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RE: Shear-off bolted connection

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Bill

It dosen't make any difference wheather the bolt is stressed to 100% or
200% of yield, as long as the bolt dosen't fail during erection, it will
perform adequately.  This is true irrespective of the way in which a bolt
is tensioned.  The reason for this is that it is the frictional resistance
provided by the clamping force that transfers the shear in the connection. 
The force is the bolt can't exceed the initial clamping force unless you
subsequently pull on the bolt in excess of the original clamping force, and
if the subsequent tensile force exceeds the capacity of the bolt it will
fail irrespective of the method of tensioning.

I find it interesting that you have had problems with bolts breaking, while
I have not had this problem.   The fact that the problem is not universal
suggests that the problem cannot be laid totally at the steps of the DTI's.
 Were any tests undertaken to verify the mill cert's?  Was the manufacturer
of the DTI's asked to comment on the problem?  

Given the polarized nature of the discussion regarding twist-off vs DTI's I
would be reluctant to jump to a conclusion until both sides have had a
chance to explain the problem.  They are both guilty of providing selective
information.


Mark Gilligan