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Re: Grade 8 Bolts

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> From: "Fountain Conner" <fconner(--nospam--at)pcola.gulf.net>

> I have an long-time industrial client who recently replaced a bunch of
> *missing* structural bolts with "Grade 8" (I assume SAE, Grade 8) bolts.  I

> repetitive load cycles -- This is a vertical bolt, attaching a crane girder
> to a column cap plate.  Can anyone say, "fatigue"?

Depends on the detail but this sounds like a classic for a fatigue or
unintended overstress location. I suspect that the bolts exist to ensure
positioning (shear) but end up with considerable prying (tension). 

> I'm not comfortable with this replacement.  So far as I can tell, the grade
> 8 machine bolt is hard, tough, and *brittle*.  'Sounds like courting
> disaster to me...
> 
> I recommended replacing the *new* bolts with A325, but the client is
> reluctant to spend money twice for the same work.  

Just returned from the steel conference in Las Vegas. This was one of
the topics in an open forum discussion. SAE bolts should NOT be used in
connections where A325 bolts are appropriate. Differences are not always
apparent in the material description (quality control, marking, threads,
head/nut sizes) so that you can't be absolutely certain of the quality
of bolt in the hole.

Whatever you put into this connection will break/loosen if the original
bolts did that and if the detail or structure has not changed. You might
even consider spec'ing a complete connection modification. If the
customer wants to keep knocking his head against the wall, that's his
perogative.

A long time client ought to know the quality of your advice and what he
should do with it.

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>