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Trailing End Anchor and AGT for MGS Double Sided W-beam for Medians

Question
State IN
Description Text
 Can the trailing end anchor tested in TRP-03-279-13 and the AGT tested in TRP 03-210-10 be used with MGS double face median guardrail?  We realize the trailing end anchor is not crash tested as an end treatment but we have a couple cases where the median guardrail end it protected by a median wall, see the attached picture.  If the AGT can be used for median applications can an anchor bolt be used instead of a through bolt to connect the thrie beam to the median barrier?


Approach Guardrail Transitions (AGTs)
Road Closure Gates
Thrie Beam Guardrails


Date May 1, 2019
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Attachment Shielded Trailing End Anchor.pdf
Response
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(active)

MwRSF did evaluate a trailing end anchorage for roadside applications. unfortunately, it cannot currently be applied to median applications without further analysis and testing. Anchorage of a dual-sided median guardrail system requires that both sides of the guardrail be anchored. The current trailing end anchorage design only has anchorage to a single rail. Incorporation of a second anchor bracket for the backside rail would require design to develop the connection and testing to verify that the additional anchorage did not adversely affect the trailing end anchorage crashworthiness.

Attachment of the median guardrail to the parapet is likely a better option at this time. However, this attachment is essentially an approach guardrail transition. Thus, attachment requires the use of reduced post spacing and other elements comment to AGTs to prevent vehicle snag and pocketing adjacent to the parapet.

Currently, no MASH TL-3 median AGT exists. We did develop a median AGT for Missouri under NCHRP 350. That is likely the best options for the attachment at this time.

https://mwrsf.unl.edu/researchhub/files/Report84/TRP-03-47-95.pdf

Note that the end of the parapet made need to be modified to mitigate vehicle snag similar to the tested transition.

I believe that TTI currently has a pooled fund project to develop at median AGT system.

Thanks

Date May 7, 2019
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(active) 		Use of the AGT in TRP-03-210-10 would be an option as well. 

There is little concern that the roadside transition that was tested to MASH TL-3 would be applicable for dual-side median applications in terms of impacts near the rigid parapet as long as appropriate snag mitigation flares and cutouts were used on the parapet. This is because the median version of the AGT would be stiffer than the single-side roadside version. 

The concern for the median AGT would more likely reside on the upstream stiffness transition. Recall that the original testing of the upstream stiffness transition demonstrated some snag potential, particularly with the 1100C vehicle. Thus, there are some concerns that a dual-sided AGT would be stiffer and make the snag somewhat more severe. 

That said, similar concerns would exist with the previously NCHRP 350 tested AGT as well. Thus, until such time as the research into the median AGTs is completed at TTI, use of a dual-sided version of the AGT in TRP-03-210-10 would be a viable option. 
Date May 8, 2019
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(active) 		Just be clear, it would not be an option to double face the AGT tested for single side traffic at bridge approaches in TRP 03-210-10?
Date May 8, 2019
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(active) 		Thank you, hopefully one last question. Since we would not call for a through bolt connection at the CMB, could we call for the use of the self-drilling ramset/redhead concrete anchor for 7/8" A325 bolt, as you called out for the Missouri AGT to median barrier in TRP-03-47-95? Is there a more generic way to callout an anchor bolt or minimum embedment length and strength?
Date May 8, 2019
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(active) 		I don't believe that the Ramset anchors used in the original study are currently available. Typical end anchorages connections specify 7/8" diameter A325/A449 bolts for attachment. I don't believe that any threaded socket type concrete anchorages exist for that size of anchorage. 

As such, the best option would likely be to use 7/8" diameter A449 or B7 threaded rods epoxied 5"-6" into the parapet. the epoxy should have a bond strength around 1,400 psi. In order to reduce vehicle snag the rods should only extend 1/8"-1/4" past the end of the nut. 

If the parapet you are attaching to is relatively thin, the anchors from opposing sides may interfere. In that case, we would recommend extending the thrie beam for an additional 6'-3" along the parapet on the non-approach side of the AGT to allow for anchor installation without interference., 
Date May 13, 2019
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