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Standardized AGT Buttress

State VA
Description Text We are trying to use the AGT that MWRSF crash tested in combination with a 32” Kansas Corral Railing (our NCHRP 350 version). 
The AGT height is 36”. Is it acceptable to use the AGT buttress at a constant 32” height (other details staying the same) and still consider it to conform to TL-3 MASH? See the Option 1 markup in the attached file

I understand that the reduction in height may make it difficult to tell if it meets MASH TL3 at the reduced height, so I have a second question. Do you think that it will perform as required at 32” with the MGS.
Virginia has implemented MGS for guardrail everywhere. As part of that we have been employing a height transition to our existing bridge terminal walls. In a few locations this height transition is causing trouble because there is not a long run of guardrail leading up to the bridge. So we propose to replace the terminal wall with the new AGT, but our bridge railing is only 32” so we propose to make the AGT 32” rather than 36” and a 24” taper to get it back down to our bridge railing. 
We want to confirm that this proposal makes sense and whether it will perform as intended after the change.

We have a second option, and that is to taper the far end of the wall down from 36” to 32” for the last 2ft. See attached markup listed as Option 2.

Any insight or guidance would be appreciated.
  • Approach Guardrail Transitions
Other Keywords none
Date August 29, 2018
Attachment Page from agt buttress paper.pdf


Option 1 is preferred for attachment to a 32” tall bridge rail.  Any time you are connecting to a 32” tall barrier, you may eliminate the vertical slope on the front end of the buttress.  We had a drawing sketched up for the project report illustrating a version of the buttress when attached to a 32” F-shape bridge rail (see below for reference).  For any geometric variation of the standardized buttress, including this height change, the size and quantity of the steel rebar should remain the same.  However, the shape may be slightly altered to fit within the various shapes, just as you noted in your attached drawing.  We believe that the shorter height will remain MASH TL-3 crashworthy.

Date August 29, 2018
Attachment agt question.jpg

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