Project Summary Report 0-1816-S
Project 0-1816: Center of Excellence in DYNA3D Analysis
Author: Roger P. Bligh, P.E.
Finite Element Analysis
of Roadside Safety Devices
Although signiﬁcant After the selection of a safety Comparison of each key
advancements have been made feature, researchers reviewed component or subsystem within
over the past three decades, available literature and test data selected roadside safety features
the roadside safety problem to examine failure mechanisms to experimental data established
remains a major source of injury, and identify critical components the accuracy and validity of
death, and economic loss. One of the system, thus providing a each component. Full-scale load
direct means of addressing this basis for initial modeling and tests of selected components and
problem is through the continued validation. materials helped quantify material
development of improved
roadside safety features.
In recent years, roadside
safety research has focused on
computer simulation technology
to better understand behavior of
roadside safety devices when hit
by vehicles. Toward this goal,
the Center for Transportation
was established at the Texas
Transportation Institute (TTI)
under joint funding by the (a) Test and Simulation at 0.0 s.
Federal Highway Administration
(FHWA), the Texas Department
of Transportation (TxDOT),
TTI, and Texas A&M University.
The purpose of the center is
to contribute to the solution of
the roadside safety problem
through the use of computer
simulation technology by
building validated models of
selected roadside hardware
devices and establishing expertise (b) Test and Simulation at 0.060 s.
that can be utilized by TxDOT,
other highway agencies, and
private industry to address safety
What We Did...
Roadside safety features
to be modeled and simulated
as part of this project were
selected in consultation with
TxDOT personnel. Modeling
systems in support of ongoing, (c) Test and Simulation at 0.493 s.
safety projects received priority. Figure 1. Comparison of Tubular W-Beam Test and Simulation.
Project Summary Report 0-1816-S –1–
properties and assisted in validation.
The approach followed was to develop
the system model from a set of
validated component models.
Full-scale crash simulations on the
system models used a detailed ﬁnite
element model of a 4405-lb (2000 kg)
pickup truck, denoted 2000P, one of
the design test vehicles recommended
by National Cooperative Highway
Research Program (NCHRP) Report
350. The results of the initial full-scale
simulations were used to evaluate the
impact performance of the roadside
When design problems were
identiﬁed through simulation
or crash testing, various design
modiﬁcations were examined to
address the deﬁciencies and improve
impact performance of the system. Figure 2. Sequential Comparison of Test and Simulation for Steel
Researchers modiﬁed the ﬁnite Post in Soil.
element model and conducted
additional simulations to assess any A ﬁnite element model of the TxDOT engineers worked together to
improvement. The results of the rail was developed to capture the evaluate the crash performance of this
simulations were used to develop performance trends of the existing barrier system and determine whether
recommended improvements for T6 bridge rail system (Figure 1) and cost-effective modiﬁcations can be
full-scale crash testing and potential evaluate potential design modiﬁcations. made to the barrier to meet NCHRP
implementation. The goal was to achieve a system that Report 350 criteria and limit dynamic
Three distinct roadside safety will meet NCHRP Report 350 criteria deﬂections to practical levels.
issues were investigated with the aid without signiﬁcantly altering the basic During the project, TxDOT
of computer simulation: design concept of the system (i.e., a engineers and TTI researchers
relatively ﬂexible, breakaway design jointly developed several retroﬁt
• An alternative to the popular capable of being installed on thin deck connection designs with the intent
T6 tubular W-beam bridge rail structures and culverts). of reducing dynamic barrier
addressed problems with vehicle Proposed modiﬁcations to the deﬂections. When developing these
instability observed in full-scale T6 system include revision of the retroﬁt design options, factors such
crash testing. breakaway post attachment detail and as impact performance, cost, ease
• A retroﬁt connection to TxDOT’s incorporation of a tubular thrie-beam of ﬁeld installation, and aesthetics
grid-slot portable concrete barrier rail element instead of the original were considered. The research team
limited dynamic barrier deﬂections tubular W-beam. During computer performed computer simulations to
to levels more practical for work simulation of this alternative, the help assess the ability of the selected
zone deployment. vehicle experienced signiﬁcantly retroﬁt connections to meet NCHRP
less roll angle and was inherently Report 350 impact performance
• Crashworthy mow strip more stable than in the comparable criteria prior to conducting the full-
conﬁgurations provided vegetation simulation with the standard tubular scale crash testing. Limitations in the
control around guard fence W-beam rail element. The results ability of existing material models to
systems to reduce the cost and risk suggest that the tubular thrie-beam accurately capture concrete fracture
associated with hand mowing. system has a high probability of and failure led to some simplifying
passing NCHRP Report 350 Test Level assumptions regarding the model of
3 impact performance requirements. the grid-slot connection. Nonetheless,
What We Found... the simulations assisted in the impact
Grid-Slot Portable Concrete Barrier performance evaluation of the existing
T6 Bridge Rail The crash performance of the and modiﬁed designs.
