Recently, the Minnesota Department of Transportation (MnDOT) funded a research project through the Midwest States Regional Pooled Fund to evaluate an existing steel post alternative for the thrie beam bullnose barrier system previously developed at the Midwest Roadside Safety Facility (MwRSF). MnDOT had an interest in the replacement of the wooden breakaway posts used in the current bullnose system with proprietary breakaway steel posts. The research project consisted of evaluation of current breakaway steel post designs, investigation and selection of a candidate post design, and full-scale testing of the bullnose system with a steel post alternative. The full-scale testing was to consist of two tests conducted according to the evaluation criteria of NCHRP Report 350:   
1)  Test 3-38, an impact of a 2000P vehicle on the Critical Impact Point (CIP) of the system at a speed of 100 km/h and an angle of 20 degrees, and   
2)  Test 3-31, an impact of a 2000P vehicle with the center of the vehicle aligned with the center of the nose of the system at a speed of 100 km/h and an angle of 0 degrees.   
The evaluation of the steel post alternative for the bullnose system project has been completed. A steel post alternative was selected followed by two full-scale crash tests. Unfortunately, both crash tests failed as the vehicle in each test ramped up the guardrail and vaulted the system. This letter summarizes the work completed

Bielenberg, Robert W.

Faller, Ronald K.

Reid, John D.

Rohde, John R.

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Final Reports & Technical Briefs from Mid-
America Transportation Center Mid-America Transportation Center 
2007 
EVALUATION OF AN EXISTING STEEL POST ALTERNATIVE FOR 
THE THRIE BEAM BULLNOSE GUARDRAIL SYSTEM 
Robert W. Bielenberg 
Ronald K. Faller 
John R. Rohde 
John D. Reid 
Follow this and additional works at: https://digitalcommons.unl.edu/matcreports 
 Part of the Civil Engineering Commons, and the Transportation Engineering Commons 
This Article is brought to you for free and open access by the Mid-America Transportation Center at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Final Reports & Technical 
Briefs from Mid-America Transportation Center by an authorized administrator of DigitalCommons@University of 
Nebraska - Lincoln. 
 
 
 
 
 
 
 
EVALUATION OF AN EXISTING STEEL POST 
ALTERNATIVE FOR THE THRIE BEAM BULLNOSE 
GUARDRAIL SYSTEM 
 
 
Submitted by 
 
Bob W. Bielenberg, M.S.M.E., E.I.T. 
Research Associate Engineer 
Ronald K. Faller, Ph.D., P.E. 
Research Assistant Professor 
 
John R Rohde, Ph.D., P.E. 
Associate Professor 
John D Reid, Ph.D. 
Professor 
 
 
 
MIDWEST ROADSIDE SAFETY FACILITY 
University of Nebraska-Lincoln 
527 Nebraska Hall 
Lincoln, Nebraska 68588-0529 
(402) 472-6864 
 
Submitted to 
 
MIDWEST STATES REGIONAL POOLED FUND PROGRAM 
Nebraska Department of Roads 
1500 Nebraska Highway 2 
Lincoln, Nebraska 68502 
 
 
 
MwRSF Research Report No. TRP-03-193-07 
 
 
August 24, 2007
 1
 
 
August 24, 2007 
 
Mohammad Dehdashti 
Minnesota Department of Transportation  
1500 W Co Rd B2 
Roseville, MN 55113 
651-234-7606 
 
Subject: Evaluation of an Existing Steel Post Alternative for the Thrie Beam Bullnose Guardrail 
System 
 
Dear Mr. Dehdashti: 
 
Recently, the Minnesota Department of Transportation (MnDOT) funded a research project 
through the Midwest States Regional Pooled Fund to evaluate an existing steel post alternative 
for the thrie beam bullnose barrier system previously developed at the Midwest Roadside Safety 
Facility (MwRSF). MnDOT had an interest in the replacement of the wooden breakaway posts 
used in the current bullnose system with proprietary breakaway steel posts. The research project 
consisted of evaluation of current breakaway steel post designs, investigation and selection of a 
candidate post design, and full-scale testing of the bullnose system with a steel post alternative. 
The full-scale testing was to consist of two tests conducted according to the evaluation criteria of 
NCHRP Report 350: 
 
