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# Re: masonry block properties

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: masonry block properties
• From: "Jason Kilgore" <jkilgore(--nospam--at)leok.com>
• Date: Wed, 30 Jul 2003 15:57:14 -0500
• Cc: <andrew(--nospam--at)baeonline.com>

```I couldn't find a "S" or "I" value for un-reinforced CMU during my quick
look, but I'm sure there are tables somewhere.

If you calculate it by hand you want to use the equation:

Fb = Mc/I

instead of the one you indicated.

Easiest way to calculate "I" would be to calculate for a solid block then
subtract the "I" for the holes.

This will give you a different value than if you base your calculations on
the "S" values for the block and holes.

----
Jason Kilgore
Leigh & O'Kane, L.L.C.
jkilgore(--nospam--at)leok.com
816-444-3144
816-444-9655 (FAX)
----- Original Message -----
From: "Andrew Kester" <andrew(--nospam--at)baeonline.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, July 30, 2003 11:41 AM
Subject: masonry block properties

> 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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