# Masonry Designer Guide



## MOOK (Oct 4, 2009)

In Masonry Designer Guide, Table 7, Appindex "A"

Does any body know how they came up with the moment of inertia = 309 in4 for 8 in wall "Face-Shell bedding"??

Is this Moment of inertia per linear foot??

Thanks


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## Hromis1 (Oct 5, 2009)

Mook, I don't have that guide, but yes it matches the reference value I have for a hollow nomimal 8" wall grouted only at the faces. It is per linear foot of wall. My source has 308.7 Inches the the fourth power/per linear foot of wall.

FYI, the civil engineering reference manual has very good tables for various section properties, grout configurations..Tables A-116, through A-119.

Why that data is not in the SERM, I'll never know.


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## MOOK (Oct 5, 2009)

Hromis1 said:


> Mook, I don't have that guide, but yes it matches the reference value I have for a hollow nomimal 8" wall grouted only at the faces. It is per linear foot of wall. My source has 308.7 Inches the the fourth power/per linear foot of wall.
> FYI, the civil engineering reference manual has very good tables for various section properties, grout configurations..Tables A-116, through A-119.
> 
> Why that data is not in the SERM, I'll never know.


Thanks Hormis1 but do you know how they came up with this number?


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## Ryan O. (Oct 5, 2009)

[12(7.625^3 x 5.125^3)]/12 = 308.7

7.625" is the overall depth of the masonry wall, 5.125" is the distance between the face shells. It's the equation to calculate Ix for equal rectangles. It is can be found in the 2005 AISC. Hope this helps.


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## MOOK (Oct 6, 2009)

Ryan O. said:


> [12(7.625^3 x 5.125^3)]/12 = 308.7
> 7.625" is the overall depth of the masonry wall, 5.125" is the distance between the face shells. It's the equation to calculate Ix for equal rectangles. It is can be found in the 2005 AISC. Hope this helps.


Ryan O.

Could you please check the equation again, it does not seem right to me.

Thanks


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## BLMedcalf (Oct 7, 2009)

MOOK said:


> Ryan O.Could you please check the equation again, it does not seem right to me.
> 
> Thanks


It is supposed to say 12(7.625^3 - 5.125^3)/12. Think of it as the Moment of Inertia of a large rectangle minus the moment of inertia of the smaller rectangle that is void.


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## Ryan O. (Oct 7, 2009)

It is supposed to be 7.625^3 - 5.125^3, my screw up.


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## MOOK (Oct 7, 2009)

Ryan O. said:


> It is supposed to be 7.625^3 - 5.125^3, my screw up.


Thanks Ryan O.


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