length of the center sill for elements in the lower half of the web. Except at the crippling crosssection, the FE results compare favorably with the test data. Because the FE model experienced 

crippling at a different location than Car 244, there is not a steep change in strain data at the 

same location as the test car. The FE model’s center sill buckled at a location adjacent to a 

cross-bearer on the restraint end of the car (Figure 78). A small inflection between 200 and 300 

inches can be observed in the FE results in Figure 86; this is the location where the incipient

buckle will cripple the model. 

While the FE model and the tested cars each experienced crippling at different locations, the 

overall crippling behaviors were very similar. Specifically, the global force-displacement 

characteristics and the sequences of structural failures were similar for all three results. In order 

to assess the strain behaviors of Car 244 and the FE model at the location where center sill 

buckling occurred, data from one location in the test but a different location in the model must be 

compared. Figure 87 shows an image of the crippled center sill from the FE model and a 

photograph of one buckled location on the center sill of Car 244. The approximate location of 

each of these areas of damage is indicated on a profile view of the undeformed car in this figure. 

Two elements are highlighted in the image of the center sill taken from the FE model, shown at 

the right in this figure. These two elements correspond to the approximate placement of strain 

gages on the web of the center sill of Car 244. Two such strain gages can be seen in the left hand 

side of this figure.
81

Figure 87. Crippling Locations for Strain Comparison, FEA (right) and Car 244 (left)

The strain versus applied load results from the crippled location on the center sill of Car 244 and

the FEA result are plotted in Figure 88. This figure shows the measurements from the four test 

strain gages on the left; the right shows the calculated strains in the FEA from four elements at 

the corresponding locations on the center sill at the buckle. 

Figure 88. Strain vs. Load Behavior at Center Sill Buckling Locations, Test (left) and FEA

(right)

In both the test and the analysis, the strain behaviors are very similar. In both cases, the four 

strain results overlay one another up to a load of approximately 1 million pounds. The inflection 

point at approximately 1 million pounds corresponds with buckling of the roof structure. 

Beyond this load the four strain results begin to diverge in both the test and the FEA. In the test, 

the two gages at the bottom of the center sill indicate a more rapid change in strain with 

additional load than do the two at the top. In the FE results, the two locations at the top of the 

center sill experience greater changes than the two locations at the bottom. Figure 87 shows that 

the FE results experienced a buckling in the top of the center sill while Car 244’s center sill 

buckled at its bottom. The strain gauges installed on the car during this test had a maximum 

capacity of +/-3,000 microstrain. Although the gage reports values up to -5,000 microstrain, 

these results have greatly exceeded the intended range of the strain gage.
82

5. Conclusions

FRA has sponsored research at the Volpe Center examining the OVI of passenger cars since 

2006. The ETF adopted criteria and procedures for evaluating OVI based, in part, on the results 

of this FRA research. In 2011, FRA performed a series of OVI tests as a means of evaluating the 

methodology developed by the ETF and developing confidence in the results obtained from 

applying the methodology. Two types of tests were performed in this series: a conventional 

800,000-pound buff strength test and two destructive crippling tests. A corresponding FE 

analysis was performed for each type of test. 

The test articles chosen for this program were two Budd Pioneer passenger cars that had been 

retrofitted with CEM systems during a previous FRA research program. These passenger cars 

were originally constructed to comply with the 800,000-pound line of draft load requirement. 

With the addition of the CEM components, these cars feature two different load paths for 

longitudinal loads: one load path for service loads and a different load path for collision loads. 

These cars represent an 800,000-pound compliant vehicle with a nonconventional collision load 

path. This particular design permitted the ETF’s criteria and procedures for collision-path 

loading to be used to evaluate the load capabilities of a vehicle designed to the conventional 

elastic load requirement.

A conventional 800,000-pound buff strength test was used to demonstrate that a passenger car 

that had been involved in a series of crash tests was still structurally sound. This test was also 

used to provide data for validating an FE model of the passenger car. Car 244 received minor 

repairs prior to this test, including the placement of a patch on each side sill over an area with 

small cracks. The car successfully met the requirements of the test, and the results were in 

satisfactory agreement with the FE model. The key results that were compared between test and 

model were the longitudinal load-displacement behavior, the vertical deflection mode, and 

strains in key longitudinal members.

