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# Re: masonry block properties

• To: seaint(--nospam--at)seaint.org
• Subject: Re: masonry block properties
• From: Keith Fix <kefix(--nospam--at)yahoo.com>
• Date: Wed, 30 Jul 2003 13:51:21 -0700 (PDT)

```This is a very quick answer, but it should work.

I have radius of gyration tables for masonry walls, as well as net area for
various grout spacings.  Since r=sqrt(I/A) and S=I/c, then S=A(r squared)/c.
Other derivations may be available, depending on your data set.  Tedious, but
effective.

-Keith Fix, PE

PS- please double-check me, as I did this very fast.

--- Andrew Kester <andrew(--nospam--at)baeonline.com> wrote:
> To prove a point, I have to determine the allowable load for an unreinforced
> 8"x 16" section of block wall. Now I know I have to check everything
> according to ACI 530-99, C-20, Sect. 2.2 Unreinforced Masonry. But, to
> calculate the bending stress in the block, ungrouted with no reinforcement,
> is completely different then standard reinforced masonry design. I am
> assuming I would use the following regular engineering mechanics formula for
> bending stress:
>
> Fb= M/S
>
> S- this is the problem, as it is hollow block. I cannot find any tables for
> this, and I have quite a few resources. Does anyone have this value in a
> table? Would it be improper to just hand calc the Sx for a 8"x16" hollow
> block? Now would a simplifed way of doing this, to be calculate Sx for a
> solid 8x16 block, then subtract the Sx for the cavities? This ignores the
> curved cavity walls, and the thickness of walls is different on the top then
> the bottom, etc.
>
> I do not see why this is wrong, then I calc. Fb as I did above. The same
> goes for Ix calc, which I need for formula (2-15) to calc Pe.
>
> Thanks in advance. If you can directly CC me that would be great because I
> get the digest list once a day.
>
> Andrew Kester, EI
> Longwood, FL
>
>
>
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