API 650 Section F.7.5

[Leinster]

In API 650 section F.7.5 states that;

"The counterbalancing weight, in addition to the requirements in 5.12, shall be designed so that the resistance to uplift at the bottom of the shell will be the greatest of the following:
a. The uplift produced by 1.5 times the design pressure of the tank (minus any specified corrosion allowance) plus the uplift from the design wind velocity on the tank.
b......

In equation form I read this as.

Mw + (1.5*Mpi) < MDL

This is always going to be greater than the equation in section 5.12 of;

0.6Mw + Mpi < MDL/1.5

If section F.7.5 is always to be considered for the overturning moment why is it not the governing calculation in place of the 5.12 as it will always be the greater of the two?

 

[JStephen]

The weight in the first case includes foundation weight. The second case is for overturning of an unanchored tank and does not include foundation weight.

 

[Leinster]

Thanks JStephen.... That makes more sense.