Raft Slab on Rock Foundation

[Ericson66]

I am designing a RAFT foundation for a RC vault. The raft measures 16m x 20m x 2m thick for the most part, the walls are 1m thick with the total design load(unfactored) 22MN. In checking punching shear, what are the parameters one should consider. Further is there a bending shear issue?

Regards,

 

[r13]

For raft supporting continuous wall, punching shear is out of the picture, just check one way shear at a distance d from the wall face is suffice.

Depends on the type and condition of the rock, the weight of structure might straight goes down to the rock through the walls, thus no bending will occur in the raft. But if the rock is compressible, then an analysis incorporating spring supports is required. Also, for an under ground vault, don't forget uplift due to ground water, which is another source of bending moment in the raft.

I don't know what is "bending shear", so no comment on it.

 

[rowingengineer]

If that is a point load then I would check punching shear. I would look to use a strut-tie analysis for determination of the required tension reinforcement, I would probably consider some fibres in the concrete to ensure good energy dissipation. I would also consider how this is going to be poured, 1m thick in ground has a lot of heat.

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