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Final Report
Modified NETC 4-Bar Bridge Rail for Steel Through-Truss Bridges
Prepared for: Structal Bridges
A DIVISION OF CANAM GROUP INC.
1445, DU GRAND TRONC
QUEBEC ,QC G1N 4G1
Prepared by: Chuck A. Plaxico and Malcolm H. Ray
ROADSAFE LLC
P.O. BOX 312
CANTON, ME 04221
December 11, 2013
(Modified 2/24/2014)
i
TABLE OF CONTENTS
Table of Contents ................................................................................................................. i
List of Figures .................................................................................................................... iii
List of Tables ..................................................................................................................... vi
List of Appendices ............................................................................................................. vi
Introduction ......................................................................................................................... 1
Objective ............................................................................................................................. 2
Project Scope ...................................................................................................................... 3
Background ......................................................................................................................... 4
Research Approach ............................................................................................................. 4
Full-Scale Crash Test Results on the NETC 4-Bar Bridge Rail ......................................... 5
Model Development............................................................................................................ 9
NETC 4-Bar Bridge Rail Model ..................................................................................... 9
8000S Single Unit Truck Model ................................................................................... 13
Model Validation .............................................................................................................. 15
Limitations of Crash Test Data for Validation ............................................................. 15
Simulated Impact Summary .......................................................................................... 23
Damage to Bridge Rail.................................................................................................. 24
Qualitative Validation ................................................................................................... 27
Sequential Views ...................................................................................................... 27
Occupant Risk Measures........................................................................................... 36
Time-History Data Comparison ................................................................................ 37
Summary ................................................................................................................... 40
Quantitative Validation ................................................................................................. 40
Time-History Evaluation .......................................................................................... 40
Time-History Evaluation Acceptance Criteria.......................................................... 41
Phenomena Importance Ranking Tables (PIRT) ...................................................... 42
Results ....................................................................................................................... 42
Summary ....................................................................................................................... 51
Conclusions for Model Validation ................................................................................ 52
Redesign of bridge rail for installation on steel THROUGH-truss bridge ....................... 54
Analysis of Original NETC 4-Bar Bridge Rail without Sidewalk ................................ 54
Simulated Impact Summary ...................................................................................... 54
Sequential Views of Original NETC Bridge Rail with and without Sidewalk ......... 56
ii
Barrier Damage ......................................................................................................... 59
Time-History Data Comparison ................................................................................ 60
Occupant Risk Measures........................................................................................... 66
Summary and Conclusions ....................................................................................... 67
Modified Design ........................................................................................................... 69
Tubular Railing ......................................................................................................... 69
Post and Base Plate ................................................................................................... 71
Design Alternatives for Post Mount ......................................................................... 71
Analysis of Post Loading on Mount Alternatives ......................................................... 75
Load Case 1 (Pendulum Impact)............................................................................... 75
Load Case 2 (Applied Displacement - Perpendicular to Post Flange) ...................... 77
Load Case 3 (Applied Displacement – 20 Degrees to Post Flange) ......................... 79
Summary and conclusions for the Analyses of the Mounting Designs .................... 81
Conduct Report 350 TL-4 crash performance evaluation of modified bridge rail ........... 82
Impact Conditions ......................................................................................................... 82
Sequential Views of Modified Design Compared with Baseline Design ................. 83
Damage to Bridge Rail.................................................................................................. 87
Impact Point A .......................................................................................................... 87
Impact Point B .......................................................................................................... 87
Damage to Bridge Floor Beams .................................................................................... 88
Time-History Data Comparison .................................................................................... 89
Occupant Risk Measures............................................................................................... 94
Impact Point A .......................................................................................................... 94
Impact Point B .......................................................................................................... 94
Quantitative Comparison .............................................................................................. 94
Summary and Conclusions ............................................................................................. 102
REFERENCES ............................................................................................................... 104
iii
LIST OF FIGURES
Figure 1. NETC 4-Bar (SBB44b) Bridge Rail.[Kimball99] .......................................................... 2 Figure 2. Impact sequence and summary of test conditions and results – Test NETC-
1.[Kimball99] ............................................................................................................... 6
Figure 3. Impact sequence and summary of test conditions and results – Test NETC-
2.[Kimball99] ............................................................................................................... 7 Figure 4. Impact sequence and summary of test conditions and results – Test NETC-
3.[Kimball99] ............................................................................................................... 8 Figure 5. Finite element model of the NETC 4-Bar bridge rail tested at SwRI. ........................... 9
Figure 6. FE mesh of post. ........................................................................................................... 10 Figure 7. FE mesh of 8x4x5/16 inch tube rail. ............................................................................ 11 Figure 8. FE mesh of rail splice. .................................................................................................. 11
Figure 9. Details of the FE model of the post mounting condition for Analysis Case NETC-
NoCurb_R131105. ..................................................................................................... 12 Figure 10. Damage to base plate in full-scale crash test NETC-3.[Kimball99] .......................... 13
Figure 11. Sequential snapshots of SUT impact into concrete single-slope barrier for test (top)
and FEA (bottom). [Miele05] .................................................................................... 14 Figure 12. Longitudinal (x-direction) acceleration measured at vehicle c.g. in Test NETC-3.
[Kimball99) ................................................................................................................ 16 Figure 13. Lateral (y-direction) acceleration measured at vehicle c.g. in Test NETC-3.
[Kimball99] ................................................................................................................ 16 Figure 14. Vertical (z-direction) acceleration measured at vehicle c.g. in Test NETC-3.
[Kimball99] ................................................................................................................ 17
Figure 15. Yaw-rate measured at vehicle c.g. in Test NETC-3.[Kimball99] .............................. 17 Figure 16. Plots of the x-acceleration for test number NETC-3 from the tabulated data in the test
report.[Kimball99] ..................................................................................................... 18 Figure 17. Plots of the y-acceleration for test number NETC-3 from the tabulated data in the test
report.[Kimball99] ..................................................................................................... 19 Figure 18. Plots of the z-acceleration for test number NETC-3 from the tabulated data in the test
report.[Kimball99] ..................................................................................................... 19 Figure 19. Plot of the yaw-rate of the vehicle for test number NETC-3 from the tabulated data in
the test report.[Kimball99] ......................................................................................... 20 Figure 20. Longitudinal velocity-time history at vehicle c.g. in Test NETC-3. .......................... 21 Figure 21. Lateral velocity-time history at vehicle c.g. in Test NETC-3. ................................... 21 Figure 22. Repaired longitudinal acceleration data for test NETC-3. ......................................... 22 Figure 23. Longitudinal velocity computed from repaired acceleration data. ............................. 22 Figure 24. Damage to bridge rail in full-scale test NETC-3 from posts 6 through 8. ................. 25
Figure 25. Damage to bridge rail in full-scale test NETC-3 from posts 8 through 11. ............... 26 Figure 26. Analysis result showing maximum permanent deflection of top rail. ........................ 27 Figure 27. Sequential views of Test NETC-3 and FE analysis from upstream viewpoint. ......... 28 Figure 28. Sequential views of Test NETC-3 and FE analysis from downstream viewpoint. .... 31
Figure 29. Sequential views of Test NETC-3 and FE analysis from overhead viewpoint. ......... 34 Figure 30. Longitudinal acceleration-time history plot from full-scale test NETC-3 and FEA
(FEA results filtered with SAE Class 60 filter). ........................................................ 38
iv
Figure 31. Lateral acceleration-time history plot from full-scale test NETC-3 and FEA (FEA
results filtered with SAE Class 60 filter). .................................................................. 38 Figure 32. Vertical acceleration-time history plot from full-scale test NETC-3 and FEA (FEA
results filtered with SAE Class 60 filter). .................................................................. 39
Figure 33. Yaw rate-time history plot from full-scale test NETC-3 and FEA (FEA results filtered
with SAE Class 60 filter). .......................................................................................... 39 Figure 34. Plot of global energy-time histories from the analysis. .............................................. 43 Figure 35. RSVVP Metric selection for validation assessment. .................................................. 44 Figure 36. Summary of results from analysis compared with full-scale crash test for validation
of the baseline model. ................................................................................................ 53 Figure 37. Sequential views of original NETC bridge rail with and without sidewalk under TL4
impact conditions. ...................................................................................................... 57 Figure 38. Results for original design (a) with and (b) without sidewalk illustrating the different
impact locations of the rear of the truck against the rail. ........................................... 60 Figure 39. 50-ms average longitudinal acceleration for baseline NETC barrier with and without
sidewalk. .................................................................................................................... 61 Figure 40. Longitudinal-velocity-time history for baseline NETC barrier with and without
sidewalk. .................................................................................................................... 61 Figure 41. 50-ms average lateral acceleration for baseline NETC barrier with and without
sidewalk. .................................................................................................................... 62
Figure 42. Lateral-velocity-time history for baseline NETC barrier with and without sidewalk. 62 Figure 43. 50-ms average vertical acceleration for baseline NETC barrier with and without
sidewalk. .................................................................................................................... 63 Figure 44. Yaw rate-time histories for baseline NETC barrier with and without sidewalk. ........ 63 Figure 45. Yaw angle-time history for original barrier with and without sidewalk. .................... 64
Figure 46. Roll rate-time histories for baseline NETC barrier with and without sidewalk. ........ 64
Figure 47. Roll angle-time history for original barrier with and without sidewalk. .................... 65 Figure 48. Pitch rate-time histories for baseline NETC barrier with and without sidewalk. ....... 65 Figure 49. Pitch angle-time history for original barrier with and without sidewalk. ................... 66
Figure 50. Summary of results for analysis of baseline design without sidewalk compared to
analysis of crash tested design with sidewalk. ........................................................... 68
Figure 51. Drawing for the NETC 4-Bar bridge rail attached to a through-truss bridge. ............ 70 Figure 52. Schematic of mount design option 09a. ..................................................................... 72
Figure 53. Schematic of mount design option 10b. ..................................................................... 72 Figure 54. Schematic of mount design option 11b. ..................................................................... 73 Figure 55. Schematic of mount design option 11c. ..................................................................... 73 Figure 56. Schematic of mount design option 12. ....................................................................... 73 Figure 57. Location of mounting bolts and post attachment to base plate. ................................. 74
Figure 58. Force-displacement history of post mount for Load Case 1. ...................................... 76 Figure 59. Contour of effective plastic strain for Load Case 1 on design Alternative 09a. ........ 77
Figure 60. Contour of effective plastic strain for Load Case 1 on design Alternative 11b. ........ 77 Figure 61. View of maximum deformation of various mount designs for Load Case 2. ............ 78 Figure 62. Force-displacement history of post-mount alternatives for Load Case 2. .................. 79 Figure 63. View of maximum deformation of various mount designs for Load Case 3. ............ 80 Figure 64. Contour of effective plastic strain on floor beam for Load Case 3. ........................... 81
v
Figure 65. Sequential views of (a) Baseline system without sidewalk, (b) Modified system at
impact point A and (c) Modified system at impact point B from an upstream
viewpoint. .................................................................................................................. 84 Figure 66. Sequential views of (a) Baseline system without sidewalk, (b) Modified system at
impact point A and (c) Modified system at impact point B from an overhead
viewpoint. .................................................................................................................. 86 Figure 67. Contours of effective plastic strain on floor beam. .................................................... 88 Figure 68. Cut-view of the beam flange showing contours of effective plastic strain through the
cross-section of bolt-hole. .......................................................................................... 89
Figure 69. 50 ms-average longitudinal acceleration-time histories for analysis of modified
designs compared with baseline analysis cases. ........................................................ 90 Figure 70. Longitudinal velocity-time histories for analysis of modified designs compared with
baseline analysis cases. .............................................................................................. 90
Figure 71. 50 ms-average lateral acceleration-time histories for analysis of modified designs
compared with baseline analysis cases. ..................................................................... 91
Figure 72. Lateral velocity-time histories for analysis of modified designs compared with
baseline analysis cases. .............................................................................................. 91
Figure 73. 50 ms-average vertical acceleration-time histories for analysis of modified designs
compared with baseline analysis cases. ..................................................................... 92 Figure 74. Yaw angle-time histories for analysis of modified designs compared with baseline
analysis cases. ............................................................................................................ 92 Figure 75. Roll angle-time histories for analysis of modified designs compared with baseline
analysis cases. ............................................................................................................ 93 Figure 76. Pitch angle-time histories for analysis of modified designs compared with baseline
analysis cases. ............................................................................................................ 93
Figure 77. Summary of results from the analysis of the modified design compared with the
analysis of the baseline design without sidewalk. ................................................... 101
vi
LIST OF TABLES
Table 1. Summary of occupant risk measures computed from test NETC-3 and FEA simulation.
................................................................................................................................... 37 Table 2. Analysis Solution Verification Table. ........................................................................... 43
Table 3. Roadside safety validation metrics rating table – time history comparison (single-
channel option). ......................................................................................................... 46 Table 4. Roadside safety validation metrics rating table – (multi-channel option). .................... 47 Table 5. Report 350 crash test criteria with the applicable test numbers. ................................... 48 Table 6. Roadside safety phenomena importance ranking table (structural adequacy). .............. 49
Table 7. Roadside safety phenomena importance ranking table (occupant risk). ....................... 50 Table 8. Roadside safety phenomena importance ranking table (vehicle trajectory). ................. 51 Table 9. Summary of barrier deflections for the original NETC 4-Bar bridge rail with and
without sidewalk under TL4 impact conditions. ....................................................... 59 Table 10. Summary of occupant risk measures comparing response for original NETC bridge
rail with and without sidewalk. .................................................................................. 67
Table 11. Geometric and mechanical properties for the bridge floor beams. .............................. 71 Table 12. Matrix of analyses used in evaluating the various mount design alternatives. ............ 75 Table 13. Results for Load Case 1 (Pendulum Impact) ............................................................... 76
Table 14. Results for Load Case 2 (Applied displacement 90 degrees to post flange). .............. 78 Table 15. Results for Load Case 3 (Applied displacement at 20 degrees to post flange). .......... 80
Table 16. Summary of barrier deflections for the Baseline design without sidewalk and the
modified design under TL4 impact conditions. ......................................................... 87 Table 17. Summary of occupant risk measures computed for the baseline design with and
without sidewalk, and the modified design at impact points A and B. ..................... 94 Table 18. Roadside safety validation metrics rating table – time history comparison (single-
channel option). ......................................................................................................... 96 Table 19. Roadside safety validation metrics rating table – (multi-channel option). .................. 97
Table 20. Roadside safety phenomena importance ranking table (structural adequacy). ............ 98 Table 21. Roadside safety phenomena importance ranking table (occupant risk). ..................... 99
Table 22. Roadside safety phenomena importance ranking table (vehicle trajectory). ............. 100
LIST OF APPENDICES
Appendix A: Full-Scale Crash Evaluation of the NETC 4-Bar Sidewalk-Mounted Steel Bridge
Railing
Appendix B: Verification & Validation Forms – Validation of Baseline Model
Appendix C: Verification & Validation Forms – Verification of Modified Design
1
INTRODUCTION
Structal is in need of an NCHRP Report 350 or MASH Test Level 4 (TL4) post-and-beam
bridge rail for installation on steel through-truss bridges used in both Canada and the United
States. Such bridges typically have two lanes with total roadway width of 24 feet. Pre-fabricated
Acrow steel deck panels are 5-3/8 inches thick with a wearing surface that is approximately 5/16
inches thick. The connections of the barrier to the floor-beams are approximately 5.4 inches
lower than the top of the roadway. The floor-beams are spaced at 10 feet center-to-center, which
requires that the bridge rail have post spacing of 10 feet in order to mount directly to the floor
beams. There is also limited space between the edge of roadway and the truss structure of the
bridge.
There are no existing bridge rail systems that meet all the requirements for installation on
these types of bridges. It was therefore suggested that an existing crash tested TL-4 system be
used as a baseline design, which could be modified to accommodate the specific installation
requirements. In accordance with the FHWA HSST memorandum May 21, 2012, finite element
analysis (FEA) will be used to simulate Report 350 test level 4 impact test conditions for the
modified design to ensure that crash performance of the modified design meets crash testing
standards. This report describes the use of FE modeling and crash simulation to determine
whether improvements to a previously tested roadside hardware item can be considered
crashworthy without additional testing.
From a review of existing bridge rail systems, the most applicable system to serve as a
baseline design is the NETC 4-bar bridge rail (AASHTO designation SBB44b), shown in Figure
1.[Kimball99] However, several modifications will be required in order to mount the system to
the steel floor beams of the bridge superstructure, including removal of the 9-inch tall
curb/sidewalk.
The SBB44b, shown in Figure 1, is a Report 350 TL4 42-inch tall bridge rail (not
including the height of the eight-inch curb/sidewalk) composed of four longitudinal tubular rails.
The top rail, the third rail from the top, and the bottom rail are fabricated from TS4x4x0.25-inch
structural tubing; the second rail from the top is fabricated from TS8x4x0.3125-inch structural
tubing. The rails are attached to W6x25 steel posts using ¾-inch diameter studs with steel
washers and lock-nuts. The posts are spaced at 8-ft center-to-center. The posts are welded to a
10x14 inch steel 1-inch thick base plate. The base plate is fastened to the top of a 9-inch tall steel
reinforced concrete sidewalk using four 1-inch diameter anchor bolts. The sidewalk is 78 inches
wide.
2
Figure 1. NETC 4-Bar (SBB44b) Bridge Rail.[Kimball99]
Each tubular rail section is 23.9 feet long and spans three posts. The rail tubes are joined
to the neighboring rails using a 20-inch long tubular sleeve inserted 9-5/8 inches into the ends of
the adjoining rails. The adjoining main rails are separated by a ¾-inch gap and the sleeve is
fastened to each main rail tube using two 5/8-inch diameter cap screws. The sleeve tube is
fabricated from ¼-inch steel plate welded along the edges. The clearance of the splice tube inside
the main rail tube is 1/16-inch on all sides. Refer to the drawings in the crash test report in
Appendix A for additional construction details.
The material for the rail bars is ASTM A500 Grade B or ASTM A501 steel. The material
for the rail posts is ASTM A709 Grade 50. The material for all other shapes and plates are
ASTM A709 Grade 36. Anchor studs, washers and exposed nuts conform to ASTM A449, which
has a minimum yield of 92 ksi, ultimate strength of 120 ksi, and 14 percent elongation. All other
bolts and nuts conform to ASTM A307 with minimum yield of 36 ksi, minimum ultimate
strength of 60 ksi and 18 percent elongation.
