Centers of Excellence in Finite Element Crash Analysis
Each year more than 6 million motor vehicle crashes occur on our Nation's roads resulting in 3 million human injuries and 42,000 premature deaths.
"Finite element analysis was used to improve the crashworthy performance of portable concrete barriers used in our State. The improved barriers will reduce injuries and save many lives."
—Paul L. Kokos, P.E., Standards & Criteria Engineer, Pennsylvannia, Department of Transportation, (717) 705-2379.
Finite element analysis (FEA) is an extremely efficient and cost-effective tool to assist in the design of safer highway guardrails, bridge supports, signposts, and other roadside structures. FEA, which can be used to predict the outcome of a crash test, provides the potential to prevent some of the 500,000 human injuries and 13,000 premature deaths resulting when motor vehicles run-off-the-road and either rollover or are involved in collisions with a roadside object or feature.
Several States have used FEA to better understand the dynamic behavior of portable concrete barriers (PCBs) during collisions by a motor vehicle. These investigations have focused primarily on the design of the connection joint between barrier segments—to limit overall deflection of the barrier and to limit the relative lateral deflection between barrier segments to prevent the impacting vehicle from colliding into the exposed blunt end of the next adjacent section. Use of FEA reduces the overall development time for new PCB designs, thereby helping States meet the AASHTO/FHWA agreement that all PCBs purchased after October 2002, for use in work zones on the National Highway System, meet NCHRP Report 350 safety requirements.
Finite element analysis, coupled with the use of high-speed computers, is a new and innovative method for developing crashworthy roadside safety structures. This method is useful for evaluating alternative designs and changes to roadside safety structures as part of a crash-testing program.
Traditional methods of designing roadside structures, by crashing vehicles into them, are extremely costly—more than $25,000 per crash—and they do not always provide definitive information. FEA can reduce the cost and time to develop roadside safety structures by replacing the trial and error process of crash testing with computer crash analysis. Using FEA, this tool can reveal with much greater insight, what actually happened and what effect a design change will have.
Once a roadside safety feature has been designed and evaluated using FEA, a final design can be fabricated and crash-tested. At the present time, FEA is not considered a replacement for actual crash testing for acceptance purposes.
FEA of roadside safety features involves analyzing the computer-generated impact of two bodies (a model of a specific motor vehicle colliding into a model of a specific roadside safety structure). Computer models of many motor vehicles that are currently in the national fleet are ready for use with this tool. These include models of specific vehicles that meet the NCHRP Report 350 vehicle criteria: a Geo Metro sedan, a Chevrolet C-2500 pickup truck, and an 18,000-lb. single-unit Ford truck. A model of a tractor-trailer is currently under development.
WHO HAS USED THE RESULTS OF FINITE
ELEMENT ANALYSIS?
Texas In a full-scale crash test of the T6 tubular W-beam bridge railing, commonly used on Texas box culvert bridges, the impact performance was unacceptable because the test vehicle, a pickup truck, overturned. Also, considerable damage to the bridge deck was observed. Texas Department of Transportation (TxDOT) personnel elected to use FEA to evaluate design modifications and to develop an improved bridge rail. FEA was used to optimize the design of the bridge rail posts to achieve controlled breakaway response, eliminate vehicle snagging, and significantly reduce deck damage. The performance of the post was verified through dynamic impact tests. In addition, a tubular thrie-beam rail replaced the W-beam in the T6 system. FEA visually depicted that this modified bridge railing will redirect the test vehicle in a stable manner and would likely meet the NCHRP Report 350 requirements.
"Finite element crash analysis was an integral part of the redesign of the T6 bridge railing. As a result of this work, TxDOT will have a flexible bridge rail that meets all requirements of NCHRP 350 and can be installed on box culverts and pan-form decks without inducing significant impact damage."
—Mark Bloschock, Special Projects Engineer, TxDOT, (512) 416-2178.
Nebraska & Seven Other Midwestern States Eight States pooled research funds and sponsored the development of a new thrie-beam bullnose guardrail system—one that meets NCHRP Report 350 requirements. FEA coupled with nine crash tests was employed to complete this development effort. Following spectacular crash test failures, two finite elements models of this guardrail system were developed. Each model emphasized different portions of the bullnose guardrail system. Two series of finite element crash analysis—each one using one of the two models—were used to determine the causes of the respective crash test failure. Subsequent crash analyses were conducted to explore the performance of the guardrail system with selective design changes incorporated. And then, crash testing confirmed the crashworthiness of the final modified design.
"Without the finite element crash analysis, it would have been very difficult to figure out the causes of the two failures. If trail-and-error crash testing ahd been used to make the design changes, many more crash tests would have been required to get the job done."
—David L. Little, P.E., Assistant District 2 Engineer, Iowa DOT, and Chairman of the AASHTO Task Force for Roadside Safety, (641) 423-7584.
Pennsylvania Certification of the weak-post guardrail system to NCHRP Report 350 crash-test requirements was difficult, because in crash testing of this system, the pickup truck occasionally overrode the guardrail and at times penetrated through the guardrail due to rail fracture. Subsequently, PennDOT sponsored a series of finite element crash analyses to evaluate possible design improvements. After making a number of modifications to the weak-post guardrail system, acceptance testing demonstrated that the guardrail system meets NCHRP Report 350 requirements for both the small car and the pickup truck test.
"Finite element crash analysis allowed us to determine the causes of these failures and improve the safety performance of this guardrail system."
—James Tenaglia, P.E., Risk Management Engineer, PennDOT, (717) 705-1442
NEED SOME HELP?
Are you finding the ins and outs of FEA to be somewhat complicated? Do you have questions? Are you aware there are experts who can help?
Centers of Excellence for Finite Element Crash Analysis and the National Crash Analysis Center (NCAC) are available to apply FEA to your roadside safety structure problems. The centers are located at:
For more information, contact:
Martin W. Hargrave, Office of Safety Research
and Development, FHWA, (202) 493-3311
martin.hargrave@fhwa.dot.gov
FHWA-RD-01-089
This RD&T marketing brochure communicates the benefits and developments of our research and services.
Publications
Manual for LS-DYNA Wood Material Model 143, FHWA-HRT-04-097, August 2007
Users Manual for LS-DYNA Concrete Material Model 159, FHWA-HRT-05-062, May 2007
Evaluation of LS-DYNA Soil Material Model 147, FHWA-HRT-04-094, November 2004
Evaluation of LS-DYNA Wood Material Model 143, FHWA-HRT-04-096, August 2005
Manual For LS-DYNA SOIL MATERIAL MODEL 147, FHWA-HRT-04-095, November 2004
Improving Roaside Safety by Computer Simulation
January/February 2001 Public Roads
Using the Computer and DYNA3D to Save Lives
January/February 2001 Public Roads
LS-DYNA: A Computer Modeling Success Story
January/February 2001
Public Roads
It's a Jungle Out There: Using the Bullnose Guardrail to Protect the Elephant Traps
January/February 1999 Public Roads
Using Finite Element Analysis in Designing Roadside Hardware
Spring 1994 Public Roads
National Crash Analysis Center
Spring 1994 Public Roads
Cutting-Edge Crash Testing: Project shows predictive use of computer simulation
by Roger Bligh
Vol. 37, No. 3, 2001 Texas Transportation Researcher Magazine
