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Guardrail Bolt Length

State WI
Description Text

I received this question from our maintenance staff.  It has to deal with bolt length on the back side of beam guard installation.  If MwRSF could provide input it would be appreciated.


Issue: The specs call for no more than ½ inch of anchor bolt to protrude beyond the fastening nut.  When this spec has been exceeded the guidance is to cut them off, chamfer and restore with zinc coating.


Question: Wondering what the issue is with bolt length and consequences thereof such as performance of the guard rail system if they are not cut?  The system in question is on a CTH system utilizing state funding in an effort to bring guard rail up to standards for a detour route.  Metal posts and plastic blockouts were used.


  • Guardrail
Other Keywords none
Date May 29, 2009


I have reviewed the information provided below and am uncertain as to the direction of the question. Are you referring to the guardrail splice bolts or the guardrail post bolt? For connecting rail ends at a guardrail splice, standard guardrail bolts are used and are specified in AASHTO-AGC-ARTBA hardware guide. There should be no reason to cut or modify these bolts if ordered using the standard hardware. For placing rail and blockouts to posts, standard post bolts are also used to make this connection. These bolts have a specified thread length and should not require cutting or modification when the appropriate length is ordered. For rail to post attachment, the length of the threads extending out of the nut would not need to be limited to 0.5 in. or less for performance reasons. In rare circumstances, a unreasonable long rod could potentially contact the hazard face sooner than if the proper length bolt were used. However, I do not see this as being a big concern. If too long of a bolt were used, it would be difficult to use since the thread length is limited, thus not allowing the nut to be tightened. Are contractors trying to use non-standard bolts which require field modification in order to install the nut? If yes, I recommend that proper bolt length be used with standard guardrail bolts to avoid these field issues.

Date June 15, 2009

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