OBJECTIVE
The objective of this project is to develop a modified design of the NETC 4-Bar bridge
rail to accommodate installation on steel through-truss bridges. The bridge rail was successfully
tested to Report 350 TL4 conditions, and it is the objective of this project to achieve Report 350
TL-4 eligibility for the modified design. Testing for Report 350 TL4 requires three tests on the
length of need (LON) of the bridge rail. Test 4-10 involves an 1800-lb (820-kg) passenger car
impacting the critical impact point of the barrier at a nominal speed and angle of 62.2 mph (100
km/hr) and 25 degrees. Test 4-11 involves a 4,400-lb (2,000-kg) ¾-ton pickup truck impacting
the critical impact point of the barrier at a nominal speed and angle of 62.2 mph (100 km/hr) and
3
25 degrees. Test 4-12 involves a 17,640-lb (8,000-kg) single unit truck (SUT) impacting the
critical impact point of the barrier at a nominal speed and angle of 50 mph (80 km/hr) and 15
degrees.
PROJECT SCOPE
The scope of the project included the (1) development and validation of a finite element
model of the crash tested bridge rail to serve as an FEA baseline, (2) modification of the system
design to accommodate mounting conditions for the steel through-truss bridge, and (3)
evaluating the crash performance of the modified design using FEA for impact conditions
corresponding to Report 350 TL-4. The modifications to the NETC 4-Bar bridge rail include:
Removing the 9-inch tall sidewalk. The railing heights are relative to the wear-surface of
the bridge deck.
Extending the post base down to the deck support beams so that the posts can be mounted
directly to the top flange of the floor beams.
Increasing the post spacing from 8 ft to 10 ft. The floor-beam spacing is fixed at 10-ft
center-to-center.
Raising the lower rail 2 inches from its original position to accommodate the 6-inch curb
fixed onto the side of the Acrow Panel system.
The mounting plate was designed such that impact loads are appropriately distributed to
the floor beams to ensure that local deformations remain elastic in the bridge superstructure
during a vehicle impact. The modified mount design has sufficient strength for the TL4 loading,
but yielding of the post will occur prior to damaging the bridge floor beams. The bolts in the
mounting connection also serve as a secondary safety “fuse” which will break when loads reach
critical values, rather than damaging the bridge superstructure. According to Section 13 of the
LRFD Bridge Design Specification, a yield-line analysis or a FE analysis may be conducted to
verify that excessive loads are not transferred into the bridge superstructure. This project was
intended to fulfill the requirement by Chapter 13 of the LRFD Bridge Design Specification for
an FE analysis.
The post length was increased from 40.5 inches to 44.6 inches, and the post spacing was
increased from 8-ft to 10-ft to allow for mounting directly to the bridge floor beams. As will be
discussed later, there is plenty of room to add stiffeners to the floor beams and the post-mount
such that the new and old systems are equally rigid at the deck level. The 6-inch curb is integral
to the Acrow Panel system and cannot be easily removed so modifications to the Acrow panels
are not desired. Thus, the lower tube rail was raised a 2 inches so that the Acrow panel curb fit
underneath the lowest tube. This modification should actually improve performance regarding
shielding the vehicle from the posts since the curb is positioned under the bottom rail and behind
the face of the barrier.
4
BACKGROUND
On May 12, 2012 the FHWA instituted a new Federal-Aid Reimbursement Eligibility
Process (see http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware) for roadside
hardware including bridge railings that is to be used for requesting eligibility letters (i.e.,
formerly called acceptance letters). The new process covers evaluation of both new hardware
designs as well as changes to currently accepted designs. When evaluating already accepted
hardware, changes are categorized into three new categories:
Significant – a change that might adversely affect the crash performance of the hardware.
These types of changes require that new crash tests be performed.
Non-Significant/Effect Uncertain – are changes that are relatively minor but it is not clear
if the changes will adversely affect the safety performance. In these cases a finite
element analysis using LSDYNA can be used to demonstrate that the change does not
adversely affect the crash performance of the hardware.
Non-Significant/Positive or Inconsequential Effect – are changes that are minor and will
either improve the performance or are unlikely to change the performance at all. In these
cases FHWA may issue a letter without either new crash tests of finite element analysis.
The documentation submitted to FHWA must include a review of the prior testing by a
registered PE stating that the modifications are non-significant and will have a positive or
inconsequential effect.
The new procedure also requires that materials submitted to the FHWA be
“independently certified” by an organization that is on the FHWA’s list of accredited
laboratories. Fortunately, Roadsafe LLC is one of the laboratories that are on the FHWA’s
accredited list and we therefore have the qualifications to submit certified results to the FHWA.
RESEARCH APPROACH
The approach used in this research was:
1. Develop a FEA model of the crash-tested version of the NETC 4-Bar bridge
railing and validate the model using the Report 350 TL4 crash test data.
2. Modify the original model by removing the sidewalk and compare the
performance results to the baseline crash tests.
3. Modify the model in step 2 (i.e., no side walk) by incorporating the design
changes required for the through-truss bridge and compare the results to the
results of the original (baseline) design without the curb/sidewalk (i.e., the results
from step 2).
The FEA crash analyses were carried out using the non-linear dynamic explicit finite
element analysis software LSDYNA. A baseline finite element model of the SBB44b bridge rail
was developed and the model was validated by comparing the FEA with results with those from
the full-scale crash tests using the procedures outlined in NCHRP Web-Document 179 to ensure
that the model results are accurate, predictive and valid. The available full-scale test data for the
5
validation task includes Tests NETC-1 (Test 4-10), NETC-2 (Test 4-11) and NETC-3 (Test 4-
12), all of which were performed under Report 350 TL-4 test conditions.
Once the baseline model was validated, the design of the bridge rail was modified to
accommodate attachment of the system to the deck support beams of the steel through-truss
bridge, remove the concrete sidewalk and increase the post spacing from 8 ft to 10 ft. Finite
element analysis was then again used to evaluate the crash performance of the modified design
based on structural capacity, occupant risk measures and vehicle stability during impact and
redirection. These results were then compared to those of the baseline system to determine if the
performance of the system meets the FHWA criteria for “insignificant change” or
“inconsequential/positive” change.
FULL-SCALE CRASH TEST RESULTS ON THE NETC 4-BAR BRIDGE
RAIL
The NETC 4-Bar bridge rail system was tested according to the crash test specifications
of NCHRP Report 350 for Test Level 4. The test article is shown in Figure 1 and included a 108
feet long section of the bridge rail mounted on a 6.5-ft wide concrete sidewalk. The side walk
was 8 inches tall at the traffic face and sloped up to 9 inches tall at the point where the bridge rail
was mounted. The distance from the face of the curb to the face of the bridge rail was 4.67 feet.
The tests were conducted at the Southwest Research Institute (SwRI). Test NETC-1
corresponded to the impact conditions of Report 350 Test 4-10 and involved a 1991 Ford Festiva
with gross static mass of 1,989 lb, including a 165-lb dummy impacting the bridge rail at 62.14
mph and 20 degrees. Test NETC-2 corresponded to the impact conditions of Report 350 Test 4-
11 and involved a 1991 Ford F-250 with gross static mass of 4,484 lb impacting the bridge rail at
62.14 mph and 25 degrees. Test NETC-3 corresponded to the impact conditions of Report 350
Test 4-12 and a 1993 International 4600 LP single unit truck ballasted to 17,875-lb, impacting
the bridge rail system at 49.8 mph and angle of 15 degrees.
The bridge rail system successfully passed all required structural adequacy and occupant
safety criteria of NCHRP Report 350. Test NETC-3 (i.e., Test 4-12) resulted in an exit trajectory
of the vehicle that would indicate intrusion into adjacent lanes; however, this is a preferred, not
required, criterion. Figure 2, Figure 3, and Figure 4 show the summary sheets from the test
report for Tests NETC-1, NETC-2 and NETC-3, respectively. The maximum permanent
deflection of the bridge rail was zero inches for NETC-1 and was 0.51 inches for both test
NETC-2 and NETC-3. Additional details of the tests and results can be found in the test report
which is included as Appendix A.[Kimball99]
6
Figure 2. Impact sequence and summary of test conditions and results – Test NETC-1.[Kimball99]
7
Figure 3. Impact sequence and summary of test conditions and results – Test NETC-2.[Kimball99]
8
Figure 4. Impact sequence and summary of test conditions and results – Test NETC-3.[Kimball99]
9
MODEL DEVELOPMENT
NETC 4-Bar Bridge Rail Model
A detailed finite element model of the NETC 4-Bar bridge rail system was developed
based on full-scale crash test NETC-3 conducted at the Southwest Research Institute (SwRI) in
San Antonio, Texas on December 18, 1997.[Kimball99] A 120-ft section of bridge rail was
modeled as shown in Figure 5. The model includes fifteen posts, fifteen sections of TS4x4x0.25
inch tubular rail, five sections of TS 8x4x0.625 inch tubular rail and a 4.67 feet wide side walk.
Figure 5. Finite element model of the NETC 4-Bar bridge rail tested at SwRI.
The cross-section of the posts were modeled according to the dimensional specifications
for W6x25 structural steel (i.e., depth = 6.38 in, flange width = 6.08 in, web thickness = 0.32 in,
and flange thickness = 0.455 in). The material properties were characterized based ASTM A709
Grade 50 steel using the properties determined in the study by Wright and Ray for AASHTO
M180 steel, which has the same yield and tensile strength properties.[Wright96] The post was
modeled with thin-shell elements (Type 2 in LS-DYNA) with nominal size of 0.6 x 0.6 inches
(15x15 mm). The bolt-holes in the front flange were modeled with diameter of 1 inch and the
elements around the immediate surface of the holes were meshed with nominal size of 0.35 x
0.35 inches (9x9 mm). A portion of the post model is shown in Figure 6.
10
Figure 6. FE mesh of post.
The tubular rail sections were modeled according to the dimensional specifications for
TS8x4x0.3125 and TS4x4x0.25 inch structural steel tubing with material conforming to ASTM
A500 Grade B. The minimum yield and tensile strength for the tube material is 46 ksi and 58
ksi, respectively. In most cases, the actual yield point of the material is considerably higher. In
many cases, suppliers provide steel tubing with yield strength exceeding 50 ksi. Since the focus
of this project is the redesign of the post mounting system, the yield stress for the tubing was
modeled with yield point equal 60 ksi (i.e., upper bound range) in order to provide a conservative
loading magnitude on the anchor system (i.e., increased load on the anchor).
The tube rails were modeled with thin-shell elements (Type 2 in LS-DYNA) with
nominal size of 1 x 1 inches for the span of rail between the posts; and with a nominal size of 0.5
x 0.5 inches in the section of rail in contact with the posts. The ¾-inch diameter stud bolts
welded to the tubes were modeled with beam elements with properties corresponding to ASTM
A307 Grade A and attached to the tube via the nodal rigid body constraint option in LS-DYNA
(e.g., it is assumed that the welds do not break during impact).
11
Figure 7. FE mesh of 8x4x5/16 inch tube rail.
The splice connection of the adjoining tube rails included a 20-inch long tubular sleeve
inserted 9-5/8 inches into the ends of the rails and fastened to each tube using two 5/8-inch
diameter cap screws. The splice tubes were modeled with the same material properties and mesh
details as the main rail tubes. The cap screw connections were simulated via the
constrained_spotweld option in LS-DYNA. Figure 8 shows the splice region of the model with
the main tube rails displayed in transparent view to illustrate the positioning of the splice tubes.
Figure 8. FE mesh of rail splice.
The welded connection of the posts to the 1-inch thick base plate is modeled using the
tied-contact option in LS-DYNA which creates an automatic constraint between the nodes of the
post and the base plate. This connection assumes that the welds on the base plate do not fail
during impact as was verified in the full-scale test. The 1-inch thick base plate was modeled with
two layers of thick-shell elements with nominal size 0.7 x 0.7 x 0.5 inches with five integration
12
points through the thickness of each element. In the non-critical impact regions of the model the
base plate was constrained at the bolt holes using the SPC option in LS-DYNA. The forces in the
x, y and z directions were then collected and monitored during the analysis to ensure that force
magnitudes did not exceed critical values.
In the critical impact region of the model (i.e. posts 6 and 7), a more detailed model of
the mount conditions were included as illustrated in Figure 9. The concrete foundation was
modeled with brick elements with nodes rigidly constrained from both translation and rotation.
The bolts fastening the base plate to the foundation were modeled explicitly using beam elements
to model the bolt shaft and solid elements to model the bolt head and nut. The 0.24-inch thick
washers were also modeled using thick shell elements. Contact between the bolts and the mount
components were defined in LS-DYNA using the “contact_automatic_general” option. The
bolts were pre-tightened to 56,600 lb prior to impact in the analysis which corresponded to
approximately 60 percent of the yield strength of the bolts. These components provided
essentially rigid behavior during the full-scale crash test with the damage to the mount isolated to
slight deformation of the base plate as shown in Figure 10. Since the mount design was the focus
of this study, however, these components were modeled with higher fidelity to ensure that the
response of the mount conditions could be modeled with reasonable accuracy.
Figure 9. Details of the FE model of the post mounting condition for Analysis Case
NETC-NoCurb_R131105.
13
Figure 10. Damage to base plate in full-scale crash test NETC-3.[Kimball99]
8000S Single Unit Truck Model
The vehicle model that was used in this study was the 8000S single unit truck model
developed at the National Crash Analysis Center (NCAC) in Ashburn, VA which has been
further modified by various researchers over the years to improve their fidelity in analysis of
impact conditions corresponding to NCHRP Report 350 Test 4-12. [Miele05] NTRCI funded the
research team of Battelle and Oak Ridge National Laboratory (ORNL) to enhance and refine a
FE model of an SUT for simulating Report 350 TL4 crash events involving roadside safety
hardware such as bridge rails and median barriers. The SUT model was originally developed by
the National Crash Analysis Center (NCAC) of George Washington University (GWU) and
required refinement and testing before it could be used by the engineering community for
infrastructure design. The result of that study was a validated SUT model that provides realistic
predictions of crash impacts into longitudinal roadside safety barriers. Figure 11 shows an
example of the model results compared to full-scale crash test 47147-17. [Miele05; Buth97] The
model was then further modified by NCAC and validated through comparison to a full scale
crash test conducted at the Federal Highway Administration’s (FHWA) Federal Outdoor Impact
Laboratory (FOIL).[Mohan07]
14
Figure 11. Sequential snapshots of SUT impact into concrete single-slope barrier for test
(top) and FEA (bottom). [Miele05]
Although the suspension of the vehicle was originally modeled with reasonable fidelity, it
had not been validated for severe loading conditions such as impact with the 9-inch curb-
sidewalk of the NETC 4-bar bridge rail test. Preliminary analyses indicated that the suspension
model did not provide proper response for such impacts. Several modifications/improvements to
the SUT model were, therefore, incorporated in this project, including:
Remodeling the u-bolt connection of the front leaf springs to the front axle,
Changing properties for the front and rear shocks to match properties measured
for the semi-tractor model (these are too stiff but provide more realistic response
than the original model),
Removing rigid constraints between the leaf-spring components, which were
making the system overly stiff,
Adding a suspension-stop on the rear suspension (based on visual inspection of a
similar Penske Truck),
Changing tie properties to match the semi-tractor model,
Changing airbag model used to inflate the tires to the simple-pressure model, and
Incorporating the initial stresses in the leaf springs due to the static gravity load of
the vehicle.
15
MODEL VALIDATION
In order to gain confidence in the model results, it was necessary to validate the model
predictions against full-scale crash test results. The validation procedures presented in NCHRP
Web Document 179 were used to assess the fidelity of the model. The finite element model was
validated by comparing the FEA analysis results to those of a full-scale crash test. The baseline
model developed in Task 1 was used to simulate full-scale crash test NETC-3, which
corresponds to test conditions for Report 350 Test 4-12 (i.e., 17,875-lb SUT impacting at 49.8
mph and angle of 15 degrees.). [Kimball99] Various checks were made during the finite element
analysis such as energy balance, mesh distortion, contact penetration, shooting nodes, etc., to
ensure that the results are indicative of a well-behaved and stable model. The validity of the
model results were also assessed using the verification and validation procedures set forth in
NCHRP Report W179 as required by the FHWA. The validation procedure has three steps:
1. Solution verification: Indicates whether the analysis solution produced numerically stable
results (i.e., ensures that basic physical laws are upheld in the model).
2. Time-history evaluation: Quantitative measure of the level of agreement of time-history
data (e.g., x, y, z accelerations and roll, pitch, and yaw rates) between analysis and test.
3. Phenomena Importance Ranking Table: A table that documents the types of phenomena
that a numerical model is intended to replicate and verifies that the model produces
results consistent with its intended use.
Limitations of Crash Test Data for Validation
The validation effort was limited by the amount of data available from the full-scale test.
The test was conducted in December 1997 and, unfortunately, the retention time for test data at
SwRI is only three years. Copies of the test videos were obtained from NETC and the FHWA;
however, the electronic time-history data from the vehicle-mounted accelerometers, which are
generally preferred in the quantitative validation process, were no longer available. Figure 12
through Figure 15 shows images of the acceleration-time histories and the yaw-rate-time history
plots from the test report and correspond to the data collected at the c.g. of the vehicle.
[Kimball99]
16
Figure 12. Longitudinal (x-direction) acceleration measured at vehicle c.g. in Test NETC-
3. [Kimball99)
Figure 13. Lateral (y-direction) acceleration measured at vehicle c.g. in Test NETC-3.
[Kimball99]
17
Figure 14. Vertical (z-direction) acceleration measured at vehicle c.g. in Test NETC-3.
[Kimball99]
Figure 15. Yaw-rate measured at vehicle c.g. in Test NETC-3.[Kimball99]
The tabulated values of the x, y, and z accelerations and yaw-rate at the c.g. of the vehicle
were also provided in the test report.[Kimball99] These included x, y and z-accelerations filtered
18
at 180 Hz; the 10-ms running averages of the x, y and z accelerations, and the yaw-rate. There
was also another data table listed which included x, y, z and resultant acceleration for the c.g.
(filter type not provided). The data were listed at a sampling rate of 100 samples per second (i.e.,
time increment of 0.01 seconds) and covered 0.99 seconds of the impact event. These data are
shown graphically in Figure 16 through Figure 19.
