Solar Accumulator Tower Slab Construction

Solar Tower description:-

I am building three solar accumulator towers in which the core material is built from local dark-coloured stone recovered from a ruin which I demolished.

Each core must be insulated from the ground slab beneath it, as best possible and at the same time, successfully support the weight. The stone-built core has a plan cross-sectional dimension of 1mtr X 1mtr and a height of c.2.5mtr and is built upon a reinforced concrete slab of same plan dims., underneath which and supporting all, I have my problem.

One idea that I have is to support the core with four groups of tightly strapped, empty stainless steel tubes set in the base slab, near each corner of the core and set in another, larger base slab under ground leaving a horizontal cavity between them.

Channeled air will enter the cavity between the larger, last mentioned slab, and the core support slab and rise by virtue of convection on all sides of the core (all housed in a double-glazed construction). The cavity will have a height of c.20cm.

My question is:

How do I strike a successful compromise between the following parameters?

1. Cost of number of ordinary grade stainless steel tubes;
2. wall-thickness and tube diameter against number of tubes in total over the four groups under each tower;
3. giving sufficient support strength in a seismic zone (southern Portugal);

I know how to calculate the cross-sectional area of the steel to support a given weight but I do not know what the figure is for this grade of steel to use in the calculation.

Any body that can seriously help will welcomed to a visit to my low energy house!

ROBIN MARSTRAND