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Re: Grade 8 Bolts

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This definitely sounds like a fatigue problem and if it is, it will likely
occur again.  Grade 8 bolts are roughly the equivalent of A490 bolts, however,
they are not typically used for structural applications.  If it is a fatigue
problem, I would assume that the bolts are located within the column flanges.
Due to the beam rotation this would cause large stress fluctuations in the bolt
since the beam will rotate about the column flanges. Short of some type of
modification to move the bolts outside the column flanges, your best option
would be to recommend frequent inspections and replacement of the bolts.

Neil J. Glaser, P.E.

Fountain Conner wrote:

> 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