The tabulated data in the report were the only data available for use in the validation of
the finite element model. Ideally, quantitative validation is performed by using the “raw” data
from test and simulation so that both sets of data can be processed (i.e., filtered, resampled, etc.)
in exactly the same way for the validation. This, of course, was not possible in this case since the
raw electronic data was no longer available. Other tabulated accelerometer data in the test report
corresponded to accelerometers mounted on the rear tandem axle, engine block, front and rear
brake calipers and instrument panel. The finite element model had accelerometers located only
at the vehicle c.g. and cabin floor.
Figure 16. Plots of the x-acceleration for test number NETC-3 from the tabulated data in
the test report.[Kimball99]
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2
Acc
eler
atio
n (
G's
)
Time (sec)
X-Acceleration
C.G.
10-ms Avg
SAE 180 Filter
19
Figure 17. Plots of the y-acceleration for test number NETC-3 from the tabulated data in
the test report.[Kimball99]
Figure 18. Plots of the z-acceleration for test number NETC-3 from the tabulated data in
the test report.[Kimball99]
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2
Acc
eler
atio
n (
G's
)
Time (sec)
Y-Acceleration
C.G.
10-ms Avg
SAE 180 Filter
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2
Acc
eler
atio
n (
G's
)
Time (sec)
Z-Acceleration
C.G.
SAE 180 Filter
20
Figure 19. Plot of the yaw-rate of the vehicle for test number NETC-3 from the tabulated
data in the test report.[Kimball99]
Although the resampled form of the data provides a more-or-less accurate “shape” for
each of the acceleration traces (i.e., SAE 180 filtered, 10-ms average, etc.), the process of
resampling can sometimes lead to aliasing of the data. From visual inspection, it is somewhat
apparent that there are discrepancies between the various acceleration curves regarding
magnitude and phase. Figure 16, for example, shows a data point with a relatively high
acceleration magnitude at approximately 0.6 seconds of the impact and again at around 0.72
seconds, for the curve filtered at 180 Hz and the curve labeled “C.G.” This would generally
imply that a meaningful event occurred at that time; however, the 10-millisecond running
average acceleration curve does not indicate such an event. Note that the acceleration plot in
Figure 12 also shows high activity at this time; but in this case the event is marked with a
random series of both positive and negative peaks with approximately equal magnitudes which
act to cancel each other out. The tabulated data, on the other hand, captured only a single data
point over that time interval.
The error in the data becomes more evident when the acceleration traces are integrated
with respect to time to obtain velocities, as shown in Figure 20 and Figure 21. These plots show
the velocity-time history taken directly from the tabulated data in the test report (denoted by the
dashed line) and the velocity time history derived from direct integration of the tabulated
acceleration data. It is assumed that the “reported velocity” was derived from the original
acceleration data and should therefore be considered as the true velocity. Note the sudden
increase in forward velocity that occurred at around 0.6 seconds and the sudden decrease in
velocity that occurred at around 0.72 seconds, which correspond to the two acceleration spikes in
the afore mentioned plots. It is common for the vehicle’s instrumentation to pick up relatively
-100
-50
0
50
100
150
0 0.2 0.4 0.6 0.8 1
Yaw
Rat
e (d
eg/
sec)
Time (sec)
Yaw Rate
10-ms Avg.
21
small increases in velocity as the vehicle springs forward slightly as components compress and
release, but it is not likely that such an increase in forward motion of the vehicle could occur
unless the vehicle was suddenly pulled or pushed forward with considerable force. The error in
the velocity is unfortunately due to the low sampling rate of the tabulated acceleration data.
Figure 20. Longitudinal velocity-time history at vehicle c.g. in Test NETC-3.
Figure 21. Lateral velocity-time history at vehicle c.g. in Test NETC-3.
10
12
14
16
18
20
22
24
0.00 0.20 0.40 0.60 0.80 1.00
Ve
loci
ty (
m/s
)
Time (sec)
reported velocity
Integrated Acc. CG
int of 10-ms acc
Integrated acc. 180
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
0.00 0.20 0.40 0.60 0.80 1.00
Ve
loci
ty (
m/s
)
Time (sec)
reported velocity
Integrated Acc. CG
int of 10-ms acc
Integrated acc. 180
22
Since this is the only data available for the validation, an attempt was made to correct for
the low sampling rate by simply replacing the questionable section of data with the data from the
10-ms average acceleration curve. It should be pointed out that the tabulated data in the report is
not in error – it actually corresponds to the exact instantaneous values of the acceleration data at
specified time increments – but the low sampling rate misses a significant number of additional
acceleration peaks which occur over this time interval. The corrected acceleration curve and
velocity curve is shown in Figure 22 (compare with Figure 16) and Figure 23 (compare with
Figure 20).
Figure 22. Repaired longitudinal acceleration data for test NETC-3.
Figure 23. Longitudinal velocity computed from repaired acceleration data.
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2
Acc
eler
atio
n (
G's
)
Time (sec)
X-Acceleration
C.G.
10
12
14
16
18
20
22
24
0.00 0.20 0.40 0.60 0.80 1.00
Ve
loci
ty (
m/s
)
Time (sec)
reported velocity
Integrated Acc. CG
int of 10-ms acc
23
None of the integrated acceleration curves agree exactly with the reported velocity, but it
seems that the data from the curve labeled as “C.G.” is the closest match. Therefore, for
validation purposes, those data were used directly as reported, with the exception of the
longitudinal acceleration, in which case the repaired data presented in Figure 22 was used.
Simulated Impact Summary
The finite element analysis of Test NETC-3 was conducted with a time-step of 1.26
microseconds for a time period of 1.5 seconds. The front-left tire of the vehicle contacted the 9-
inch curb within a few milliseconds of the start of the analysis. At 0.04 seconds the front
suspension was fully compressed as the front-left tire mounted the curb and the truck-cab began
to roll clockwise. From a top view perspective the vehicle began to yaw slightly clockwise. The
left-rear tires impacted the curb at 0.24 seconds. At 0.26 seconds the front bumper and fender of
the vehicle impacted the two top rails (Rail 3 and Rail 4) of the bridge rail at 26.9 inches
upstream of Post 6 at 99 inches upstream of a tube-rail splice. At 0.28 seconds the front-left tire
contacted the lower rail and at 0.3 seconds the second lowest rail was engaged by the front tire.
Also at 0.28 seconds the left rear suspension was fully compressed and engaged the bump-stop
as the tire mounted the curb. The cargo box then began to pitch upward, while the roll angle of
the cargo box remained relatively stable. At 0.3 seconds the simulated shear-pin between the
front-left suspension and front axle failed and the front axle began to slide backward on the leaf
springs. At 0.56 seconds the rear of the cargo box reached its highest vertical displacement of
13.9 inches. At 0.58 seconds the truck was parallel to the rail and the bottom of the cargo box
began to pass over the top of the bridge rail. The left-rear tires contacted all tube rails
simultaneously at 0.61 seconds. At 0.62 seconds the bridge rail experienced its highest lateral
dynamic deflection of 1.4 inches (36 mm). At 0.68 seconds the bottom rear of the cargo box
impacted the top of the bridge rail. There were no snags between the cross-beams of the cargo
box and rail; although, the potential for snag was apparent as the cross beams slid across the top
of the splice connection and past posts. At 0.69 seconds the lower edge of the cargo box reached
its maximum lateral displacement of approximately 15 inches behind the front face of the bridge
rail. The cargo box continued to slide along the top of the rail. As the vehicle was approaching its
highest roll angle, the front right tire raised off the ground at 0.75 seconds. At 0.8 seconds the
cargo box reached its highest counter-clockwise roll angle of 5.5 degrees. This resulted in a
maximum lateral displacement at the top of the cargo box of 21.3 inches behind the front face of
the bridge rail. The vehicle then began to roll clockwise away from the barrier. The right front
tire re-contacted the roadway at 0.87 seconds. The left rear tires re-contacted the ground at 1.07
seconds. At 0.79 seconds the cargo box lifted off the rail and then re-contacted the top of the rail
at 1.00 second. The back corner of the cargo box was just about to exit from bridge rail when the
termination time for the analysis was reached (i.e., 1.5 seconds).
The analysis was terminated at 1.5 seconds, at which time:
The roll angle of the truck cabin was 10.4 degrees away from the barrier and decreasing,
24
The pitch angle of the truck cabin was 2.95 degrees and constant,
The yaw angle of the truck cabin was 5 degrees clockwise (away from the barrier) and
increasing,
The roll angle of the cargo box was 12.9 degrees away from the barrier and decreasing,
The pitch angle of the cargo box was 2.31 degrees and constant,
The yaw angle of the cargo box was 5.64 degrees counter-clockwise (toward the barrier)
and constant,
The forward velocity of the vehicle was 36.9 mph.
Damage to Bridge Rail
The crash test installation received minor damage as shown in Figure 24 and Figure 25.
The test resulted in only minor scrapping of the rail and tire marks. The maximum dynamic
deflection of the bridge rail was 1.0 inch (25 mm) occurring at the top two rails at the splice
connection between posts 6 and 7. The resulting permanent deflection at these locations was
reported as 0.51 inches (13 mm). Posts 6 and 7 were tilted back and the base plates of both posts
were raised upward at the center approximately 0.14 inches (3.5 mm).
The damage to the bridge rail in the finite element analysis was similar to that of the full-
scale test. The tires and body of the vehicle model were in contact with the barrier from post 6
through post 11. The bottom of the truck box was in contact with the top of the rail through post
12. The maximum dynamic deflection of post 6 and post 7 was 0.94 inch (24 mm) and 1.1 inches
(29 mm) with resulting permanent deflections of 0.3 inches and 0.49 inches, respectively. The
greatest deflections of the bridge rail system occurred at the splice connection between posts 6
and 7. The maximum permanent deflection of Rail 1 (lowest rail) was 0.40 inch; the maximum
permanent deflection of Rail 2 was 0.47 inch, the maximum permanent deflection of Rail 3 was
0.51 inch; and the maximum permanent deflection of Rail 4 (top rail) was 0.66 inches. Figure 26
shows the results from the analysis illustrating the deformation (shaded component) of Rail 4
relative to the original position (black lines). As post 7 was tilted back, the base plate was
deflected upward at the front-center of the plate 0.08 inches (2 mm), compared to 0.14 inches
(3.5 mm) in the full-scale test. Overall, the simulated barrier response was very similar to that
observed in the full-scale test.
25
Figure 24. Damage to bridge rail in full-scale test NETC-3 from posts 6 through 8.
26
Figure 25. Damage to bridge rail in full-scale test NETC-3 from posts 8 through 11.
27
Figure 26. Analysis result showing maximum permanent deflection of top rail.
Qualitative Validation
Sequential Views
A qualitative assessment was made by comparing sequential snapshots of the full-scale
crash test with the results of the simulation to verify vehicle kinematic response as well as
sequence and timing of key phenomenological events. The results from the FE analysis compare
reasonably well with the results from full-scale crash test NETC-3. Figure 27 shows sequential
snapshots of the impact event from an upstream viewpoint. Figure 28 shows the sequential views
from an oblique (downstream and behind the barrier) viewpoint. Figure 29 shows sequential
views from an overhead view point. Based on visual inspection the model appears to simulate
the basic kinematic behavior of the truck and adequately captures the basic phenomenological
events that occur during impact.
28
Figure 27. Sequential views of Test NETC-3 and FE analysis from upstream viewpoint.
0.1 seconds
0.2 seconds
0.3 seconds
0.000 seconds
0.4 seconds
29
Figure 27. [CONTINUED] Sequential views of Test NETC-3 and FE analysis from
upstream viewpoint.
0.5 seconds
0.6 seconds
0.9 seconds
0.7 seconds
0.8 seconds
30
Figure 27. [CONTINUED] Sequential views of Test NETC-3 and FE analysis from
upstream viewpoint.
1.0 seconds
1.1 seconds
1.4 seconds
1.2 seconds
1.3 seconds
31
Figure 28. Sequential views of Test NETC-3 and FE analysis from downstream viewpoint.
0.1 seconds
0.2 seconds
0.3 seconds
0.4 seconds
0.000 seconds
32
Figure 28. [CONTINUED] Sequential views of Test NETC-3 and FE analysis from
downstream viewpoint.
0.6 seconds
0.7 seconds
0.8 seconds
0.9 seconds
0.5 seconds
33
Figure 28. [CONTINUED] Sequential views of Test NETC-3 and FE analysis from
downstream viewpoint.
1.1 seconds
1.2 seconds
1.3 seconds
1.4 seconds
1.0 seconds
34
Figure 29. Sequential views of Test NETC-3 and FE analysis from overhead viewpoint.
0.1 seconds
0.2 seconds
0.3 seconds
0.4 seconds
0.000 seconds
35
Figure 29. [CONTINUED] Sequential views of Test NETC-3 and FE analysis from
overhead viewpoint.
0.6 seconds
0.7 seconds
0.8 seconds
0.5 seconds
36
Occupant Risk Measures
Acceleration-time histories and angular rate-time histories were collected at the center of
gravity of the truck and at the floor pan inside the truck cabin using the *Element-Seatbelt-
Accelerometer option in LS-DYNA, which is the preferred method suggested by LS-DYNA for
collecting acceleration data.[LSDYNA13] The accelerometers were connected to the vehicle
model using *Nodal-Rigid-Body-Constraints (NRB). The time-history data was collected from
each accelerometer in a local reference coordinate system which rotates with the accelerometer
in the same way that test data is collected from physical accelerometers. The data was collected
at a frequency of 30 kHz which was determined to be sufficient to avoid aliasing of the data in
the numerical model.
The occupant risk assessment measures were computed using the three acceleration time-
histories and the three angular-rate time histories collected at the center of gravity of the vehicle.
The Test Risk Assessment Program (TRAP) calculates standardized occupant risk factors from
vehicle crash data in accordance with the National Cooperative Highway Research Program
(NCHRP) guidelines and the European Committee for Standardization (CEN).(TTI98)
Table 1 shows the occupant risk measures from the full-scale test and the quantities
computed from the FEA analysis. The test results were obtained directly from the test report,
while the FEA results were computed using TRAP software. The acceleration data from the
analysis was filtered using the SAE Class 180 filter prior to input in TRAP. The table shows the
two occupant risk factors recommended by NCHRP Report 350, which include: 1) the lateral and
longitudinal components of Occupant Impact Velocity (OIV) and 2) the maximum lateral and
longitudinal component of vehicle acceleration averaged over 10 millisecond intervals after
occupant impact, i.e, the occupant ridedown acceleration (ORA). Also shown in the table are the
EN 1317 occupant risk factors computed in the FE analysis, which include the Theoretical Head
Impact Velocity (THIV), the Post Impact Head Deceleration (PHD) and the Acceleration
Severity Index (ASI). These quantities were not reported in the NETC-3 crash test report.
The results indicate that the occupant risk factors for both the full-scale test and the
simulation are similar with the FEA analysis generally being more conservative. The occupant
impact velocity in the longitudinal direction was predicted from the simulation to be 2.4-m/s
(0.75 m/s higher than the test OIV of 1.65 m/s) at 0.2898 seconds. In the transverse direction the
occupant impact velocity predicted in the simulation was 5.5-m/s (2.61 m/s higher than the test
OIV of 2.9 m/s). The highest 0.010-second occupant ridedown acceleration in the longitudinal
direction was 9.4 g (0.45 g higher than the test ORA of 8.95 g) between 0.7290 – 0.7390
seconds. In the transverse direction the highest 0.010-second occupant ridedown acceleration
was 14.6 g (0.3 g higher than the test ORA of 14.3) between 0.7573 and 0.7673 seconds. In the
longitudinal direction the maximum 50-ms moving average acceleration value computed in the
analysis was 3.3 g’s compared to 2.7 g’s measured in the full-scale test. In the transverse
direction the maximum value computed in the analysis was 7.3 g’s compared to 5.8 g’s measured
in the full-scale test.
37
Table 1. Summary of occupant risk measures computed from test NETC-3 and FEA
simulation.
Time-History Data Comparison
Figure 30 through Figure 32 show a comparison of the acceleration-time histories for the
full-scale test and the FE analysis. These figures were taken directly from the test report and
were overlaid with the results from the FE analysis (see pages D1-D4 in Appendix A). Figure 33
shows a comparison of the yaw-rate between the test vehicle and FE analysis. Values for the
quantitative evaluation metrics are also shown on the time-history plots. The values in red font
indicate poor correlation between test and analysis results, while the values in black font indicate
good correlation. The quantitative metrics are discussed in more detail in the Quantitative
Evaluation section of this report.
Test 471470-26 FEA (R131114)
Occupant Impact Velocity x-direction 1.65 2.4
(m/s) y-direction 2.89 5.5
at time (0.222 sec) (0.2898 sec)
- 5.8
- (0.289 sec)
Ridedown Acceleration 8.95 9.4
(g's) (0.725 sec) (0.7290 - 0.7390 sec)
14.3 14.6
(0.582 sec) (0.7573 - 0.7673 sec)
- 14.7
- (07573 - 0.7673 sec)
- 0.82
Max 50-ms moving avg. acc. 2.7 3.3
(g's) (0.308 - 0.358 sec) (0.6877 - 0.7377 sec)
5.8 7.3
(0.557 - 0.607 sec) (0.8820 - 0.9320 sec)
- 4.3
- (0.2573 - 0.3073 sec)
PHD
Occupant Risk Factors
THIV
(m/s)
x-direction
y-direction
(g's)
ASI
x-direction
y-direction
z-direction
38
Figure 30. Longitudinal acceleration-time history plot from full-scale test NETC-3 and
FEA (FEA results filtered with SAE Class 60 filter).
Figure 31. Lateral acceleration-time history plot from full-scale test NETC-3 and FEA
(FEA results filtered with SAE Class 60 filter).
S-G (M) = 28.5S-G (P) = 37ANOVA = 2.92SD = 33.57
X-Acceleration
S-G (M) = 22.7S-G (P) = 34.9ANOVA = 2.12SD = 30.61
Y-Acceleration
39
Figure 32. Vertical acceleration-time history plot from full-scale test NETC-3 and FEA
(FEA results filtered with SAE Class 60 filter).
Figure 33. Yaw rate-time history plot from full-scale test NETC-3 and FEA (FEA results
filtered with SAE Class 60 filter).
