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RE: Precast DT's & topping next to wall

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	Glenn,
		No. That does not mean Option 2 is the best approach,
though.
		In you case, with a CIP wall, I like Option 1. I would
have the CIP subcontractor hold the shearwall down a foot and extend the
double tee flange 6" over it. Then, the #4s can be bent down (around a
pipe for proper radius) and when the topping is poured the top of the
wall can be completed.
		We usually use P/C shearwalls and "pretopped" - that is
full-thickness flange - double tees, and connect between them with PSA
slotted inserts from JVI if they carry enough load. When they do not we
tend to end up with a long loose plate welded to a lot of inserts - or
maybe a series of them to help adjust for tolerances, though this can
develop more local moment. An angle welded below can support the flange
edge though not as well as pouring beneath it.
	Jim Getaz
	Chief Engineer
	Shockey Precast Group
	Winchester, Virginia

-----Original Message-----
From: Glen Underwood [mailto:gunderwood(--nospam--at)clarkpacific.com] 
Sent: Monday, May 01, 2006 1:22 PM
To: seaint(--nospam--at)seaint.org
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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