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RE: Anchor Bolts Again

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• To: seaint(--nospam--at)seaint.org
• Subject: RE: Anchor Bolts Again
• From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
• Date: Wed, 27 Sep 2000 17:36:04 -0500
Recheck the formula for masonry.  I don't have the 1997 UBC here right now,
but the 1994 UBC has the following:
Btn=0.4Ap(Fy)

Ap is predicated on the embedment length and is the pullout cone
area.

Frankly, I don't understand the UBC masonry anchor bolt provisions, nor do I
agree with them.

The ACI 530 anchor bolt provisions reside in the Allowable Stress Section
and are:
The lesser of:
Ba=0.5*(Ap)*sqrt(f'm)
Ba=0.2*(Ab)*(fy)

The anchor bolt design methodology is in the process of changing for
masonry.

The big difference between anchor bolt design for masonry and concrete is
that masonry anchor bolts are not embedded in a homogeneous material, and
require a higher factor of safety.  I know that we assume that masonry is
homogeneous and that there is one f'm, but the reality is that you could
have a face shell of 800 psi, a grout strength of 3000 psi, and a prism
strength of 1200 psi.  Part of the issue is how components are tested and
how prisms are tested.  But the reality is that you could have an anchor
bolt embedded a total of 2 inches with a face shell of 1 3/4" leaving only
1/4" in the higher strength grout.  The formulas would have you predicate
the calculations on the overall f'm, when the face shell strength would
limit the strength.

This area is a work in progress.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Mark Pemberton [SMTP:Markp(--nospam--at)lbdg.com]
> Sent:	Wednesday, September 27, 2000 1:19 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	Anchor Bolts Again
>
> Does anybody know why the tensile strength of an anchor
> bolt in concrete is so much higher than in masonry?
> (Assuming the stress in the bolt governs)
>
> Concrete: Pss = 0.9Ab(fut)
> Masonry: Btn = 0.4Ab(Fy)
>
> For an A36 rod I get: Pss = 0.9Ab(58) = 52.2Ab
>                                Btn = 0.4Ab(36) = 14.4Ab
>
> Am I missing something?
>
> Mark Pemberton, P.E..
>

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