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Strong Post Deck Mounted Guardrail

Question
State IN
Description Text

We have had a lot of question about guardrail over large culverts adjacent driveways or roadways.  With the close proximity of the roadways, our standard nesting system is too long.  We are in the process of possibly moving toward the MGS system but are still showing strong post guardrail with an 8" blockout in our standard drawings.  Could you recommend a good connection system for culvert mounted strong post guardrail?  Would it still be an option to use the SRG05 Culvert Mounted W-Beam Guardrail in the Guide to Standardized Highway Barrier Hardware, see attached. 

I also have one other question, a lot of designers have proposed to just cross these large culverts with our modified post that we use in our nested guardrail system, see attached standard drawing sheets.  We believe these modified post should only be used as part of a system, modified posts (E 601-NWGA-03, attached) should be proceeded and followed by 4-6'-0" length steel posts w/routed wood blockouts (E 601-NWGA-01 and -02, attached).   They should not stand alone.  Do you know of any mounted post systems that are similar to our nested guardrail modified post that can stand along over a bridge?


Road Closure Gates
Thrie Beam Guardrails


Date August 23, 2016
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Attachment SRG05 Cuvlert Mounted Guardrail - Copy.pdf Attachment E601-NWGA INDOT Nested Guardrail System.pdf
Response
Response
(active)
We have looked into similar questions previously for several states. I have placed links below to simialr questions that  have additional details that you may wish to refer too. 

http://mwrsf-qa.unl.edu/view.php?id=322
http://mwrsf-qa.unl.edu/view.php?id=799

It appears from the question you submitted that you cannot use a long span guardrail and need to attach posts to the culvert. MwRSF previously developed system for this purpose that was evaluated to NCHRP Report 350. The system used metric height W-beam with 1/2 post spacing and special posts that were mounted to the culvert. Subsequent research on that system also evaluated an epoxy adhesive anchorage for the posts. This system has not been tested to MASH, nor has it been evaluated with the MGS. However, it is believed to be likely that the system would perform acceptably under MASH. As such, Kansas DOT has adopted the system for use with 31" guardrail. Details are attached. The reports on the MwRSF research and testing of this system are located below.

http://mwrsf.unl.edu/researchhub/files/Report144/TRP-03-114-02.pdf 
http://mwrsf.unl.edu/researchhub/files/Report280/TRP-03-278-13.pdf

TTI recently (2012) tested a similar design with a 31 inch high w-beam guardrail and posts at a standard spacing. This design uses a slightly different base plate and uses full post spacing. This design passed MASH TL-3, but partial tearing of the W-beam guardrail was noted. They also tested a similar system under NCHRP Report No. 350 that was installed at 27". 

http://www.roadsidepooledfund.org/files/2012/02/405160-23-2-box-culvert-rev2.pdf
http://www.roadsidepooledfund.org/files/2011/03/405160-5-1-box-culvert.pdf

Thus, several options exist for attachment for strong post guardrail to culverts. Please review the attached information and let me know if you have further questions. 

As for the modified detail you attached, I have not seen any similar system tested or evaluated. There are some concerns that the use of the BCT post in a foundation tube would limit the energy absorption of the posts in the system. This could potentially increase deflection and rail loads to undesirable levels. Thus, we would recommend using one of the tested systems noted above.
Date August 23, 2016
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Attachment rd617d.pdf Attachment rd617e.pdf