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Numerical Analysis of a H4a heavy
containment Level Transition
ALI OSMAN ATAHAN*-GUIDO BONIN**
*Department Head, Department of Civil Engineering, Mustafa Kemal University, Hatay, Turkey
** Department of Hydraulics, Transportation and Roads, University of Roma ``La Sapienza'', Roma
Abstract. ± Unfortunately European highway safety personnel are not aware of
the significance of transition barriers. As a result, most countries do not use
transition designs on their highways. On the other hand, the ones that are currently
in use lack adequate detailing and do not provide the required level of protection
during a collision event. In this paper, the impact performance of a standard U.S.
flared back guardrail-to-bridge rail transition is evaluated using a 30,000 kg heavy
goods vehicle according to European EN1317 test TB71 requirements. A highly
acceptable and versatile non-linear finite element code, LS-DYNA, is used for the
analysis. Simulation results show that the transition fails to contain the vehicle. The
vehicle overrides the transition due to insufficient rail height. To upgrade the impact
performance of the transition to H4a, high containment level, an additional rail
element was added to the current design to increase the rail height from 810 mm to
1050 mm. Subsequent simulation results show that the modified transition design
meets the EN1317 test TB71 requirements. It is therefore recommended that the
current U.S. standard flared back guardrail-to-bridge rail transition design should
have a minimum of 1050 mm rail height to satisfy European crash testing guidelines
for H4a, heavy containment level transition.
Introduction
In this paper, crash test behavior of a previously studied flared-back
guardrail-to-bridge rail transition design was analyzed using a heavy vehicle
impact. A finite element analysis program, LS-DYNA provided by the Livermore
Software Technology Corporation [1] was used to evaluate the performance of
the transition. Analysis results showed that the current design found to be an
inadequate H4a high level containment level transition due to vehicle override.
Based on this finding, the rail height of the transition was increased from 810
mm to 1050 mm. Subsequent simulation predicts that the improved design suc-
cessfully contained and redirected the 30,000 kg heavy goods vehicle in an
acceptable manner. The rest of the paper documents the details of the computer
simulation study.
Description of flared-back guardrail-to-bridge rail transition stu-
died
The vertical flared-back concrete guardrail-to-bridge rail transition evaluated in
this study consisted of a thrie beam with rub rail and steel posts. The concrete safety
shape simulated bridge rail was 2,440 mm long and had a foundation wall that extended
940 mm below grade. The wingwall extended from the simulated bridge rail a
longitudinal distance of 3,900 mm. The wingwall was embedded 2300 mm below grade.
The traffic face of the wingwall transitioned from a safety shape to a vertical face over a
distance of 2,300 mm. The vertical face extended another 750 mm and then flared back
a distance of 215 mm over a longitudinal distance of 850 mm. The height of the vertical
wall was 810 mm. The approach guardrail (7,620 mm long) was a 2.67-mm-thick (12-ga)
W-beam mounted on W150 14 steel posts spaced at 1,905 mm with 150 mm wide
200 mm deep 356 mm long wood blockouts. Mounting height to the rail element
was 810 mm at top of the rail.
The transition, starting from the guardrail end, consisted of a 3,810 mm length of
2.67-mm-thick (12-ga) W-beam mounted on W150 14 steel posts and 150 mm wide
200 mm deep 356 mm long wood blockouts. Proceeding toward the transition, two
nested, 2.67-mm thick (12-ga) thrie beam sections were used and connected to the
concrete bridge rail with a 2.67-mm thick (12-ga) standard terminal connector. A 168.3-
mm-diameter by 250-mm-long steel spacer tube was installed between the thrie beam
and flared back bridge rail. The first four posts adjacent to the concrete bridge rail at
the transition section were spaced at 476 mm. The first three posts located at the same
section were W200 19 2290 long and were embedded 1,605 mm into the ground.
The rub rail was a C152 12.2 channel section and made from bent plate. Tapered
wood blockouts were used at the first three posts, no blockout at post 4, and the rub rail
was bent back and terminated on the field side of post 5. Holes, 610 mm in diameter,
were drilled for each post. Additional details on this particular bridge rail-to-guardrail
transition design can be found in the test report by Buth et al. [2]. A picture of the
transition, including the rub rail, posts, and connections, is shown in Figure 1. Note that
these pictures are demonstrated only to give an idea about the transition design. In the
study reported herein, W-beam was replaced with a thrie beam which is 50% wider that
W-beam. All other details remain identical.
FIGURE 1. ± Picture of Flared Back Bridge Rail-to-Guardrail Transition Design.
