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RE: A325 anchor bolts

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Chris,

I have had a similar experience.  Please consider the following:

1.	You probably do not have an A325 bolt.  (I would bet the farm)  Find out what was provided.  If it was a hot headed A449 or 1170 steel you will never be able to develop the bolt.  You will initiate a failure at the head.  The max length of a stock A325 bolts is about 8 inches.  Any high strength anchor bolt should be tested unless you use a treaded end with a nut to form the anchorage, and you specify A193-B7 material for your A449 bolt.  Require all material certifications to be submitted.  This is a much bigger problem than most people are aware of.

2.	Do you have oversized holes in the base plate?  If so, do you have a plate washer?  How or is the anchor bolt tensioned?  Plate washers, greased shaft, and bolt tensioning are all necessary for a properly performing moment base plate connection.  Preloading the anchor bolt will also test the bolt, because you should preload the bolt with a higher load than the service load.  (another topic)

3.	Although required by AISC, you do not need to fully engage all of the threads to fully develop the anchor bolt.  The pullout load (provide your own safety factor) formula is.
P = 1/3 * (Pi * dm * Fs * L) 
where:
   P = the pull out load
   dm = mean diameter of threaded hole
   Fs = material ultimate or yield shear stress
   L = length of thread engagement

   the 1/3 factor is empirical and allows for some mismatch of threads.

   RE: Richard T. Barrett, "The Fastener Design Manual", NASA Reference Publication 1228, Lewis Research Center, Cleveland, Ohio, March 1990.
             or
   J.N. Goodier, "The Distribution of Load on the Threads of Screws", Journal of Applied Mechanics, March, 1940.  (I know... It was before I was born too.  But it is what the IFI used as a reference.)

Please note that the L is thread engagement.  There is generally a tapered end on the bolt that will not have an engaged thread.

Harold Sprague, PE
Krawinkler, Luth & Assoc.

-----Original Message-----
From:	Chris Palmateer [SMTP:chrisp(--nospam--at)vlmk.com]
Sent:	Friday, September 04, 1998 7:17 AM
To:	seaint(--nospam--at)seaint.org
Subject:	A325 anchor bolts

I have a job in which the contractor installed the anchor bolts for moment 
frame to low.  The bolts are 1-1/4 in. A325 with heavy head nuts.  How many 
threads does it take to fully develop the bolt?  If the bolts lack 1/4 to 
3/8 of an inch from extending through the nut completely, how does one 
calculate the reduction in the capacity of the bolt?

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