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RE: Masonry wall with epoxy anchors

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Dave,

Not to be picky, but that is only part of ACI 530 (the code) not ACI 530.1
(the specification).  OK, so that was picky.  <grin>

Let me ask...did the contractor provide ANY horizontal reinforcement?
Your previous post seemed to imply that he did bond beams at 5'-4" on
center.  Did he also provide some joint reinforcement (it is fairly
typical to at least do joint reinforcement at 16" oc [every other course]
on all walls as a minimum...at least in my neck of the woods) as well?

I have to say that while he did not provide what was called for on the
drawings which is required per code, I am not sure that it is a huge deal.
Take a look at the commentary for that section.  It states:

"The requirements seperating running bond from stack bond are shown in
Fig. 1.11-1.  The amount of steel required in this section is an ARBITRARY
amount to provide continuity across the head joints.  This reinforcement
can be used to resist load." (note I added the capitalization)

My point is that the committee pointedly admits that this is an arbitrary
requirement.  So, one could argue that as long as there is some decent
amount of horizonatl steel the goal may still be achieved (i.e. providing
continnuity across the head joints).  So, unless you need to resist load
and the code minimum steel would do that but the steel provided
(presumably less that minimum...does the steel provided meet the 0.00028
times the gross vertical cross-section requirement - about 0.04 sq in per
1 ft? or is the only "violation" the bond beams spaced no more than 48
in?) would not, I am not sure that I would make a huge deal over it.  I am
not even sure the reinforcing (bolts & plates) are really needed.  It does
not meet code, but could still be fine.  If so, then it becomes a question
of what you are comfortable with both from a personal liability and
techinical point of view.

Now, if you let the contractor off the hook and don't require the
reinforcing, then at a minimum the contractor should be giving the owner a
credit (since s/he provide less that what was called for on the drawings
and required by code), pay for your time to review it, and pay for any
delays/problems that might arise if the building official raises the issue
(and pay for changes if the building official requires a fix).

Now, if you need to resist load, then the reinforcing might still be
needed.  Then, the answers to your questions before would depend on what
load is being resisted.  If it is just to meet minimum steel requirements
of the code rather than also resist load and you choose to force the
reinforcement, then I answers would be a little different again.

Just my 2 cents.

Regards,

Scott
Adrian, MI


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

> Hi Scott,
>
> The section in question of ACI 530 & ACI 530.1 is 1.11 - Stack Bond Masonry
>
> The Wisconsin Enrolled Commercial Building Code has a very similar section 2109.6.5.2 regarding this same issue.
>
> Regards,
>
> Dave
>
>
>
> Dave,
>
> Can you cite specifically where this requirement is that you are referring
> to in ACI 530.1 (or ACI 530)?  I don't actively recall such a requirement
> at the moment (call it a "senior moment"...kind of sad for someone so
> young and handsome <grin>) and cannot find it.  Which version of the MSJC
> (ACI 530/530.1)?  With that information, I will be in a between position
> to offer ideas.
>
> Regards,
>
> Scott
> Adrian, MI
>
>
> On Thu, 8 Sep 2005, Nuttall, Davin J. wrote:
>
> > 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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