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RE: Grade 8 Bolts

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Fountain,

The biggest difference in Grade 8 bolts and A325 or A490 is the requirement
for installation and tensioning the bolts.  Grade 8 bolts have no
requirements for tensioning.  You would have to write your own, or simply
require installation per A490.

If properly designed, a tensioned bolt should never experience a load higher
than the tensioning force.  As such, there would be no fatigue.  If the bolt
is not tensioned, high strength bolts especially A490 and Grade 8 can
withstand very few cycles to the proof load level.  This was demonstrated
following the collapse of the Kemper Arena roof in the late 1970's.  (4 A490
bolts in direct tension)

If you go through an inspection to verify tension, use a Skidmore and a good
torque wrench.  Keep in mind that torque is only applicable for arbitration
and is only an indicator of tension.  I like the load indicating washers.

Grade 6 and 8 Bolts are the bolts that had a problem with foreign
counterfeiting a few years ago.  But if you tension the bolts, they will
break upon installation.  And if successfully installed and tensioned, they
will never experience a higher load unless they were designed incorrectly.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Fountain Conner [SMTP:fconner(--nospam--at)pcola.gulf.net]
> Sent:	Friday, February 25, 2000 10:00 AM
> To:	seaint(--nospam--at)seaint.org
> Cc:	StructTX
> Subject:	Grade 8 Bolts
> 
> 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
> can only guess what happened to the original bolts.  I'm sure they weren't
> stolen, so that leaves the options of working loose or breaking under
> repetitive load cycles -- This is a vertical bolt, attaching a crane
> girder
> to a column cap plate.  Can anyone say, "fatigue"?
> 
> 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.  
> 
> Guidance and counsel, anyone?  
> 
> Fountain E. Conner, P.E.
> Gulf Breeze, Fl. 32561
>