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MGS with Posts Skipped

Question
State
Description Text

I think this is related to another question that I had a few weeks ago.  We are putting together Tollway guardrail guidelines for designers to use.  I would like to provide some guidance on conflicts with posts within a run of guardrail.  We have some drainage structures that are about 9' across.  If one of these drainage structures falls at a post, would it be better to just leave one post (or 2?) out or shuffle the post spacing and use all of the posts.  Shifting the posts around would place posts where there are no pre-drilled holes in the rail.  Is that an issue?

 

If post(s) are left out does anything else need to be done as long as there is plenty of room for deflection?  If one post is left out, what is the anticipated deflection?

 

We would rather not use any special posts if possible.

Keywords
  • Guardrail
Other Keywords none
Date February 15, 2010


Response
Response

The MGS Long-Span system was developed for use to span transverse culverts measuring 24 ft wide or less. In this circumstance, three posts would be removed from the system. This system also utilizes three CRT posts on each side of the culvert structure. For culverts measuring less than 24 ft wide and where one or two posts are omitted, it still would be necessary to utilize the CRTs on each side of the unsupported segment of rail.

 

Although it may be possible for the MGS to work with one post removed and without CRTs adjacent to the long span, it should be noted that crash testing has not been performed on this MGS system nor to verify that acceptable performance would result. As such and in the absence of test data, we recommend that the CRTs be installed in systems where one, two, or three posts are removed.

 

In locations where posts are left out, dynamic barrier deflections and working widths would be expected to increase. Test results are available for the case with three posts removed from the MGS. However, data is not available for cases with one or two posts removed. BARRIER VII computer simulations could be performed to estimate barrier deflections and working widths. A small modeling study would be necessary to validate the model for the MGS long-span system and then predict barrier performance with fewer posts removed.

Date February 18, 2010


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