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Re: Masonry wall with epoxy anchors

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Scott,

       I agree with you completely.

Regards,

H. Daryl Richardson


----- Original Message ----- From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, September 08, 2005 12:52 PM
Subject: RE: Masonry wall with epoxy anchors


While in a black and white world (i.e. a pure principled view), this
approach would make a ton of sense, here in the real world I would argue
that it is not such a simple call.  Ideally, the contractor screwed up and
should have to remove and replace what he screwed up.

But...if you want to advocate such a thing, then you should be prepared to
have to pay for a complete tear down and replace of an item that you may
have designed incorrectly and later discover your error after it has been
built.  After all, why should the owner have to live with a cludged
solution due to an engineer's screw up just to save the engineer money?

In otherwords, if you want to be completely intolerant of others mistakes
(intential or not), then be prepared for people to be completely
intolerant of your mistakes.  What comes around goes around.

In reality, when a error occurs (no matter why it happened), it is usually
best to figure out how the error effects things and then use the most
efficient (from time, cost, etc) solution to fix the error.  Sometimes
this will be to rip the stuff down and do it over again right.  Sometimes
this will be to repair/reinforce it in some manner.

Regards,

Scott
Adrian, MI


On Thu, 8 Sep 2005, Eli Grassley wrote:

I would tell them to tear the whole thing down and do it per the plans!
When you give the contractor a "fix" for this kind of a performance, you are
just feeding the monster.

~~ Eli ~~


-----Original Message-----
From: Nuttall, Davin J. [mailto:dnuttall(--nospam--at)somervilleinc.com]
Sent: Thursday, September 08, 2005 11:13 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Masonry wall with epoxy anchors

Hi Scott,

We specified a running bond in the original contract documents.  The
contractor took it upon himself to change to a stack bond. By changing to stack bond, he also did not provide enough minimum horizontal reinforcement
in the wall.  He could have added bond beams not to exceed 4'-0" o.c. or
provided horizontal ladder reinforcement at each course, but he did neither.

The bond beams he did provide were spaced at approximately 5'-4" o.c.  I
added the plate and bolts between the in-place bond beams to maintain the
minimum steel and spacing requirements of ACI 530.1 for stack bonded walls.

Regards,

Dave



Dave,

See comments below:


On Thu, 8 Sep 2005, Nuttall, Davin J. wrote:

> List,
>
>
> Due to contractor error, I had to externally reinforce a 12" CMU stack
> bonded cavity wall after-the-fact.

If I may ask, why the stacked bond.  If the wall will be furred out, then
it appears that appearance is not the driving factor, so running bond
should have been the better choice.  The exception could be that only one
side will be furred and the exterior a face of the wall will be exposed.
If such is that case, then I have to wonder what the type of load the wall must carry is, how was it deemed insufficient as constructed, and what are
the full details of the repair.  It sounds as if it could be flexure due
to wind pressure and repair could be external steel plates as flexural
reinforcement (all speculation...could be something else).  If so, then
reinforcing one side would not seem to solve the potential problem as the
wind in such as situation could be either positive pressure (resulting in
tension stresses on the inside face) or negative (resulting in tension
stresses on the exterior face).  Just curious.

>
> My detail included continuous steel plates with epoxy anchors drilled
> into the center of existing solid grouted cores.  The wall will be
> furred out, so the repair will not be visible after the project is
> finished.
>
> I now find out that the contractor ignored portions of the submitted
> fix, and in some cases, located the anchors right in a mortar joint.
>
> Questions:
>
> 1.  Because the wall is grouted solid, would you be concerned with edge
> distance of the bolt relative to the edge of the individual block?

Generally, I would say no. It will in general be the edge distance of the
bolt to the edge of the masonry assembly not the unit.  This would be
largely true even if ungrouted.  This is assuming you are looking at it
from a global point of view.  Where edge distance to a individual block
could be an issue is for local effects that could further weakness in the
"weak points" (i.e. say you use an expansion style anchor in a mortar
joint...could cause the joint to crack/fail due to the expansive force,
which in an ungrouted situation could cause the generally considered
weakest point - the mortar joint - to be even weaker).

>
> 2.  Are the blocks considered as individual units with respect to the
> new bolts and their capacities, or is the entire cmu wall acting as 1
> monolithic unit?

Generally considered acting as 1 monolithic unit.  But again, it depends
on what "thing" (i.e. failure mode, behaviour, etc) you are looking at.
Masonry is a "non uniform" material, so some failure modes can be governed
by the individual components more readily than the overall assembly.  So,
it will require knowledge of how masonry behaves and what the bolts are
"doing" (i.e. how are the bolts loading the masonry) to really make such a
determination.  And I don't have enough information of the specific
situation to make such an assessment in this situation.

>
> 3.  How much of a strength reduction would you take because the bolt is
> located in or right next to a mortar joint, and not the published
> distance away from a free edge?

Again, it depends on what the bolt is "doing" and the configuration of the
bolts as well as the configuration of the wall as is and what kind of
loads it must carry. More than likely if the bolts are engaging the grout
in the cores, it will likely not matter if the bolt is in a mortar joint
or not.

>
> The worst case scenario would be to remove and relocate the plate and
> bolts to the specified location(s). As always, time is a major > concern,
> and they would like to move on with minimal rework.
>
> Thanks
>
> Dave Nuttall, P.E.
> Green Bay, WI
>


HTH,

Scott
Adrian, MI

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