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Re: Concrete Column Footings

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seaint(--nospam--at),Internet writes:

I have a 20' concrete column that is only supported by 7'X7'X3' footing.


  Is it sufficient to use the moments at the bottom of the column for
finding footing bearing pressure, or do I need to add the footing thickness
to the moment arm?

Chris Towne, E.I.T.

No, that would underestimate the bending moment at eh soil surface. 
Overturning/bending is about the bottom surface of the footing, not the top
surface/bottom of column.  That is where the soil stresses occur.  If you use
the moment at the bottom of column/top of footing then you need to add an
addition moment caused by the horizontal shear force with a moment arm of the
footing thickness.

Richard Lewis, P.E.
Missionary TECH Team

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.