There is a very straight forward handbook published by AISI called "STEEL TANKS
FOR LIQUID STORAGE-STEEL PLATE ENGINEERING DATA- VOL. 1" The edition that I know
about is dated 1982, I'm sure that there must be a newer version. Lets face it,
what has really changed in foundation design in the last 18 years?
Perhaps you can contact The American Iron and Steel Institute (AISI) and see if
they have a more updated handbook.