Following the successful validation of the FE model with the 800-kip test data, the model was 

modified to represent the condition of the test car in the crippling test. In order to permit loads to 

be applied along the collision load path, the endframes and energy absorbing components of the 

CEM system were removed. These components were also removed from the FE model. The 

model was used to simulate loading of the carbody up to its crippling load; it estimated a 

crippling load of approximately 1.19 million pounds.

A newly constructed loading frame and hydraulic control system at TTC were used to perform 

the crippling tests. A shakedown test was performed to ensure the proper operation of the new 

system before the crippling test of Car 244 was performed. The shakedown test featured limited 

instrumentation installed on a car of similar design, Pioneer Car 248. The car was loaded until 

crippling occurred at a load of 1.15 million pounds. 

Following the successful shakedown test, the fully instrumented test of Car 244 was run. The 

instrumentation used in this test included displacement transducers on the underframe of the car, 

load cells at each loading and restraint location, and strain gages on key longitudinal members. 

Car 244 behaved similarly to Car 248 in reaching its crippling load. Both cars also experienced 

global behavior similar to the FE model, although there were differences in the locations where 
83

buckling occurred in each case. Car 244 had a measured crippling load of nearly 1.2 million 

pounds.

This research program has demonstrated that a carefully executed program of elastic testing and 

model validation is capable of estimating the crippling behavior of a passenger railcar. This 

program has also confirmed the sound technical basis for the OVI criteria and procedures 

adopted by the ETF. The results of the tests and analyses performed in this program indicate that 

the alternative OVI methodology provides an effective means of evaluating the OVI of passenger 

rail equipment.

85

6. References

[1] Petition of Capital Metropolitan Transportation Authority for Shared Lease and Waiver of 

Federal Railroad Administration Regulations. Docket No. FRA-2006-25040. 

[2] Petition of the Denton County Transportation Authority for Waiver Acceptance of nonCompliant Self-Propelled Rail Vehicles (Stadler GTW 2/6 Diesel Multiple Units). Docket No. 

FRA-2010-0180. 

[3] Petition of Peninsula Corridor Joint Powers Board/Caltrain for Approval of Mixed Use and 

Waiver of Certain Federal Railroad Administration Regulations. Docket No.FRA-2009-0124. 

[4] DesertXpress Enterprises, LLC’s Petition for Waivers from Federal Railroad Administration 

Regulations. Docket No.FRA-2010-0098. 

[5] Federal Register/Vol. 74, No. 156/ Friday, August 14, 2009/ Notices. Department of 

Transportation, Federal Railroad Administration [Docket No. FRA-2000-7257; Notice No. 56]. 

Railroad Safety Advisory Committee (RSAC); Working Group Activity Update. Page 41181.

[6] “Technical Criteria and Procedures for Evaluating the Crashworthiness and Occupant 

Protection Performance of Alternatively Designed Passenger Rail Equipment for Use in Tier I 

Service,” U.S. Department of Transportation Report No. DOT-FRA-ORD-11/22. Washington, 

DC: Federal Railroad Administration, Office of Railroad Policy Research and Development, 

October 2011.

[7] White, J.H., “The American Passenger Railway Car,” The John Hopkins University Press, 

1978.

[8] U.S. Department of Transportation, Federal Railroad Administration, “49 CFR Part 216 et 

al., Passenger Equipment Safety Standards; Final Rule,” Federal Register, May 12, 1999. 

[9] Carolan, M., Perlman, B.A., Tyrell, D., “Evaluation of Occupant Volume Strength in 

Conventional Passenger Railroad Equipment,” American Society of Mechanical Engineers, 

Paper No. RTDF2008-74026, September 2008.

[10] Carolan, M., Muhlanger, M., “Strategy for Alternative Occupant Volume Testing”

American Society of Mechanical Engineers, Paper No. RTDF2009-18025, October 2009.

[11] Carolan, M., Muhlanger, M.P. “Update on Alternative Occupant Volume Testing.” 

American Society of Mechanical Engineers, Paper No. JRC2010-36020., April 2010.
86

[12] Kirkpatrick, S., and MacNeil, R. “Development of a Computer Model for Prediction of 

Collision Response of a Railroad Passenger Car.” Proceedings of the 2002 IEEE/ASME Joint 

Railroad Conference, Institute of Electrical and Electronics Engineers, Catalog Number 

CH37356-TBR, 2002. 

[13] Jacobsen, K., Tyrell, D., and Perlman, A.B. “Impact Test of a Crash-Energy Management 

Passenger Rail Car.” American Society of Mechanical Engineers, Paper No. RTD2004-66045,

April 2004.

