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Re: More confusion with concrete

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I am not sure what you are trying to get across, but:

1) The provision for thin members in the 2000 IBC (section 1913.6.2.4)
that I believe you are referring to _IS_ in Appendix D of the 2002 ACI 318
(section D.6.2.4).

2) I an not sure what you mean by saying "let Av exceed nAv0", but both
the 2000 IBC and Appendix D of ACI 318 (sections 1913.6.2.1 and D.6.2.1
respectively) expressly state "Av shall not exceed nAv0, where n is the
number of anchors in the group".

Regards,

Scott
Adrian, MI


On Wed, 8 Jun 2005, Shapton & Partners wrote:

> Okay.  Set c1 to h/1.5 and let Av exceed nAvo. I do not have my copy of
> the 2000 IBC handy, but believe they had a reference to thin members
> which is not part of Appendix D.  This is what I think caused the
> problem.  I spoke with Basile Rabbat ( PCA) who directed me to Hilti
> who, in turn, recommended the Concrete International article.
> Everybody's guessing was somewhat entertaining.  Sorry you let this
> degenerate into a political discussion.
> Elias Hahn wrote:
>
> >I'm trying to use 1 1/2" anchors spaced at 6" (not my idea, I've requested
> >the spacing be doubled to 12").  They have an hef of 12" (8d) and I'm trying
> >to get away with a 18" footing, but I think I'll bump that up.  I am
> >currently using a 10d edge distance (15".)  This is for the foundation of a
> >prefab metal structure (thus the spacing that I don't like.)  Ummm,
> >f'c=4000... I think that's about it.  But I've sort of given up on 6"
> >spacing, and I've requested that the building manufacture increase the size
> >of the baseplate they are using, so we'll see if that flies.
> >
> >-----Original Message-----
> >From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> >Sent: Wednesday, June 08, 2005 3:46 PM
> >To: seaint(--nospam--at)seaint.org
> >Subject: RE: More confusion with concrete
> >
> >Elias,
> >
> >What is your particular case (give the specific example with numbers) that
> >you are trying to look at?  I believe you gave it before, but I deleted
> >that message.
> >
> >Regards,
> >
> >Scott
> >Adrian, MI
> >
> >
> >On Wed, 8 Jun 2005, Elias Hahn wrote:
> >
> >
> >
> >>Ahhh see, so there it is.  I didn't catch/understand/pay attention to the
> >>doubling factor.  It still seems a little silly, and for my case with a
> >>relatively big couple of anchors trying to get away with a relatively thin
> >>footing, I'm still losing capacity by increasing my edge distance, which
> >>
> >>
> >is
> >
> >
> >>not how it should work.  Or can I double it because the force is in fact
> >>parallel to an edge?  (c1=c2, so either way it is both parallel and
> >>perpendicular to an edge.)
> >>
> >>-----Original Message-----
> >>From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> >>Sent: Wednesday, June 08, 2005 3:27 PM
> >>To: seaint(--nospam--at)seaint.org
> >>Subject: RE: More confusion with concrete
> >>
> >>Elias,
> >>
> >>Yes...you are correct in what you wrote below...but your are forgeting
> >>that there is another c1 in the overall equation for the shear breakout
> >>strength.  Remember the overall breakout strength is Av/Av0*(a bunch of
> >>factors depending on either single anchor or group of anchors)*Vb.  The
> >>key is that Vb is a function of c1^1.5.
> >>
> >>So, your case of the long beam in the "big" c1 direction...Av will be
> >>(c2+c2)*h (unless you want to consider a REALLY deep beam such that
> >>h>1.5c1). and Av0 will be 4.5*c1^2.  Thus, Av/Av0 will nominally be 1/c1^2
> >>if you consider c2 and h to be negligble compared to c1.  But then Vb is
> >>some value*c1^1.5.  So, in fact, you end up with Vcb being proportional to
> >>1/c1^.5.  Now, keep in mind that you have some "constant"/value there as
> >>well, so it is not just 1/c1^.5 but rather a/c1^.5.  And then beyond that
> >>section (c) of D.6.2.1 states: "for shear force parallel to an edge, Vcb
> >>or Vcbg shall be permitted to be twice the value for shear force
> >>determined from Eq. (D-20) or (D-21), repectively, with psi6 taken equal
> >>to 1"...and your "big" c1 direction is such a case.  Thus, the end result
