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RE: Shear Walls extending to Basement Level

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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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