[14] Abaqus/Explicit Version 6.10. Dassault Systemes Simulia Corp., Providence, RI, USA. 

2010.

[15] MathCAD 15. Parametric Technology Corporation, 2011.
87

Appendix A. 

Estimated Car Stiffness

In the crippling tests of Pioneer 248 and 244, the displacement at each load point on the live end 

of the car was controlled so as to keep all four load points at the same displacement at any given 

point in time. Because the car was supported at the back end at the corresponding locations as 

on the front, the load was nearly entirely axial with little bending component. As a check on the 

FE results, the car was approximated as an axially loaded member and its stiffness was 

calculated.

For an axially loaded member:

∆=PL/AE (Eq. 1)

Where

∆ - change in axial length

P – applied load

L – member length

A – cross-sectional area

E – Young’s modulus

k=P/∆

Through rearrangement and substitution,

k=EA/L (Eq. 2)

The Budd Company calculated the Pioneer car to have an effective cross-sectional area of 30.8 

in2

. The length from the energy absorber supports on the live end to the energy absorber 

supports on the back end measures approximately 871.75 inches. The carbody is made of 

stainless steel, with a Young’s modulus of 3 x 107 psi. Substituting these values in Equation 2 

gives the estimated stiffness of the car as:

kcar = (3x107)(30.8)/(871.75) = 1,006 kips/inch

The estimated stiffness of the car is plotted against the applied load versus change-in-car-length 

data from Car 244 and the crippling FE analysis in Figure A 1.
88

Figure A 1. Estimated Car Stiffness and Reduction in Car Length Results
89

Appendix B. 

Estimated Frame Stiffness

During the shakedown test of Car 248, the only displacement measurements made were of the 

stroke length of each hydraulic actuator. Because the test frame expanded in response to the load 

transmitted through the car, the expansion of the frame must be taken into account when 

modeling the response of the system. The frame is made up of four longitudinal members: two 

upper beams and two lower beams. The stiffness of each type of member is calculated below.

Upper Member

Each beam is approximated as an axially loaded member. From Equation 2,

k=EA/L

For steel beams, Young’s modulus is 3 x 107 psi. The measured length of the frame, from lateral 

end restraint at the live end to lateral end restraint at the restrained end, is 1017.5 inches. The 

upper members are beams having a cross-sectional area of 20.6 in2

. Substituting these values in 

Equation 2 gives the estimated upper member stiffness as

kupper = (3x107)(20.6)/(1017.5) = 607 kips/inch

Lower Member

Each beam is approximated as an axially loaded member. From Equation 2,

k=EA/L

For steel beams, Young’s modulus is 3 x 107 psi. The measured length of the frame, from lateral 

end restraint at the live end to lateral end restraint at the restrained end, is 1017.5 inches. The 

lower members are beams having a cross-sectional area of 35.9 in2. Substituting these values in 

Equation 2 gives the estimated upper member stiffness as

klower = (3x107)(35.9)/(1017.5) = 1,058 kips/inch

System Stiffness

The four longitudinal beams making up the frame can be represented by a single spring of 

equivalent stiffness as follows:

kframe=(2 x kupper) + (2 x klower) = 3,330 kips/inch

The combined stiffness of the car and frame is referred to as the system stiffness. Because the 

hydraulic actuators and the frame are grounded at the live end, the load-displacement outputs of 

these actuators describe the overall system behavior.

1/ksys = 1/kcar + 1/kframe

ksys = 773 kips/inch

The estimated system stiffness is plotted against the load-actuator displacement results from the 

two crippling tests and the crippling FEA in Figure A 2. 
90

Figure A 2. Estimated System Stiffness and Load-Actuator Displacement Results
91

Appendix C. 

Car 244 Strain Data and FE Results

A total of 64 single-axis strain gages were installed for both the 800-kip elastic test and the 

crippling test of car 244. In the crippling test, additional strain gages were placed at the roof and 

floor energy absorber supports where the load was applied and reacted. The strain gage channel 

names are provided in Table A 1.

