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circular concrete plate floor

circular concrete plate floor

circular concrete plate floor

(OP)
5 years ago, we designed a 16m diameter reservoir concrete floor over 24 piles as a bi-directional plate slab. This thread is not about the piles, only about concrete design.

The piles are resting on rock and aligned orthogonally. Design was done by hand and moments double checked with a simple FEM form Advance Design America.

Now, similar projects has to be done for heavier load or larger diameter. The orthogonal distribution of piles is not as economic as for the first project in order to satisfy capacity of piles, symmetry and spans in the concrete slab. So I am looking for a radial disposition of the piles (3 or 4 concentric rings of piles). For example, with the new 18m diameter tank, the orthogonal disposition solve with 35 piles and a radial approach will only need 32 piles.

My first approach is to use radial and tangential rebars but I don't really know how to take account of the by-directional effect.

I know this is not a new problem so there is no need for a new solution.

Does anybody knows about a design example?
What as been done in similar projects in the past?

RE: circular concrete plate floor

A few years ago, I did a 160 ft diameter water tank supported by piles (528 I think). We did an orthogonal pile pattern except at the edge where they followed the tank exterior. I like radial and circumferential bars as I feel I have more control over the lengths, laps and spacing. I wouldn't get too refined over the bar direction, just how many you have at each support. The spacing over the piles is roughly orthogonal. And the curvature of the bars is very small, except toward the center.
The other thing I would advise is not to get too concerned over the number of piles or the reinforcing. Be conservative! By the time they mobilize, a few extra piles is pretty insignificant. Also consider that the installer has to lay out the pile and an orthogonal layout is easier (although I'm sure they can do either).
Also reinforcing and slabs on grade are pretty cheap. You don’t want to be wasteful, but sleeping at night is also important.

RE: circular concrete plate floor

Orthogonal layout and orthogonal bar layout are simpler.

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