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# RE: CMU Wall Rigidity

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: CMU Wall Rigidity
• From: "Lutz, James" <James.Lutz(--nospam--at)earthtech.com>
• Date: Wed, 7 Sep 2005 10:14:37 -0700

```Couldn't read your graphic, but it looked like you were trying to describe
what's show below. A simplistic approach to this is to treat each wall
section between the openings as a floor to ceiling pier and ignore the
contribution of the connections. This underestimates the rigidity of the
assembly but may not be too bad of an estimate for actual behavior once
things start breaking down. It's fast but conservative. The total rigidity
becomes the inverse of the sum of the inverses of the rigidities for the
piers.

For a "pure" analysis, compute the rigidity for each wall section A thru G
as if it they were individual fixed piers. You can write an equilibrium
equation for each panel section where the sum of the shears at the base
equals the sum of the shears at the top. You can also write a deflection
equation for each panel, where the total deflection at the top equals the
deflection at the bottom plus the change in deflection, which equals the
horizontal shear in the panel divided by its rigidity. Boundary conditions
will make several of the unknowns equate, simplifiying the equation set.
Deflection at the base is set to zero, top and bottom shears are set equal
to 1, and 1/top deflection equals the rigidity of the assembly.

This isn't as tough as it sounds. Once you have the equations set up, you
can just plug the coefficients into a spreadsheet, invert the matrix, and
spit out the solution.

<<...OLE_Obj...>>

-----Original Message-----
Sent: Wednesday, September 07, 2005 9:28 AM
To: seaint(--nospam--at)seaint.org
Subject: CMU Wall Rigidity

I have a question regarding CMU wall rigidities.  For the current method of
Solid Wall - Strip with openings + Piers, all my references naturally show
openings with the same elevation.  Usually either a door and window with the
top of the openings at the same level; or several windows with the same
height and elevation.  Since architects are strange creatures, this is not
always the reality.  How would you go about calculating the rigidity of a
wall with openings as shown below (apologies in advance for the crude ASCII
drawing).

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