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Re: masonry block properties

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Two questions please. For context, I am interested in reinforced masonry

1. Do you know why the values you have are different for properties
based on full mortar bedding and properties based on block dimensions?

2. Why would the h/r value for determining allowable axial stresses
always be based on the r value based on block dimensions? I've always
thought the r had to be calculated based on the I and A accounting for
actual grouted cells and mortar bedding conditions.

Rick Burch
Columbia, SC

Scott Maxwell wrote:

> For stress calculations, you need to use the dimension of "contact" in the
> mortar bed, not just the block dimensions.  This will then depend on the
> whether you are using either face shell mortar bedding (i.e. mortar at
> just the front and back face shells but not on the webs) or full mortar
> bedding (both face shells AND the webs get "buttered").  This values from
> tables that I have BOTH are different that section properties determined
> from just block dimensions.  For an 8" block:
>                         face shell bedding      full bedding
> A                       30.0 in^2               41.5 in^2
> I                       309 in^4                334 in^4
> S                       81.0 in^3               87.6 in^3
> ek (kern ecc)           2.70 in                 2.11 in
> r                       3.21 in                 2.84 in
> >
> > 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.
> For the h/r and other parts of the axial load/stress determination, you do
> use the section properties of the block based upon the block dimensions.
> For 8" ungrouted block:
> A = 50 in^2
> I = 364 in^4
> S = 95 in^3

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