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Re: masonry block properties

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Jim,

And I would say more than likely you would be significantly off the mark
with that guess.  For an unreinforced masonry wall subject to out of plane
bending, the "allowable" wind load (and wind speed) would be governed by
the allowable tensile capacity of the mortar joints rather than the
allowable compressive capacity of the mortar and/or the blocks.  This
value would be on the order of 9 to 25 psi (assuming the wall spans
vertically), depending on the type of mortar used.  Now, IF the wall was a
load bearing wall, then the compressive stresses from the vertical load
would help the wall "carry" more lateral wind pressure as the compressive
stress from the gravity load would "counteract" some of the tensile stress
from the wind.  You would still get some of the same effect
from the weight of the wall even if it is not a loadbearing
wall.  Ultimately, you have to remember that masonry
(like concrete) does not have the same capacity in tension as it does in
compression (at least above a certain, rather small level).

HTH,

Scott
Ypsilanti, MI


On Wed, 30 Jul 2003, jim jensen wrote:

> I'd call the Manufacture of the CMU. I would guess
> it's 1800 psi,I hate guessing. Jim Jensen
> --- 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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