foundation partly on soil and partly on concrete
foundation partly on soil and partly on concrete
(OP)
I am designing a foundation which rests partly on soil and partly on a existing concrete foundation. I am modelling it in Staad pro. I know the modulus of subgrade for soil. My question, how should I model the portion of foundation slab on the existing foundation? What are the constants that I may require at this stage?. Useful suggestions are welcome and appreciated. Thank you.





RE: foundation partly on soil and partly on concrete
Bottom line is that before anyone could help here, we'd need to know a lot more about the structure and the existing concrete.
RE: foundation partly on soil and partly on concrete
Well, the foundation is for a pipe support. There are 4 points of loading on it. The main load is a 56 kips couple at 2 pairs of supports. These 4 points rest on the foundation. There is an existing foundation close by and part of the new foundation requires to be laid on it(old fdn). Preliminary size of fdn is 11'x 16'.
RE: foundation partly on soil and partly on concrete
Make sure that you do not overstress the soil under the existing foundation. Do you plan to just pour over the existing foundation or dowel into it? You may also provide some sort of compressible material to isolate the new footing from the existing.
RE: foundation partly on soil and partly on concrete
Well, here's what I did. The portion of the foundation on existing foundation is anchored. The peripherial portion of the new fdn is connected to the existing fdn by driving anchor bars. So, I defined those support points as fixed in my model and all the other interior supports as pinned. I defined spring support for that portion of the foundation on soil. I could notice that the pressure experienced by soil was very low which meant that the foundation behaved as a cantilever. I adequately provided reinforcement for the maximum bending cantlever moment. Assuming that there may not be cent percent fixity, I reinforced the bottom portion of the slab too with the same reinforcement.
I believe this was the best approach I could utilize, but would certainly like to know your views for this case.
Appreciate further discussions.