Table A 1. Strain Gage Channel Names and Locations

Channel Name Instrumented Member Location

S1CSBL Center Sill Cross-Section 1, bottom left

S1CSTL Center Sill Cross-Section 1, top left

S1CSBR Center Sill Cross-Section 1, bottom right

S1CSTR Center Sill Cross-Section 1, top right

S1SSL Side Sill Cross-Section 1, left side

S1SSR Side Sill Cross-Section 1, right side

S1BRL Belt Rail Cross-Section 1, left side

S1BRR Belt Rail Cross-Section 1, right side

S1RRL Roof Rail Cross-Section 1, left side

S1RRR Roof Rail Cross-Section 1, right side

S1PL Purlin Cross-Section 1, left side

S1PR Purlin Cross-Section 1, right side

S2CSBL Center Sill Cross-Section 2, bottom left

S2CSTL Center Sill Cross-Section 2, top left

S2CSBR Center Sill Cross-Section 2, bottom right

S2CSTR Center Sill Cross-Section 2, top right

S2SSL Side Sill Cross-Section 2, left side

S2SSR Side Sill Cross-Section 2, right side

S2BRL Belt Rail Cross-Section 2, left side

S2BRR Belt Rail Cross-Section 2, right side

S2RRL Roof Rail Cross-Section 2, left side

S2RRR Roof Rail Cross-Section 2, right side

S2PL Purlin Cross-Section 2, left side

S2PR Purlin Cross-Section 2, right side

S3CSBL Center Sill Cross-Section 3, bottom left
92

Channel Name Instrumented Member Location

S3CSTL Center Sill Cross-Section 3, top left

S3CSBR Center Sill Cross-Section 3, bottom right

S3CSTR Center Sill Cross-Section 3, top right

S3SSL Side Sill Cross-Section 3, left side

S3SSR Side Sill Cross-Section 3, right side

S3BRL Belt Rail Cross-Section 3, left side

S3BRR Belt Rail Cross-Section 3, right side

S3RRL Roof Rail Cross-Section 3, left side

S3RRR Roof Rail Cross-Section 3, right side

S3PL Purlin Cross-Section 3, left side

S3PR Purlin Cross-Section 3, right side

S4CSBL Center Sill Cross-Section 4, bottom left

S4CSTL Center Sill Cross-Section 4, top left

S4CSBR Center Sill Cross-Section 4, bottom right

S4CSTR Center Sill Cross-Section 4, top right

S4SSL Side Sill Cross-Section 4, left side

S4SSR Side Sill Cross-Section 4, right side

S4BRL Belt Rail Cross-Section 4, left side

S4BRR Belt Rail Cross-Section 4, right side

S4RRL Roof Rail Cross-Section 4, left side

S4RRR Roof Rail Cross-Section 4, right side

S4PL Purlin Cross-Section 4, left side

S4PR Purlin Cross-Section 4, right side

S5CSBL Center Sill Cross-Section 5, bottom left

S5CSTL Center Sill Cross-Section 5, top left

S5CSBR Center Sill Cross-Section 5, bottom right

S5CSTR Center Sill Cross-Section 5, top right

S5SSL Side Sill Cross-Section 5, left side

S5SSR Side Sill Cross-Section 5, right side

S5BRL Belt Rail Cross-Section 5, left side

S5BRR Belt Rail Cross-Section 5, right side

S5RRL Roof Rail Cross-Section 5, left side
93

Channel Name Instrumented Member Location

S5RRR Roof Rail Cross-Section 5, right side

S5PL Purlin Cross-Section 5, left side

S5PR Purlin Cross-Section 5, right side

S6SSL Side Sill Cross-Section 6, left side

S6SSR Side Sill Cross-Section 6, right side

S6BRL Belt Rail Cross-Section 6, left side

S6BRR Belt Rail Cross-Section 6, right side

SRBL* Roof EA Support B-end, left side

SRBR* Roof EA Support B-end, right side

SBPEAM1L* Primary EA Support B-end, outboard, left side

SBPEAM2L* Primary EA Support B-end, inboard, left side

SBPEAM1R* Primary EA Support B-end, outboard, right side

SBPEAM2R* Primary EA Support B-end, inboard, right side

SRAL* Roof EA Support A-end, left side

SRAR* Roof EA Support A-end, right side

SAPEAM1L* Primary EA Support A-end, outboard, left side

SAPEAM2L* Primary EA Support A-end, inboard, left side

SAPEAM1R* Primary EA Support A-end, outboard, right side

SAPEAM2R* Primary EA Support A-end, inboard, right side

*Channel only used in crippling test
94

800-kip Buff Strength Test

Cross-Section 1

Purlins

Roof Rails

Belt Rails
95

Side Sills

Center Sill, Top

Center Sill, Bottom
96

Cross-Section 2

Purlin

Roof Rail

Belt Rail
97

Side Sill

Center Sill, Top

Center Sill, Bottom
98

Cross-Section 3

Purlin

Roof Rail

Belt Rail
99

Side Sill

Center Sill, Top

Center Sill, Bottom
100

Cross-Section 4

Purlin

Roof Rail

Belt Rail
101

Side Sill

Center Sill, Top

Center Sill, Bottom
102

Cross-Section 5

Purlin

Roof Rail

Belt Rail
103

Side Sill

Center Sill, Top

Center Sill, Bottom
104

Cross-Section 6

Belt Rail

Side Sill
105

Crippling Test of Car 244

