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Re: Tilt-Up

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Walter,

I do consider tilt-up panels as "shearwalls" and I evaluate every little segment of concrete as a shear element based upon its in-plane rigidity.

The term "Wall Pier" is a code definition that applies to tilt-up panels when you have panel segments that are too short to be defined as shearwalls and too long to be classified as columns. It is a length/unsupported height to thickness of concrete ratio. Walls piers, basically require you to create a vertical beam, with stirrups, cross ties, and maybe even hoops to resist the concentrated shear and moment and remain ductile because you are essential relying on frame action of the panel when there are big openings and small legs. If you have it, check out 1997 UBC sections 1921.6 for the definitions of the various types of "shearwall" you need to consider. 

I'm not sure with what code you are trying to comply with (if any), but it simply wouldn't work in the US in seismic zone 4 and probably not in seismic zone 0 if you are using WWF as your primary reinforcing. It sounds like you have the ability to do testing and go with the results. I would be very cautious on relying on any data that is not collected under a CYCLIC testing protocol. Pushing concrete until it breaks is a lot different when you push and pull on it a bunch or times at much lower loads.

Because you are talking about platform framing with tilt-up panels, this is similar to wood framed residential construction procedures in the western US. Look there for many construction techniques that may be cost savers b

Engineering wise, stacking walls could be accomplished if you use a closure strip (cast in place) to lock together exposed rebar from the already cast panel to transfer shear but you would need to support upper panel until the strip is set.

I think your only possible approach is to use two story bearing/lateral tilt panels where the top of the panel runs a few feet beyond the second floor. Then use lateral only tilt panels above that with a closure strip to lock it together. You may also need a vertical closure strip ( or cast in place pilasters) at each end of each panel to take care of the bending at the edges and develop the trim bars. WWF absolutely cannot be relied on to transfer anything from panel to panel.

These are simply force transfer options. In the US and other places, we also have to follow detailing practices to ensure ductility. Confinement in splices, extra development lengths, staggering of splices, additional ties etc... If you look at most of the collapsed building in Turkey and India from the last two big earthquakes, you will see very little confinement steel in the concrete if it is even there at all. Confinement is the key to everything in keeping concrete ductile.

-gerard
>>> wsp(--nospam--at)terra.com.pe 06/08/01 09:56AM >>>
Hmm,

If I understand correctly, you don't consider tilt up walls as shear walls?
If this is right, then I should forget tilp up.

What I want is concrete shear walls and concrete slabs, but somehow I want
to avoid the forms, that's why I thought about Tilt-Up.

Thanks,

Walter
----- Original Message -----
From: "Gerard Madden" <GMadden(--nospam--at)mplusl.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, June 08, 2001 11:35 AM
Subject: Re: Tilt-Up


Hugh,

Thanks for the links.

I don't see the economy what so ever for anything bigger than 2 stories in
Seismic Zone 4. Two stories generally means office use with maybe some
warehouse. Office means lots of windows which means lots of wall piers. Lots
of wall piers mean lots of steel in a small area. Lots of steel mean thick
panels to try to reduce the steel and to actually fit all the bars required.
The mass of two floors or more than two floor requires that you use panels
no less than 9" thick at the lower levels if you have at least one solid
shearwall per (or several long chunks of wall). The bearing of tilt panels
can be accommodate with pilasters and thickened ledges. It's the in-plane
capacity that is the problem. Steel braced frame is the way to go for 3-8
story buildings and dual systems above that for high seismic regions. Any
concrete building taller than two stories should be shearwall , moment
frame, or dual.

Collectors are very difficult to get to work in just 1 story buildings that
utilize high load wood diaphragms to deliver seismic. Trying to get 175 kips
to drag into a 9" thick panel is very tough.

Walter, have you looked at the option of Reinforced CMU masonry
construction. It is very conducive to economy when labor is plentiful.

-Gerard
>>> HBAP(--nospam--at)aol.com 06/08/01 07:43AM >>>
The 5th Edition of The Tilt-Up Design & Construction Manual covers the '97
UBC. It is now published by the Tilt-Up Concrete Association (TCA) and a 6th
Edition is planned to debut at TCA's biannual tilt-up design/construction
symposium in Washington, DC, in September. For more information visit
www.tilt-up.org and www.tilt-up.com. Three-and four-story buildings are very
common with full-height tilt-up and panel thickness is little affected since
floors provide lateral support. You can see illustrations on the above
referenced Websites.
Hugh Brooks, SE


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