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Re: Out of plane shear in hollow CMU

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Ben:

First, since you reference chapter 7, I am assuming that you are using a
1995 (or older) MSJC (aka ACI 530).  So, at a minimum, I would encourage
you to get an updated MSJC (as a lot has changed), unless the local code
used in your area still references that older version.

While a lot has changed, shear for allowable stress design has not changed
all that much.  In answer to your question, the short answer is "yes".  I
would use the sqrt(f'm) value for an allowable shear stress at the mortar
joint.  This would deal with the situation of masonry "wanting" to fail
and the masonry's weak point should be the mortar joint (actually the
mortar to masonry unit interface).

You would still need some sort of check of the anchor to masonry interface
and this would depend on how the anchor works.  As the PTA-422 seems to
accomplish this by bearing from the clip surface to the masonry, you many
need to check the masonry for bearing failure (most likely in the form of
a crushing of the masonry type mode, but also could be bending of the face
shell between web...i.e. a mini-beam/slab of the face shell running
between the "support" webs).  Presumably, Hohmann & Barnard should have
some testing and/or evaluation reports that show this allowable load value
(and it may also account for the potential shear failure at the mortar
joints/adjacent masonry).

HTH,

Scott
Adrian, MI


On Thu, 9 Mar 2006, Benjamin Cornelius wrote:

> Has anyone ever checked an unreinforced hollow CMU wall for punching shear
> at the anchorage to the roof diaphragm?
>
> I have an existing non-load bearing CMU panel (which is resisting wind and
> seismic loads out of plane) that is anchored to the roof slab on deck with
> channel-type anchors (called a PTA-422 from Hohmann & Barnard) at 4'-0 on
> center, and there is no bond beam at the top of the panel, so the masonry at
> the anchor is hollow.
>
> I looked through ACI 530, but it only talks about shear stresses in solid
> masonry or grout-filled masonry.  Can I still use the SQRT(f'm) value in
> Chapter 7 and just apply it to the area of the face shell?
>
> Thanks in advance.
>
> Ben
>
>
>
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