Storage tank strength

Hydrostatics & materials strength isn't my area - but just a thought: you haven't said where this is to be used - is there any danger of the water freezing?

Neglecting rotational and radial restraint at the bottom, the stress of a cylindrical shell under hydrostatic pressure is a pure tension varying from 0 at the top to pr/2t at the bottom where p is the pressure, r is the radius and t is the thickness.

If you wish to calculate the bending moment at the bottom due to continuity with the bottom of the vessel, you would need to consult a book such as "Theory of Plates and Shells" by Timoshenko and Woinowsky-Krieger.

The safety factor depends on what you assume to be the strength of the material. For glass, it is quite variable. For acrylic, I have no idea what it is.

Sorry, the ring tension is pr/t, not pr/2t.

Ahhhhhhhh - The Great Timoshenko; I was going to suggest his work as well.

The exact solution that you are looking for is on page 486 (2nd Ed.) of "Theory of Plates and Shells" (one of the classics). It is much too involved to detail here - you should obtain a copy, perhaps from your local university library.

Note that bracing along the top edge is really only required for rectangular tanks, or open round tanks subject to wind, or closed tanks subject to pressure. If your tank is open to atmosphere and there are no other loadings, other than pure hydrostatic, such as wind or nozzles, then the upper edge should be fine (there is no pressure/force on the upper wall edge). Picture the bottom half of an hour glass if you will, that is the approximate shape the walls will try to form with the greatest displacement near the bottom). The problem area will be on the lower edge in accordance with Timoshenko's bending moment formula.