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Guardrail Post Bolt Hole Size

State WI
Description Text

My question is about placing a slotted hole in the post flange that is
larger than what was used in the crash test. This is shown on the
attachment. Thanks.

  • Guardrail
Other Keywords none
Date September 17, 2014
Attachment Slotted Holes.pdf

Response In general, it is not a good idea to change a critical element of the design from its crash tested variation. An increased hole size in the critical front flange would reduce the capacity of the steel post to resist bending. Horizontal slots would exaggerate this reduction of post capacity, especially for those located closest to the base plate when moments are maximized. Of course, the overall effect that the slot versus hole has on a barrier system safety performance would depend on how conservative was the design initially. At this point, we have not been provided much information in terms of design/test level, construction details, and actual crash testing results. Further details and information would be needed to further explore this issue.

Alternatively, it may be possible to integrate slots into the rail at splice and/or post locations to improve constructability without decreasing capacity. 

Date September 19, 2014

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