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RE: High Strength Bolts Requiring Full Pretensioning

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Rick, 

The commentary is correct, but that same observation can be made regarding any HS bolt installation.  The critical element is that you must have special inspection and you must have a bolt tension indicating device (Skidmore) on site for verification of any method, even DTI washers.

It is critical with any method to bring the faying surfaces into contact prior to tensioning the bolts.

The inspector has to watch the process.  The process and materials must be verified prior to final tensioning using the Skidmore.

Bob Shaw teaches the steel special inspection course, and does a very good job of covering how this is accomplished.  

There were some studies a while back complete with bell curve distributions on actual bolt tensions and where the mean lined up relative to required pretension.  I believe these studies were done by Bethlehem.

One negative with some twist offs (some twist offs have a rounded head) is that there will be some bolts that will require turn of the nut for clearance reasons.  The head can not be restrained from turning.  In that case you must match mark the bolt, nut, and the part.  The point is specify hex head twist offs.

Harold Sprague, PE
Krawinkler, Luth & Assoc.


-----Original Message-----
From:	Rick.Drake(--nospam--at)fluordaniel.com [SMTP:Rick.Drake(--nospam--at)fluordaniel.com]
Sent:	Friday, July 24, 1998 4:48 AM
To:	seaint(--nospam--at)seaint.org
Subject:	High Strength Bolts Requiring Full Pretensioning

     Does anybody have any experiences to share regarding the use of "twist 
     off" bolts for situations where full pretensioning is required?  AISC 
     refers to them as "Alternate Design Bolts" in their High Strength Bolt 
     specifications.  I am particularly interested in their use in 
     slip-critical connections in high seismic zones.
     
     The AISC HSB Specification Commentary indicates "The sheared off 
     splined end merely signifies that at some time the bolt has been 
     subjected to a torque adequate to cause the shearing.  If the 
     fasteners are installed and tensioned in a single continuous 
     operation, they will give a misleading indication to the Inspector 
     that the bolts are properly tightened.  Therefore, the only way to 
     inspect these fasteners with assurance is to observe the job site 
     testing of the fasteners and installation procedure and then monitor 
     the work while in progress to ensure that the specified procedure is 
     routinely followed."  This is consistent with the UBC Special 
     Inspection requirements for high-strength bolting.
     
     Thanx,
     
     Rick Drake, SE
     Fluor Daniel, Irvine

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