Raft Foundation Design

[ali.safiaddine]

Hello there,

I am designing a raft foundation usign autodesk robot 2014 and i am facing some problems

First question:

Whats the difference between defining the stiffness of the soil Kz in the thickness of the plate or as a support?

2nd question:

what is the proper way to define the soil stiffness as a support? is it defining it as a Uz support at different points at a certain distance??

Third question :

when defining Kz in the thickness of the plate, after running the analysis a warning message appears "no supports" is it ok? if not what is the proper support to define for a raft foundation?

Thanks in advance,

Ali

[Rafal.Gaweda]

Whats the difference between defining the stiffness of the soil Kz in the thickness of the plate or as a support?

First option - as a results you get soil reaction map.

Second option - as a results you get nodal reactions

what is the proper way to define the soil stiffness as a support? is it defining it as a Uz support at different points at a certain distance??

Your choice but I suggest first option mentioned above

when defining Kz in the thickness of the plate, after running the analysis a warning message appears "no supports" is it ok?

 it is OK, but remember to block UX, UY displacements somewhere

[ali.safiaddine]

ok great answers for my questions thank you

I am facing another problem, when calculating the required reinforcement a calculation status appear "incorrect material"

the file is attached

Thank you,

Ali

[Rafal.Gaweda]

C30 is a timber material

Use C30/37 or any other concrete.

[marios_karipis]

From where can i block the ux and uy displacements?

[Rafal.Gaweda]

Displacement can be blocked adding relevant supports but if it is not the case please explain what you mean by your question?

[marios_karipis]

i want to design a raft foundation with beams of a steel structure. I assigned the elastic foundation coefficient kz. Do I have to assign planar support on the slab with fixed directions ux and uy?

[Rafal.Gaweda]

I suggest to do so at least in one node (somewhere in the center) or in panel corners or in case having no lateral loads, nor seismic, you may not apply such support(s)