S-G (M) = 35.8S-G (P) = 47.1ANOVA = 0.55SD = 51.02
Z-Acceleration
S-G (M) = 13.9S-G (P) = 16ANOVA = 4.2SD = 19.11
Yaw-Rate
40
Summary
The intent of the qualitative evaluation was to verify overall model response through a
general comparison with a full-scale crash test. The general response of the FE model appears
reasonable with regard to the basic kinematic response of the vehicle and barrier damage. The
occupant risk measures computed from the time-history data collected at the c.g. of the vehicle
also correlated reasonably well with the test data (refer to Quantitative Evaluation for further
comparison of occupant risk measures).
Quantitative Validation
The quantitative validation assessment of the model’s results was based on validation
procedures of NCHRP Web Document 179 (W179). [Ray10] The purpose of these guidelines is
to establish accuracy, credibility, and confidence in the results of crash test simulations that are
intended to support policy decisions and to be used for approval of design modifications to
roadside safety devices that were originally approved with full-scale crash testing.
The validation procedure has three steps:
1. Solution verification: Indicates whether the analysis solution produced numerically stable
results (ensures that basic physical laws are upheld in the model).
2. Time-history evaluation: Quantitative measure of the level of agreement of time-history
data (e.g., x, y, z accelerations and roll, pitch, and yaw rates) between analysis and test.
3. Phenomena Importance Ranking Table (PIRT): A table that documents the types of
phenomena that a numerical model is intended to replicate and verifies that the model
produces results consistent with its intended use.
The following is a discussion of the time-history evaluation metrics, their acceptance
criteria, and the Phenomena Importance Ranking Table for crash simulation.
Time-History Evaluation
The RSVVP (Roadside Safety Verification and Validation Program) software, which was
developed as part of NCHRP Project 22-24, was used to compute the comparison metrics
between analysis and full-scale test data. RSVVP computes fifteen different metrics that
quantify the differences between a pair of curves. Since many of the metrics share similar
formulations, their results are often identical or very similar and there is no reason to include all
the variations. The metrics recommended in Report W179 for comparing time-history traces
from full-scale crash tests and/or simulations of crash tests are the Sprague & Geers metrics and
the ANOVA metrics. The Sprague-Geers metrics assess the magnitude and phase of two curves
while the ANOVA examines the differences of residual errors between them. The definitions of
these metrics are shown below:
Sprague & Geers
41
22
22
1
2
2
)( iveComprehens
cos1
)( Phase
1)( Magnitude
PMC
mc
mcP
m
cM
ii
ii
i
i
ANOVA
2
max
)(1
)(Deviation Standard
1)()(Error Residual
r
ii
iir
ecmn
nm
cme
Where,
deviation standard relative
error residual average relative
valuealexperiment measured maximum
quanties measured
quantities calculated
max
r
i
i
e
m
m
c
Time-History Evaluation Acceptance Criteria
Once a measure of comparison is obtained using a quantitative metric, it is necessary to
establish an acceptance criterion for deciding if the comparison is acceptable. Because of the
highly nonlinear nature of crash events, there are often considerable differences in the results of
essentially identical full-scale crash tests as demonstrated in the W179 report. Likewise, a
computational model may not match “exactly” the results of a physical test, but the difference
should be no greater than what is expected between physical tests. The approach taken in the
W179 was to determine the realistic variation in the deterministic shape comparison metrics for a
set of identical physical experiments and use that variation as an acceptance criterion. The
current acceptance criteria are based on the results of a quantitative comparison of ten essentially
identical full-scale crash tests that were performed as part of the ROBUST project involving
small car impact into a vertical rigid wall at 100 km/hr and 25 degrees.[ROBUST02; Ray08]
The resulting acceptance criteria recommended by W179 for assessing the similarity of two
time-history curves are:
Sprague-Geers
o Magnitude should be less than 40 percent
o Phase should be less than 40 percent
ANOVA metrics
o Mean residual error should be less than 5 percent
o Standard deviation should be less than 35 percent.
42
Phenomena Importance Ranking Tables (PIRT)
The PIRT includes evaluation criteria corresponding to NCHRP Report 350 for TL-4
impacts and is patterned after the full-scale crash test evaluation criteria listed in Table 5.1 in
NCHRP Report 350. [Ross93] The values for the individual metrics from the full-scale test and
the computer analysis were reported and both the relative difference and absolute difference for
each phenomenon were computed. If the relative difference is less than 20 percent or if the
absolute difference is less than 20 percent of the acceptance limit in NCHRP Report 350 then the
phenomena are considered to be replicated.
Results
The quantitative evaluation was based on comparison of acceleration-time histories and
angular rate-time histories computed in the analysis to those measured in full-scale crash test
NETC-3. The impact conditions for the simulation matched exactly those from the full-scale test
(i.e., 17,875-lb SUT impacting at 49.8 mph and angle of 15 degrees.).[Kimball99] These impact
conditions correspond to NCHRP Report 350 test 4-12. A summary of the quantitative
comparison results are provided herein. Additional comparison data can be found in Appendix B.
Solution Verification
The first step in the validation process is to perform global checks of the analysis to
verify that the numerical solution is stable and is producing physical results (e.g., results conform
to the basic laws of conservation). The analysis was modeled as a closed system, which means
that energy is not being added or removed during the analysis. Thus, the total energy should
remain essentially constant throughout the analysis and should be equal to the initial kinetic
energy of the impacting vehicle. The one exception in this case is any kinetic energy generated
due to the gravity load which should be minimal during the short time period of the crash event
relative to the initial kinetic energy of the vehicle. Table 2 shows a summary of the global
verification assessment based on criteria recommended in Report W179. Figure 34 shows a plot
of the global energy-time histories from the analysis.
43
Table 2. Analysis Solution Verification Table.
Verification Evaluation Criteria
Change
(%) Pass?
Total energy of the analysis solution (i.e., kinetic, potential, contact, etc.)
must not vary more than 10 percent from the beginning of the run to the
end of the run.
0% Y
Hourglass Energy of the analysis solution at the end of the run is less
than five percent of the total initial energy at the beginning of the run. 0% Y
Hourglass Energy of the analysis solution at the end of the run is less
than ten percent of the total internal energy at the end of the run. 0% Y
The part/material with the highest amount of hourglass energy at the end
of the run is less than ten percent of the total internal energy of the
part/material at the end of the run.
0% Y
Mass added to the total model is less than five percent of the total model
mass at the beginning of the run.
177 lb
0.5% Y
The part/material with the most mass added had less than 10 percent of its
initial mass.
0.8%
Rail Tube Y
The moving parts/materials in the model have less than five percent of
mass added to the initial moving mass of the model. 0% Y
There are no shooting nodes in the solution? Y Y
There are no solid elements with negative volumes? Y Y
Figure 34. Plot of global energy-time histories from the analysis.
As shown in Table 2, all the solution verification parameters were satisfied so it can be
reasonably assumed that the solution represents a physically plausible impact event that obeys
basic conservation laws. This is confirmed as well by Figure 34 which shows that the total
energy remains fairly constant during the simulated event. The solution meets all the
recommended global energy balance criteria and appears to be free of any major numerical
problems. This does not indicate that the simulation is necessarily valid, only that the results
adhere to the basic laws of physics and that the solution is numerically stable.
44
Time-History Validation
The RSVVP computer program was used to compute the Sprague-Geer metrics and
ANOVA metrics using time-history data from the full-scale test (i.e., true curve) and analysis
data (i.e., test curve). The multi-channel option in RSVVP was used since this option computes
metrics for each individual channel as well as for the weighted composite of the combined
channels. The comparison involved the x-acceleration, y-acceleration, z-acceleration, and yaw-
rate. The roll-rate and the pitch-rate were not available for the full-scale test and were also not
reported in the test report, thus comparison of those data channels could not be performed.
The data for the full-scale test was obtained directly from tabulated data in the test report,
which was reported at a sampling rate of 100 data points per second. Due to the low frequency of
the sampling rate, no filtering was used on the full-scale test data. The FEA data was recorded at
a sampling rate of 30,000 data points per second and was filtered in TRAP using a SAE class 60
filter. The shift and drift options in RSVVP were not used for the FEA or the physical test data.
From visual inspection, the physical test data appeared to show no initial offset of acceleration
magnitude or drift. The data was synchronized in RSVVP prior to computing the evaluation
metrics.
The default metrics in RSVVP were selected for the quantitative evaluation. These
included the Sprague and Geers and the ANOVA metrics, as illustrated in Figure 35. The curves
were evaluated over 1.0 seconds of the impact event, which corresponded to the limits of the data
reported in the full-scale test.
Figure 35. RSVVP Metric selection for validation assessment.
Based on the validation metrics, a comparison of the individual components of
acceleration indicated good agreement for the x and y channels and mixed results for the z
channel. The results also indicated very good agreement for the yaw-rate data. The results are
shown in Table 3 and are summarized below:
Sprague-Geers Metrics
45
The Sprague-Geers metrics for the x-acceleration were good regarding both magnitude
(i.e., M = 28.5) and Phase (i.e., P = 37), which indicates that the simulation is in
agreement with the test.
The Sprague-Geers metrics for the y-acceleration were good regarding both magnitude
(i.e., M = 22.7) and Phase (i.e., P = 34.9), which indicates that the simulation is in
agreement with the test.
The Sprague-Geers metrics for the z-acceleration were good regarding magnitude (i.e., M
= 35.8), but the phase score was poor (i.e., P = 47.1).
The Sprague-Geers metrics for the yaw-rate were good regarding both magnitude (i.e., M
= 13.9) and phase (i.e., P = 16), which indicates that the simulation is in agreement with
the test.
ANOVA
The ANOVA metrics for the x-acceleration were good regarding both the mean residual
error (i.e., 2.92 percent) and the standard deviation of residual error (i.e., 33.57 percent),
which indicated that the simulation is in agreement with the test.
The ANOVA metrics for the y-acceleration were good regarding both the mean residual
error (i.e., 2.12 percent) and the standard deviation of residual error (i.e., 30.61 percent),
which indicated that the simulation is in agreement with the test.
The ANOVA metrics for the z-acceleration were good regarding the mean residual error
(i.e., 0.55 percent), poor regarding the standard deviation of residual error (i.e., 51.02
percent).
The ANOVA metrics for the yaw-rate were good regarding both the mean residual error
(i.e., 4.2 percent) and the standard deviation of residual error (i.e., 19.11 percent), which
indicated that the simulation is in agreement with the test.
46
Table 3. Roadside safety validation metrics rating table – time history comparison
(single-channel option).
Evaluation Criteria
Time interval [0.99 seconds]
O Sprague-Geers Metrics List all the data channels being compared. Calculate the M and P metrics using RSVVP and enter the results. Values less than or equal to 40 are acceptable.
Channel
RSVVP Curve Preprocessing Options
M P Pass? Filter
Option Sync.
Option
Shift Drift
True Curve
Test Curve
True Curve
Test Curve
x-acceleration SAE 60 Y none None none None 28.5 37 Y
y-acceleration SAE 60 Y None None None None 22.7 34.9 Y
z-acceleration SAE 60 Y None None None None 35.8 47.1 N
Yaw-rate SAE 60 Y None none None none 13.9 16 Y
P ANOVA Metrics List all the data channels being compared. Calculate the ANOVA metrics using RSVVP and enter the results. Both of the following criteria must be met:
The mean residual error must be less than five percent of the peak
acceleration ( Peakae 05.0 ) and
The standard deviation of the residuals must be less than 35 percent
of the peak acceleration ( Peaka 35.0 ).
Me
an R
esi
du
al
Sta
nd
ard
Dev
iati
on
of
Re
sid
ual
s
Pass?
x-acceleration 2.92 33.57 Y
y-acceleration 2.12 30.61 Y
z-acceleration 0.55 51.02 N
Yaw-rate 4.2 19.11 Y
Exception Notes: The “true curve” data for the full-scale crash test was recorded at a sample rate of 100 samples per second. This seems to have resulted in aliasing of the data, particularly for the x-channel which shows a sudden increase in velocity at 0.58 seconds.
Since the metrics computed for the individual data channels did not all satisfy the
acceptance criteria, the multi-channel option in RSVVP was used to calculate the weighted
Sprague-Geer and ANOVA metrics for the four channels of data. The Area II method is the
default method used in RSVVP for weighting the importance of each data channel. The Area (II)
method determines the weight for each channel based on a pseudo momentum approach using
the area under the curves.
Table 4 shows the results from RSVVP for the multi-channel option using the Area (II)
method. The resulting weight factors computed for each channel are shown in both tabular form
and graphical form in the tables. The results indicate that the x- and y-accelerations dominate the
47
translational motion of the vehicle, which implies that the velocity change in the z-direction is
insignificant compared to the change in velocity in the x- and y-directions. The weighted metrics
computed in RSVVP in the multi-channel mode all satisfy the acceptance criteria; therefore, the
time history comparison can be considered acceptable.
Table 4. Roadside safety validation metrics rating table – (multi-channel option).
Evaluation Criteria (time interval [__1.0 seconds_])
Channels (Select which were used)
X Acceleration Y Acceleration Z Acceleration
Roll rate Pitch rate Yaw rate
Multi-Channel Weights
X Channel: 0.185
Y Channel: 0.289 Z Channel: 0.026 Yaw Rate Channel: 0.5 Roll Channel: N.A.
Pitch Channel: N.A.
O Sprague-Geer Metrics Values less or equal to 40 are acceptable. M P Pass?
19.7 26.1 Y
P
ANOVA Metrics Both of the following criteria must be met:
The mean residual error must be less than five percent of the
peak acceleration
( Peakae 05.0 )
The standard deviation of the residuals must be less than 35
percent of the peak acceleration ( Peaka 35.0 ) Me
an R
esi
du
al
Sta
nd
ard
Dev
iati
on
o
f R
esi
du
als
Pass?
2 25.9 Y
Exception Notes:
PIRT – Crash Specific Phenomena
The last step in the validation procedure is to compare the phenomena observed in both
the crash test and the numerical solution. Table 5 contains the Report 350 crash test criteria with
the applicable test numbers. The criteria that apply to test 4-12 (i.e., corresponding to this
particular test case) are marked with a red square. These include criteria A, D, G, K and M.
Table 6 through Table 8 contain an expanded list of these same criteria including additional
specific phenomena that were measured in the test and that could be directly compared to the
numerical solution. Table 6 contains a comparison of phenomena related to structural adequacy,
Table 7 contains a comparison of phenomena related to occupant risk, and Table 8 contains a
comparison of phenomena related to vehicle trajectory.
0
0.1
0.2
0.3
0.4
0.5
0.6
X acc Y acc Z acc Yaw rate Roll rate Pitch rate
48
Table 5. Report 350 crash test criteria with the applicable test numbers.
Evaluation
Factors Evaluation Criteria
Applicable Tests
Structural
Adequacy A Test article should contain and redirect the vehicle; the vehicle
should not penetrate, under-ride, or override the installation although
controlled lateral deflection of the test article is acceptable.
10, 11, 12, 20, 21, 22, 35, 36,
37, 38
B The test article should readily activate in a predictable manner by
breaking away, fracturing or yielding. 60, 61, 70, 71, 80, 81
C
Acceptable test article performance may be by redirection, controlled
penetration or controlled stopping of the vehicle.
30, 31,, 32, 33, 34, 39, 40, 41,
42, 43, 44, 50, 51, 52, 53
Occupant
Risk D
Detached elements, fragments or other debris from the test article
should not penetrate or show potential for penetrating the occupant
compartment, or present an undue hazard to other traffic, pedestrians
or personnel in a work zone.
All
E
Detached elements, fragments or other debris from the test article, or
vehicular damage should not block the driver’s vision or otherwise
cause the driver to lose control of the vehicle. (Answer Yes or No)
70, 71
F The vehicle should remain upright during and after the collision
although moderate roll, pitching and yawing are acceptable.
All except those listed in
criterion G
G It is preferable, although not essential, that the vehicle remain
upright during and after collision.
12, 22 (for test level 1 – 30,
31, 32, 33, 34, 35, 36, 37, 38,
39, 40, 41, 42, 43, 44)
H
Occupant impact velocities should satisfy the following:
Occupant Impact Velocity Limits (m/s)
Component Preferred Maximum
10, 20, 30,31, 32, 33, 34, 36,
40, 41, 42, 43, 50, 51, 52, 53,
80, 81 Longitudinal and
Lateral 9 12
Longitudinal 3 5
60, 61, 70, 71
I
Occupant ridedown accelerations should satisfy the following:
Occupant Ridedown Acceleration Limits (g’s)
Component Preferred Maximum
10, 20, 30,31, 32, 33, 34, 36,
40, 41, 42, 43, 50, 51, 52, 53,
60, 61, 70, 71, 80, 81 Longitudinal and
Lateral 15 20
Vehicle
Trajectory K After collision it is preferable that the vehicle’s trajectory not intrude
into adjacent traffic lanes. All
L
The occupant impact velocity in the longitudinal direction should not
exceed 40 ft/sec and the occupant ride-down acceleration in the
longitudinal direction should not exceed 20 G’s.
11,21, 35, 37, 38, 39
M The exit angle from the test article preferable should be less than 60
percent of test impact angle, measured at the time of vehicle loss of
contact with test device.
10, 11, 12, 20, 21, 22, 35, 36,
37, 38, 39
N Vehicle trajectory behind the test article is acceptable. 30, 31, 32, 33, 34, 39, 42, 43,
44, 60, 61, 70, 71, 80, 81
49
Table 6. Roadside safety phenomena importance ranking table (structural adequacy).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Stru
ctu
ral A
deq
uac
y
A
A1
Test article should contain and redirect the vehicle; the vehicle should not penetrate, under-ride, or override the installation although controlled lateral deflection of the test article is acceptable. (Answer Yes or No)
Y Y Y
A2 Maximum dynamic deflection: - Relative difference is less than 20 percent or - Absolute difference is less than 6 inches
0.51 in 1.19 in 133%
0.68 in Y
A3 Length of vehicle-barrier contact: - Relative difference is less than 20 percent or - Absolute difference is less than 6.6 ft
40 ft 35 ft 12.5%
5 ft Y
A4 Number of broken or significantly bent posts is less than 20 percent.
0 0 0% 0
Y
A5 Did the rail element rupture or tear (Answer Yes or No) N N Y
A6 Were there failures of connector elements (Answer Yes or No).
