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Re: Precast DT's & topping next to wall

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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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