Sathya R
Not much information in your question.
For FRP (or GRP in Europe) implying a glass and resin structure
the design codes are BS4994 and ASME RTP-1.
As an alternative (not helpful) try EN13121.
What was the tank originally designed to?
Brackets can be designed by FEA based on data gleaned from
a standard ie stain, stress and Modulus.
Trust this helps.
Ed Clymer
Resinfab & Associates
England