Circular footings 2

[tvanniekerk]

I need mathematical methods for determining the bearing stress of a circular footing where the overturn moment is the dominant factor. If the foundation is starting "lift at the heel", ie the whole surface is not in contact with the soil, the geometry of the footing rapidly changes as the contact reduces, thereby constantly changing the contact area, hence bearing pressures increas sharply, but not linear. I am using empirical methods at the moment, but would like confirmation by way of mathematical methods.

 

[Focht3]

How are you modelling the soil? If you are simply using a bearing pressure, then you should try using a (one way) Winkler spring approach. Talk to your geotechnical consultant - he/she should be able to provide you with a range of values to use.

A Winkler spring model (used in a 3D structural analysis of the elevated water tank) will tell you very quickly if you have a stability problem...

A closed form solution doesn't exist - at least not as I understand your question.

 

[Ron]

Check the API tank overturning stress variation equations. Those will likely apply to your situation.

Otherwise use a specific modeling approach as Focht3 described.

 

[TYL]

Try API RP2A this covers circular foundations in all respects and has some useful references

 

[tvanniekerk]

Thanks for the info, where do I get this API RP2A? I am from South Africa, and have not come across reference.

 

[Focht3]

API - American Petroleum Institute. Check with the local universities that have classes covering offshore design and construction; it should be in their library. If not, contact someone with Exxon, Shell or BP in your area and try to borrow a copy. If all else fails, contact API.

 

[euygar]

Do you mean a circular mat or plate by saying 'circular foundation' ? How large is your foundation ? I know that for industrial process tower bases and for chimneys this type of foundations are used commonly. You can find some closed-form solutions for such systems which are based on the analysis of a circular plate on an elastic foundation. I can suggest you to have a look at the practical methods provided by Chu and Afandi (1966) and Smith and Zar (1964) which both employ empirical procedures.

Eris Uygar