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Re: Masonry Control Joints

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--- Jim Kestner <jkestner(--nospam--at)somervilleinc.com> wrote:
> This may sound like a basic question, but I will ask it anyhow.
>
> I have seen many details with a vertical rebar on each side of a masonry
> control joint.

> If the wall spans vertically between supports, what is the
> reason for these bars?

Call it a "spandrel bar".  It does not necessarily need to be in the cell
adjacent to the joint, however; if it is not, I would neglect that cell for
capacity calculations (but include it for load calculations).

> Is it required to stiffen the edge of the wall against out of plane loading?

"Required" is a tricky word.  Technically, no, but it makes sense, and is an
easy practice to adapt to typical engineered masonry work.

> Is it the end of a shear wall because of the discontinuity of the joint?

Yes and no.
Yes, it is necessary if the wall carries ANY in-plane shear load.
No, it is not necessary, but then the effective length of the wall for in-plane
shear is shorter by one (or more) cells.

> Is there a particular code that requires this?

See ACI 530-99 1.13, among others.

> Is it necessary only in seismic zones?

Per code, yes.  You should carefully consider your lateral load system before
skipping vertical reinforcing at either side of the joint, even in low-wind
areas.

Check out Structural Engineer magazine, October 2001.
My personal reference book is Amrhein's "Reinforced Masonry Engineering
Handbook", from which I learned most of my masonry design and shear wall
analysis.

Out of curiosity, what's the back-up system?  And how do you intend to attach
it to the masonry?  I've used several (sometimes odd) methods for attachment to
steel frames, and haven't yet adopted one as my favorite.

-Keith Fix, PE

>
> Jim Kestner
> Green Bay, WI
>
>
>



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