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RE: Masonry wall with epoxy anchors

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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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