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Re: Shear Key in Basement walls

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Gautam,

Not only does the first floor provide some lateral support, it "does"
provide lateral support.  That retaining wall will not rotate 1% to justify
active pressure.  The reaction at the base will be half of what you have
currently assumed.  That is good.  What you need to check is that the
balance of the lateral load is distributing through the lumber diaphragm and
into the shearwalls and it is a permanent load that needs to be added to the
short term loads you have already designed for.

Good luck,


Jeff Coronado, S.E.
West Covina, CA.

----- Original Message -----
From: "G M" <newabhaju(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, July 10, 2003 6:47 PM
Subject: Shear Key in Basement walls


> To all:
>
> I recently designed a basement wall as a cantilever retaining wall with a
> shear key.  The slab within the two ends of the retaining walls is a 5
inch
> slab on grade.  Due to field condition, the contractor does not want to
> intstall  the shear keys.
>
> One way to reduce the shear demand at the base of the retaining wall is to
> account for the fact that the first floor provides some lateral support.
> However, because the first floor consists of wood construction, I am
> hesitant to do this and prefer to be conservative. ( I do reinforce the
wall
> stem for this condition,though).
>
> The second alternative is to assume that the active force on the retaining
> wallls at the opposite ends of the basement cancells each other out -
> therefore, a shear key is not necessary.  This condition should hold true
no
> matter how far the two retaining walls are located - in finite terms,
thoguh
> - provided they are of the same height and have simillar backfill.  The
> slab-on-grade will be subjected to compressive forces from the retaining
> wall and should act as a plate with compressive forces on all four sides (
> four sides of the basement).
>
> My question to you all is - how do you design the slab?  I am thinking of
> taking a unit width of slab and finding the allowable compressive load
based
> on Euler's formula with a factor of safety.  Since water will be drainded,
> moment due to water pressure should not be an issue.
>
> If the wall design were to include  seismic forces  - (Mononobe-Okabe
> equation)- how would one dissipate the shear for the worst case scenario
for
> seismic forces acting in the same direction for the two opposite walls.
>
> Your comments would be highly appreciated.
>
> Gautam
>
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