1) Test 3-38, an impact of a 2000P vehicle on the Critical Impact Point (CIP) of the 
system at a speed of 100 km/h and an angle of 20 degrees, and  
2) Test 3-31, an impact of a 2000P vehicle with the center of the vehicle aligned 
with the center of the nose of the system at a speed of 100 km/h and an angle of 0 
degrees.  
 
The evaluation of the steel post alternative for the bullnose system project has been completed. A 
steel post alternative was selected followed by two full-scale crash tests. Unfortunately, both 
crash tests failed as the vehicle in each test ramped up the guardrail and vaulted the system. This 
letter summarizes the work completed.  
 
Alternative Steel Post Selection 
 
The first phase of the development of a steel post alternative for the bullnose system was 
investigation and selection of a candidate steel post. The scope of the project dictated that the 
breakaway steel post design be chosen from the field of existing proprietary steel post designs 
due to the cost and time associated with development of a new, non-proprietary breakaway steel 
post design specifically for this application. To this end, current breakaway steel post 
manufacturers were contacted and asked to submit candidate steel post designs as well as sample 
posts and design details. Review of the manufacturer responses along with engineering input 
from MwRSF researchers led to the selection of two potential post designs. These designs were 
 2
the Road Systems, Inc. (RSI) Hinged Steel Post and the RSI Plug Weld Post. The selected posts 
are shown in Figures 1 and 2.  
 
In order to evaluate the candidate steel post designs, component testing was conducted on both of 
the potential steel post designs and the wooden CRT post used in the current bullnose system. 
The component testing consisted of impacting all three post types with a 728-kg bogie vehicle at 
a speed of 31.19 km/h and an angle of 36 degrees from the weak axis of the posts. The impact 
behavior of these types of breakaway posts was well quantified under weak and strong axis 
impacts. However, the behavior of the posts when impacted at intermediate angles was not 
documented. Thus, the impact angle for the component tests was chosen to simulate an oblique 
impact angle on the posts similar to what would be observed in the CIP test of the bullnose 
system. The goal of the testing was to determine the peak loads and energy levels generated by 
the posts in order to decide which post would perform best in the bullnose system. 
 
The results from the component testing are shown in Figures 3 and 4. Figure 3 displays the force 
versus deflection properties for the three posts, and Figure 4 displays the energy versus 
deflection data. Comparison of the data from the three post types yielded valuable insight into 
selection of an alternative breakaway steel post for the bullnose system. The force deflection data 
from the testing showed that both the RSI Plug Weld Post and RSI Hinged Steel Post developed 
lower peak loads than a wooden CRT post. However, investigation of the energy data found that 
the RSI Plug Weld Post did not release cleanly upon impact and absorbed much more energy 
than either the RSI Hinged Steel Post or the CRT post. The RSI Hinged Steel Post was observed 
to absorb the least amount of energy prior to release.  
 
Discussions were held with the researchers, the project sponsor, and the post manufacturer to 
determine which steel post alternative to use in the bullnose system. The researchers believed 
that any alternative breakaway post design used with the bullnose system would need to develop 
peak loads less than or equal to those of the CRT post used in the original design and disengage 
or fail in a brittle manner in order to function properly. It was clear from the component testing 
that the RSI Hinged Steel Post failed in a much more brittle manner and absorbed far less energy 
than the RSI Plug Weld Post, and thus would be expected to perform more like the CRT posts 
used in the original bullnose system. Discussions with RSI also revealed that the RSI Hinged 
Steel Post would be their primary manufactured breakaway post design in the future and that 
supplies of the RSI Plug Weld Post would be potentially limited. Thus, it was decided that the 
RSI Hinged Steel Post was the best alternative post option for the bullnose system. 
 