N N Y
A7 Was there significant snagging between the vehicle wheels and barrier elements (Answer Yes or No).
N N Y
A8 Was there significant snagging between vehicle body components and barrier elements (Answer Yes or No).
N N Y
Exception Notes:
50
Table 7. Roadside safety phenomena importance ranking table (occupant risk).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Occ
up
ant
Ris
k
D
Detached elements, fragments or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment, or present an undue hazard to other traffic, pedestrians or personnel in a work zone. (Answer Yes or No)
N N Y
F
F1 The vehicle should remain upright during and after the collision although moderate roll, pitching and yawing are acceptable. (Answer Yes or No)
Y Y Y
F2 Maximum roll of the vehicle: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
N.A.
F3 Maximum pitch of the vehicle is: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
N.A.
F4 Maximum yaw of the vehicle is: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
L
L1
Occupant impact velocities: - Relative difference is less than 20 percent or - Absolute difference is less than 2 m/s.
Longitudinal OIV (m/s) 1.7 2.4 41% 0.7
Y
Lateral OIV (m/s) 2.9 5.5 89% 2.6 m/s
N
THIV (m/s) N.A. 5.8
L2
Occupant accelerations: - Relative difference is less than 20 percent or - Absolute difference is less than 4 g’s.
Longitudinal ORA 8.95 9.4 5%
0.45 g Y
Lateral ORA 14.3 14.6 0% 0.3 g
Y
PHD N.A. 14.7
ASI N.A. 0.82
Exception Notes: The lateral OIV was higher in the analysis, but for subsequent use of the model for evaluating system modifications this is considered a conservative, and therefore acceptable, value.
51
Table 8. Roadside safety phenomena importance ranking table (vehicle trajectory).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Veh
icle
Tra
ject
ory
M
M1 The exit angle from the test article preferable should be less than 60 percent of test impact angle, measured at the time of vehicle loss of contact with test device.
27% 3% Y
M2 Exit angle at loss of contact: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
4.1 deg 0.5 deg 88%
3.6 deg Y
M3 Exit velocity at loss of contact: - Relative difference is less than 20 percent or - Absolute difference is less than 10 km/hr.
35.8 mph 39.6 mph 11%
3.8 mph Y
M4 One or more vehicle tires failed or de-beaded during the collision event (Answer Yes or No).
Y Y Y
N N1 Vehicle travelled behind the test article (Answer Yes or No). N N Y
Exception Notes:
All the applicable criteria in Table 6 through Table 8 agree (i.e., the relative or absolute
difference between the numerical solution and the test was less than maximum allowable values),
except for the lateral OIV. In this case the model predicted a higher value than that measured in
the test (i.e., 5.5 m/s vs. 2.9 m/s). However, both results are relatively low for this metric with
respect to the Report 350 acceptance criteria and thus the slightly higher value in the model is
consider conservative and, therefore, acceptable for application in predicting collision
performance as it pertains to NCHRP Report 350 crash test evaluation criteria. Note that
although OIV measures are generally collected and reported for Test 4-12, they are not
considered in the assessment of system performance (refer to Table 5).
Summary
The finite element model of the NETC 4-Bar bridge rail was validated by comparing the
analysis results to those of full-scale crash test NETC-3 using the recommended procedures
defined in NCHRP Report W179. Test NETC-3 was conducted by SwRI to evaluate
performance compliance to Report 350 Test 4-12 (i.e., 17,875-lb SUT impacting at 49.8 mph and
angle of 15 degrees).
From a general comparison of the sequential snapshots of the crash test and simulation,
the general response of the FE model appears reasonable with regard to the basic kinematic
response of the vehicle and barrier damage. The occupant risk measures computed from the
time-history data collected at the c.g. of the vehicle also correlated reasonably well with the test
data. The analysis solution also met all the recommended global and material energy balance
criteria and was determined to be free of any major numerical problems.
The results of the quantitative validation assessment showed that there was good
agreement for the x-acceleration, y-acceleration, and yaw-rate, but showed mixed results for the
z component of acceleration. The Sprague-Geers magnitude metric was in good agreement for all
52
channels; however, the phase metric was high for the z-channel (i.e., P = 47.1 vs. allowable P =
40). Using the multi-channel procedure in Report W179, which weights the individual channels
based on their influence on the overall response of the system, the results indicated that the
analysis was a valid representation of the full-scale test. The weighted results indicated that the
yaw-rate and the y-acceleration had the most influence on vehicle response during the collision,
while the z-acceleration was comparatively inconsequential.
Comparison of the crash phenomena that is generally evaluated for compliance testing of
roadside hardware (e.g., structural adequacy, occupant risk, and vehicle stability) further
indicated that the analysis provided accurate results in predicting collision performance as it
pertains to NCHRP Report 350 crash test evaluation criteria. The summary sheet comparing the
results of the analysis to the full-scale test is shown in Figure 36.
Conclusions for Model Validation
The finite element analysis of the NETC 4-bar bridge rail system under NCHRP Report
350 Test Level 4 conditions demonstrated that the model replicates the basic phenomenological
behavior of the system in a redirection impact with an 8000S vehicle. There was good agreement
between the test and the simulations with respect to event timing, overall kinematics of the
vehicle, bridge rail damage and deflections. Quantitative comparison of the time-history data
indicated that the finite element model accurately replicates the results of the baseline crash test.
Thus, the model is considered valid for use in assessing the effects of incremental modifications
to the bridge rail system.
53
Figure 36. Summary of results from analysis compared with full-scale crash test for validation of the baseline model.
Date: 11/22/2013
Comparison:
Device Name:/Variant: Submissions Type: Non-Significant -- Effect is Uncertain
Testing Criterion: Non-Significant -- Effect is Positive
Test Level: Non-Significant -- Effect is Inconsequential
FHWA Letter: X Baseline Validation of Crash Test to FEA Analysis.
Test Number: Test FEA Occupant Risk (cont.) Test FEA
Vehicle: A1 - Acceptable perf.? Yes Yes L1 – Long. OIV 1.7 m/s 2.4 m/s
Vehicle Mass: A2 – Permenant 0.51 in 0.66 in L1 – Lat. OIV 2.9 m/s 5.5 m/s
Impact Speed: A3 – Contact Length 40 ft 35 ft L2 – Long. ORA 8.95 g 9.4 g
Impact Location: A5 – Comp. Failures? No No L2 – Lat. ORA 14.3 g 14.6 g
Tested Hardware: Original Design A6 – Connection Failure? No No Vehicle Trajectory
FEA Hardware: Original Design A7 – Wheel Snagging? No No M2 – Exit Yaw Angle 4.1 deg 0.5 deg
A8 – Vehicle Snagging? No No M3 – Exit Velocity 35.8 mph 39.6 mph
Total Energy: 5.0% Pass Occupant Risk Test FEA
Hourglass Energy: 0.0% Pass D – Detached elements? No No Sprague-Geer Magnitude < 40 19.7 Pass
Mass Added: <1% Pass F2 – Max. Vehicle Roll Unk Sprague-Geer Phase < 40 26.1 Pass
Shooting Nodes: No Pass F3 – Max. Vehicle Pitch Unk ANOVA Mean 2 Pass
Negative Volumes: No Pass F4 – Max. Vehicle Yaw Unk ANOVA Standard Deviation 25.9 Pass
(FHWA Memorandum)
W-179 Table E-5: Roadside PIRTS
Finite Element Analysis Determination of Elibibility for Reimbursement under the Federal-Aid Highway Program
SwRI NETC-3
8000S
NETC 4-Bar w/ Side Walk
NCHRP Report 350
TL 4
B50
Crash tested original design to FEA of original design
Structural Adequacy
Bridge RailSystem Type:
Baseline Crash Test
W-179 Table E-1: Verification Evaluation Summary
W-179 Table E-3 (Multi-Channel Method)
17,875 lb
49.8 mph / 15 deg
27 in. upstream of Post 6
0.40 sec 0.60 sec 0.80 sec 1.00 sec0.20 sec
FEA
An
alys
isC
rash
Te
st
54
REDESIGN OF BRIDGE RAIL FOR INSTALLATION ON STEEL
THROUGH-TRUSS BRIDGE
The design for the SBB44b bridge rail was modified for installation on steel through-
truss bridge decks. The modified system retained as much of the baseline design as possible in
order to stay within the FHWA requirements for non-significant changes. This is important
because FHWA policy allows acceptance of a modified system with non-significant changes if
the changes do not adversely affect performance. In such cases, the FHWA will classify the
modified system to have the same eligibility as the baseline system (i.e., Report 350 TL4 for the
SBB44b). The general modifications to the NETC 4-Bar bridge rail included:
Removing the 9-inch tall sidewalk such that the railing heights would be relative to the
wear-surface of the bridge deck,
Increasing post spacing from 8 ft to 10 ft so that the posts can be directly connected to the
floor-beams which are spaced at 10-ft center-to-center,
Raising the lower rail 2 inches from its original position to accommodate the 6-inch curb
fixed onto the side of the Acrow Panel system, and
Extending the post and connecting the post base to the deck support floor beams which
are located 5.4 inches below the roadway surface.
In the full-scale test of the original system, the kinematics of the vehicle as it impacted
and traversed the 9-inch tall sidewalk resulted in the cargo-box passing over the barrier allowing
the rear tandems of the truck to impact directly against the side of the railing. The removal of the
9-inch tall sidewalk was expected to not only affect the kinematics of the vehicle, but also result
in the cargo box impacting directly against the railing. As a first iteration of the design, an
analysis was conducted to evaluate the performance of the original bridge rail without the
sidewalk. These results were then compared to the original design with the sidewalk to: 1) verify
that the sidewalk was not critical to the successful performance of the system and 2) serve as the
baseline for comparison of the modified design without sidewalk. In the context of the FHWA
procedure, removal of the sidewalk/curb would be a non-significant modification likely resulting
in positive change in impact performance.
Analysis of Original NETC 4-Bar Bridge Rail without Sidewalk
An analysis of the original NETC 4-Bar bridge rail without sidewalk was performed
using FEA (i.e., Analysis Case NETC-NoCurb_R131114). The bridge rail model for the
analysis was exactly the same as was used for the validation, except that the curb/sidewalk was
removed.
Simulated Impact Summary
The analysis was conducted with a time-step of 1.26 microseconds for a time period of
1.0 seconds. The SUT model impacted the bridge rail at 24 inches upstream of post 6 at a speed
of 49.7 mph and 15 degrees (i.e., same impact conditions used in validation analysis). At 0.01
55
seconds the front bumper and fender of the vehicle impacted the two top rails (Rail 3 and Rail 4)
and at 0.02 seconds the front impact-side tire contacted rails 2 and 3. At 0.05 seconds the
vehicle started to yaw clockwise toward the barrier. At 0.067 seconds the simulated shear-pin
between the front-left suspension and front axle failed and the front axle began to slide backward
on the leaf springs. The rear U-bolt on the front suspension failed at 0.08 seconds. At 0.10
seconds the cargo box started to roll toward the barrier. The peak dynamic displacement of the
bridge rail resulting from the frontal impact occurred at approximately 0.12 seconds of the
impact as the front of the truck slid across the splice connection at post 7. The resulting peak
deflection was 1.5 inches for Rail 4, 1.25 inches for Rail 3, 1.0 inch for Rail 2 and 0.65 inch for
Rail 1. The front, lower corner of the cargo box impacted the top rail at Post 6 at 0.15 seconds,
which resulted in deformation of the cross-beams on the bottom of the cargo box. At 0.18
seconds the front axle had slid to the back of the leaf spring and was held by the remaining U-
bolt. At 0.20 seconds the front right tire lifted off the roadway and 0.24 seconds the rear, right
tandem wheels lifted off the roadway as the vehicle continued to roll toward the barrier. Also at
0.24 seconds, the front of the truck moved passed post 8. At 0.31 seconds the vehicle became
parallel to the rail as the rear of the cargo box impacted against the rail. The rear tandem axle of
the vehicle was approximately 8 inches downstream of Post 6 at the time of the impact. At 0.35
seconds the bridge rail experienced its highest lateral dynamic deflection of 3.4 inches at the
splice connection between posts 6 and 7. At 0.36 seconds the cabin of the truck reached a
maximum roll angle of 5.2 degrees counter-clockwise toward the barrier. At 0.42 second the
cargo box reached a maximum roll angle of approximately 10.2 degrees toward the barrier. The
roll of the truck box resulted in the top corner of the truck bed extending 17.5 inches behind the
face of the barrier. There were no snags between the cross-beams of the cargo box and rail;
although, the potential for snag was possible as the edge of the cross beams slid across the side
of the top rail splice connections. At 0.5 seconds, the vehicle lost contact with the barrier as it
was rolling away from the barrier. At this point the front of the vehicle was approximately 10
inches downstream of Post 10. The right front tire re-contacted the roadway at 0.51 seconds and
the vehicle reached a maximum pitch angle of 4.1 degrees at 0.60 seconds. The damaged front,
impact-side suspension caused the vehicle to turn back toward the barrier and resulted in the
front wheel re-contacting the barrier at 0.68 seconds. The impact caused the remaining U-bolt
on the suspension to fail, allowing the front axle to separate. The right rear tires re-contacted the
ground at 0.80 seconds. The analysis was terminated at 1.0 seconds, at which time:
The roll angle of the truck cabin was 13.4 degrees away from the barrier and increasing,
The pitch angle of the truck cabin was 4 degrees and stable,
The yaw angle of the truck cabin was 6.4 degrees counterclockwise (toward the barrier)
and stable,
The roll angle of the cargo box was 6.8 degrees away from the barrier and increasing,
The pitch angle of the cargo box was at a peak of 5 degrees stable,
The yaw angle of the cargo box was 5 degrees counterclockwise (toward the barrier) and
slightly increasing,
The forward velocity of the vehicle was 37.8 mph.
56
Sequential Views of Original NETC Bridge Rail with and without Sidewalk
Figure 37 shows side-by-side sequential views of the original NETC 4-Bar FEA
simulation with and without the 9-inch tall sidewalk from an upstream view point. The dynamics
of the vehicle as it impacted and traversed the sidewalk resulted in the vehicle impacting the
barrier with increased angular rates. In particular, as the truck crossed the sidewalk and
approached the barrier, the cargo box experienced a significantly higher vertical displacement, as
well as a roll angle away from the barrier. The increased pitch of the cargo box allowed it to pass
over the top of the rail during the impact. Whereas, in the case without the sidewalk the vertical
displacement of the cargo box was actually slightly negative and resulted in a direct impact
between the rear of the cargo box and the top rail of the barrier.
57
Figure 37. Sequential views of original NETC bridge rail with and without sidewalk under
TL4 impact conditions.
0.35 seconds
0.45 seconds
0.55 seconds
0.25 seconds
0.65 seconds
a) NETC w/ Sidewalk b) NETC wo/ Sidewalk
0.1 seconds
0.2 seconds
0.3 seconds
0.4 seconds
0.0 seconds
58
Figure 37. [Continued] Sequential views of original NETC bridge rail with and without
sidewalk under TL4 impact conditions.
0.6 seconds
0.7 seconds
0.8 seconds
0.9 seconds
a) NETC w/ Sidewalk b) NETC wo/ Sidewalk
0.5 seconds
0.85 seconds
0.95 seconds
1.05 seconds
0.75 seconds
1.15 seconds
59
Barrier Damage
Although the removal of the sidewalk affected the subsequent dynamics of the vehicle as
it impacted against the barrier, the general response of the barrier itself was very similar to that
of the original design with sidewalk. The direct lateral impact of the cargo box against the side
of the bridge rail resulted in slightly higher rail deflections than occurred in the original case.
The maximum dynamic deflection of post 6 and post 7 was 3.33 inches (84.2 mm) and 0.91
inches (23.3 mm) with permanent deflections of 2.0 inches and 0.33 inches, respectively. The
greatest deflections of the rail elements occurred at the splice connection between posts 6 and 7.
The maximum permanent deflection of Rail 1 (lowest rail) was 0.32 inch; the maximum
permanent deflection of Rail 2 was 0.49 inch, the maximum permanent deflection of Rail 3 was
0.89 inch; and the maximum permanent deflection of Rail 4 (top rail) was 2.03 inches. Table 9
shows a comparison of barrier deflections for the original design with and without the sidewalk.
The deflection of post 6 and 7 was primarily due to yielding of the base plate. As the rear
of the cargo box impacted the rail at Post 6 the, the base plate deflected upward at the front-
center of the plate resulting in a permanent deflection of 0.33 inches (8.46 mm). The permanent
deflection of the base plate at Post 7 was 0.052 inch (1.3 mm). In the full-scale test and the
analysis of the bridge rail with the sidewalk the rear tandems of the truck impacted against the
rail at the midpoint between posts 6 and 7; whereas, in the case without the sidewalk the rear of
the cargo box impacted the rail at a point 6 feet upstream of Post 6, as illustrated in Figure 38.
Table 9. Summary of barrier deflections for the original NETC 4-Bar bridge rail with and
without sidewalk under TL4 impact conditions.
Baseline
Test NETC-3
with Sidewalk
(in)
NETC Model
with Sidewalk
(in)
NETC Model
without Sidewalk
(in)
Post 6 0.3 2
Post 7 0.49 0.33
Rail 1 0.4 0.32
Rail 2 0.47 0.49
Rail 3 0.51 0.89
Rail 4 0.51 0.66 2.03
Post 6 Base Plate 0.02 0.05 0.33
Post 7 Base Plate 0.02 0.08 0.052
Maximum Permanent Deflections
Component
Original
60
Figure 38. Results for original design (a) with and (b) without sidewalk illustrating the
different impact locations of the rear of the truck against the rail.
Time-History Data Comparison
Figure 39 through Figure 49 show a comparison of the acceleration, velocity, angular-rate
and angular displacement time histories for the TL4 baseline analysis of the NETC bridge rail
with and without the 9-inch tall sidewalk. The data for the analysis with the sidewalk was shifted
along the time axis by -0.25 seconds so that the time-zero point in the plots corresponded to the
time of impact with the barrier. The timing of the peaks in the acceleration plots was somewhat
out of sync due to the effects of the sidewalk; however, the magnitudes of the peaks were very
similar in all cases. The yaw rate and angle were also very similar up to the point when the rear
of the cargo box impacted against the rail for the case without the sidewalk.
