How Can I get the equivalent uniform thickness of the tank sheel?

[BOGO PARK]

According the API 650

Ti (impulsive period) calculation need the tu;equivalent uniform thickness of the shell

But they don't explain how can i get tu ( equivalent uniform thickness of the shell).

Is any one know that??

plz, help me.

thank you

[KP SAHU]

Pl note that weightage has to be given to the distance of shell courses from top surface of liquid, I send you a formula for that, pl wait