Required Minimum Section Modules of an Intermediate Wind Girder

Comments I have a question regarding the required minimum section modules of an intermediate wind girder for an API 650 tank.

The H1 in the formula of paragraph 5.9.7.6 API 650. Is that
a. the calculated transposed value from paragraph 5.9.7.1
b. the actual transposed distance between the girder under investigation and the girder/top above.
c. the actual distance between the girder under investigation and the girder/top above.


If it is C. What about is the effect if the spacing between two girders consists of shell courses with equal thicknesses or consists of shell courses with different thicknesses.


And if it is a or b
Example: you have two identical tank Tank A and B with both 3 wind girders. Of tank A the top course is 2 mm thinner than the top course of tank B. All other courses and spacing are identical. Top course is also the thinnest.Top intermediate girder on course below top course.

If Option a is correct:
So the H1 of formula 5.9.7.1 will be smaller. If you look at the lowest wind girder of tank A. This will need a smaller min. section modules then B. Even if the condition from bottom until top wind girder are identical for both tanks.

If option b is correct:
Even the actual transposed distance between girder 2 and 3 is lower. So also the required section modulus for tank A will be smaller.

Which H1 to use a,b,c?


Thanks in advanced.

Regards,

Norb