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RE: Shear-off bolted connection

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I'd like to add my $.02 worth.

On Tue, 19 Jan 1999, WILLIAM R. KEEN (and practically everyone else) wrote:

> For our military construction projects in years past, we always asked for 
> mock-ups of the LIW bolt assemblies to be tested in the field (The military 
> used to require LIWs). The results were always highly variable to the point 
> of being unreliable. Then we had problems bolts breaking during installation. 
> Mill cert's were required for all of these bolts.....

I've tested DTI's (should not be called LIWs) for the Idaho Transportation
Department when they've had problems with bolt installations, and have
found that the DTI's made by Applied Bolting, Beth-Fast, and J&M Turner
are pretty reliable and consistent.  However, DTI's made to the current
ASTM specifications seem to be more consistent than those made prior to
1993-1994.  Some of the older DTI's were not as consistent as they could
have been.

> It's that experience and feedback from erectors and fabricators that have 
> moved us to specify twist-offs vs. LIWs. No system is perfect, or ever will 
> be. In my opinion (par value .02), twist-offs are the way to go.

Erectors and fabricators prefer Twist-offs since the bolt can be installed
by one worker, and there is almost no inspection required. 

However, Twist-off's do not actually indicate bolt tension.  If there
are a large number of plys, or very thick plys,  then a mock-up should be
made to insure that the Twist-off's fully tension the bolts.

> In response to Mark, I agree that you are probably OK tensioning the bolt to 
> 110% of proof in most cases, but what happens if the LIW is not compressed at 
> 110% and you end up at 140% of proof? That's almost ultimate for an A325.

If the bolt breaks before the the DTI's are compressed, then you probably
had a bad bolt.  If the bolt hasn't broken, and you haven't exceeded
ultimate, then you are probably fine.


Ed.S.
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Edwin R. Schmeckpeper, P.E., Ph.D.
Department of Civil Engineering                   Phone  : (208) 885-6702 
University of Idaho                               FAX    : (208) 885-6608
Moscow, Idaho 83844-1022                          E-Mail : eds(--nospam--at)uidaho.edu
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