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RE: Inverted Key vs Starter Wall

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Maybe I do not understand this thread.  You are talking about a 2x4, or 2x6
key as has traditionally (at least in the past) been used at the bottom of a
retaining wall stem to footing?  If so, why not use shear friction at the
cold joint with the waterstop?  As we speak, I'm working on a circular
concrete water tank.  I'm getting Vu=4.7 k/ft.  Using the formulas for plain
concrete from ACI 318-02 a 2x8 Key in a 12" thick wall will not resist the
load (I get phi Vn = .55x12x7.25x(4/3)x sqrootf'c = 4.0 kips), but shear
friction works just fine.  Am I not understanding something here?  Please
set me straight if I'm wrong.

Thanks,
Joe

Joseph R. Grill, P.E. (Structural)
Shephard - Wesnitzer, Inc.
Civil Engineering and Surveying
P.O. Box 3924
Sedona, AZ  86340
PHONE (928) 282-1061
FAX (928) 282-2058
jgrill(--nospam--at)swiaz.com
 


-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com] 
Sent: Friday, March 31, 2006 12:02 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Inverted Key vs Starter Wall

I have used an inverted key a lot.  But never on a tank for the reasons that

you mentioned.  Of course the contractors would prefer an inverted key, but 
they will not be in the crosshairs if the tank leaks.  Some engineers will 
use inverted keys on a tank, I won't.  It is a serviceability issue and 
ultimately it is your call.

Regards,
Harold Sprague





>From: "Mark Urback, P.E." <murback(--nospam--at)ehrainc.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Inverted Key vs Starter Wall
>Date: Fri, 31 Mar 2006 11:29:50 -0600
>
>Our standard detail for a wastewater tank wall is to provide a starter
>wall on the slab with a key and PVC waterstop in the joint.  The
>contractor has proposed an inverted key using 1x4 form attached to the
>inside of the vertical rebar with a PVC waterstop at the top of the key.
>My concern with this method is that the base of the key is at the
>slab/wall interface.  If the key were to crack at the slab (where the
>bottom of the joint is located), there would be a potential water path
>because the water stop would be above the crack.  Has anyone used the
>inverted key and have there been any problems?
>
>
>
>Thank you,
>
>
>
>Mark L. Urback, PE
>
>Assistant Manager
>
>Public Infrastructure Services
>
>Edminster, Hinshaw, Russ and Associates
>
>10555 Westoffice Drive
>
>Houston, Texas  77042
>
>713-784-4500 ofc
>
>713-784-4577 fax
>
>713-202-1579 cell
>
>
>

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