deflection of circular tank walls

[oneintheeye]

does anyone have an approach for calculating deflections in the above? Normally i would use span/depth checks as cantilever but I am appraising an existing design.
I also know that the ACI recommend a min wall thickness of 12" (300mm) but no such recomendation exists in British codes (that I can find) anyone have a comment on this?

Cheers

 

[csd72]

Doesnt it become a ring tension, thus the calculation is one of axial elongation rather than bending?

 

[JStephen]

See Timoshenko's "Theory of Plates and Shells" or the circular shell formulas in Roark's "Formulas for Stress and Strain" or other similar references.

The situation is similar to a beam on elastic foundation, with the "elastic foundation" being furnished by hoop stresses in the shell.

 

[oneintheeye]

yes, your right, subject to depths, radius etc.

 

[Ussuri]

BS8007 doesn't explicitly give a minimum thickness. It does say for wall slabs less than 200mm all the reinforcement should be in one face. However, the table of T1 values only starts at 300mm thickness, so read into that what you will. EC2 doesn't appear to say anything either. BS8110 allows quite thin walls, which are dictated by fire resistance requirements (not applicable here).

I would say that your span to depth approach is not applicable for circular tanks. If your base joint is detailed as sliding then deflection is due to ring tension only. If it is fixed or pinned it is a combination of ring tension and bending. The restraint at the bottom causes rotation at the top.

You might be able to get something in Roarks, with some fudging. Alternatively the PCA tables for rectangular tanks has coefficients for approximating deflection. IO do not have a copy of the PCA tables for circular tanks but they have the same thing. I'm sure some of our US based members can confirm that.