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RE: Levelling plates or shims ?

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I believe that the "magic" number for hydrogen embrittlement is a tensile
strength around 200 ksi. This is why A490 bolts (max tensile of 170 ksi) are
not allowed to be galvanized. I would think that since most anchor rod
material is 120 ksi and below, hydrogen embrittlement would not be a
problem, at least for static loads. Is this a fatigue issue?

Heath Mitchell

> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)]
> Sent: Wednesday, February 27, 2002 12:00 PM
> To: 'seaint(--nospam--at)'
> Subject: RE: Levelling plates or shims ?
> David,
> These structures are different.  You have access to the bottom nut, they
> are
> light weight, and they are generally isolated and not dependent on other
> columns (for relative elevation).  There is nothing wrong with leveling
> nuts
> in those applications.
> I would caution however that in the high winds (that you get down in your
> neck of the woods) to take into account the fatigue on the reduced section
> of the anchor rod.  You can't preload to avoid stress cycles.
> The Australians did a study for glazing a while back that said for one
> given
> storm, they could get 10,000 cycles on elements.  This is the study that
> fed
> into the impact resistant glazing performance requirements.
> I would also urge caution on galvanizing high strength bolts.  You can
> create a problem for hydrogen embrittlement.  This is not a pleasant mode
> of
> failure.  There is no warning.
> Do you hot dip galvanize the bolts in Florida?
> Regards,
> Harold O. Sprague

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