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RE: Precast DT's & topping next to wall

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In the upper mid-west, the precasters seem to prefer Option #2, with vertically slotted inserts in the precast panels. With Option #1, I would think that cracking the flange would be a real possibility as LL increases. 

-----Original Message-----
From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net]
Sent: Tuesday, May 02, 2006 9:01 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Precast DT's & topping next to wall


Glen,

I would pursue option one with the additional pre-caution of bottom steel in 
the flange (or center steel) that has been checked for the potential reverse 
curvature as the flange tries to support the web instead of vice-versa. 
You may also look at providing some #3 hoops into the topping slab to 
prevent separation if the dowels are in the topping slab, or connecting the 
flange to the wall with the same weld plates you use to connect the other 
flanges.

Paul Feather PE, SE
www.SE-Solutions.net
pfeather(--nospam--at)SE-Solutions.net
----- Original Message ----- 
From: "Glen Underwood" <gunderwood(--nospam--at)clarkpac.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, May 01, 2006 10:24 AM
Subject: Precast DT's & topping next to wall


> We have a parking structure that uses long span precast double tees, with 
> cast-in-place topping, framing into cast-in-place shear walls.  At the 
> ends of the building, where the last DT runs parallel to the end wall (not 
> supported by it), we have a compatibility issue.  The DT is designed to 
> free-span the 60', but the diaphragm to shear wall connection is #4's at 
> 12 in o.c. doweled into the wall and cast into the topping.
>
> It seems there are two ways to approach this -
>
> 1.  Let the wall support the slab & DT flange, and check the slab to wall 
> connection for the reactions it would see to be sure it could carry the 
> load.  The trib width to the connection would probably be at least 1/2 the 
> full DT width (not just the cantilevered flange portion).
>
> -or-
>
> 2.  Try to allow for vertical deflection of the slab relative to the wall. 
> Use a bond-breaker, and either slotted inserts, or foam wrapped rebar.
>
> I do not care for option 2 - as I don't think it is realistic to design 
> and detail a proper connection that would both allow vertical deflection 
> but still provide a positive diaphragm to shear wall connection.
>
> This must come up frequently in precast construction.  Is option 1 the 
> common approach/solution?
>
> Glen A. Underwood, S.E.
> Clark Pacific
>
>
>
>
>
>
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