Hi All,

Here's some information for you regarding the tank design.

The Development Technology Unit at the University of Warwick has a
good report called
Recommendations for Designing Rainwater Harvesting System Tanks
http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/reviewed/rwh/eu/a6.pdf
You should all take a look at it.

The stress analysis you need to do for the tank is described in pages 8-11.
You need to solve the hoop stress, bending stress, and shear stress
equations on page 10 and generate the stress curves shown on page 11.
I recommend putting this into a spreadsheet, so that you can try
different tank dimensions (height, radius, and wall thickness) and see
which design has the lowest stresses.

I have been reading through a lot of the tank design literature and
there is a general concern that brick (or stone) masonry is not well
suited to large volume tank construction because it
has a poor strength in tension.  Having an extra thick wall as
proposed will help, but we'll have to see if it is enough after you do
the calculations.

There are a also a few other options to address this concern:
One option is to add external reinforcing with steel packing straps
The Development Technology Unit at the University of Warwick has a
good instructions for this at:
http://www2.warwick.ac.uk/fac/sci/eng/research/dtu/pubs/tr/rwh/tr-rwh02.pdf
It would be good to check with Jean Paul to see if it is available there.

Another option is to construct the tank out of ferrocement. This is
very good material for tank construction according to the literature.
There is a good reference on this at:
http://www.itacanet.org/eng/water/Section%205%20Tanks/Ferrocement_water_tanks.pdf

If you want to meet again to discuss some of this before next
Thursday, just let me know.  I have a work meeting the evening of the
12th though, so I can't make your regular meeting.  In the meantime
feel free to email me if you have any questions.

-Mike