NUMERICAL ANALYSIS OF A H4A HEAVY CONTAINMENT LEVEL TRANSITION 367
Finite Element Simulation Study
To evaluate the crash test performance of the existing flared-back guardrail-to-
bridge rail transition under heavy vehicle impact, a detailed finite element simulation
study was performed. Necessary time and effort was spent to make the study as
accurate as possible. Details about the simulation study as well as finite element
models used are given in the following sections.
As described in a previous study by Atahan and Cansiz [3], a considerable amount
of effort was spent when modeling the bridge rail-to-guardrail transition. As shown in
Figure 2, the transition model consisted of standard guardrail, approach guardrail,
transition guardrail, wingwall and concrete bridge rail sections. The bridge rail and
wingwall was modeled using 8-noded solid elements. Since both bridge rail and
wingwall were constructed from concrete material, they were modeled as rigid
material. This definition required the material properties of concrete, such as density,
modulus of elasticity and Poisson's ratio and these values were input in the program.
Also, movement of both bridge rail and wingwall was restricted throughout the impact
event due to their large foundation structure. For this reason, movement of both bridge
rail and wingwall were constrained using SPC option in LS-DYNA. This approximation
was fairly accurate in representing the rigid nature of concrete sections. A steel pipe
was also modeled between the wingwall and thrie beam using 4-noded shell elements.
Material and section properties were similar to other steel members in the model.
The heavy goods vehicle model used in the study consisted of 13,457 elements and
12,072 nodes. A total of 49 different parts, 48 different property sets, 54 different
materials, 148 brick or solid elements, 118 beam elements and 13,175 shell elements, 16
discrete elements, 10 constrained joints were utilized in the 30 ton heavy goods vehicle
model. The axles are modeled with beam elements. Belytschko-Schwer tubular beam
with cross-section integration formulation was used to accurately model the beam
FIGURE 2. ± Picture of Flared Back Bridge Rail-to-Guardrail Transition Design.
368 ALI OSMAN ATAHAN - GUIDO BONIN
elements. The model also contained some discrete elements to represent the suspen-
sion system. Discrete elements were suited better to represent the suspension system
since these elements can be specified to act like a simple linear damper. The
suspension system was modeled in the shape of a semi-elliptic leaf spring. The wheels
are connected to the axles via a revolution joint, to model their rotation correctly.
Further details about the model can be found in a paper by Atahan et al. [4].
810 mm Tall Barrier Simulation
The transition was subjected to 30,000 kg vehicle impact in accordance with the
EN1317 test TB71 requirements. The velocity of the vehicle was 65 km/h and it
contacted the transition at an angle of 20 degrees. The initial contact occurred between
the fifth and sixth posts from the concrete wall. At around 60 ms, fifth post from the
wall separated from the thrie rail and vehicle began to redirect. As the vehicle moved
forward, third and fourth posts were also deflected and separated from rail at 105 ms.
Beyond this point, the front impact side wheel began to deform upwards and rotated
counter clockwise about its center. At around 150 ms, front impact side wheel began to
climb over the already deflected thrie rail. Wheel continued its upward movement and
as a result, final two posts supporting the transition section separated from the thrie
rail. At around 210 ms, most of the thrie rail was pulled down by the wheel and this
created a ramp for the vehicle. As a result, vehicle impact side completely overrode the
transition at 285 ms. A picture obtained from the 810 mm tall barrier crash test
simulation is shown in Figure 3. As noticed from these pictures, vehicle easily overrode
the barrier due to the large vertical height difference between the wheel and top of the
thrie rail. Figure 3 clearly demonstrates the wheel override event in a close up view. All
parts other than wheel and rails were turned off due to clarity.
Based on the simulation results, it can be concluded that the crash tested
installation is not an adequate heavy containment level, H4a class barrier in its current
form. It is obvious that in order for the barrier to contain the 30,000 kg vehicle use of a
taller barrier is essential.
FIGURE 3. ± 810 mm tall barrier crash test simulation (a) 0.330 sec. of simulation, (b) wheel
override.
NUMERICAL ANALYSIS OF A H4A HEAVY CONTAINMENT LEVEL TRANSITION 369
1050 mm Tall Barrier Simulation
Based on the simulation results obtained from the 810 mm tall transition, the need
for a taller barrier became apparent. In the 810 mm tall design, the vertical distance
between the wheel and thrie rail was approximately 190 mm and this difference caused
wheel to climb over the rail during impact. To improve the current design to a H4a, high
containment level transition the barrier height was increased to 1050 mm. This height
was selected because it is almost equal to the top wheel height of 1090 mm, and it
supports most of the wheel load during impact. Therefore, it is expected that in the
improved design the wheel should not ride over the barrier.
