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post placement for long spans

Question
State WI
Description Text

We have a project where if the MGS Long-span is installed as crash tested will reduce the shoulder down to 1'.

We have room to install a longer MGS system (box is only a 6' 4" wide).

Could we install a longer span box culvert and have the face of rail closer to the head wall?

We would not have to worry about post rotation issues. 

The only potential issue I do see is that we may allow more of the vehicle to extend over the box culvert during a crash.  Extending how much the vehicle is over the culvert may increase the likelihood of the vehicle interacting with the wing walls. 

The head wall does not extend above the ground line.

I have some photos of the culvert in question.  They look pretty bad, but I understand that the culvert had some repair work done on it after it got hit.


Keywords
  • Guardrail
Other Keywords Long-span
Date November 10, 2015
Attachment 2015-11-10_7-22-25.pdf
Attachment box culvert-guard rail (003).docx


Response
Response After reviewing the proposed installation, we have concerns with respect to extending the long span an moving the system closer to the culvert. At this time, we have not performed any analysis or or testing that would shed light on the effects of moving the system closer to the edge of the culvert. The concern would lie mostly with the extension of the vehicle over the culvert and the potential for this to compromise the safety performance of the barrier. Keeping the the unsupported length less than the 25' that was full-scale crash tested may limit the extension somewhat, but the amount of the reduction is not quantified. 

A better solution in this case my be to use the MGS mounted to culverts with the side mounted sockets for the S3x5.7 post. Note that we would recommend the extended backup plates on this design based on the results of the MGS in mow strip testing. 

http://mwrsf.unl.edu/researchhub/files/Report293/TRP-03-277-14.pdf 
Date November 17, 2015


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