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Re: FNDT: Shearwall and slab foundation question

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I would agree in the real world, but lets make some assumptions for the fun
of it. First, lets assume that the wire mesh is placed where it belongs and
extends down into the foundation or thickened edge of the slab. How much
tension is accumulated at the end or along the length of the beam to help
resist the uplift of the wall? Next, how much of the "returns" (considering
the foundation edge is continuious) can you consider if the slab edge
reinforcement is continuous and bent properly around the corners?
It isn't just a simple spread footing that we are trying to use as a
dead-man.
I'm curious since I would think that there is more capacity in the
continuous fndt and attached (monolithic) slab than we give credit to.
It was not uncommon to see HD8A's (or larger) used at perimeter foundations
without specifying more than the foundation wall or thickened slab edge. I
think that this was pretty well a conventional framing or undesigned
standard. I do not remember, while accessing damage after Northridge, of any
damaged foundations from either tension or compression chords of shear
walls. I did inspect plenty of damage where soil changes occured by either
upheaval from below or by liquifaction, but I could not attribute anything I
saw to exceeding bearing pressure by loading of the shearwall compression
chord. For that matter, the damage seemed to be restricted to the shear
panel or plate connection to foundation (many spit and skipped off the
foundation).
Dennis

-----Original Message-----
From: Tom Chiu <Tomchiu(--nospam--at)worldnet.att.net>
To: seaoc(--nospam--at)seaoc.org <seaoc(--nospam--at)seaoc.org>
Date: Wednesday, February 04, 1998 5:34 PM
Subject: Re: FNDT: Shearwall and slab foundation question


>For HD8 holdown, the allowable force is almost 8 kips, that means you
>would need , say a spread footing of 5' x 5' x 24" deep, if your actual
>uplift force in that wall corner is 8 kips. I don't think that
>conventional thickened edge even connected to the slab-on-grade with WWF
>will work. First, you don't have enough slab weight to counteract the
>uplift force. Second, the WWF quite often end up at the bottom of the
>slab without proper concrete cover and will rust and therefore
>ineffective.
>
>Tom Chiu, SE
>Thomas Engineering