Rear of cargo box impacts railPost 5 Post 6 Post 7
(b) Original design without sidewalk
Truck tandems impacts railPost 5 Post 6 Post 7
(a) Original design with sidewalk
61
Figure 39. 50-ms average longitudinal acceleration for baseline NETC barrier with and
without sidewalk.
Figure 40. Longitudinal-velocity-time history for baseline NETC barrier with and without
sidewalk.
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
-0.25 0 0.25 0.5 0.75 1
X-A
cce
lera
tio
n (
G's
)
Time (sec)
Baseline w/ sidewalk
Baseline wo/ Sidewalk
Rear of cargo box impacts with barrier (without sidewalk)
Rear tandems impact with barrier (original with sidewalk)
30
35
40
45
50
55
-0.25 0 0.25 0.5 0.75 1
Ve
loci
ty (
mp
h)
Time (sec)
With Sidewalk
Without Sidewalk
Rear of cargo box impacts with barrier (without sidewalk)
62
Figure 41. 50-ms average lateral acceleration for baseline NETC barrier with and without
sidewalk.
Figure 42. Lateral-velocity-time history for baseline NETC barrier with and without
sidewalk.
-4
-3
-2
-1
0
1
2
3
4
5
-0.25 0 0.25 0.5 0.75 1
Y-A
cce
lera
tio
n (
G's
)
Time (sec)
50-ms Average
Baseline w/ sidewalk
Baseline wo/ Sidewalk
0
2
4
6
8
10
12
14
16
18
20
-0.25 0 0.25 0.5 0.75 1
Ve
loci
ty (
mp
h)
Time (sec)
With Sidewalk
Without Sidewalk
63
Figure 43. 50-ms average vertical acceleration for baseline NETC barrier with and without
sidewalk.
Figure 44. Yaw rate-time histories for baseline NETC barrier with and without sidewalk.
-3
-2
-1
0
1
2
3
-0.25 0 0.25 0.5 0.75 1
Y-A
cce
lera
tio
n (
G's
)
Time (sec)
50-ms Average
Baseline w/ sidewalk
Baseline wo/ Sidewalk
-60
-40
-20
0
20
40
60
80
100
-0.25 0 0.25 0.5 0.75 1
Yaw
Rat
e (
de
g/se
c)
Time (sec)
With Sidewalk
Without Sidewalk
64
Figure 45. Yaw angle-time history for original barrier with and without sidewalk.
Figure 46. Roll rate-time histories for baseline NETC barrier with and without sidewalk.
0
5
10
15
20
25
-0.25 0 0.25 0.5 0.75 1
Yaw
An
gle
(d
eg)
Time (sec)
With Sidewalk
Without Sidewalk
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
-0.25 0 0.25 0.5 0.75 1
Ro
ll R
ate
(d
eg/
sec)
Time (sec)
With Sidewalk
Without Sidewalk
65
Figure 47. Roll angle-time history for original barrier with and without sidewalk.
Figure 48. Pitch rate-time histories for baseline NETC barrier with and without sidewalk.
-15
-10
-5
0
5
10
-0.25 0 0.25 0.5 0.75 1
Ro
ll A
ngl
e (
de
g)
Time (sec)
With Sidewalk
Without Sidewalk
-100
-80
-60
-40
-20
0
20
40
60
-0.25 0 0.25 0.5 0.75 1
Pit
ch R
ate
(d
eg/
sec)
Time (sec)
With Sidewalk
Without Sidewalk
66
Figure 49. Pitch angle-time history for original barrier with and without sidewalk.
Occupant Risk Measures
Table 10 shows a comparison of the occupant risk measures for the barrier with and
without a sidewalk. The occupant impact velocities in the x- and y-directions were 1.8 m/s and
3.9 m/s, respectively. The highest 0.010-second occupant ridedown accelerations in the x- and y-
directions were 6.8 g and 15 g, respectively. The maximum 50-ms moving average accelerations
in the x-, y- and z- directions were 2.1 g, 6.6 g and 2.1 g, respectively. As indicated in Table 10,
the removal of the sidewalk from the bridge rail system had an insignificant effect on the
occupant risk measures.
-4
-3
-2
-1
0
1
2
3
4
-0.25 0 0.25 0.5 0.75 1
Pit
ch A
ngl
e (
de
g)
Time (sec)
With Sidewalk
Without Sidewalk
67
Table 10. Summary of occupant risk measures comparing response for original NETC
bridge rail with and without sidewalk.
Summary and Conclusions
An analysis was conducted to evaluate the response of the NETC 4-Bar bridge rail
without a sidewalk under TL-4 impact conditions. Comparing the results from this analysis to
the results from the previous analysis (and full-scale test) of the bridge rail with the sidewalk
showed that:
The velocity-time histories for both cases were similar.
The yaw-time histories for both cases were similar up to the point when the rear
of the truck’s cargo box impacted against the rail.
There were notable differences in the roll and pitch of the vehicle for the two
cases.
The barrier deflections were slightly higher for the case without a sidewalk.
Occupant risk measures were very similar for both cases.
The differences in the barrier’s response for these two cases were attributed to the
differences in the vehicle orientation and dynamics (i.e., attitude) resulting from impact with the
9-inch tall sidewalk. In particular, the increased pitch angle of the cargo box after impacting and
traversing the vertical curb resulted in the box passing over the top of the barrier; whereas, the
cargo box impacted directly against the side of the barrier in the analysis without the sidewalk.
Although the sidewalk does indeed affect the specific response of the vehicle as it interacts with
the barrier, the overall response of the barrier with and without the sidewalk were similar and
were well within the limiting criteria of NCHRP Report 350. The summary sheet comparing the
results of the analysis of the baseline design with and without sidewalk is shown in Figure 50.
Without Sidewalk
Test FEA (1114) FEA
x-direction
(m/s) 1.65 2.4 1.8
y-direction
(m/s) 2.89 5.5 3.9
- 5.8 4
x-direction 8.95 9.4 6.8
y-direction 14.3 14.6 15
- 14.7 15.4
- 0.82 0.76
x-direction 2.7 3.3 2.1
y-direction 5.8 7.3 6.6
z-direction - 4.3 2.1
Test 4-12 for NETC 4-Bar Barrier
With Sidewalk
Occupant Impact Velocity
THIV (m/s)
Ridedown Acceleration
(g's)
PHD (g's)
ASI
Max 50-ms moving avg. acc.
(g's)
Occupant Risk Factors
68
Figure 50. Summary of results for analysis of baseline design without sidewalk compared to analysis of crash tested design
with sidewalk.
Date: 11/24/2013
Comparison:
Device Name:/Variant: Submissions Type: Non-Significant -- Effect is Uncertain
Testing Criterion: Non-Significant -- Effect is Positive
Test Level: X Non-Significant -- Effect is Inconsequential
FHWA Letter: Baseline Validation of Crash Test to FEA Analysis.
Analysis Number: w/ sidewalk wo/ sidewalk Occupant Risk (cont.) w/ sidewalk wo/ sidewalk
Vehicle: A1 - Acceptable perf.? Yes Yes L1 – Long. OIV 2.4 m/s 1.8 m/s
Vehicle Mass: A2 – Permenant 0.66 in 2.0 in L1 – Lat. OIV 5.5 m/s 3.9 m/s
Impact Speed/Angle: A3 – Contact Length 35 ft 20 ft L2 – Long. ORA 9.4 g 6.8 g
Impact Location: A5 – Comp. Failures? No No L2 – Lat. ORA 14.6 g 15.0 g
Original Hardware NETC with sidewalk 8-ft span A6 – Connection Failure? No No Vehicle Trajectory
Modified Hardware NETC without sidewalk 8-ft span A7 – Wheel Snagging? No No M2 – Exit Yaw Angle 0.5 deg 0.6 deg
A8 – Vehicle Snagging? No No M3 – Exit Velocity 39.6 mph 42.5 mph
Total Energy: 0.0% Pass Occupant Risk w/ sidewalk wo/ sidewalk
Hourglass Energy: 0.0% Pass D – Detached elements? No No Sprague-Geer Magnitude < 40 N.A.
Mass Added: <1% Pass F2 – Max. Vehicle Roll 5.5 deg 10.4 deg Sprague-Geer Phase < 40 N.A.
Shooting Nodes: No Pass F3 – Max. Vehicle Pitch 3.3 deg 3.4 deg ANOVA Mean N.A.
Negative Volumes: No Pass F4 – Max. Vehicle Yaw 0.5 deg 4.1 deg ANOVA Standard Deviation N.A.
W-179 Table E-1: Verification Evaluation Summary
W-179 Table E-3 (Multi-Channel Method)
17,875 lb
49.8 mph / 15 deg
24 inches upstream of Post 6
(FHWA Memorandum)
W-179 Table E-5: Roadside PIRTS
Finite Element Analysis Determination of Elibibility for Reimbursement under the Federal-Aid Highway Program
NETC-3_R131114
50_F800-131025_FullBallast.k
Baseline NETC 4-Bar wo/ Sidewalk
NCHRP Report 350
TL 4
Crash tested original design to FEA of original design
Structural Adequacy
Bridge RailSystem Type:
Baseline Crash Test
0.20 sec 0.40 sec 0.60 sec 0.80 sec0.00 secWit
ho
ut
Sid
ewal
kW
ith
Sid
ewal
k
69
Modified Design
Figure 51 shows the installation drawing of the NETC 4-Bar bridge rail attached to
Structal’s steel through-truss bridge. The modifications to the bridge rail design were kept
minimal and included only those necessary for attachment to the bridge structure and for
maintaining bridge rail performance. Of critical importance in the design was the attachment of
the post and base plate to the floor beams of the bridge superstructure. In particular, it was
necessary to ensure that the mount was sufficiently strong enough to withstand TL-4 impact
loads, while not causing damage to the floor beams. In other words, the forces from the post-
mount should be appropriately distributed onto the floor beams such that no plastic deformations
of the bridge structure occur. The specific modifications relative to each system component is
discussed in the following sections.
Tubular Railing
The tubular rails for the modified design were the same structural sections used in the
original design (i.e., TS4x4x0.25-inch structural tubing for the top and the two lower rails and
TS8x4x0.3125-inch structural tubing for the second rail from the top). According to the
specifications of the original design, the rail must be attached to at least two posts. The post
spacing for the modified design is 10-feet; therefore, the minimum required length of the tubular
sections for the modified system is 20 feet, with the splice connection located at 24 inches
upstream of the post. The standard length for the tubular rails was set to 30 feet to reduce the
number of splice connections. It was assumed that longer spans and fewer splices would improve
crash performance and reduce construction cost. Note that the standard length of the tubular rails
in the crash tested design was 24 feet and also spanned three posts.
The material for the tubular rails in the modified design was the same as that specified for
the original system, which was AASHTO A500 Grade B with a minimum tensile strength of 58
ksi. Contractors often prefer to use A500 Grade C structural tubing, which has a minimum
tensile strength of 62 ksi. The analysis of the modified bridge rail was performed using ASTM
A500 Grade B steel in order to conform to the baseline system properties. However, if the
system performs well with this lower grade steel, then the higher Grade C steel (with slightly
higher strength) should also be acceptable.
70
Figure 51. Drawing for the NETC 4-Bar bridge rail attached to a through-truss bridge.
71
Post and Base Plate
The modified design retains the same W6x25 steel posts used in the original system with
ASTM A709 Grade 50 steel; however, the length of the posts were extended in order to fasten
them to the top flange of the floor-beam which is located 5.4 inches below the surface of the
roadway. The original design used a 1-inch thick steel base plate welded to the bottom of the
post. It was determined from review of the full-scale test results, as well as the finite element
simulation, that the base plate was the “weak point” of the post-mount system. For example, the
deflection of the posts in the full-scale TL-4 test and in the simulated impact was due primarily
to the deflection of the base plate as the front, center of the plate bent and lifted upward when the
bridge rail pushed back during the impact event.
For the modified design, the thickness of the base plate was increased to 1.5 inches to
account for the increased bending moment at the base of the post - resulting from the longer post
length in the modified system. As will be discussed in the following sections, this thicker base
plate resulted in an overall stiffness for the post-mount system that was slightly higher than the
original design.
A 0.787 inch (20 mm) thick gusset plate also exists between the base plate and the floor
beam. The gusset plate primarily serves as the connection of the floor beam to the main chord of
the bridge (refer to Figure 51), but it also provides additional rigidity to the floor beam. Given
the increased thickness of the base plate plus the thickness of the gusset, the effective increase in
post length for the modified design was only 4.1 inches.
Design Alternatives for Post Mount
As previously mentioned, a critical aspect of the design involved ensuring that TL-4
loading on the bridge rail does not compromise the bridge superstructure. Key to the success of
the design was ensuring that the loads from the bridge rail were properly distributed onto the
bridge’s floor beams. As shown in Figure 51, the floor beams are W27x146 structural steel
sections with material conforming to CSA G40.21 350W (US equivalent steel is ASTM A572).
The geometric and material properties of the floor beams are listed in Table 11.
Table 11. Geometric and mechanical properties for the bridge floor beams.
Several mounting options were evaluated, but only those considered to be the most
promising are presented herein. Figure 52 through Figure 56 illustrates the various mounting
options. In all cases:
The base plate is 1.5 inches thick;
The mounting bolts are the same diameter and material as the original system (i.e., 1-inch
diameter ASTM A449);
The bolt pattern for fastening down the base plate is the same as the original system;
Web Min. Min.
Thickness Width Thickness Zx Zy Yield Strength
(in2) (in) (in) (in) (in) (in3) (in3) (ksi) (ksi)
W27x146 42.9 27.38 0.605 14 0.975 461 97.5 50.76 450 19
Plastic ModulusFlange
Designation
Area Depth Min. Percent
Elongation
72
The post is positioned 0.67 inches (17 mm) farther back on the base plate relative to its
original position, as illustrated in Figure 57. The base plate is positioned as far back from
the roadway as possible, without interfering with the existing bolts that fasten the gusset
to the floor beam. An additional offset of the post was necessary, however, to maintain
the minimum allowable offset distance for the barrier relative to the edge of the roadway.
Figure 52. Schematic of mount design option 09a.
Figure 53. Schematic of mount design option 10b.
73
Figure 54. Schematic of mount design option 11b.
Figure 55. Schematic of mount design option 11c.
Figure 56. Schematic of mount design option 12.
74
Figure 57. Location of mounting bolts and post attachment to base plate.
Mounting option 09a is the simplest option regarding installation and includes a 1.25-
inch thick bearing plate placed on the bottom side of the flange to distribute the bolt-loads over a
larger area of the flange. Mounting option 10b is the most robust and includes two sets of two
full-length vertical stiffeners placed between the flanges on each side of the floor beam and
oriented perpendicular to the floor beam web. The stiffener plates are placed 1.5 inches fore and
aft of the bolt holes in the flange and are joined to the floor beam using full-length welds along
the flange and the web. Mounting option 11b is the second most economical alternative and
includes a single ¾-length vertical stiffener oriented perpendicular to the floor beam and placed
between the flanges on each side of the floor beam. The stiffener plate is placed 1.5 inches in
front of the front bolt hole in the flange and is joined to the floor beam with full-length welds
along the flange and web. Mounting option 11c is similar to mounting option 11b but includes
two ¾-length vertical stiffeners on each side of the floor beam. Mounting option 12 includes a
full-length 0.563-inch thick vertical stiffener plate oriented parallel to the floor beam and welded
to the top and bottom flanges on each side of the floor beam. The stiffener plates for alternative
12 are 10 inches wide.
10 in
14 in
10 in
1.81 in
2 in
10 in
1.14 in
(a) Original position
(b) Modified position
75
Analysis of Post Loading on Mount Alternatives
Finite element analysis was used to evaluate the response of the post-mount system under
impact loading and the potential for damage to the bridge floor beam. Three loading cases were
evaluated. Load Case 1 involved a 2,372-lb pendulum impacting the post at 35 inches above
grade and at an impact speed of 10 mph. This impact condition is similar to that traditionally
conducted for measuring dynamic response of guardrail posts. The resulting dynamic deflection
of the post at the impact point was similar to the dynamic deflection of the post in the TL-4
simulated impact of the NETC-4Bar bridge rail without sidewalk (refer to Table 9) and is thus
considered to be analogous to the 85th
percentile maximum loading for bridge rail.
For Load Cases 2 and 3, a 13.8 in (350 mm) displacement was applied to the top of the
post over a time interval of 0.09 seconds; and the displacement loading was applied at a constant
rate. For load Case 2 the displacement was applied perpendicular to the face of the post. Case 3
involved the loading applied at 20 degrees with respect to the face of the post. Both cases
represent extreme loading scenarios which may occur, for example, as a result of a high impact-
severity crash or from a vehicle snagging on a post. The purpose of these loading cases was 1) to
ensure that the overall stiffness of the post-mount system was greater than or equal to that of the
original design and 2) to ensure that the post-mount system would yield or fail prior to the floor
beam experiencing critical forces. In particular, Load case 3 creates a torsional loading about the
weak axis of the floor beam. The analysis matrix for this study is shown in Table 12.
Table 12. Matrix of analyses used in evaluating the various mount design alternatives.
The lateral extension of the gusset to the left and right of the floor beam as well as the
connections of the gusset to other components of the bridge structure were not included in the
model. This effectively yielded a conservative loading on the floor beam, since the effect of the
gusset plate on the stiffness of the floor beam was not considered. Figure 51 Section B-B shows
a plan view of the bridge structure illustrating the lateral extent of the gusset and its connection
to the bridge structure.
Load Case 1 (Pendulum Impact)
Only two design alternatives were evaluated for Load Case 1. These included the design
options with the least amount of stiffness added to the floor beam and were therefore considered
to represent a lower-bound stiffness for all the post-mount alternatives. The results of the
analyses are shown in Table 13 and in Figure 58. Both design alternatives showed an increased
stiffness for the post-mount system and resulted in approximately a 25 percent reduction in post
Standard
Pendulum Loading
Load Case 1 Load Case 2 Load Case 3
Original x x x
09a x x x
10b x x
11b x x x
11c x x
12 x x
"High" Displacement LoadingDesign Alt.
76
deflection compared to the original design. For alternative 09a, the maximum plastic strain in the
floor beam was 0.005 and occurred at the juncture of the beam flange and the web, as shown in
Figure 59. For alternative 11b, a maximum plastic strain of 0.004 occurred in the floor beam.
