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

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It sounds to me like you are trying to make the cladding studs the lateral resisting system.

Not only is this a bad idea for several reasons, but I don't think it's allowed by code. I believe light framed structures (certainly wood framed) cannot support concrete construction over 1 story and 1 story only in limited cases. Your filled metal deck on 3 stories would negate that right there.

I don't understand what you mean with the retaining walls and walk out. Why does the fact tha few of the walls needing to be basement walls affect your choice of lateral system?

I hope the building is in seismic zone 0. Not trying to be smug here, but I don't see how a LGS framed system could withstand the forces of a three story structural steel building in a seismic event.

Use structural steel braced frames (CBF or EBF) moment frames, or a dual system.

Using concrete shearwalls at the basement level is fine and done all the time, but not in conjunction with LGS Shearwalls or Tension only strapped walls.

-g

On 8/17/07, Jeff Hedman <jeff_h(--nospam--at)lrpope.com> wrote:

Gerard,

My diaphragm is metal deck filled with concrete.  The building has structural steel beams and columns with light gauge studs with wood sheathing shear walls.  I normally wouldn't want to mix and match shear wall types, but this building is basically a 3 story building with a "walk out" bottom level.  The architect has designed it such that I only need a basement wall in a few places, he has used diamond block retaining walls to retain the soil on much of the bottom floor to let in more light than typical window wells.  So I have a building perimeter that has only about 10% (if that much) that needs to be a basement wall.  I may be able to look at the heights of the stairs in the shaft and make my wall shorter with shorter concrete stem walls as the stairs go down to avoid having so much shear transfer into the one concrete wall.

 

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

email: jeff_h(--nospam--at)lrpope.com

-----Original Message-----
From: Jeff Hedman [mailto:
jeff_h(--nospam--at)lrpope.com]
Sent:
Thursday, August 16, 2007 4:10 PM
To:
seaint(--nospam--at)seaint.org
Subject: Rigid diaphragm with framed shear walls and concrete shear walls

 

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