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# Re: Foundation A.B. Capacity

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Foundation A.B. Capacity
• From: Jake Watson <jwatson(--nospam--at)inconnect.com>
• Date: Tue, 20 Jul 1999 20:01:43 -0600

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Seaintonln(--nospam--at)aol.com wrote:
>
> Jake, here is some comments:
>
> 1. Typically, the concrete will fail before the steel does. I am not sure
> what type of foundation you have, but the deeper the embedment, the larger
> the cone (concrete cone failure). If you are considering a stem wall for a
> raised foundation, your capacity should not (in my opinion) consider the stem
> as helping to resist the tension. I would develop the capacity in the footing.

I agree with you, but here is the exact problem:

8" FNDN Wall
4" Edge Distance (2 sides) ed = 4"

12" Embedment (le = 12")
Projected area = 106.4 in^2 (Ap), this has taken into account that the
wall is only 8" thick (I truncated the shear cone).

Therefore, phiPc = (0.65)*(1)*(4)*(106.4)*(2500^(1/2)) = 13.83 kips

Edge distance reduction, (13.83)*(4/12)*(4/12) = 1.54 kips

30" Embedment (le = 30")
Projected area = 251.32 in^2 (Ap), this has taken into account that the
wall is only 8" thick (I truncated the shear cone).

Therefore, phiPc = (0.65)*(1)*(4)*(251.32)*(2500^(1/2)) = 32.67 kips

Edge distance reduction, (32.67)*(4/30)*(4/30) = 0.58 kips

See the dilema?  Note the edge distance reduction seems to overpower the
increase in depth.  Because it is on two sides, the reduction must be
taken twice.  As a side note. This also happens with only 1 truncated
edge, but not to the same degree.

> 2. This generally means designing the footing of the all to resist bending so
> as to distribute enough load into a rectangular foundations to allow for
> sufficient concrete to act as a "deadman" before failing as a beam.  Although
> this is starting to get a bit beyond my talents (since I would have created a
> deeper deadman type resistance for the anchor) I would assume that you can
> use the stem of the foundation wall and model the foundation as a "T" section
> in bending.

I have designed the footing / foundation wall as a grade beam to
compensate for the uplift.  The real problem is getting the forces into
the foundation in the first place.

Can anyone see a flaw in my logic (or bad math?)

Thanks again,
Jake Watson, E.I.T.
Salt Lake City, UT

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