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RE: wall

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> -----Original Message-----
> From: Joe Grill
> Sent: Tuesday, November 09, 2004 9:49 AM
> I tried to reply to this earlier this morning, but it doesn't
> look like it went through.  Basically, the wall is very high
> with a sloping backfill. The restraint loads to be transferred
> into to diaphragm were too large in my opinion to make a
> reasonable connection from the top of the wall into the
> diaphragm.  In addition, the diaphragm that I had to work with
> was not adequate for the imposed shear from the restraint forces.
> It would have caused a lot of headaches for everyone, especially
> me.  Therefore, I went with a cantilever wall.  Since most of the
> construction around here is CMU, I used a concrete stem for a
> portion of the height and then switched to CMU.
> The architect and contractor had ask if the concrete portion
> could be constructed of CMU.  I told them it would increase beyond
> a 12" thickness, but the still ask.  Hence, all my questions.

Potential problem here; if it's designed and constructed as a cantilever
wall it WILL deflect at the top, so the forces are transferred into your
floor diaphragm anyway.  Also, since you're restrained, you will have the
higher "passive" soil pressure instead of the "active" pressure typically
used for cantilever walls.

One option would be to require that the backfill be in place and compacted
before constructing the floor.  This way the majority of the deflection has
already occurred.

What I typically do in this situation is design the wall as a fixed-pinned
using passive pressure.  The base is fixed and the top is pinned. The force
transferred into the floor diaphragm is reduced to 1/6 of the total instead
of 1/3 for a pinned-pinned wall.

Jason Kilgore
Leigh & O'Kane, LLC
Kansas City, Missouri

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