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RE: Tilt-up connections (UNCLASSIFIED)

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Classification:  UNCLASSIFIED 
Caveats: NONE

I have one of those Tilt-up Construction Association manuals that I loaned to
a friend so I don't have it in front of me right now but I think it shows the
wall anchored to a slab closure strip and not connected to the foundation.  

Just being devil's advocate here, but for a one story building if there is no
uplift and assuming that the shear can be taken out in the slab on grade with
a closure strip, why force a minimum positive connection to the footing? 

I could see having a minimum connection for a multistory precast building
where the connection to the footing transmits shear or overturning or you are
doing a blast design.    

-----Original Message-----
From: Jake Watson [mailto:jake.watson1(--nospam--at)] 
Sent: Wednesday, January 03, 2007 10:41 AM
Subject: Tilt-up connections

    ACI-318 05 has revised the precast seismic connection requirements.  The
new concepts on the surface appear to be well considered.  However, some
local firms have taken an interesting twist on them.  I generally anchor tilt
panels to the footing for a 10 kip minimum per the precast chapter,
regardless of the demand.  Now under the new provisions we will also make
that connection meet the new ductility provisions in chapter 21.  We were
doing this before with a slightly different philosophy, but it appears to get
very close to the same results.  

    A competing local engineer pointed out that the PCA Notes to 318 05 state
the ductility provisions and minimum connections don't apply to tilts.  SEAOC
and some letters to Stuctures Magazine feel anchoring to the slab only is a
bad idea in high seismic zones (say seismic design category C+).  Some local
firms will do an overturning calculation with an R of 5, determine there is
no net uplift, and only anchor to the slab.  How does PCA justify that
statement and is there any rational reason in ACI 318 to support it?

Jake Watson, P.E.
Salt Lake City, UT

Classification:  UNCLASSIFIED 
Caveats: NONE

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