The strain data measured in the roof and floor energy absorber supports during the crippling test 

of Car 244 are plotted in this section. These instrumented locations are indicated in Figure 38

and Figure 39.

Roof Energy Absorber Supports

Outboard Floor Energy Absorber Support Location

Inboard Floor Energy Absorber Support Location
106

The strain data from the crippling test of Car 244 are plotted against the results of the FE analysis 

at the corresponding locations in the six cross-sections through the occupant volume.

Cross-Section 1

Purlin

Roof Rail

Belt Rail
107

Side Sill

Center Sill, Top

Center Sill, Bottom
108

Cross-Section 2 

Purlin

Roof Rail

Belt Rail
109

Side Sill

Center Sill, Top

Center Sill, Bottom
110

Cross-Section 3

Purlin

Roof Rail

Belt Rail
111

Side Sill

Center Sill, Top

Center Sill, Bottom
112

Cross-Section 4

Purlin

Roof Rail

Belt Rail
113

Side Sill

Center Sill, Top

Center Sill, Bottom
114

Cross-Section 5

Purlin

Roof Rail

Belt Rail
115

Side Sill

Center Sill, Top

Center Sill, Bottom
116

Cross-Section 6

Belt Rail

Side Sill
117

Appendix D. 

Car 244 Displacement Data and FE Results

String potentiometers were placed on the underframe of Car 244 both during the 800-kip elastic 

validation test and during the crippling test to measure the displacements experienced by the car. 

In the elastic test, a total of nine locations on the center and side sills of the car were 

instrumented with string pots. In the crippling test a total of 11 locations were instrumented. 

These locations are indicated in Figure 10.

Because any point on the car may simultaneously experience motion in the vertical, lateral, and 

longitudinal (VLL) directions, it was necessary to instrument each location with a VLL array of 

string pots (Figure A 3). Although each string pot was initially oriented with its string along a 

single axis, motion of the instrumented point in any one direction could result in a change in 

length to all three strings. It was necessary to process the test data and resolve the recorded 

changes to the length of each string in the VLL directions. 

Figure A 3. VLL Array of String Pots

Processing the raw change-in-string-length data accomplished two goals. First, the data were

transformed from each array’s local coordinate system to a universal coordinate system for the 

test car. Second, the change-in-length data were resolved into motion in the three principal 

directions, correcting each string’s data for off-axis motion. Figure A 4 shows an exemplar set 

of labeled axes used during the processing of the string pot data. These axes represent the global 

coordinate system and correspond to the orientation of the string array shown in Figure A 3.
118

Figure A 4. Axes Used for String Pot. Data Processing

A system of equations was written to relate the change in length of each string to a 

corresponding displacement in the global X, Y, and Z directions. The origin for each VLL array 

was placed at Point B, the point on the car being measured. The initial length of each string was 

measured prior to application of any load to the car. 

The coordinates for the position of the grounded end of each channel were then entered into the 

global coordinate system:

Point D (vertical): (0, 0, -Initial length)

Point A (longitudinal): (Initial length, 0, 0)

Point C (lateral): (0, Initial length, 0)

For each data point recorded during the test, the change in string length was added to the initial 

string length to determine the length of each string at a given point in time.

The system of equations used to resolve the data into X, Y, and Z motion is:

Equation 1. System of Equations for Resolving String Pot Data

Where

Lvert=new length of vertically oriented string pot

Llong=new length of longitudinally oriented string pot

Llat=new length of laterally oriented string pot

k=index

 Δxb=displacement of point B in x-direction
119

Δyb=displacement of point B in y-direction

Δzb=displacement of point B in z-direction

xa, ya, za=coordinates of point A

xc, yc, zc=coordinates of point C

zd, yd, zd=coordinates of point D

A solver (the commercial software MathCAD [15]) was used to solve the system for Δxb, Δyb, 

and Δzb. This system of equations was solved at each time point where data were simultaneously 

collected at the three channels making up each array.

