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RE: Tilt-Up Walls as a Seismic System

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I went to a tilt-up seminar put on by T.C.A. a couple of years ago.  I suggested that the code implicated that the connection to the foundation (at strength level) be check for the omega force level.  I was told, "Yeah, nobody does that.  Next question."  Nice.
 
Mark Pemberton, S.E.
Pemberton Engineering

Jake Watson <jwatson(--nospam--at)utahisp.com> wrote:
318-99 Talks a lot about "monolithic emulation", those provisions were meant
for frames. Many people tried to extend them to tilt, myself included.
Until I read an article about their origins. If you have tried using those
provisions as a backdrop to the '03 code, ignore them.

When you select an R value in the '03 IBC, it sends you to a specific
detailing section in ACI. Look at the table in Chapter 16. It will send
you to a specific section for the R you select. In my opinion, you can use
weld embed if they are detailed appropriately. When I do these connection,
I try and make them meet the following criteria:

1-Make the connection strong enough to yield the wall (impossible 99.99% of
the time.)

2-Design the connection for the "Amplified" load case (Omega), then detail
it to fail with a ductile steel element. This is much easier said than
done. I usually end up with hairpins around headed stud anchors in the
wall. The embed otherwise will fail by concrete fracture (brittle). You
then need to make sure the embed in the footing is good for about 1.5 yield
of the connection in the wall.

Say you use two #4's as hairpins in the wall. Yield is then 1.5*60*.4=36
kips. That is the force you use to design the embed in the footing. Which
again, should be governed by yielding of the headed studs, not breakout.

This is my approach, and I admit to being in the minority here in Salt Lake.
The vast majority of people here don't go to nearly this much trouble. But
I firmly believe these connections must be ductile. The wall itself won't
yield. And if the wall won't yield, where is the energy dissipation?

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

-----Original Message-----
From: Paul Crocker [mailto:pcrocker(--nospam--at)reidmidd.com]
Sent: Tuesday, October 26, 2004 5:48 PM
To: seaint(--nospam--at)seaint.org
Subject: Tilt-Up Walls as a Seismic System


What lateral system designation are people using for tilt-up wall panels
under the IBC? For seismic design category D, it appears that ordinary
walls are not permitted. It would be easy enough to reinforce tilt-up as a
special wall, except for the foundation connections. Welded embed plates
appear to be outside the typical wall detailing. ACI 318-02 in 21.13 talks
about some detailing for something called "intermediate precast structural
walls". The term intermediate is not something that the IBC applies to
shear walls, they are either special or ordinary. I know that tilt-up is
still being used in seismic country, so I assume that the R factor and the
detailing requirements are coming from somewhere. Can anyone shed any light
on how this is done?

Paul Crocker, PE, SE


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