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MGS Weak Post Questions

State WI
Description Text We would like to add small anti-drop plates to the MGS weak post bridge rail system to prevent the posts from falling through the sockets during installation.

Is what I am showing acceptable for the welding that anti-drop plates to the s3x5.7
  • Bridge Rails
  • Guardrail
Other Keywords MGS Bridge Rail
Date March 1, 2016
Attachment s3x5 7 and anti-drop plates-1.jpg


I think the welding you have listed is fine. I did not realize that you had plates on the front and back side of the S3x5.7. Welding plates to both sides effectively makes the base of the post a tube. This may potentially stiffen the base of the post and change the location that the post yields at.


Do you have any issues with just welding one plate across the back flange? See Below. This would keep things out of the way and still support the post while limiting the effect on the post behavior. 
Date March 2, 2016
Attachment s3x5 7 and anti-drop plates-2.jpg


More questions for the side mounted assembly.  See attached.

Date March 3, 2016
Attachment side mount assembly.pdf


Answers to your questions.


1.       In terms of minimum headwall thickness for bolting through, there is no minimum thickness. Instead, we would recommend that the headwall have equal or greater capacity to the design we evaluated. We selected a headwall that was on the lower end of headwall strengths.

2.       In terms of clear cover for the end of the rod, the main concern would be blowout of the back side. The effect of end cover on epoxy would be minimal. We would recommend that the embedment depth is met. If you were referring to the clear cover of to the top of the headwall, that would be defined by the geometry of the headwall and the attachment bracket and should not change.

3.       In terms of the post length and embedment, we would recommend that a post without a soil plate as shown have a minimum of 42” of embedment. We have used this embedment in the cable median barrier work and it has proven to develop proper soil resistance without the soil plate. If you use the soil plate version of the post, the post can be 36” long I believe.

4.       In terms of distance from a slope, we recently did testing of S3x5.7 posts with the soil plate adjacent to steep slopes for NDOR. In that work, it was found that offsets as low as 1’ were acceptable, but a 6” offset resulted in blowout of the post through the slope. Thus, we would recommend a minimum offset of 1’. We also believe that the 1’ offset would be acceptable with the 42” embedded post without the soil plate.

5.       For the post installed 4” from the wingwall, the wingwall will provide additional resistance and help develop the forces to yield the post. As the posts in the weak post MGS system are intended to yield at groundline with minimal rotation in the soil, this should not be an issue.



Date March 4, 2016

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