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We have been looking at the TL-2 AGT tested by TTI for some limited uses on our projects.  Below are some questions about the end post design as well as the link to the report for the TL-2 AGT.

1. The tests were conducted using a 36” single slope rail/barrier with the toe clipped to be vertical under the thrie-beam and no vertical taper for the rail height.  Would attaching to a vertical 36” or 42” parapet be an issue? 


2. I know on other AGT’s swapping 10 ga. thrie for nested 12 ga. thrie has been acceptable.  Would there be any issues here?


3. We generally use a 4” sloped curb with our current AGT.  Should we ensure the curb extends up stream of the W-to-Thrie transition piece, stop it before, or just avoid terminating under the W-to-Thrie piece?
   
   
   
   1. See attached
   
   
   
   


4. Link to report:https://www.roadsidepooledfund.org/wp-content/uploads/2016/10/9-1002-8-final.pdf

As you may recall from a couple of previous emails and questions, we are working to move our AGT and end post/buttress designs to MASH tested designs.  Our Bridge Office has settled on the standardized buttress, but for the AGT we were wondering which AGT y’all recommend to use with the standardized buttress.  We were looking at adapting our current design in previous emails, but we are also open to moving to different design.  This is our current AGT, but below are some general factors we were looking at when looking for MASH AGT.

1. Standards push to use steel posts and composite blocks

2 .Preference for allowance of nested 12 ga thrie beam (ease of inspection)

3. 4” slope curb above is generally present

thank you

I provided responses to your questions below in RED.

1. The tests were conducted using a 36” single slope rail/barrier with the toe clipped to be vertical under the thrie-beam and no vertical taper for the rail height.  Would attaching to a vertical 36” or 42” parapet be an issue? 

Going with a vertical shape as opposed to a single slope should be acceptable. The clipped toe of the SS would resemble a vertical parapet below the rail, so the two shapes would pose the same issues for vehicle snag.  Vertical barriers tend to provide more stable redirections too.

If you wanted to use a 42” tall parapet, I would use a vertical taper to prevent snag above the rail.  We typically recommend vertical tapers of 6L:1H, and I would begin with a 32” height and taper up to 42”, so the vertical taper would be (42-32)*6 = 60”, or 5 ft long.

2. I know on other AGT’s swapping 10 ga. thrie for nested 12 ga. thrie has been acceptable.  Would there be any issues here?

I do not see any issues with using nested 12 ga. thrie beam instead of the as-tested 10-ga. thrie beam. Nested option should be a little stronger.

3. We generally use a 4” sloped curb with our current AGT.  Should we ensure the curb extends up stream of the W-to-Thrie transition piece, stop it before, or just avoid terminating under the W-to-Thrie piece?

I would definitely recommend against terminating it under the w-to-thrie segment (snagging  and wedging concerns).  Since the TL-2 AGT is so short, I would extend the curb beyond the w-to-thrie segment before terminating it.

4. What MASH AGT would we recommend using:

Any MASH tested system would work fine, but if I was to pick, I would go with Nebraska’s AGT.  It uses W6x15 posts at 37.5”.  Thus, it provides a little more space between the parapet/buttress and the first transition post, and it would tend to have fewer issues with ground obstructions preventing proper post installation.  Further, this AGT was tested with a height of 34”, making it crashworthy both before and after roadway overlays. You don’t have to install it at 34”, you can install at the nominal height of 31”, but it does give you options if Georgia overlays their roadways and bridges.   Here is a link to the testing of NDOT’s AGT:    https://mwrsf.unl.edu/researchhub/files/Report359/TRP-03-367-19-R1.pdf

Let me know if you have any further questions.