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Re: Rigid diaphragm with framed shear walls and concrete shear walls

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Rigid diaphragm with framed shear walls and concrete shear walls
• From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
• Date: Thu, 16 Aug 2007 18:02:51 -0700

If you have a rigid diaphragm, it is unwise to mix and match shearwall types at the same story.

The concrete walls will be so much more rigid than the metal stud walls (light-framed construction) that the concrete walls will do all the work.

What is your diaphragm? Why is it rigid, is it metal deck filled with concrete?

Clarify the opening line "steel framed building"...you mean structural steel floors and light gage lateral system (not good) or light gage steel framed building?

-g

On 8/16/07, Jeff Hedman <jeff_h(--nospam--at)lrpope.com> wrote:

I am doing a steel framed building with light gauge steel shear walls on the top two floors but on the bottom floor there are some walls which will be basement/concrete shear walls.  My question is has anyone done a rigid diaphragm analysis with walls that aren't all the same materials?  If I use the masonry wall deflection calculations and the steel stud shear walls deflection calculations and then invert them to obtain my rigidity factors, the differences in rigidity seem to be too extreme (i.e. 1 specific concrete wall calculates out as 670 times more rigid than the equivalent steel stud wall).  Using these numbers, my ex is 1.17' from the left hand side of the building and my ey is 29' from the bottom of the building.  This building is 162'-2" long and 84'-3' wide so my center of rigidity is way down in the bottom left corner. The biggest factor on this is one concrete wall that is approximately 32'-0' long because of a sub grade concrete stairway on that side of the building.  I have other 20'-0" long steel stud shear walls in the same direction, but with the differences in rigidity, these other walls are not helping to keep the center of rigidity towards the center.  Are there any suggestions for another way to do this, like calculating a standard rigidity for all walls but then multiplying the concrete walls by a factor at the end instead of calculating the deflection for each wall separately?

Jeff Hedman  , E.I.T.

L.R. Pope Engineers & Surveyors, Inc.

1240 East 100 South Suite # 15B

St. George , Utah   84790

Office: 435-628-1676

Fax: 435-628-1788

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-gm