The Texas T6 bridge rail is a TxDOT Type 2 precast concrete trafﬁc A steel strap bolted to the toe
breakaway bridge rail system that is barrier (PCTB-90) with joint type of the barrier across the joint
designed for use on culvert headwalls A was unproven with respect to the between adjacent barrier segments
and thin bridge decks. In full-scale NCHRP Report 350 guidelines. A is considered to be the best
crash testing, the Texas T6 bridge rail full-scale crash test was therefore retroﬁt alternative for limiting
system did not satisfy NCHRP Report conducted to evaluate the impact barrier deﬂections from among
350 criteria for high-speed (i.e., Test behavior of the barrier. Although the connections investigated. A
Level 3) applications. Although the the test vehicle was contained and subsequent crash test demonstrated
bridge rail contained and redirected redirected, large barrier deﬂections that this connection limited the barrier
the vehicle, the vehicle rolled onto its occurred when one of the barrier deﬂection to only 4 feet under design
impact side as it exited the installation. joints separated. TTI researchers and impact conditions compared to other
Project Summary Report 0-1816-S –2–
Grid-Slot Portable Concrete Barrier
The addition of 4-inch wide ×
3/16-inch thick steel straps bolted to
the face of the barrier segments across
the joints substantially reduced the
maximum dynamic deﬂection of the
barrier. The maximum lateral barrier
movement experienced in the test was
4 feet under design impact conditions.
Use of the steel strap connection will,
therefore, permit the grid-slot barrier
to be used in more restricted work
Subsequent to the crash test of
this system, additional simulations
were conducted to optimize the size
of the steel strap. It was observed in
the crash test of this connection detail
that one of the steel straps failed in
tension on the ﬁeld side of the barrier.
Figure 3. Sequential Comparison of Simulation and Test Results for Wood If the strength of the connection can be
further increased to avoid failure of the
Post in Asphalt.
strap without inducing failure of the
options that had deﬂections ranging of different mow strip conﬁgurations anchor bolts, the barrier deﬂection can
from 9 feet to 12.4 feet. indicated that impact performance be further decreased. It was determined
should be acceptable under some that if the size of the steel strap is
Guard Fence Encased in Mow Strip conditions. Compliance with increased to 6 inches wide × 1/4 inch
Design variables that were NCHRP Report 350 guidelines was thick, tensile failure of the strap can be
considered in the investigation of subsequently conﬁrmed in two full- avoided and barrier deﬂections will be
guard fence encased in mow strip scale crash tests conducted as part of reduced to approximately 3.25 feet.
include mow strip material type, mow research Project 0-4162. There was no Besides the change in plate
strip thickness, size and shape of leave damage to the mow strip that would dimensions, all other details of the
outs, type of backﬁll material used require repair other than replacing the connection, including anchor bolt
in the leave outs, and type of guard sacriﬁcial grout backﬁll around the size and location, remain the same
fence post. Given the large number guardrail posts in the region of impact. as those used in the test installation.
of design variables and treatment Since this reduction in deﬂection can
options that exist for this practice, be achieved with only a small increase
full-scale crash testing of the entire The Researchers in material cost, it is recommended
matrix would be cost-prohibitive. Recommend... that the 6-inch wide × 1/4-inch thick
Rather, subcomponent testing and steel straps be implemented when site
full-scale simulations were performed T6 Bridge Rail conditions cannot accommodate the
to develop a better understanding of The researchers recommend a larger deﬂections associated with the
the response of mow strip systems full-scale crash test on a tubular thrie- drop-in plate or grid connectors.