> >>is that I am willing to bet in most cases the Vcb of the "big" c1
> >>direction will still be bigger than the Vcb of the "small" c1 direction.
> >>
> >>Let's do an example with some numbers.  Say it is a 24"x42" concrete beam
> >>that spans 24 ft.  Put a 1" dia. anchor in the middle of the beam with an
> >>embedment of say 24".  OK.
> >>
> >>For the "big" c1 case: c1 is 144".  c2 is 12".  h is 42".  d0 is 1".
> >>l is 8*d0 or 8".  Let's make f'c equal to 3000 psi.  psi7 will be the same
> >>for either case.  psi6 will be 1.  So, Av will be (c2+c2)*h or 1008 sq in.
> >>Av0 will be 4.5c1^2 or 93312 sq in.  So, Av/Av0 is .0108.  Vb is
> >>7*(l/d0)^0.2*d0^0.5*f'c^0.5*c1^1.5 or 1004200.4 lbs.  So, Vcb will be
> >>10845.4 lbs (assuming psi7 is 1.0), but section (C) let's us double that
> >>to 21690.7 lbs.
> >>
> >>For the "small" c1 case: c1 is 12".  c2 is 144".  h is 42".  d0 is 1".  l
> >>is 8".  Using f'c of 3000 psi again.  psi6 will be 0.7.  So, Av will be
> >>1.5*c1*(1.5*c1+1.5*c1) or 4.5c1^2.  Av0 will be 4.5*c1^2.  So, Av/Av0 will
> >>be 1.  Vb will be 24157.3 lbs.  Vcb will end up being 16910.1 lbs (again
> >>assuming that psi7 is 1.0).
> >>
> >>Thus, here you have a situation that you describe in basics terms but this
> >>time with some specific numbers.  You can see that the "big" c1 direction
> >>does produce a higher breakout condition than the "small" c1 direction.
> >>
> >>Now, one could argue that this may still not fit the intuitive sense,
> >>which for me would want to say that the "big" c1 direction should be
> >>SIGNIFICANTLY larger than the "small" c1 direction is such a case and
> >>while it is bigger, I would say not "big enough" to match the intuitive
> >>feel...and I would agree with this arguement.  But, from a structural
> >>point of view in checking the anchor, while it might not be completely
> >>accurate, it does produce the expected result of the "small" c1 direction
> >>being the "weak link".
> >>
> >>HTH,
> >>
> >>Scott
> >>Adrian, MI
> >>
> >>
> >>On Wed, 8 Jun 2005, Elias Hahn wrote:
> >>
> >>
> >>
> >>>Agreed, the problem I have with formulas is that if you increase c1
> >>>
> >>>
> >until
> >
> >
> >>it
> >>
> >>
> >>>is "big" (ie, 1.5c1 is greater than c2 and/or h), Av/Avo gets small. (or
> >>>conversely, have a thin slab, or a corner condition where c1 is roughly
> >>>equal to c2.)
> >>>
> >>>Ok, now my long hypothetical - feel free to not read:
> >>>The problem in my mind is if you take a long beam, and put an anchor in
> >>>
> >>>
> >>it,
> >>
> >>
> >>>and look at the calculated strength of that anchor (side-face blow out)
> >>>
> >>>
> >in
> >
> >
> >>>both directions.  Now, in one direction, c1 is "big", much bigger than
> >>>either c2 or h, while in the other direction c1 is "small."  Now on the
> >>>
> >>>
> >>case
> >>
> >>
> >>>were c1 is "big" Avo is great, but Av is small, (assume c2 and h are
> >>>negligible in that direction, Av/Avo tends to 1/(3*c1), which makes the
> >>>overall equation roughly (a number less than one)*(Square root(c1)).
> >>>
> >>>
> >Now
> >
> >
> >>if
> >>
> >>
> >>>you look at the other direction, were Av/Avo tends to one, you now end
> >>>
> >>>
> >up
> >
> >
> >>>with an overall equation of (a number greater than one)*(c2)^1.5)).  It
> >>>
> >>>
> >is
> >
> >
> >>>easy to see that the direction without much edge distance could have a
> >>>larger concrete side-face blow out strength...
> >>>
> >>>
> >>>-----Original Message-----
> >>>From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> >>>Sent: Wednesday, June 08, 2005 10:21 AM
> >>>To: seaint(--nospam--at)seaint.org
> >>>Subject: Re: More confusion with concrete
> >>>
> >>>Elias,
> >>>
> >>>First, I would say that you need to be a little clearer about what kind
> >>>
> >>>
> >of
> >
> >
> >>>condition you are looking at.  The edge distance, the effective
> >>>
> >>>
> >thickness
> >
> >
> >>>of the concrete (h), and the number of anchors can affect the "view" of
> >>>things.
> >>>
> >>>Take a simple basic condition...a single anchor in a concrete element
> >>>
> >>>
> >that
> >
> >
> >>>is MUCH thicker than the depth of the anchor and is only at a side, not
> >>>
