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Re: Increasing Bearing Capacity - Case Study

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I agree with you 100%.  It seems to me that the design engineer is
applying standard practices to a non-standard situation.  

> 1. The angle between the column base and the side of the enlarged
> footing, thus the radial steel, was too small (13° instead of 45°) to
> work as a truss and that the load would be transfered to the old
> footing.

The angle is too shallow to even begin to engage the added footing.

> 2. The soil underneath the old footing is more "rigid" than the
> unconsolidated soild underneath the enlarged part of the footing thus
> making the old footing more stiff and prone to take up much more of the
> load.

Absolutly! A soil that has been loaded for so long has a greater
capacity than the soil that has been disturbed to support the added

> 3. Adding to the above that the old and new footings are not
> interconnected makes predicting the behavior of this composite footing
> very hard.

If you know the compressibilty of the soil, can't you model it using
spring supports?

> Well my arguments were ignored and the footings were enlarged. This was
> facilitated by the fact that the client did not mind the extra costs.

If this is already built, is there anything that you can still do about
it?  Anyway, your first assumption that the original footing can take
the load is valid, and that's probably what is going to hold the
building-up with the added loading.

> I would like to get some opinions on this footing enlargement. So if
> anyone is interested, I could email an AutoCad file with the sketch
> since it's not easy to visualize my description of the enlargement
> scheme.

Please send me the Acad file.

Janah A. Risha, S.E.