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# Re: Relative Stiffnesses of Masonry Shear Walls (Compared to Concrete)

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Relative Stiffnesses of Masonry Shear Walls (Compared to Concrete)
• From: William Haynes <gtg740p(--nospam--at)gmail.com>
• Date: Mon, 13 Sep 2010 16:06:52 -0400

"I want to model the walls assuming they are concrete elements with the thickness of those elements reflecting the relative stiffness compared to a solid concrete wall"

Solve for the equivalent thickness of concrete wall by setting the shear and bending deformation equations of the equivalent concrete shear wall (with concrete's elastic modulus and shear modulus) to the shear and bending deformation equations of the "equivalent solid thickness" partially grouted masonry shear wall (with the masonry elastic and shear modulus).  I think the shear modulus is about 0.4xmodulus of elasticity for each material so you should be able to come up with the single equivalent thickness of concrete that can be used to represent both the shear and bending deformation terms of the partially grouted masonry.

Will

On Mon, Sep 13, 2010 at 2:16 PM, David Topete wrote:
Bill,
As others have mentioned, the Ahmreim reference is great for this info.  Also, IIRC, I think I had found some of this info from an USACE Technical Manual on Masonry Design.  I'd have to search for it, but I believe you can find it at www.wbdg.org as a pdf download.  As Neil noted, an 8" cmu wall, grouted at 32"o.c. will have an equivalent "solid wall" thickness of about 4".  Find the relative rigidities for each wall for distribution below the podium slab.  Good luck.

On Mon, Sep 13, 2010 at 9:57 AM, Drew Morris wrote:
Just use the equations from Armheim in masonry design.  You have a wall height, length, thickness and modulus of elasticity.  You can model the CMU wall as either canted or fixed-fixed.  The CMU deflection equations are not dependent on the cell reinforcing and grouting.  This brings up an interesting point, it would appear that by changing the reinforcing spacing, there should be some effect on the rigidity but the formulas do not reflect this.

On 9/11/2010 1:37 PM, Bill Polhemus wrote:
Trying to model a complicated building base. Building is a wood-framed apartment, 3 storeys (sorry, like the Brit spelling better this time), sitting atop a "podium" constructed of a thick concrete slab supported by a forest of concrete columns in the interior, and 8-inch CMU shearwalls all along the boundary.

The CMU walls have grouted cells every 32".

I'm trying to figure out the shear demand for the walls in this (very) irregular building, and as it has been a long time, I need to remember how to show the "stiffness" of those walls acting as shear elements. I recall that the spacing of grouted cells has a part to play (i.e. the smaller the spacing the more stiff the wall), and I want to model the walls assuming they are concrete elements with the thickness of those elements reflecting the relative stiffness compared to a solid concrete wall (in effect the masonry walls would be "thinner" than their nominal thickness in the real world.

I need some guidance here. Anyone?

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David Topete, SE