Design details for the RSI Hinged Steel Post and the thrie beam bullnose system with the RSI 
Hinged Steel Post substituted for the wooden breakaway posts are shown in Figures 5 through 
17. The bullnose system was unchanged from the original design other than post nos. 1 through 9 
which were replaced with RSI breakaway steel posts. Note that the post no. 1 in the original 
bullnose system was a wooden BCT post in a 2,438-mm long steel foundation tube. This post 
was replaced by an RSI steel anchorage post that differed from the RSI Hinged Steel Post in that 
it used a breakaway mechanism based on fracture at the base of the post, it had a soil plate on the 
lower section for development of anchor loads, and the top section was fabricated with a cutout 
in the web to accommodate a standard cable anchorage. This design was then used to conduct the 
first full-scale crash test.  
 3
 
Test No. SBN-1 
 
The first test of the thrie beam bullnose system with breakaway steel posts, test no. SBN-1, was 
conducted according to NCHRP Report 350 test designation 3-38. The test consisted of a 2000-
kg pickup truck impacting the CIP of the bullnose at a speed of 100 km/h and an angle of 20 
degrees. The CIP for a non-gating system, such as the bullnose, was defined as the point in the 
installation where it was unknown if the system would capture or redirect the vehicle. For test 
SBN-1, this point was located at post no. 2. The CIP test was chosen as the first test because it 
was believed that the CIP impact would be the more difficult of the two test conditions for the 
system to pass. This was based on the fact that the breakaway steel posts would be loaded at an 
intermediate angle rather than directly along the strong or weak axis.  
 
In test no. SBN-1, a 2,020-kg pickup truck impacted the CIP of the bullnose system at a speed of 
103.1 km/h and an angle of 20.1 degrees. The results from test no. SBN-1 are summarized in 
Figure 18. During test no. SBN-1, the bullnose system with breakaway steel posts failed to 
capture the impacting vehicle. As the pickup truck penetrated into the system, the vehicle ramped 
up the guardrail and vaulted the system. Review of the test results and comparison of the 
behavior of the system with the successful testing of the original bullnose system revealed that 
the failure of the test was largely due to the upstream anchorage at post no. 1. In test no. SBN-1, 
post no. 1 was an RSI steel anchorage post. This post developed upstream anchorage far longer 
during the impact event than the wooden BCT post used in the original design. Film analysis 
showed that the upstream anchorage at post no.1 remained active until approximately 240 msec 
in test no. SBN-1, while in the CIP test of the original bullnose, test no. MBN-8, the upstream 
anchor at post no. 1 remained active for only 154 msec. The retention of the upstream anchorage 
in test no. SBN-1 led to a reduction in the penetration of the pickup truck into the system and a 
corresponding reduction in the formation of a pocket in the guardrail to effectively capture the 
front of the vehicle. This can be observed in the comparison of the overhead sequential 
photographs from test nos. MBN-8 and SBN-1, as shown in Figures 19 and 20, respectively. 
 
Design No. 2 
 
Two options were proposed following test no. SBN-1 to improve the performance of the system. 
The first option was to develop a controlled release anchorage system. This option involved 
quantifying the required performance of the anchorage system for a variety of impacts. Impacts 
from the critical impact point and further downstream would require sufficient anchorage 
capacity to redirect the vehicle. Impacts occurring upstream of the CIP would require release of 
the anchorage. It was not known exactly what level of fixed anchorage capacity that would 
accomplish these two desired results. This option would have required additional simulation, 
component testing, and full-scale testing and may have lead to significant added time and cost to 
the project. 
 
