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RE: Keyway Details

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I typically use Option 3 with a 6" PVC waterstop but with a roughened joint
in lieu of a keyway, although Contractors sometimes complain that it is
difficult to form the "starter wall".  I don't like to have the waterstop in
contact with the top mat of slab steel, due to the potential water path
along the waterstop. I count on shear-friction at the joint in lieu of a
keyway for shear - typically the normal flexural reinforcement provides
adequate shear-friction steel. 

On small pump stations and junction boxes, I sometimes use Option 2 but with
an expansive waterstop. I like this detail but haven't yet made the jump to
extensive use of expansive waterstops in lieu of PVC waterstops on larger
projects. 

And on rare occasions I have used Option 1 with 6" PVC waterstop but with a
roughened joint and 4" clear at the top steel - mainly when the base slab is
of such thickness that extra cover on the top steel doesn't hurt the slab
design that much. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Michael L. Hemstad [mailto:hemstad.ml(--nospam--at)tkda.com] 
> Sent: Wednesday, June 16, 2004 3:29 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Keyway Details
> 
> We do a fair amount of wastewater and water treatment work 
> involving concrete tanks.  We go round and round about the 
> joint between the slab and the bottom of the wall.  These 
> joints need to resist shear and moment.  Basically we have 
> three options we keep arguing about.
> 
> 1. Finish slab flat, with keyway.  Put waterstop in bottom of 
> keyway.  1
> 1/2 inch key plus half a 6 inch waterstop makes 4 1/2 inches. 
>  Thus, either make the slab 3 inches thicker than needed and 
> hold the top mat down, or bend the bars down under the wall 
> (reducing their depth just where it's most needed).
> 
> 2. Finish slab flat.  Roughen under wall, dispensing with 
> keyway.  Use a
> 4 inch waterstop, touching the top mat; tie it to the inside 
> vertical rebar.
> 
> 3. Hang a 3 1/2 inch tall wall form, placing joint, key, and 
> waterstop up above the base slab.
> 
> I like option 2 myself; it's the simplest.  The wall will be 
> rough there anyhow because of the dowels sticking up in the 
> way of the finisher.
> Does anyone have any better ideas, or opinions on which of 
> these options is best?  Please weigh in with opinions and reasoning.
> 
> Thanks,
> 
> Mike Hemstad, P.E.
> TKDA
> St. Paul, Minnesota
> 
> P.S.  I've tried to send this several times.  By coincidence 
> I notice that the Digest was very short yesterday.  Has 
> anyone else had trouble sending to the List?
> 
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