Hi i would like to ask the following:
when i have to insert inputs for Seismic data for bottom plate thickness,min.yield strength of bot.pl. and min.yield strength of weld material should i use annular plates characteristics or bottom plate's.Thanks

Bottom plate.

Thanks for your quick reply.Another thing I want to ask is that Tank calculates seismic requirements only according to mapped ASCE 7 and site specific methods.What about sites not defined by ASCE Methods?

See Section E.4.3. If you have 11th Edition Addendum 1, check out the Commnetary Section EC.4.3.