A little more information is appropriate. Is this a ring foundation or a flat, cicular slab? What is the slab/ring supporting? It may be a simple task of evaluating the stress induced by the supported load and looking up a value in Roark's Formulas for Stress and Strain. If, on the other hand, you're looking for the stress in the soil I believe there are several texts on soil mechanics which deal with circular foundations (Bousinessq Method). If not, a text on elastcity will be helpful - check out Prandtl's stress.
Hi Qshake, This is a circular pad foundation for a 40m high lighting mast, with large overturning moment, shear and a small axial load. Any help would be appreciated but in the meantime will check out Bousinessq. Must find those old collage notes!!!
A quick look into Bowles Foundation Analysis and Design yields the following empirical procedures: Chu and Afandi (1966) "Analysis of Circular and Annular Slabs for Chimney Foundations" - Journal ACI vol 63 no 12 Dec. pp 1425-1446 and Smith and Zar (1964) "Chimney Foundations" Journal ACI vol 61 no 6 June pp673-700.
Again, if you're looking to designing the actual slab I would also look into Roarks. There are stress formulas for just about every imaginable configuration.
Why are you doing a circular foundation? A circle is an efficient shape for keeping as much material close to the center as possible but in the case of a cantilever mast foundation you want the opposite. It can be much more efficient to use a cruciform foundation or I suppose the most efficient would be a Y shaped foundation. There was some discussion on a footing for a telecommunications tower that I posted a question on a while back on this forum and you might like to look that up. Carl Bauer
Thanks for the tip. got the ACI documents (eventually - because our Admin staff wouldn't open the post as it came from America and waited until I returned from the States) and they contained just what I was looking for. Certainly will make life easier.
I need to review all methods of estimating the settlement under a thin circular foundation on compressible soil so as to compare the results with a more structural approach. I also need to find more info on the methods of estimating the stresses and moments in the foundation. Can anyone suggest?