A second option was proposed based on the anchorage of the original bullnose design. The 
anchorage system employed in the original bullnose development used a 2,438-mm long 
foundation tube and a BCT post. This setup was proposed to replace the design for post no. 1 
used in test no. SBN-1. This or course would require the use of wood in the system. While this 
 4
option addressed the anchorage release, there was no way at this juncture to quantify whether the 
system would respond in the same way as the original bullnose testing, and full-scale crash 
testing of this option would be required.  
 
Based on the reduced cost and time required, it was decided that the project would proceed using 
the second option. Thus, a second full-scale test was conducted on the bullnose system with 
breakaway steel posts with post no. 1 replaced with a wooden BCT post in a 2,438-mm long 
foundation tube, as shown in Figure 21. 
 
Test No. SBN-2 
 
In test no. SBN-2, a 2,002-kg pickup truck impacted the CIP of the bullnose system at a speed of 
101.3 km/h and an angle of 20.7 degrees. The bullnose system design for this test was unchanged 
from test no. SBN-1 other than the replacement of post no. 1 with a standard BCT post. The 
results from test no. SBN-2 are summarized in Figure 22. During test no. SBN-2, the bullnose 
system with breakaway steel posts failed to capture the impacting vehicle. As the pickup truck 
penetrated into the system, the vehicle ramped up the guardrail and vaulted the system. Review 
of the test results and comparison of the behavior of the system with the previous test nos. MBN-
8 and SBN-1 yielded information regarding the failure of the test. The initial performance of the 
system in test no. SBN-2 was improved over that of the previous test. The upstream anchor 
released earlier in the event and the vehicle penetrated farther into the system and was more 
effectively captured. However, as the vehicle was being captured, it appeared that the vehicle 
rode up the debris from the failed steel posts and attached wood blockouts, thus causing the 
vehicle to vault the guardrail and resulting in the subsequent failure of the test due to loss of 
vehicle containment. Because the RSI Hinged Steel Posts were hinged about the base as their 
failure mechanism, the tops of the posts and the blockouts did not disengage and clear away from 
underneath the guardrail and provided collected materials for the impacting vehicle to climb up.  
 
Summary and Discussion 
 
The objective of research described in this summary letter was to evaluate existing steel 
breakaway post alternatives for the thrie beam bullnose barrier system. The research began with 
identifying and selection of a candidate steel breakaway post. The RSI Hinged Steel Post was 
chosen as the most appropriate available post based on engineering judgment and component 
testing. Next, a full-scale crash test, test no. SBN-1, was conducted on the bullnose system with 
breakaway steel posts. Test no. SBN-1 was an impact of a 2,020-kg pickup truck on the CIP of 
the bullnose system at a speed of 103.1 km/h and an angle of 20.1 degrees. The CIP for the 
system was located at post no. 2. Test no. SBN-1 was unsuccessful due to the upstream 
anchorage at post no. 1 remaining active longer than the standard BCT anchorage, which resulted 
in ineffective vehicle capture and vaulting of the guardrail. It was decided that the second test, 
test no. SBN-2, would be conducted as a repeat of the first test with post no. 1 replaced by a 
standard wooden BCT post. Test no. SBN-2 was an impact of a 2,002-kg pickup truck on the 
CIP of the bullnose system at a speed of 101.3 km/h and an angle of 20.7 degrees. Test SBN-2 
was also deemed unsuccessful due to failure of the system to capture the impacting vehicle and 
override of the guardrail. However, it should be noted that the initial performance of the system 
in test no. SBN-2 was significantly improved. Override of the guardrail in test no. SBN-2 was 
 5
attributed to the pickup truck riding up the debris of the failed RSI Hinged Steel Posts and 
blockouts.  
 
Review of the research conducted herein suggests that replacement of the original wood 
breakaway posts used in the thrie beam bullnose design with steel breakaway posts is a difficult 
task. While steel breakaway posts have been successfully used for end terminal designs in the 
past, it appears that the bullnose system is more sensitive to some of the subtle differences 
between wooden and steel breakaway posts. The wooden CRT and BCT posts used in the 
original design take advantage of several inherent properties of wood that are difficult to 
replicate with steel breakaway post designs. These properties include brittle fracture at relatively 
low impact loads and clean disengagement of the post from its base. The researchers at MwRSF 
believe that currently available breakaway steel posts designs do not adequately take this 
combination of factors into account.  
 
