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RE: Bolt question

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Title: Bolt question

David,

This issue comes up from time to time.  You are correct A325 bolts are limited to 1 ½" diameter.  If a 2" bolt is required, you would have to go to an A449 bolt.  You also touched on the next dilemma.  There are no RCSC rules for installation for A449 bolts.  You have to create your own.  Basically you have to ask the question if you need a bolt to be tensioned or not.  Generally if you have any cyclic load in a bolt, you should tension the bolt.  Low frequency fatigue is a big problem for HS bolts because of the notch effect created at the root of the threads.  Tensioning the bolt eliminates this problem. 

 

Simply requiring installation compliant to A325 does not quite cut it.  Ultimately you are trying to apply a tension into the bolts.  I would take elements of the A325 RCSC installation requirements (like bringing the faying surfaces into contact prior to tensioning the bolts), and then I would require the use of a hydraulic tensioner.  You can not use DTI's, turn of the nut, I never use calibrated wrench, and as we all know torque wrench is not approved for installation.  Torque is only an arbitration technique. 

 

The use of a hydraulic tensioner to apply a bolt tension force of 70% of the minimum tensile strength is not a problem for a hydraulic tensioner.  I do not know of any other method that would work.  Again, I would require inspection and verification with a Skidmore similar to what is required by the RCSC.

Regards,
Harold O. Sprague

-----Original Message-----
From: Chan, David [mailto:DCHAN(--nospam--at)ladpw.org]
Sent:
Monday, October 27, 2003 6:32 PM
To:
seaint(--nospam--at)seaint.org
Subject: Bolt question

 

Here's a question for you bolt experts out there.  I'm reviewing drawings for a crane supported on a steel structure.  Drawings show 2" diameter A325SC anchor bolts.  Looking in the steel manual, A325's only come in a size up to 1-1/2 inches.  Would it be appropriate to use a 2" diameter A449 bolt for this application? 

One of my concerns is the vibration associated with the crane.  I'm guessing the engineer wanted a slip critical bolt for the pretensioning.  Are all A449 bolts pretensioned?  If not, do you just indicate them on drawings with "pretensioned A449 bolt"?  Is the pretensioning of an A449 similar to A325's and A490's at 70% of min tensile strength?

David
Los Angeles, CA