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Re: ACI & PCA Embedded Anchor Design

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• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: ACI & PCA Embedded Anchor Design
• From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
• Date: Fri, 8 Nov 2002 19:03:06 -0500 (EST)

```Richard,

First, I think you mean eq D-20 not D-5.  D-20 is the shear equation while
D-5 is for tension loading.

You are correct that on face value it does not appear to make sense.  But
then you neglected at term when you spelled out the equation for Vcb.

Vcb=(Av/Avo)*psi6*psi7*Vb
or as you put it Vcb=(Av/Avo)* some PSI factors*Vb

You seem to have left out the Vb.  And Vb is proportional to c1^1.5
according to eq D-23.  Thus, as c1 increases, the Vb will increase at a
higher than linear rate.

Thus, you are correct that the (Av/Avo) ratio will decrease.  Avo is
4.5*c1^2.  Av in your case will be 1.5c1*beta*c1 (I am calling beta*c1=c2
where c2<c1).  Thus, the (Av/Avo) ratio will become 1.5*beta/4.5 or
beta/3.  Beta will decrease linearly as c1 moves further from the edge.
Thus, the (Av/Avo) ratio will decrease linearly as c1 increases linearly.

Thus, Vcb will still increase since the Vb value should increase faster
than the (Av/Avo) ratio decreases.

Take an example.  Lets assume that c2=.5*c1(initial).  Thus, (Av/Avo)
would be 1.5*.5/4.5=.167.  Now, double the c1.  So,
c2=.5*c1(initial)=.25*c1(final).  Thus, (Av/Avo) would now be
1.5*.25/4.5=0.83.  Thus, (Av/Avo)initial/(Av/Avo)final=2, which means that
the (Av/Avo) ratio decreased by a factor of 2.  Vb would increase by a
factor of 2^1.5 or 2.828.  Thus, Vcb would increase by about 41%.

Make sense?  Or did I mess something up?

HTH,

Scott
Ypsilanti, MI

On Fri, 8 Nov 2002, richard lewis wrote:

> I have a question regarding the design of anchors using PCA or ACI 318-02
> recommendations.  I believe these are essentially the same.
>
> The situation deals with anchors near the end of a wall with shear
> parallel to the wall line.  Essentially the shear wants to push off the
> edge corner under the anchor.
>
> Eq. D-5 (ACI) & A-16b (PCA) is Vcb = (Av/Avo) * some PSI factors.  Av is
> the projected area of the concrete anchor group.  Avo is the projected
> area of a single anchor neglecting any edge distance.  It becomes the
> value of Avo=4.5*c1^2.  The problem I am having is that as the c1
> distance increases, meaning the anchor group is pushed further into the
> wall, away from the end, Avo increase dramatically and Av increases
> slightly.  So since Avo is in the denominator the allowable shear value
> decreases as the edge distances increases.  This does not make sense to
> me.  Am I looking at this situation correctly?
>
> Thanks for your help.
>
> Rich
>
>
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