The names and locations of the string pot channels installed in VLL arrays in the validation test 

of Car 244 and the crippling test of Car 244 are provided in Table A 2.

Table A 2. String Pot Channel Names and Locations

Channel Name Orientation Location

SPAX Longitudinal A-end lateral cross-member

SPAY Lateral A-end lateral cross-member

SPAZ Vertical A-end lateral cross-member

SPSSALX Longitudinal A-end left side sill

SPSSALY Lateral A-end left side sill

SPSSALZ Vertical A-end left side sill

SPSSARX Longitudinal A-end right side sill

SPSSARY Lateral A-end right side sill

SPSSARZ Vertical A-end right side sill

SPCSAX Longitudinal Center sill between A-end and midpoint of car

SPCSAY Lateral Center sill between A-end and midpoint of car

SPCSAZ Vertical Center sill between A-end and midpoint of car

SPCSCX Longitudinal Center sill at midpoint of car

SPCSCY Lateral Center sill at midpoint of car

SPCSCZ Vertical Center sill at midpoint of car

SPCS4-5X* Longitudinal Center sill between cross-bearer 4 and 5

SPCS4-5Y* Lateral Center sill between cross-bearer 4 and 5

SPCS4-5Z* Vertical Center sill between cross-bearer 4 and 5

SPCS5X* Longitudinal Center sill at cross-bearer 5

SPCS5Y* Lateral Center sill at cross-bearer 5

SPCS5Z* Vertical Center sill at cross-bearer 5

SPCSBX Longitudinal Center sill between B-end and midpoint of car
120

Channel Name Orientation Location

SPCSBY Lateral Center sill between B-end and midpoint of car

SPCSBZ Vertical Center sill between B-end and midpoint of car

SPSSBLX Longitudinal B-end left side sill

SPSSBLY Lateral B-end left side sill

SPSSBLZ Vertical B-end left side sill

SPSSBRX Longitudinal B-end right side sill

SPSSBRY Lateral B-end right side sill

SPSSBRZ Vertical B-end right side sill

SPBX Longitudinal B-end lateral cross-member

SPBY Lateral B-end lateral cross-member

SPBZ Vertical B-end lateral cross-member

*Channel only used in crippling test
121

800-kip Validation Test of Car 244

The following series of graphs contains the displacement results from the 800-kip elastic 

validation test and corresponding FE analysis. In each graph the test data have been resolved 

into their x, y, or z components. Because the test frame stretched in response to the applied load, 

the test data have had the longitudinal displacement of the restraint end (SPBX) subtracted from 

all other longitudinal channels’ data.

Longitudinal Data
122
123

Lateral Data

Lateral displacement data were collected during the test at each of the nine VLL arrays. 

Corresponding lateral displacements were recorded in the FE model. Because the FE model 

employed longitudinal-vertical symmetry, nodes along the symmetry plane were not permitted 

lateral displacement. In the test, the car experienced very small lateral displacements at all 

locations (< 0.2 inches). 
124
125

Vertical Data

Vertical data were recorded at each of the nine VLL array locations. Vertical displacement 

results were also recorded at the corresponding locations within the FE model. In general, the 

vertical displacement results in the FE analysis compare favorably with the vertical displacement 

data recorded during the test.
126
127

Crippling Test of Car 244

The following series of graphs contains the displacement results from the crippling test and 

corresponding pretest FE analysis. In each graph the test data have been resolved into their x, y, 

or z component. The A-end array of string pots on the center sill has been omitted from these 

results because of a suspected error in the data collected at this location.

Longitudinal Data

The longitudinal test data presented in each of the following figures have had the restraint-end 

displacement measurement subtracted from the measured longitudinal displacement data.
128
129
130

Lateral Data
131
132

Vertical Data
133
134

Abbreviations and Acronyms

CFR Code of Federal Regulations

ETF Engineering Task Force

FE Finite Element

FRA Federal Railroad Administration

OVI Occupied Volume Integrity

RSAC

SEPTA

Railroad Safety Advisory Committee

Southeastern Pennsylvania Transportation Authority

VLL Vertical, Lateral, Longitudinal