The plastic deformations in for this case were located on the top flange and were isolated to the
local area immediately surrounding the front bolt holes, as shown in Figure 60.
Table 13. Results for Load Case 1 (Pendulum Impact)
Figure 58. Force-displacement history of post mount for Load Case 1.
Dynamic Permanent
(in) (in) (kips) (kips) (ksi)
Original - 3.2 2.4 36 114 145
09a 0.005 3.0 1.8 43 106 135
11b 0.004 2.9 1.9 44 104 132
Load Case 1
Max Plastic
Strain in
Floor Beam
Max Disp. of PostDesign
AlternativeMax Force
on Post
Max Force
on Bolt
Max Stress
on Bolt
0
5
10
15
20
25
30
35
40
45
50
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Forc
e (
kip
s)
Displacement (inches)
Original Design
Alt 09a
Alt 11b
77
Figure 59. Contour of effective plastic strain for Load Case 1 on design Alternative 09a.
Figure 60. Contour of effective plastic strain for Load Case 1 on design Alternative 11b.
Load Case 2 (Applied Displacement - Perpendicular to Post Flange)
The results for Load Case 2 are shown in Figure 61 and Figure 62 and a summary of the
results are provided in Table 14. All of the design alternatives resulted in a higher effective
stiffness for the post-mount system compared to the original design. Note that the post is the
same W6x25 steel section used in the original design, thus the increase in stiffness was due
primarily to the increased thickness of the base plate. Recall, however, that the post was set back
0.67 inches relative to its original position on the base plate (refer to Figure 57) which effectively
78
increased the moment arm between the front bolts and the post. This repositioning of the post
resulted in a reduction of approximately 14 percent in the tensile loads of the front mounting
bolts, compared to the original design, which further reduces the stresses in the base plate. Figure
61 shows the maximum deformation of the base plate for the various design alternatives
compared to the original design, illustrating the reduced deflections of the base plate for the
design alternatives.
Table 14. Results for Load Case 2 (Applied displacement 90 degrees to post flange).
Figure 61. View of maximum deformation of various mount designs for Load Case 2.
Flange Web
(in) (in) (kips) (ksi)
Original - - - 133 169
09a 0.006 0 0.079 0.000 113 144
10b 0.004 0 0.031 0.000 115 146
11b 0.004 0 0.026 0.000 116 148
11c 0.005 0 0.031 0.000 116 148
12b 0.003 0 0.031 0.000 115 146
Max Stress
on Bolt
Load Case 2
Max Force
on Bolt
Max Plastic Strain
in Floor Beam
Flange Web
Design
Alternative
Max Disp. of Floor
Beam
OriginalDesign
Alternative 09a Alternative 10b
Alternative 11b Alternative 11c Alternative 12b
79
Figure 62. Force-displacement history of post-mount alternatives for Load Case 2.
The plastic strains in the floor beam for this loading condition were local to the area
around the front bolt holes in the flange, with the exception of design alternative 09a. Stiffeners
were not attached to the floor beam flange in design alternative 09a, thus allowing the flange to
flex upward under the load. This resulted in higher deflections of the flange, as indicated in
Table 14, and thus higher strains at the juncture of the beam’s flange and web (refer to Figure
59).
Load Case 3 (Applied Displacement – 20 Degrees to Post Flange)
The results for Load Case 3 are shown Figure 63 and Figure 64 and summarized in Table
15. Figure 63 shows the deflected shape of the structure at the point of maximum loading;
whereas Figure 64 overlays the deflected shape with contours of effective plastic strain on the
floor beam. The most significant plastic strains occurred for design alternatives 11b and 11c with
magnitudes of 0.01 and 0.007, respectively. The plastic strains for these two cases were isolated
to the lowest point of the weld between the stiffener plate and the web of the floor beam. Based
on the low magnitude and the location of the plastic deformations, their effects on the bridge
structure are considered to be of little significance. The remaining design options resulted in
negligible plastic deformation of the floor beam.
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12
Forc
e (
kip
s)
Disp (inches)
Original Design
Alt. 09a
Alt. 10b
Alt. 11b
Alt. 11c
Alt. 12b
Original Alt. 11b
80
Table 15. Results for Load Case 3 (Applied displacement at 20 degrees to post flange).
Figure 63. View of maximum deformation of various mount designs for Load Case 3.
Flange Web
(in) (in) (kips) (ksi)
Original - - -
09a 0.005 0.000 0.200 0.051 80.7 103
10b 0.002 0.000 0.025 0.004 75.5 96
11b <0.001 0.010 0.080 0.141 91.4 116
11c 0.002 0.007 0.059 0.130 75.8 97
12b 0.001 0.000 0.097 0.039 70.8 90
Design
Alternative
Load Case 3Max Plastic Strain
in Floor Beam
Max Disp. of Floor
Beam Max Force
on Bolt
Max Stress
on Bolt
Flange Web
OriginalDesign
Alternative 09a Alternative 10b
Alternative 11b Alternative 11c Alternative 12b
Image not available
81
Figure 64. Contour of effective plastic strain on floor beam for Load Case 3.
Summary and conclusions for the Analyses of the Mounting Designs
Three loading cases were evaluated to ensure that the overall stiffness of the post-mount
design were greater than or equal to that of the original design and to ensure that the post or base
plate would yield or fail prior to the floor beam experiencing critical damaging load levels. Load
Case 1 involved a 2,372-lb pendulum impacting the post at 35 inches above grade and at an
impact speed of 10 mph; Load Cases 2 and 3 involved a displacement-time history applied to the
top of the post at constant velocity. The loading was applied perpendicular to the post in Load
Case 2 and at 20 degrees to the post for Load Case 3; both cases were considered to represent
extreme loading conditions which may result from high impact-severity collisions (e.g., tractor-
trailer impact) or from a vehicle snagging on a post.
The results of the analyses indicated that each of the design alternatives presented herein
provided acceptable stiffness for mounting of the bridge rail post directly to the floor beam. That
is, the effective stiffness of the floor beam for each of the five design alternatives was
sufficiently greater than that of the post-mount to ensure that deformation of the bridge structure
would be negligible.
OriginalDesign
Alternative 09a Alternative 10b
Alternative 11b Alternative 11c Alternative 12b
Image not available
82
CONDUCT REPORT 350 TL-4 CRASH PERFORMANCE EVALUATION
OF MODIFIED BRIDGE RAIL
The baseline model of the NETC 4-Bar bridge rail was modified to include the design
changes specified in the previous section for design alternative 11b. This design was selected
because it was considered the most practical for installation and it also represents the worse-case
scenario for all options considered. Thus, successful performance of this design should translate to
successful performance for the other design alternatives as well.
Finite element analysis was used to evaluate the crash performance of the modified NETC
bridge rail system based on structural adequacy, vehicle stability during and after redirection, and
occupant risk factors using criteria specified in Report 350 for Test 4-12. Report 350 requires that
the barrier must redirect the vehicle without allowing the vehicle to penetrate the system; detached
elements should not show potential for penetrating the occupant compartment; deformations of, or
intrusions into, the occupant compartment that could cause serious injury are not permitted; it is
preferable, although not essential, that the vehicle remain upright during and after collision, and it is
preferable that the vehicle’s trajectory not intrude into adjacent traffic lanes. The following sections
of this report present the results of the analysis. The results were also compared to the results of the
baseline analysis of the NETC 4-Bar bridge rail without a curb to determine if the design changes
meet the FHWA criteria for either “insignificant change” or “inconsequential/positive” change.
Impact Conditions
The impact conditions for the analysis involved the 17,875-lb single unit truck model striking
the bridge rail at speed of 49.7 mph and at an impact angle of 15 degrees. These conditions are
consistent with those used in the assessment of the original NETC bridge rail system in the full-scale
crash test and the baseline FE analysis cases. Recall that the impact point for the baseline case was
approximately 24 inches upstream of post number 6 which also corresponded to a distance of
approximately 7.9 feet upstream of the tube-rail splice located between Posts 6 and 7. For the
analysis of the modified design, two impact points were evaluated:
Impact Point A: The vehicle impacted the rail at 24 inches upstream of Post 6, which was 9.9
feet upstream of the tube-rail splice between Posts 6 and 7.
Impact Point B: The vehicle impacted at Post 6, which was 7.9 feet upstream of the tube-rail
splice between Posts 6 and 7.
Impact Point A corresponds to the critical impact point for loading of the posts and floor
beams. This impact case was also considered to be very similar that of the baseline system and
thus result in comparable time-history data collected at the vehicle c.g. Impact Point B
corresponds to the critical impact point for evaluating the splice connection located between
posts 6 and 7. This loading case resulted in the highest deflections of the rail, which occurred
just upstream of the splice connection.
83
Sequential Views of Modified Design Compared with Baseline Design
Figure 65 and Figure 66 show side-by-side sequential views for the modified design and
for the baseline analysis from upstream and overhead viewpoints. The dynamics of the vehicle
during the impact event was similar for all three cases. The maximum roll angle of the truck box
was 10.3 degrees for the modified system at impact point A, which resulted in the top corner of
the truck bed extending 16.8 inches behind the face of the barrier. There were no snags between
the vehicle and the bridge rail during the simulated impact event. At approximately 0.5 seconds,
the vehicle lost contact with the barrier as it was rolling away from the barrier.
84
Figure 65. Sequential views of (a) Baseline system without sidewalk, (b) Modified system at
impact point A and (c) Modified system at impact point B from an upstream
viewpoint.
c) Modified (Impact Point B)
0.1 seconds
0.2 seconds
0.3 seconds
0.4 seconds
0.0 seconds
a) Baseline wo/ Sidewalk b) Modified (Impact Point A)
85
Figure 65. [CONTINUED] Sequential views of (a) Baseline system without sidewalk, (b)
Modified system at impact point A and (c) Modified system at impact point B
from an upstream viewpoint.
0.6 seconds
0.7 seconds
0.8 seconds
0.9 seconds
0.5 seconds
c) Modified (Impact Point B)a) Baseline wo/ Sidewalk b) Modified (Impact Point A)
86
Figure 66. Sequential views of (a) Baseline system without sidewalk, (b) Modified system at
impact point A and (c) Modified system at impact point B from an overhead
viewpoint.
c) Modified (Impact Point B)
0.2 seconds
0.4 seconds
0.6 seconds
0.8 seconds
0.0 seconds
a) Baseline wo/ Sidewalk b) Modified (Impact Point A)
87
Damage to Bridge Rail
Impact Point A
The analysis of the modified bridge rail at impact at Point A resulted in maximum
dynamic deflections of 3.6 inches and 1.0 inches for post 6 and post 7, respectively, with
permanent deflections of 2.24 inches and 0.38 inches. The highest deflections of the rail
elements occurred at approximately 29 inches upstream of the splice connection between posts 6
and 7. The maximum permanent deflection of Rail 1 (lowest rail) was 0.47 inch; the maximum
permanent deflection of Rail 2 was 0.82 inch, the maximum permanent deflection of Rail 3 was
1.26 inch; and the maximum permanent deflection of Rail 4 (top rail) was 2.75 inches. The
deflection of post 6 and 7 was due to yielding of the posts, rather than deflections of the base
plate. The maximum permanent deflection at the front, center point of the base plates was
approximately 1/16 inch. Table 16 shows a comparison of barrier deflections for the modified
bridge rail and the baseline case without sidewalk.
Impact Point B
The analysis of the modified bridge rail at impact at Point B resulted in maximum
dynamic deflections of 3.7 inches and 0.90 inches for post 6 and post 7, respectively, with
permanent deflections of 2.27 inches and 0.24 inches. The highest deflections of the rail
elements occurred at approximately 27 inches upstream of the splice connection between posts 6
and 7. The maximum permanent deflection of Rail 1 (lowest rail) was 0.57 inch; the maximum
permanent deflection of Rail 2 was 0.86 inch, the maximum permanent deflection of Rail 3 was
1.0 inch; and the maximum permanent deflection of Rail 4 (top rail) was 2.62 inches. Again, the
deflection of post 6 and 7 was due to buckling of the posts, rather than deflections of the base
plate. The maximum permanent deflection at the front, center point of the base plates was less
than 1/16 inch. Refer to Table 16 for a summary of results for the baseline and modified designs.
Table 16. Summary of barrier deflections for the Baseline design without sidewalk
and the modified design under TL4 impact conditions.
Baseline NETC
wo/ Sidewalk
(in)
Modified NETC
Impact Point A
(in)
Modified NETC
Impact Point B
(in)
Post 6 2 2.24 2.27
Post 7 0.33 0.38 0.24
Rail 1 0.32 0.47 0.57
Rail 2 0.49 0.82 0.86
Rail 3 0.89 1.26 1.00
Rail 4 2.03 2.75 2.62
Post 6 Base Plate 0.330 0.043 0.045
Post 7 Base Plate 0.052 0.067 0.030
Maximum Permanent Deflections
Component
88
Damage to Bridge Floor Beams
The analysis results indicated that no visible damage to the floor beams occurred in the
simulation of Test 4-12. Figure 67 shows contours of effective plastic strain at the time of maximum
loading on the floor beam at post number 6. The highest value of strain was 0.018 which occurred in
the local region around the bolt holes where the base plate fastens to the floor beam. Figure 68
shows a section view of the beam flange illustrating the strain contours through the cross-section of
the downstream bolt holes. The strains were isolated to the upper thickness of the flange at both the
upstream and downstream sides of the bolt hole, which indicate that they were likely the result of a
local stress concentration caused by the bolt bearing against the backside of the hole. These low
levels of strain in the floor beam are considered acceptable and should not affect the performance of
the bridge structure.
Figure 67. Contours of effective plastic strain on floor beam.
89
Figure 68. Cut-view of the beam flange showing contours of effective plastic strain
through the cross-section of bolt-hole.
Time-History Data Comparison
Figure 69 through Figure 73 show a comparison of the acceleration- and velocity-time
histories for the modified design at impact points A and B compared with the results from the
baseline analysis. The angular displacement-time histories are shown in Figure 74 through
Figure 76. From visual inspection, the results from for the modified design are essentially
identical to the baseline analysis case without the sidewalk during the time interval that the
vehicle was in contact with the bridge rail (i.e., first 0.5 seconds of impact). After the vehicle
exited the barrier, the damage to the front suspension of the truck resulted in varying kinematic
response of the vehicle during redirection.
90
Figure 69. 50 ms-average longitudinal acceleration-time histories for analysis of modified
designs compared with baseline analysis cases.
Figure 70. Longitudinal velocity-time histories for analysis of modified designs compared
with baseline analysis cases.
-3
-2
-1
0
1
2
3
-0.25 0 0.25 0.5 0.75 1
50
-ms
avg.
x-a
cce
lera
tio
n (
g's)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
30
35
40
45
50
55
-0.25 0 0.25 0.5 0.75 1
Ve
loci
ty (
mp
h)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
91
Figure 71. 50 ms-average lateral acceleration-time histories for analysis of modified
designs compared with baseline analysis cases.
Figure 72. Lateral velocity-time histories for analysis of modified designs compared with
baseline analysis cases.
-4
-3
-2
-1
0
1
2
3
4
-0.25 0 0.25 0.5 0.75 1
50
-ms
avg.
y-a
cce
lera
tio
n (
g's)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
0
2
4
6
8
10
12
14
16
18
20
-0.25 0 0.25 0.5 0.75 1
Y-V
elo
city
(m
ph
)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
92
Figure 73. 50 ms-average vertical acceleration-time histories for analysis of modified
designs compared with baseline analysis cases.
Figure 74. Yaw angle-time histories for analysis of modified designs compared with
baseline analysis cases.
-4
-3
-2
-1
0
1
2
3
4
-0.25 0 0.25 0.5 0.75 1
50
-ms
avg.
z-a
cce
lera
tio
n (
g's)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
0
5
10
15
20
25
30
-0.25 0 0.25 0.5 0.75 1
Yaw
An
gle
(d
eg)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
93
Figure 75. Roll angle-time histories for analysis of modified designs compared with
baseline analysis cases.
Figure 76. Pitch angle-time histories for analysis of modified designs compared with
baseline analysis cases.
-15
-10
-5
0
5
10
15
-0.25 0 0.25 0.5 0.75 1
Ro
ll A
ngl
e (
de
g)
Time (sec)
Baseline w/ Sidewalk
Baseline wo/ Sidewalk
Modified at IP A
Modified at IP B
-4
-3
-2
-1
0
1
2
3
4
-0.25 0 0.25 0.5 0.75 1
Pit
ch A
ngl
e (
de
g)
Time (sec)
Baseline w/ SidewalkBaseline wo/ SidewalkModified at IP AModified at IP B
94
Occupant Risk Measures
Table 1 shows a summary of the occupant risk measures for the analysis of the modified
design at impact points A and B compared with the results from the baseline analysis case of
original NETC 4-Bar bridge rail without sidewalk.
Impact Point A
The occupant impact velocities in the x- and y-directions for impact point A were 1.4 m/s
and 2.5 m/s, respectively. The highest 0.010-second occupant ridedown accelerations in the x-
and y- directions were 7.8 g and 17.1 g, respectively. The maximum 50-ms moving average
accelerations in the x-, y- and z- directions were 3.1 g, 7.5 g and 4.0 g, respectively.
Impact Point B
The occupant impact velocities in the x- and y-directions for impact point B were 2.6 m/s
and 3.8 m/s, respectively. The highest 0.010-second occupant ridedown accelerations in the x-
and y- directions were 8.0 g and 13.3 g, respectively. The maximum 50-ms moving average
accelerations in the x-, y- and z- directions were 3.4 g, 7.3 g and 3.7 g, respectively.
Table 17. Summary of occupant risk measures computed for the baseline design with and
without sidewalk, and the modified design at impact points A and B.
The results indicate that the occupant risk factors for the modified design compare very
well to those for the baseline design, with the exception of the lateral ridedown acceleration for
impact point A on the modified design. Recall that this analysis case represents the critical
loading condition for the post and floor beam.
