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Re: Bolt question

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Identify it to the designer. The person who wrote the note is unaware of
the real A325 specifications. They are the ones to determine a
replacement.

> One of my concerns is the vibration associated with the crane.  I'm
> guessing the engineer wanted a slip critical bolt for the pretensioning.

Guessing: slip critical would be due to potential load reversal, brittle
fracture and fatigue. Whether slip critical or not, A325 connections
should be pre-tensioned for dynamic conditions. I'm not sure that the
RCSC envisaged anchors to concrete in this category.

> Are all A449 bolts pretensioned?  If not, do you just indicate them on
> drawings with "pretensioned A449 bolt"?  Is the pretensioning of an A449
> similar to A325's and A490's at 70% of min tensile strength?

A325 is a headed bolt, so longer lengths, as might be required for a 2"
diameter anchor, will probably not be readily available, even if you
could get 2" dia A325. The A325 spec, in a footnote referenced from the
title,  specifically redirects to A449 for studs (threaded rod). Unlike
A307 threaded rod, A325 does not suggest that A449 is a direct
substitute.

Pretensioning requirements for A449 would (probably) follow the same
guide lines as A325. Designer's decision.

Pretension in embedded anchors is a crap-shoot. Here today, gone
tomorrow. Let the designer spec tightening methods and maintenance
torquing as they see fit.

On the reality side; this type of anchor is probably mis-specified
regularly, substituted and installed adequately, on a daily basis, all
over the place. The scary part is an unqualified substitution. Any long
term performance issues will probably be seen as maintenance issues.

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

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