> >>>
> >a
> >
> >
> >>>corner.  Kind of like what is shown in Fig. RD.6.2.1(a) and RD.6.2.1(c)
> >>>
> >>>
> >in
> >
> >
> >>>the 2002 ACI 318.  In such a case, c2 and h don't enter the picture.
> >>>
> >>>In such a case, then Av is equal to Av0.  Both have a value of 4.5*c1^2.
> >>>Av/Av0 will be 1.
> >>>
> >>>Ok, now make it two anchors that are spaced 3*c1 apart.  This will be
> >>>
> >>>
> >that
> >
> >
> >>>same as above but Av will be twice as big because the failure surface
> >>>
> >>>
> >(Av)
> >
> >
> >>>will still be bottom of two FULL half pyramids with a base of 3*c1 by
> >>>1.5*c1.  This is because you now have two anchors with FULL failure
> >>>surfaces that do not interesect (remember Av is the failure surface for
> >>>the entire group of anchors).  So, Av/Av0 will be 2.
> >>>
> >>>OK, now decrease that space of the two anchors.  The failure "half
> >>>pyramids" will now overlap.  Av will become 1.5*c1 (depth of failure
> >>>plane) times 1.5*c1+s+1.5*c1 where s is less than 3*c1.  The result is
> >>>that Av/Av0 will be less than 2 and approaching 1 as s decreases toward
> >>>zero.
> >>>
> >>>I will leave it to you to look at more complitcated, "less perfect"
> >>>
> >>>
> >cases
> >
> >
> >>>such as when concrete thickness is not much greater than anchor depth
> >>>(i.e. h<1.5*c1) or corners or multiple rows of anchors parallel to the
> >>>edge.
> >>>
> >>>This is as it should be.  Av0 is the shear breakout of ONE anchor
> >>>
> >>>
> >assuming
> >
> >
> >>>"perfect" edge conditions (i.e. no other anchors to overlap the failure
> >>>surface, at just a plain edge not corner, and concrete thickness much
> >>>greater than the anchor depth).  Av is the shear breakout of the entire
> >>>anchor group, which could in fact be single anchor in the group [if you
> >>>have an isolated anchor] or an actual group of anchors, under
> >>>
> >>>
> >potentially
> >
> >
> >>>less than ideal conditions (i.e. close spacing, at a corner, and/or
> >>>concrete thickness less than 1.5*c1).  Thus, things like spacing,
> >>>
> >>>
> >another
> >
> >
> >>>edge (i.e. at a corner), or "thin" concrete will affect Av.  The point
> >>>
> >>>
> >is
> >
> >
> >>>that under "perfect" conditions (i.e. spacing greater than 3*c1, edges
> >>>
> >>>
> >not
> >
> >
> >>>corners, concrete thickness much greater than anchor depth [i.e.
> >>>h>1.5*c1], anchors all in one parallel row/line that is parallel to the
> >>>edge) Av will be a integer number multiple of Av0, where the integer
> >>>multiple is the number of anchors.  This multiple becomes a non-integer
> >>>and less than the number of anchors as the conditions become less than
> >>>perfect.
> >>>
> >>>Now, I can only hope that I am remembering/explaining this right...I
> >>>am little scatter-brained today.
> >>>
> >>>HTH,
> >>>
> >>>Scott
> >>>Adrian, MI
> >>>
> >>>
> >>>On Wed, 8 Jun 2005, Elias Hahn wrote:
> >>>
> >>>
> >>>
> >>>>So, I come again to this list with a question stemming primarily from
> >>>>
> >>>>
> >>ACI
> >>
> >>
> >>>>318.
> >>>>
> >>>>
> >>>>
> >>>>I'm "designing" some anchor bolts, and I'm confused about the formula
> >>>>
> >>>>
> >>for
> >>
> >>
> >>>>concrete breakout strength of anchor bolts.  Specifically about
> >>>>
> >>>>
> >Av/Avo.
> >
> >
> >>>>Because Avo is a function of 1.5*c1, and Av is a function of 1.5*c1,
> >>>>
> >>>>
> >c2,
> >
> >
> >>>and
> >>>
> >>>
> >>>>h - it seems like the larger c1 gets, the smaller Av/Avo gets, which
> >>>>
> >>>>
> >>seems
> >>
> >>
> >>>>counter-intuitive.
> >>>>
> >>>>
> >>>>
> >>>>The reason it gets so small is because as c1 gets large, 1.5*c1 will
> >>>>
> >>>>
> >be
> >
> >
> >>>much
> >>>
> >>>
> >>>>larger than h and c2, so that Av becomes much smaller than Avo.
> >>>>
> >>>>
> >>>>
> >>>>My confusion is why is Avo a function of c1 if it supposed to
> >>>>
> >>>>
> >>approximate
> >>
> >>
> >>>>the "surface area of full breakout prism. unaffected by edge
> >>>>
> >>>>
> >distance"?
> >
> >
> >>>>
> >>>>Thank you,
> >>>>
> >>>>Elias Hahn
> >>>>
> >>>>Evergreen Engineering, LLC
> >>>>
> >>>>phone 503.502.0698
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
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