Raft Foundation, Initial Sizing of Raft Slab

[Anonymous]

Hi Hi, 

I am building a model (of a building) supported by raft slabs; the intention is to do an initial sizing for the thickness of the raft slab. 

How do I verify whether a certain thickness of the raft slab is adequate to support the building? 

I have defined the raft slab for "type: bending + compression/tension", and input the Elastic foundation coefficient of the slabs Kz to various suitable values, I have run the Plate/Shell reinforcement calculation, most of the slabs have the cracking and deflection values exceeding the admissible values.

Do I thicken my slabs until there is no deflection and cracking issue? or is there other more accurate/correct methods to check whether the thickness of raft slab is sufficient?

any help is appreciated. 

Thank you

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

IMHO you should 'exclude' cracked deflection form the analysis as the raft foundation will only deflect as per displacement of soil below it according to KZ value you defined. In other words just check the displacements of the slab for SLS combinations obtained from the static analysis of the model. On the other hand you should make sure the cracks are within the specified limit.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Thank you for the help. 

[samih__ayad]

please sir can you answer my question .. raft foundation is defined as shell or plate ??? am confused because the reinforcement calculation is different between those 2

[samih__ayad]

and slabs is defined as shell or plate ??