Bearing capacity of a grade beam and raft foundation

[LucaCSM]

Hi to everyone. I would like to know a reasonable way to calculate the bearing capacity of a grade beam, using a spreadsheet. Obviously, it would be better to perform the analysis with a FEM software but, for a two-storey building I think it's possible to use a spreadsheet.
If I have the vertical load, the bending moment and shear parameters for every singular column can I calculate the resultant forces, then the eccentricity and finally use as imput data the resultant vertical load, moment and shear acting on the top of the grade beam foundation BxL?
What's about a raft foundation where I have manifold loads?

PS: the design approach is according to the Eurocode 7 and 8.

Thanks very much in advance for your help
LUCA

 

[ishvaaag]

To dimension the beam itself for a given set of support (compression only) springs commensurated to the width you need to program in the worksheet the effects of moments and vertical loads. Along the foundation beam forces you can make a centered axial set of forces and more moment action, but usually this is scarcely considered. Then use the principle of superposition and add the effect of the standing loads for the projected beam on elastic foundation.

Please be more precise if you want us to expand more on soil things proper.