|Logged in as: Public User|
|Description Text||Are you aware of any minimum and/or maximum allowable height guidance for thrie-beam guardrail?|
|Date||September 21, 2010|
I am not aware of a documented height tolerance for thrie beam guardrail systems. Initially, one may attempt to argue that the minimum height could be as low at that corresponding to W-beam guardrail systems. However, I would suspect that mounting thrie beam with a top height of 27¾ in. would potentially increase the propensity for vehicle climb, barrier override, and/or rollover upon redirection due to the increase face below normal W-beam rail with same top height.
At this time, the roadside safety community has considered the minimum top height for W-beam rail to be approximately 27¾ in., while the maximum top height for the MGS is 32 in. At the minimum W-beam top height, a thrie beam element would extend downward to 7¾ in., thus potentially creating new safety risks. Selected thrie beam guardrail systems have successfully met crash testing guidelines when installed with a top height of 34 in. As such, it is my opinion that the minimum height tolerance for modified thrie beam guardrail may be somewhere around 31 in. for NCHRP 350, while the top height tolerance may be closer to 39 to 40 in. at the TL-3 impact conditions.
Thrie beam has been successfully crash tested over the years. Below, I have provided a few of the test results but not those for the T-39 thrie beam guardrail system.
Test No. System Description Top Rail Height Result
404211-5a Modified Thrie Beam w/ 81" Steel Post & Tapered Block 34" Passed 8000S TL-4 test
404211-11 Strong-Post Thrie Beam w/ 81" Wood Post & Wood Block 31.65" Passed 2000P TL-3 test
404211-10 Thrie Beam w/ 81" Steel Post and Routed Wood Block 31.65" Passed 2000P TL-3 test
471470-31 Thrie Beam (G9) w/ 78" Steel Post and Steel Block 32" Failed 2000P TL-3 test
471470-30 Modified Thrie Beam w/ 81" Steel Post and Tapered Block 33.6" Passed 2000P TL-3 test
Recent Test Thrie Beam (G9) w/ 78" Steel Post and Full-Depth Wood Block 31.5" Failed 2270P TL-3 test (MASH)
Although I have yet to see the results of the recent failed MASH test, it would seem reasonable that improved safety performance could be obtained by using a shortened wood blockout or the modified steel tapered (collapsible) blockout " both of which reduced climb and allow the lower corrugation to fold back.
|Date||December 13, 2010|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
The information contained on the Midwest Roadside Safety Facility (MwRSF) website is subject to change without prior notice. The University of Nebraska and the MwRSF is not responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the use or misuse of or reliance upon any such content, goods, or services available on this site.