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Re: Bolting issues, generation II

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Hi Charlie and everyone else,

On Sun, 24 Jan 1999, Charlie Carter wrote:

> Are there a lot of ironworkers spending extra time turning nuts on A325
> bolts five, six and seven full rotations? If they did the
> pre-installation verification testing that is required in the RCSC
> Specification, they would find that, depending upon bolt length and
> diameter, 1/3 to 2/3 turn from snug is commonly sufficient to induce the
> pretension. If they are out there cranking nuts around and around and
> around, however, one of two things will happen: either the bolt will
> break or it won't (duh!). If it does break, we're OK because we know the
> bolt was turned too far...more importantly, they know it was turned too
> far AND have to replace it. If it doesn't break, we never made it over
> the hump in the plastic portion of the bolt load-deformation curve. 

Be careful about overtightening.

We ran into a lot of bolts on a recent bridge job where the threads
stripped off the bolt prior to the bolt breaking.  The bolts were
installed with the DTI's completely flattened, so some of the nuts were
removed to inspect the bolts.  The bolt threads appeared to be overcut
(cut too deep).  When the nuts were tightened one or more turns past the
point where a DTI would indicate "minimum tension achieved" the threads
stripped.

7/8" A325 Galvanized bolts, various lengths from 3" to 5".

Again, going back to what Charlie Carter said:  The correct procedures
must be followed, or any method will produce unsatisfactory results.

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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