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RE: Shear Key in Basement walls

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I usually avoid shear keys at the bottoms of walls and use shear friction as you do. I think shear keys just weaken the joint.
 
I don't like to use hydrophilic waterstops unless it's in a non-critical area, or the wall is short, or there's just no other way. It's not that they don't work, but if your jobs are in an area where it rains a lot, how do you keep them dry until the concrete goes in the form?
 
I do a lot of hydraulic structures, and contractors gripe continually about the upturned starter wall that is frequently detailed to make room for conventional waterstops to clear the floor steel. When I can, I drop the bars at the wall or just put more cover on the slab steel to avoid this detail. Some contractors would rather just install a retrofit waterstop on top of the slab instead of dealing with the usual embedded waterstop detail.
-----Original Message-----
From: Tripp Howard [mailto:tripphoward(--nospam--at)yahoo.com]
Sent: Friday, July 11, 2003 5:45 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Shear Key in Basement walls

Just curious how many people use shear keys.  I've moved away from them since they can be hard to form and make installing waterstops difficult.  I typically just roughen the surface between the wall and the footing and check it with the shear friction provisions.  What do others think about doing it this way? 
 
On another note, I've gone away from using the traditional rubber waterstops due to the difficulty in installing them properly.  If I need a waterstop, I've been using a swellable hydrophilic waterstop such as Volclay's Waterstop RX.  You can adhere it to roughened surfaces and to join ends you just but them together.  No welding or special glues required.  What are others opinions on these alternate types of waterstops?

G M <newabhaju(--nospam--at)hotmail.com> wrote:
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 ret! aining 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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