A second study has subsequently been funded by MnDOT to develop a universal, non-
proprietary breakaway post. This effort will design a breakaway post that does not use wood, but 
that mimics the behaviors of the wooden CRT posts that are used in a wide variety of roadside 
hardware systems. This study is currently underway, and it is hoped that the results of this design 
effort will be applicable to the thrie beam bullnose system as well. 
 
If you have any questions regarding this information or need any other information, please feel 
free to contact me by phone at (402) 472-9064 or by email at rbielenberg2@unl.edu.  
 
Sincerely, 
 
 
Robert W. Bielenberg, M.S.M.E., E.I.T. 
Research Associate Engineer 
Midwest Roadside Safety Facility 
527 Nebraska Hall 
Lincoln NE, 68588-0529 
402-472-9064 
rbielenberg2@unl.edu 
 6
 
Figure 1. Breakaway Post Component Testing, Plug Weld Post Design 
 7
 
Figure 2. Breakaway Post Component Testing, Hinged Steel Post Design 
 8
Force Versus Deflection (EDR3)
-2
0
2
4
6
8
10
0 5 10 15 20 25 30 35 40
Deflection (In.)
F
o
r
c
e
 
(
K
i
p
s
)
Wood CRT post Single bolt, hinged post Plug-welded post
 
Figure 3. Component Test Results, Force vs. Deflection 
 9
Energy Versus Deflection (EDR3)
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40
Deflection (In.)
E
n
e
r
g
y
 
(
K
i
p
-
I
n
.
)
CRT Wood post Single bolt, hinged post Plug-welded post
 
Figure 4. Component Test Results, Energy vs. Deflection 
 10
 
Figure 5. Steel Post Bullnose System, Test No. SBN-1 
 11
 
Figure 6. Steel Post Bullnose System, Test No. SBN-1 
 12
 
Figure 7. Steel Post Bullnose System, Test No. SBN-1 
 13
 
Figure 8. Steel Post Bullnose System, Test No. SBN-1 
 14
 
Figure 9. Steel Post Bullnose System, Test No. SBN-1 
 15
 
Figure 10. Steel Post Bullnose System, Test No. SBN-1 
 16
 
Figure 11. Steel Post Bullnose System, Test No. SBN-1 
 17
 
Figure 12. Steel Post Bullnose System, Test No. SBN-1 
 18
 
Figure 13. Steel Post Bullnose System, Test No. SBN-1 
 19
 
Figure 14. Steel Post Bullnose System, Test No. SBN-1 
 20
 
Figure 15. Steel Post Bullnose System, Test No. SBN-1 
 21
 
Figure 16. Steel Post Bullnose System, Test No. SBN-1
 22
 
 
 
Figure 17. Steel Post Bullnose System, Test No. SBN-1
 23
 
Figure 18. Summary of Test Results and Sequential Photographs, Test No. SBN-1 
 24
 
 
 
Figure 19. Overhead Sequential Photographs, Test No. MBN-8
 25
 
 
 
 
 
 
 
 
 
Figure 20. Overhead Sequential Photographs, Test No. SBN-1
 26
          
    SBN-1         SBN-2 
 
Figure 21. Post No. 1 for Test Nos. SBN-1 and SBN-2 
 27
 
 
Figure 22. Summary of Test Results and Sequential Photographs, Test No. SBN-2 


EVALUATION OF AN EXISTING STEEL POST ALTERNATIVE FOR THE THRIE BEAM BULLNOSE GUARDRAIL SYSTEM

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EVALUATION OF AN EXISTING STEEL POST ALTERNATIVE FOR THE THRIE BEAM BULLNOSE GUARDRAIL SYSTEM

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