subjected to dynamic impact loads. beam system to verify the predicted
The ﬁrst step developed ﬁnite impact performance. The tubular Guard Fence Encased in Mow Strip
element models of the key components thrie-beam system could be improved The successfully tested mow strip
and validated them against component prior to testing by redesigning the systems have been implemented
test data (Figures 2 and 3). Component post baseplate connection to further through a new standard detail sheet
modeling allows the researchers increase its strength. The strength developed by TxDOT’s Design
to gain conﬁdence in the accuracy values should be chosen to reduce the Division. In addition to providing
of smaller-scale models before number of posts broken to a total of greatly enhanced impact performance,
assembling the full system model and six or seven posts. This would limit mow strip conﬁgurations featuring
using it in predictive simulations. travel of the vehicle over the edge of grout-ﬁlled leave-outs around the
The results of full-scale vehicle the deck, which might further reduce guard fence posts appear more
impact simulations of a guard fence the vehicle roll angle. Maintenance practical based on ease of repair after
system directly encased in a pavement and repair costs could also be reduced. an impact.
mow strip without leave-out sections If a crash test is successful, the Any increase in post conﬁnement
tubular thrie-beam system would beyond that provided by the grout
around the posts indicated a low
provide a replacement for the popular backﬁll material used in the leave-out
probability that such a system will
T6 bridge rail for use on high-speed sections formed around the guardrail
meet NCHRP Report 350 performance
roadways. As with the T6 rail, the posts should be further evaluated.
criteria. Researchers recommended
tubular thrie-beam is designed to limit Additional guidance on acceptable
that such practice be discontinued. structural damage when installed on mow strip variations is contained in
Additional predictive simulations thin bridge decks and culverts. Report 0-4162-2.
Project Summary Report 0-1816-S –3–
For More Details . . .
The research is documented in the following reports:
Report 0-1816-1: Evaluation of Roadside Safety Devices Using Finite Element Analysis
Report 0-4162-2: Dynamic Response of Guardrail Systems Encased in Pavement Mow Strips
Research Supervisor: Roger P. Bligh, TTI, email@example.com, (979) 845-4377
Researchers: Akram Y. Abu-Odeh, TTI, firstname.lastname@example.org, (979) 862-3379
Mark E. Hamilton, Texas A&M University
N. Ryan Seckinger, SCA Consulting Engineers, Houston, Texas
TxDOT Project Director: Mark Marek, TxDOT, email@example.com, (512) 416 2653
To obtain copies of reports, contact Nancy Pippin, Texas Transportation Institute, TTI Communications,
(979) 458-0481, or e-mail firstname.lastname@example.org. See our online catalog at http://tti.tamu.edu.
TxDOT Implementation Status—December 2004
TTI.PSR0501.0405.100 PSR 0-1816-S
This project involved primary research in the development of the DYNA-3D model for vehicle barrier interaction.
While there was not direct implementation of the DYNA-3D model for TxDOT, the model was used to develop road-
side hardware such as T6 bridge rail, guardrail to bridge rail transitions, and concrete barrier connections for full-scale
crash testing and ultimate development into standard detail sheets that TxDOT now uses in construction plans.
For additional information, contact Sharon Barta, P.E., RTI Research Engineer, at (512) 465-7403 or e-mail
YOUR INVOLVEMENT IS WELCOME!
The contents of this report reﬂect the views of the authors, who are responsible for the facts and the accuracy of the data, opinions, ﬁnd-
ings, and conclusions presented herein. The contents do not necessarily reﬂect the ofﬁcial views or policies of the Texas Department of
Transportation (TxDOT), the Federal Highway Administration (FHWA), The Texas A&M University System, or the Texas Transportation
Institute. This report does not constitute a standard, speciﬁcation, or regulation. Its contents are not intended for construction, bidding, or
permit purposes. In addition, the above listed agencies assume no liability for its contents or use thereof. The names of speciﬁc products or
manufacturers listed herein do not imply endorsement of those products or manufacturers.
This research project was conducted under a cooperative program between the Texas Transportation Institute, the Texas Department of
Transportation, and the U.S. Department of Transportation, Federal Highway Administration.
Texas Transportation Institute/TTI Communications
The Texas A&M University System
College Station, TX 77843-3135