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RE: Shear Walls extending to Basement Level

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Jim,

Ah, the crystal ball becomes more clear...it says that you are correct in
determining my errant assumption.  The spirits ask me to thank your for
correcting me.  <grin>

Scott
Ypsilanti, MI


On Mon, 11 Nov 2002, Jim Kestner wrote:

> Scott,
>
> I think that you have made the assumption that I am talking about a shear
> wall over the top of the perimeter foundation wall....I am not. I am asking
> about a shear wall located on the interior of the building which goes down
> to the basement floor.
>
> Jim K.
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Monday, November 11, 2002 1:12 PM
> To: 'SEAINT'
> Subject: Re: Shear Walls extending to Basement Level
>
>
> Jim,
>
> One thing to keep in mind is that you will likely get a SEVERE change in
> stiffness when you go from your shearwall above grade to your basement
> wall below grade.  This would be due to the likely change in the length of
> the walls.  Your shearwall above grade is more than likely to be
> significantly shorter in length than the basement wall, which will likely
> extended in length around the full perimeter of the building (and only
> really being broken or weakened at vertical construction joints).  The end
> result, if true, would be that the load from the shearwalls would likely
> go down into basement walls directly rahter than transfer into the 1st
> floor diaphragm, especially if the 1st floor diaphragm connects to the
> basement walls (i.e. the "transition" from shearwall to basement wall is
> either slightly above the 1st floor or right at the 1st floor).  Keep in
> mind that load tends to be attrached by stiffer elements.
>
> You are still correct that even in the scenario that I paint above, there
> is still the possibility of some load going into the 1st floor diaphragm,
> but not as much as you might be envisioning.
>
> HTH,
>
> Scott
> Ypsilanti, MI
>
>
> On Mon, 11 Nov 2002, Jim Kestner wrote:
>
> > Picture a shear wall extending to the basement level. It would seem that
> if
> > the 1st floor diaphragm was tied into the shear wall with rebar (and that
> > the diaphragm could transfer load to the perimeter foundation walls) that
> > the shear wall would try to act as a cantlivered beam using the foundation
> > in the basement and the 1st floor diaphragm as its supports. It would seem
> > to me that this would potentially create a large cranking force on the 1st
> > floor diaphragm that would be difficult to design for since the shear
> would
> > be magnified.
> >
> > All my references show examples of shear walls going to grade level and
> not
> > to the basement level.
> >
> > How is this condition normally handled? Is it practical to isolate the
> shear
> > wall from the diaphragm at the 1st floor level so that all overturning and
> > shear forces are transfered to the foundation at the basement level? It
> > doesn't seem practical to stop the shear wall at the 1st floor level. The
> > 1st floor shear wall would have to be designed as a transfer beam and
> > columns on either end would have to extend into the basement to transfer
> the
> > up and down forces.
> >
> > How are these designed on high rises where there may be multiple basement
> > levels to contend with?
> >
> > Jim K.
> >
> >
> >
> >
> >
> >
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