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