To increase the rail height in the current transition, a rail element was added above
the thrie rail. Due to its strength and design simplifications, the new rail was selected to
be a rub rail identical to existing rub rail in 810 mm tall design. One end of the new rail
was attached to concrete wall and the other end was lowered to the ground level
behind the barrier. A picture of the improved transition design is shown in Figure 4.
After retrofitting the existing transition model, it was subjected to 30,000 kg heavy
vehicle impact according to EN1317 test TB71 requirements. This time, impacting side
wheel showed no sign of barrier override, and transition successfully contained and
redirected the vehicle. Other than the first post from the concrete wall, all of the posts
at transition deflected. At 0.815 ms after impact, vehicle reached a maximum of 38
degrees roll angle, which is acceptable. A picture of the improved model impact
simulation is shown in Figure 5. As noticed from this figure, damage to vehicle was
concentrated on the impacting side wheel assembly, fender and bumper and con-
sidered to be minimal. Accelerations of the vehicle are within acceptable limits
specified in EN1317. Lateral barrier deformation at the transition was about 450 mm,
which is acceptable. Based on the simulation results, it can be easily concluded that the
improved design with 1050 mm tall rail height is a good candidate for H4a, high
containment level transition.
FIGURE 4. ± Improved transition design.
370 ALI OSMAN ATAHAN - GUIDO BONIN
Summary and Conclusion
In this study, crash test performance of a flared back guardrail-to-bridge rail
transition design was analyzed in detail. A versatile, widely accepted finite element
analysis program LS-DYNA used to perform the analyses. Two successive simulations
were run to complete the study and reach a conclusion. Both simulations were
performed in accordance with EN1317 test TB71 crash test conditions. This test
requires impact of a 30,000 kg heavy goods vehicle traveling at 65 km/h and contacting
transition at 20 degrees angle. In the first simulation, the height of the transition was
810 mm. Results showed that the design did not meet the crash test requirements and
vehicle tend to override the transition due to insufficient height of the design. It was
decided that the height of the transition should be approximately equal to height of the
wheel to contain the vehicle. Thus, an improved transition model was developed. In
this model, the height of the transition was increased to 1050 mm by adding an extra rail
element to the design. The intent was to better contain the vehicle wheel and thus
successfully redirect vehicle. Simulation results predicted that the improved model
performed as intended. It successfully contained and redirected the 30,000 kg vehicle
in a stable manner. No vehicle override was observed. Vehicle deceleration data
showed that there would be no serious threat to vehicle occupants during impact
sequence. Deflection of posts and rail at transition was also within acceptable limits.
Damage to vehicle and transition was moderate. Based on the data obtained from the
simulation, it was concluded that the improved design is an acceptable H4a heavy
containment level transition. Therefore, its full-scale crash test evaluation and possible
implementation to European Highway System is recommended.
Acknowledgements. The work has been performed under the Project HPC-EUROPA
(RII3-CT-2003-506079), with the support of the European Community ± Research
Infrastructure Action under the FP6 ``Structuring the European Research Area''
Programme. Authors also wish to acknowledge the following people for their
FIGURE 5. ± 1050 mm Tall Barrier after Crash Test Simulation.
NUMERICAL ANALYSIS OF A H4A HEAVY CONTAINMENT LEVEL TRANSITION 371
contribution to the study: Dr. Hayes E. Ross, Jr of Texas A&M University, College
Station, Texas, USA, Dr. Giovanni Erbacci and High Performance Computing staff
members at CINECA Interuniversitary Computing Center, Bologna, Italy, and finally,
Mr. Rainer Keller at HLRS Supercomputing facility in Stuttgart, Germany.
Publications
[1] Livermore Software Technology Corporation, LSTC (2000) ``A general purpose dynamic
finite element analysis program, LS-DYNA version 960 user's manual'', Livermore Software
Technology Corporation, Livermore, California, 2002.
[2] BUTH C.E., MENGES W.L. and BUTLER B.G. (1998) ``NCHRP Report 350 test 3-21 of the vertical
flared back transition'' Texas Transportation Institute, Test No. 404211-4, Federal Highway
Administration, Publication No. FHWA-RD-99-062, Washington, D.C.
[3] ATAHAN A.O. and CANSIZ O.F. (2005) ``Impact analysis of a vertical flared-back bridge rail-to-
guardrail transition using simulation'', Finite Elements in Analysis and Design, Vol. 41, No. 4,
371-396.
[4] ATAHAN A.O., BONIN G. and EL-GINDY, M. (2005) ``Design and validation of a 30,000 kg heavy
goods vehicle using LS-DYNA'', Paper No. IMECE2005-80200, Proc. of International
Mechanical Engineering Congress and Exposition, IMECE, Washington D.C.
372 ALI OSMAN ATAHAN - GUIDO BONIN
