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Clipped Guardrail Bolts for MGS

Description Text

We were
recently reviewing the MwRSF Pool Fund Questions and Answers section of your
website and came across Question #1131
from the state of Ohio regarding
“rail release” of the MGS.   While our team was reviewing
state specifications, we also came across some examples of where state
specification drawings, utilizing MGS, are using “clipped” post
bolts.    Please keep in mind that we have only provided a
sample of two states specification drawings, there is likely others … based on
the information provided below

See the attached SCDOT and
MDOT standard sheets indicating only clipped bolts are specified to be
used in those states.   

Also attached is a AASHTO
M180-4 drawing from 2015 showing both clipped bolts and the standard
bolts as alternatives.

Additionally attached is
the current TF13 FBB01-05 drawing, showing only the clipped bolt option.

·    From MwRSF TestTRP-03-276-13, the following three (3) images are provided, as a quick sample –
which may not be representative of all MwRSF testing.    Shows
that standard round head guardrail post bolts were utilized and the MTR
following those three (3) photographs indicates the post bolts were provided by
THP and our nomenclature for clipped bolts is not printed on the MTR.

      Are clipped post bolts recommended (or allowed) for use in the MGS? 

  • Guardrail
Other Keywords none
Date March 22, 2017
Attachment Round_head_1.jpg
Attachment Round_head_2.jpg
Attachment Round_head_3.jpg
Attachment 20170322 SC & MI Clipped Post Bolt HD.PDF
Attachment M180-12 5.pdf
Attachment fbb01-05.pdf
Attachment rd400s_all 4.pdf


With respect to the clipped bolts, we don’t believe that these should pose an issue. We have not typically tested the MGS with clipped bolts in the past. However, the shape of the ovalized shoulder on the bolt forces the bolt to be installed such that the rounded sides of the bolt head overlap the top and bottom edges of the guardrail slot similar to a circular dome head bolt. Thus, release from the middle region of the guardrail slot should be similar for the clipped head bolt. A clipped head bolt may have slightly less overlap on the edge of the guardrail slot as compared to a circular dome head bolt if the bolt is positioned at either end of the slot. However, this release load would still be equal or greater to either bolt head near the middle of the guardrail slot. As such, I don’t anticipate an issue using the clipped head version of the bolts with the MGS, and believe that either the standard round head or the clipped head would function acceptably.

It should be noted that the shoulder should be oriented perpendicular to the clipped sides of the bolt. Orientation of the shoulder parallel to the clipped sides would prevent effective attachment of the guardrail to the post.

Date March 23, 2017

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Email: mwrsf@unl.edu
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