Quantitative Comparison
The RSVVP software was used to quantitatively determine the similarity of the results
for the modified design compared to the results from the analysis of the baseline design without
sidewalk. The impact conditions for analysis of the modified design matched exactly those used
in the analysis of the baseline case (i.e., 17,875-lb SUT impacting at 49.8 mph and angle of 15
degrees at 24 inches upstream of post number 6.). These impact conditions correspond to
Without Sidewalk Impact point A Impact point B
Crash Test FEA FEA FEA FEA
x-direction
(m/s) 1.65 2.4 1.8 1.4 2.6
y-direction
(m/s) 2.89 5.5 3.9 2.5 3.8
- 5.8 4 3.1 4.6
x-direction 8.95 9.4 6.8 7.8 8.0
y-direction 14.3 14.6 15 17.1 13.3
- 14.7 15.4 17.4 13.4
- 0.82 0.76 0.84 0.6
x-direction 2.7 3.3 2.1 3.1 3.4
y-direction 5.8 7.3 6.6 7.5 7.3
z-direction - 4.3 2.1 4.0 3.7
Test 4-12 for Modified Barrier
Max 50-ms moving avg. acc.
(g's)
Occupant Impact Velocity
THIV (m/s)
Ridedown Acceleration
(g's)
Test 4-12 for Baseline System
With Sidewalk
Occupant Risk Factors
PHD (g's)
ASI
95
NCHRP Report 350 test 4-12. The quantitative evaluation was based on point-to-point
comparison of acceleration and angular rate-time histories. The time-history data was collected
at a sampling rate of 30,000 Hz. A summary of the quantitative comparison results are provided
herein. Additional comparison results can be found in Appendix C.
Time-History Validation
The multi-channel option in RSVVP was used to compute the Sprague-Geer metrics and
ANOVA metrics. In the following figures, the “true” curve represents the baseline analysis case
and the “test” curve represents the modified design. The comparison involved all six degrees of
freedom at the c.g., which included the x-acceleration, y-acceleration, z-acceleration, yaw rate,
roll rate and pitch rate. The data was recorded at a sampling rate of 30,000 data points per
second and was filtered in TRAP using a SAE class 60 filter. The shift and drift options in
RSVVP were not used and no additional filtering of the data nor synchronization was performed
prior to computing the evaluation metrics. Based on the validation metrics the results of the
modified design were in good agreement with the baseline design regarding each of the
individual components of acceleration and angular rates. The results summarized in Table 18.
96
Table 18. Roadside safety validation metrics rating table – time history comparison
(single-channel option).
Evaluation Criteria
Time interval [1.00 seconds]
O Sprague-Geers Metrics List all the data channels being compared. Calculate the M and P metrics using RSVVP and enter the results. Values less than or equal to 40 are acceptable.
Channel
RSVVP Curve Preprocessing Options
M P Pass? Filter
Option Sync.
Option
Shift Drift
True Curve
Test Curve
True Curve
Test Curve
x-acceleration SAE 60 N None None none None 0.4 30.4 Y
y-acceleration SAE 60 N None None None None 2.5 22.5 Y
z-acceleration SAE 60 N None None None None 0 32.3 Y
Yaw-rate SAE 60 N None None None None 5.5 3.9 Y
Roll-rate SAE 60 N None None None None 0.2 6.4 Y
Pitch-Rate SAE 60 N None None None None 3.6 13.4 Y
P ANOVA Metrics List all the data channels being compared. Calculate the ANOVA metrics using RSVVP and enter the results. Both of the following criteria must be met:
The mean residual error must be less than five percent of the peak
acceleration ( Peakae 05.0 ) and
The standard deviation of the residuals must be less than 35 percent
of the peak acceleration ( Peaka 35.0 ).
Me
an R
esi
du
al
Sta
nd
ard
Dev
iati
on
of
Re
sid
ual
s
Pass?
x-acceleration 0.58 14.32 Y
y-acceleration 0.13 15.07 Y
z-acceleration 0.21 25.96 Y
Yaw-rate 1.0 5.23 Y
Roll-rate 0.2 7.65 Y
Pitch-rate 0.64 16.21 Y
Exception Notes:
Since the metrics computed for the individual data channels all satisfy the acceptance
criteria, the multi-channel option in RSVVP was not necessary; however, the results for the
multi-channel assessment were computed and presented here for completeness. Table 19 shows
the results from RSVVP for the multi-channel option using the Area (II) method. The resulting
weight factors computed for each channel are shown in both tabular form and graphical form in
the tables. The results indicate that the x- and y-accelerations dominate the translational motion
of the vehicle, which implies that the velocity change in the z-direction was insignificant
compared to the change in velocity in the x- and y-directions. The analysis also indicated that the
yaw rate and the roll rate were also influential in the results of the analysis, with the pitch rate
showing much less contribution.
97
Table 19. Roadside safety validation metrics rating table – (multi-channel option).
Evaluation Criteria (time interval [_1.00 seconds_])
Channels (Select which were used)
X Acceleration Y Acceleration Z Acceleration
Roll rate Pitch rate Yaw rate
Multi-Channel Weights
X Channel: 0.253
Y Channel: 0.225 Z Channel: 0.022 Yaw Rate Channel: 0.249 Roll Channel: 0.184
Pitch Channel: 0.066
O Sprague-Geer Metrics Values less or equal to 40 are acceptable. M P Pass?
2.3 16.5 Y
P
ANOVA Metrics Both of the following criteria must be met:
The mean residual error must be less than five percent of the
peak acceleration
( Peakae 05.0 )
The standard deviation of the residuals must be less than 35
percent of the peak acceleration ( Peaka 35.0 ) Me
an R
esi
du
al
Sta
nd
ard
Dev
iati
on
o
f R
esi
du
als
Pass?
0.0 11.4 Y
Exception Notes:
PIRT – Crash Specific Phenomena
Refer to Table 5 for the applicable Report 350 crash test criteria. The criteria that apply to
test 4-12 (i.e., corresponding to this particular test case) are marked with a red square. These
include criteria A, D, F, L and M. Table 20 through Table 22 contain an expanded list of these
same criteria including additional specific phenomena that were collected in the analysis. Table
20 contains a comparison of phenomena related to structural adequacy, Table 21 contains a
comparison of phenomena related to occupant risk, and Table 22 contains a comparison of
phenomena related to vehicle trajectory.
0
0.05
0.1
0.15
0.2
0.25
0.3
X acc Y acc Z acc Yaw rate Roll rate Pitch rate
98
Table 20. Roadside safety phenomena importance ranking table (structural adequacy).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Stru
ctu
ral A
deq
uac
y
A
A1
Test article should contain and redirect the vehicle; the vehicle should not penetrate, under-ride, or override the installation although controlled lateral deflection of the test article is acceptable. (Answer Yes or No)
Y Y Y
A2 Maximum permanent deflection: - Relative difference is less than 20 percent or - Absolute difference is less than 6 inches
2.0 in 2.24 in 12%
0.24 in Y
A3 Length of vehicle-barrier contact: - Relative difference is less than 20 percent or - Absolute difference is less than 6.6 ft
20 ft 24 ft 20% 4 ft
Y
A4 Number of broken or significantly bent posts is less than 20 percent.
0 0 0% 0
Y
A5 Did the rail element rupture or tear (Answer Yes or No)
N N Y
A6 Were there failures of connector elements (Answer Yes or No).
N N Y
A7 Was there significant snagging between the vehicle wheels and barrier elements (Answer Yes or No).
N N Y
A8 Was there significant snagging between vehicle body components and barrier elements (Answer Yes or No).
N N Y
Exception Notes: The vehicle model exited the rail and then turned and re-contacted the rail. The data compared here refer to the events of the first impact.
99
Table 21. Roadside safety phenomena importance ranking table (occupant risk).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Occ
up
ant
Ris
k
D
Detached elements, fragments or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment, or present an undue hazard to other traffic, pedestrians or personnel in a work zone. (Answer Yes or No)
N N Y
F
F1 The vehicle should remain upright during and after the collision although moderate roll, pitching and yawing are acceptable. (Answer Yes or No)
Y Y Y
F2 Maximum roll of the vehicle: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
10.4 deg 0.5 sec
10.3 deg 0.44 sec
1% 0.1 deg
Y
F3 Maximum pitch of the vehicle is: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
3.4 deg 0.64 sec
3.0 deg 0.66 sec
12% 0.4 deg
Y
F4 Maximum yaw of the vehicle is: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
15.6 deg 0.54 sec
16.6 deg 0.53 sec
6% 1.0 deg
Y
L
L1
Occupant impact velocities: - Relative difference is less than 20 percent or - Absolute difference is less than 2 m/s.
Longitudinal OIV (m/s) 1.8 1.4 22% 0.4
Y
Lateral OIV (m/s) 3.9 2.5 36% 1.4 m/s
Y
THIV (m/s) 4.0 3.1 23%
0.9 m/s Y
L2
Occupant accelerations: - Relative difference is less than 20 percent or - Absolute difference is less than 4 g’s.
Longitudinal ORA 6.8 7.8 15% 1 g
Y
Lateral ORA 15.0 17.1 14% 2.1 g
Y
PHD 15.4 17.4 13% Y
ASI 0.76 0.84 11% Y
Exception Notes: The vehicle model exited the rail and then turned and re-contacted the rail. The data compared here refer to the events of the first impact.
100
Table 22. Roadside safety phenomena importance ranking table (vehicle trajectory).
Evaluation Criteria Known Result
Analysis Result
Difference Relative/ Absolute
Agree?
Veh
icle
Tra
ject
ory
M
M1 The exit angle from the test article preferable should be less than 60 percent of test impact angle, measured at the time of vehicle loss of contact with test device.
8.7% 3.3% Y
M2 Exit angle at loss of contact: - Relative difference is less than 20 percent or - Absolute difference is less than 5 degrees.
1.3 deg 0.5 deg 62%
0.8 deg Y
M3 Exit velocity at loss of contact: - Relative difference is less than 20 percent or - Absolute difference is less than 10 km/hr.
42.5 mph 42.4 mph 0%
0.1 mph Y
M4 One or more vehicle tires failed or de-beaded during the collision event (Answer Yes or No).
Y Y Y
N N1 Vehicle travelled behind the test article (Answer Yes or No). N N Y
Exception Notes: The vehicle model exited the rail and then turned and re-contacted the rail. The data compared here refer to the events of the first impact.
All applicable criteria in Table 20 through Table 22 agree (i.e., the relative or absolute
difference between the numerical solution and the test was less than maximum allowable
values); therefore the analysis of the modified design can be considered essentially identical to
those of the baseline analysis case. A summary sheet for the comparison of the modified and
baseline designs is shown in Figure 77.
101
Figure 77. Summary of results from the analysis of the modified design compared with the analysis of the baseline design
without sidewalk.
Date: 11/24/2013
Comparison:
Device Name:/Variant: Submissions Type: Non-Significant -- Effect is Uncertain
Testing Criterion: Non-Significant -- Effect is Positive
Test Level: X Non-Significant -- Effect is Inconsequential
FHWA Letter: Baseline Validation of Crash Test to FEA Analysis.
Analysis Number: Baseline Modified Occupant Risk (cont.) Baseline Mod
Vehicle: A1 - Acceptable perf.? Yes Yes L1 – Long. OIV 1.8 m/s 1.4 m/s
Vehicle Mass: A2 – Permenant 2.0 in 2.24 in L1 – Lat. OIV 3.9 m/s 2.5 m/s
Impact Speed/Angle: A3 – Contact Length 20 ft 24 ft L2 – Long. ORA 6.8 g 7.8 g
Impact Location: A5 – Comp. Failures? No No L2 – Lat. ORA 15.0 g 17.1 g
Original Hardware NETC wo/ sidewalk 8-ft span A6 – Connection Failure? No No Vehicle Trajectory
Modified Hardware NETC w/ Mount 11b and 10' span A7 – Wheel Snagging? No No M2 – Exit Yaw Angle 0.6 deg 1.6 deg
A8 – Vehicle Snagging? No No M3 – Exit Velocity 42.5 mph 42.4 mph
Total Energy: 0.0% Pass Occupant Risk Baseline Modified
Hourglass Energy: 0.0% Pass D – Detached elements? No No Sprague-Geer Magnitude < 40 2.3 Pass
Mass Added: <1% Pass F2 – Max. Vehicle Roll 10.4 10.3 Sprague-Geer Phase < 40 16.54 Pass
Shooting Nodes: No Pass F3 – Max. Vehicle Pitch 3.4 3 ANOVA Mean 0 Pass
Negative Volumes: No Pass F4 – Max. Vehicle Yaw 15.6 16.6 ANOVA Standard Deviation 11.4 Pass
(FHWA Memorandum)
W-179 Table E-5: Roadside PIRTS
Finite Element Analysis Determination of Elibibility for Reimbursement under the Federal-Aid Highway Program
NETC-NoCurb_131112
50_F800-131025_FullBallast.k
Modified NETC 4-Bar wo/ Sidewalk
NCHRP Report 350
TL 4
Crash tested original design to FEA of original design
Structural Adequacy
Bridge RailSystem Type:
Baseline Crash Test
W-179 Table E-1: Verification Evaluation Summary
W-179 Table E-3 (Multi-Channel Method)
17,875 lb
49.8 mph / 15 deg
24 inches upstream of Post 6
0.20 sec 0.40 sec 0.60 sec 0.08 sec0.00 secMo
dif
ied
Sys
tem
Bas
elin
e M
od
el
102
SUMMARY AND CONCLUSIONS
A finite element model of the NETC 4-Bar bridge rail system was developed and
validated through comparison with full-scale crash test NETC-3; the crash test was conducted by
Southwest Research Institute in 1999 for the New England Transportation Center. The impact
conditions for this test case corresponded to NCHRP Report 350 Test 4-12 and involved an
18,000-lb single unit truck impacting the bridge rail system at 50 mph and 15 degrees. The
validation was carried out based on procedures outlined in NCHRP Web-Only Document 179.
The original design of the NETC bridge rail entailed mounting the steel wide-flange posts
to a 9-inch tall 6.5-ft wide sidewalk. As a first iteration of the bridge rail design, an analysis was
conducted to evaluate the original design without a sidewalk, since installation of the sidewalk
was not an option for the through-truss bridge. These results were then compared to the original
design with the sidewalk to: 1) verify that the sidewalk was not critical to the successful
performance of the system and 2) serve as the baseline for comparison of the modified design
without sidewalk. The results indicated that the velocity-time histories and yaw angle time-
histories for both cases were similar, as well as the occupant risk metrics. There were, however,
notable differences in the roll and pitch of the vehicle for the two cases and the deflections of the
barrier were slightly higher for the case without the sidewalk. These differences were attributed
to the differences in the vehicle orientation and dynamics (i.e., attitude) resulting from impact
with the 9-inch tall sidewalk. In particular, the increased pitch angle of the cargo box after
impacting and traversing the vertical curb resulted in the box passing over the top of the barrier;
whereas, the cargo box impacted directly against the side of the barrier in the analysis without
the sidewalk. Although the sidewalk does indeed affect the specific response of the vehicle as it
interacts with the barrier, the overall response of the barrier with and without the sidewalk were
similar and were well within the limiting criteria of NCHRP Report 350. In the context of the
FHWA procedure, the sidewalk/curb was found to be a non-significant modification with
inconsequential effects. This design was then used as the baseline for evaluating subsequent
modifications of the system for installation on the bridge structure.
Next, several mount designs were developed and evaluated for installation directly to the
top flange of the bridge floor beams. The modifications to the bridge rail design were kept
minimal and included only those necessary for attachment to the bridge structure and for
maintaining bridge rail performance. Of critical importance in the design was ensuring that the
mount was sufficiently strong enough to withstand TL-4 impact loads, while not causing damage
to the floor beams. Although all the mount design alternatives presented herein were found to be
applicable for the bridge rail, only one was selected for further analysis under Test 4-12 impact
conditions. The selected design included a 1.5-inch thick base plate with the post positioned
0.67 inches (17 mm) farther back relative to its original position on the base plate. A single ¾-
length vertical stiffener oriented perpendicular to the floor beam and placed between the flanges
on each side of the floor beam was also added. The stiffener was implemented to strengthen the
floor beam in the local vicinity of the post-mount location to prevent in-elastic deformation of
the bridge structure. This particular design was considered to be the most practical for
installation, and it also represented the worse-case scenario for all options considered. Thus,
successful performance of this design should translate to successful performance for the other
design alternatives as well.
103
The baseline model of the NETC 4-Bar bridge rail was then modified to include these design
changes, and finite element analysis was again used to evaluate the crash performance of the system
under Test 4-12 impact conditions. In the original design, the base plate was determined to be the
weak-point of the post-mount system and as a result the stiffness capacity of the post was not
optimized. Since the modified bridge rail has a greater post spacing, it was necessary to increase the
effective stiffness of the post-mount system. By increasing the thickness of the base plate to 1.5
inches, the stiffness capacity of the post-mount system was sufficiently increased without increasing
the post size. Because the modifications included wider post spacing and a modified mounting
condition, two critical impact points were used in the evaluation of the system. The first case
represented the critical impact point for maximum dynamic loading of the posts; the second case
represented the critical impact point for maximum loading and deflection of the splice connection.
The results of the analyses indicated that the response of the modified system with 10-ft post spacing
was essentially equivalent to the baseline design with 8-ft post spacing regarding barrier deflections,
occupant risk measures, and vehicle kinematics during the impact event. A quantitative comparison
of the results for the modified design and the baseline design further verified that the response of the
two designs was essentially equivalent.
Based on the results of the analyses, the design modifications presented herein were
determined to meet all structural capacity, occupant risk measures and vehicle stability criteria
set forth in NCHRP Report 350. The design modifications are further considered to be non-
significant, regarding the changes to the original Report 350 TL4 design, since the effects of the
changes were shown to be inconsequential to the performance of the system with respect to the
baseline design.
Based on these findings, it was further concluded that the analysis of the modified system
under NCHRP Report 350 Test 4-10 and Test 4-11 were unnecessary. As shown in the crash test
report for the original system (see Appendix A), both the small car and pickup truck tests
resulted in (1) negligible damage to the barrier, (2) very stable redirection of the vehicles, and (3)
reported occupant risk measures that were well below the limits of NCHRP Report 350. In
particular, the small car test (i.e., Test NETC-1) resulted in OIV values of 4.6 ft/s and 21 ft/s in
the longitudinal and lateral directions, respectively (compared to the limit of 39.4 ft/s); and
maximum longitudinal ORA value of 6.4 g (compared to the limit of 20 g). Likewise, the pickup
test (i.e., Test NETC-2) resulted in longitudinal OIV of 13.1 ft/s and maximum longitudinal
ORA of 2.6 g.
104
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