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Top mounted Post to Box Culvert Design

Question
State WY
Description Text

Top mounted Post to Box Culvert Design – MwRSF tested a box culvert design for 27 2/4 inch high corrugated beam guardrail using a half post spacing in 2002. The results are described in TRP-03-114-02. A recent project was to simplify the weld detail. I believe the recommendation was to leave the weld the same as the original design. There was no upper bound listed for the amount of fill above the culvert. The lower bound was 9 inches of fill. Is there an upper bound to the amount of fill for the post to function properly? Can this design be used for 31 inch high MGS guardrail as well?

TTI recently (2012) tested a similar design with a 31 inch high w-beam guardrail and posts at a standard spacing. Again, there was no upper bound recommended for the depth of fill on top of the culvert. Is there a limit or does post performance either improve or stay about the same with greater fill depths.

I think I heard TTI also tested another box culvert mount using weak posts at a half post spacing. Is this true and do you have any details about the design and/or contact information?

Any other comments about this design would be appreciated. We love the Midwest side mounted socket design, but there are several existing box culverts where we cannot mount the guardrail that far out due mainly to grading issues for the approach guardrail.

Keywords
  • Guardrail
Other Keywords box culvert, top mount
Date March 27, 2014
Attachment Q-Top mounted Post to Box Culvert Design.docx


Response
Response
See responses below in red.

Top mounted Post to Box Culvert Design – MwRSF tested a box culvert design for 27 2/4 inch high corrugated beam guardrail using a half post spacing in 2002. The results are described in TRP-03-114-02. A recent project was to simplify the weld detail. I believe the recommendation was to leave the weld the same as the original design. There was no upper bound listed for the amount of fill above the culvert. The lower bound was 9 inches of fill. Is there an upper bound to the amount of fill for the post to function properly? Can this design be used for 31 inch high MGS guardrail as well?

The guardrail attached to culvert design was developed and tested with the minimum allowable fill level. It is believed that increased soil fill levels will function similarly. 

This system has been adapted for use with the MGS by KDOT based on guidance provided by MwRSF. We are still recommending that 1/2 post spacing be used at this time. I have attached the KDOT details below. 

There is a proposal in the upcoming Year 25 Pooled Fund to evaluate the system with full-post spacing and minimum offset to the culvert headwall. 

TTI recently (2012) tested a similar design with a 31 inch high w-beam guardrail and posts at a standard spacing. Again, there was no upper bound recommended for the depth of fill on top of the culvert. Is there a limit or does post performance either improve or stay about the same with greater fill depths. 

As with the system developed at MwRSF, we would expect the system performance to remain similar for increased fill depths for the TTI system as well. 

I think I heard TTI also tested another box culvert mount using weak posts at a half post spacing. Is this true and do you have any details about the design and/or contact information?

TTI tested a TL-2 version of the MGS bridge rail with full-post spacing and S3x5.7 weak posts that were attached to a bridge deck using through bolted base plates. This system would likely work at TL-3 with 1/2 post spacing. TTI did have some deck reinforcement modifications for this design in order to place it near the edge of the bridge deck. I do not have the report for this system, but I do have a presentation with details and have attached it. William Williams at TTI can provide more information on this system as well. 

Any other comments about this design would be appreciated. We love the Midwest side mounted socket design, but there are several existing box culverts where we cannot mount the guardrail that far out due mainly to grading issues for the approach guardrail.
Date March 31, 2014
Attachment rd617d.pdf
Attachment rd617e.pdf
Attachment TXDOT-T631BridgerailWFW-TTI.pdf


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