Wednesday, June 24, 2009

RE: Anchor rods set too low (again!)

With respect, the "Steel Interchange" issue is not the same as an anchor rod.  The question in the "Steel Interchange" was in respect to high strength bolts as opposed to anchor rods.  With the RCSC and A325 or A490 bolts, it is all or nothing.  This is more by edict than engineering.  And it is easy to just replace the bolts in a steel to steel connection.  Replacing an anchor rod is more problematic.  The RCSC defines:
("Sufficient Thread Engagement" Having the end of the bolt extending beyond or at least

flush with the outer face of the nut; a condition that develops the strength of the bolt.) 

But a bolt can be fully developed with less than the defined RCSC "sufficient thread engagement".  Interestingly, the only place you will see the term "sufficient thread engagement" in the RCSC is in the glossary and commentary.  That makes it a problem for strict enforcement in the field. 

Anchor rod thread engagement requires the application of first principles.  For this question, you can rely on research (it exists) or the compilation of this research into a guide NASA 1228 "Fastener Design Manual" by Barrett.  Richard Barrett sent me a copy of this document over 15 years ago.  The NASA 1228 is available on line at:
If all else fails, go to the plug weld.  Your material is weldable, but is probably not necessary if you look at the data in the NASA 1228. 

Regards, Harold Sprague


Subject: RE: Anchor rods set too low (again!)
Date: Tue, 23 Jun 2009 11:51:15 -0700

This exact question was just submitted in the "steel interchange" section of the June 2009 issue of Modern Steel Construction, you can view the magazine for free on their website.  The answer to the question was that it is an all or nothing situation, you do not get reduced capacities for reduced engagement to the nut.


Joe Goldbronn, PE



From: Drew Morris []
Sent: Tuesday, June 23, 2009 10:16 AM
Subject: Anchor rods set too low (again!)


I have a case where the anchor rods have been set too low (again). They are F1554-36 1 1/4" diameter.  To make things worse, the columns have fixed bases and have been installed with the grout below the base plate installed.  I'm not sure why the contractor even bothered to call this in this late. 

Typically, if the rod head is flush with the top of the nut, we use the full strength of the rod. Is there a way to determine what the connection strength is between the nut and the rod if less than the entire rod is engaged?  I can't enlarge the holes in the baseplate for couplers without affecting the anchor rods and I am leery of welding on an extension of the threaded rod.

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