slab load on pile caps

[amazing azza]

Hi guys, a question...

I have a piled foundation consisting of - pile sets, caps and a grade beam that goes around the perimeter. Inside the sandbox formed by the grade beam, sits the slab. The slab is to be entirely within the grade beam, thus imposing no vertical load on it. There are no connections between the slab and the grade beam. The slab is supported mainly by grade, but it does overlap the pile caps.

Diagram below. This is a section of a portal frame, only foundation elements and slab are shown:

Question:
1. Should the pile groups be calculated to bear a portion of the slab load?
2. What portion is that?

 

[hokie66]

Looks like just a slab on grade to me. I wouldn't worry about the slab on grade loading the deep foundation.

 

[amazing azza]

hokie66,

Wouldn't the slab load transmit though the thin strip of soil to the pile cap?
Also, if the grade settles, at extreme case the slab would be supported at two points - the cap (via the soil strip) and somewhere along the settled grade?

 

[MIStructE_IRE]

In theory - possibly.

In reality, I wouldn’t sweat it. Like hokie I’d probably ignore it to be honest.

As for settlement question - if you’ve that degree of settlement there are bigger problems. If the slab was sitting directly on the pile cap then yes I’d consider this. But not in this case.