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# RE: Tension equations for anchors in CMU

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Tension equations for anchors in CMU
• From: "Joe Grill" <jgrill(--nospam--at)swiaz.com>
• Date: Fri, 5 Nov 2004 12:23:42 -0700

```Scott,
Until recently, I've never had to calculate tension values in the top of a
CMU wall.  So what you are saying is that if you have an anchor bolt (with
tension) at 3" from the edge of the wall then Ap=28.3 sq. inches and a
pullout strength of only 550# even if the anchor has an embedment of say
10".  The strength design approach makes way more sense in that the
truncated edge would be there but Ap would be much larger around 150 square
inches for a 10 in. embedment in a 8" wall.
Joe

Joseph R. Grill, P.E. (Structural)
Shephard - Wesnitzer, Inc.
Civil Engineering and Surveying
1146 W. Hwy 89A Suite B
Sedona, AZ  86340
PHONE (928) 282-1061
FAX (928) 282-2058
jgrill(--nospam--at)swiaz.com

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Friday, November 05, 2004 12:03 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Tension equations for anchors in CMU

Joe:

I doubt it is a typo...if so, then it is a typo that has existed since the
1995 edition of the MSJC (ACI 530/ASCE 5/TMS 402).  So, I have to believe
that if it was in fact a typo, that SOMEONE would have caught it in the
past 9+ years.

I believe eq 2-4 is the allowable stress method for a necessary "cone
breakout strength" reduction when the anchor bolts are too close to the
edge of a wall relative to the embedment depth.  In such a case, the
"breakout cone" will be truncated.

It likely does not "match" well with the similar provisions in the
strength chapter as they have not really been "coordinated" as of yet (to
my knowledge at least).  So, the strength chapter handles that reduction a
little different.

I will ask someone that I know on the committee for their thought.

Regards,

Scott

On Fri, 5 Nov 2004, Joe Grill wrote:

> A couple of days of slack time have prompted a flurry of posts to the list
> by yours truly.  Today, I'm trying to put together a small spread sheet
for
> allowable tension for an anchor in the top of a CMU wall.  Not a big deal
> for hand calcs, and I've done this a number of times, but I'm trying to
> minimize embedment requirements for holdown anchors possible being a
little
> more "custom" from job to job as embedment depths I've called out before
> tended to be pretty conservative for more lightly loaded holdowns.  Most
> stem wall construction around here is CMU.
>
>
>
> I hadn't noticed this before, but equation 2-4 in ACI 530/02 uses l sub be
> for one determination of A sub p.  The definition for l sub be seems
> incorrect for the tension application and should be used for shear
> applications toward a free edge.  The strength design section uses l sub b
> for calculating A sub pt.  The definition for A sub pt and the explanation
> for overlapping cones and deduction of areas of A sub pt which fall
outside
> the masonry surface, seems to make more sense, and I think should be used
in
> the service load equations also.  Is there a typo error?  Has there been
any
> errata's?  The way equation 2-4 is written seems extremely conservative to
> me.
>
>
>
> So, wazup?
>
>
>
> Thanks,
>
> Joe
>
>
>
>
>
>
>
> Joseph R. Grill, P.E. (Structural)
>
> Shephard - Wesnitzer, Inc.
>
> Civil Engineering and Surveying
>
> 1146 W. Hwy 89A Suite B
>
> Sedona, AZ  86340
>
> PHONE (928) 282-1061
>
> FAX (928) 282-2058
>
> jgrill(--nospam--at)swiaz.com
>
>
>
>  <http://inet/index.htm>
>
>
>
>

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