Windgirder requirements for Open Top Tanks bigger than 200' diameter

[jafloresl]

Hello people.

This is my first post and it is about the windgirder requirements for an Open Top Tank.

D = 284’
V=200 mph
H=61’

Per 5.9.7.
Considering (course 1 is bottom course):

Max height of unstiffened shell:

H1 = 7.9781’ Using a Diameter of 284’
H1 = 13.5’ Using a Diameter of 200’


Number of intermediate Stiffeners (similar calculation as V.8.2.1)

N + 1 = Wtr/H1
N = 3.8161 – 1 = 2.8161 (rounded up)
N = 3 Using a Diameter of 284’
N = 2 Using a Diameter of 200’

L0 = 30.4457 / (3 + 1) = 7.6114’ Using a Diameter of 284’
L0= 10.1485 Using a Diameter of 200’


L0 is the spacing between stiffeners.


We require a Top Windgirder at 42” from the Tank Top.

A couple of questions about this, does the number of intermediate stiffeners from the API formula does not count the Top Windgirder? In other words, the number of intermediate stiffeners (windgirders) required will be the result of the N PLUS the Top Windgirder?.
I have the feeling that it is, because if we count the Top Windgirder in the total, the spacing for the intermediate stiffeners will be more than the max calculated with H1 (5.9.7.1).

And another one, as you have seen, I did te calculation of H1 and N using the real diameter 284’ and 200’ per the footnote of 5.9.6.1.

For Tank diameter bigger than 200’, do we need to consider 200’ (by agreement per customer and manufacturer) for all windgirder calculations (number required, max spacing, section modulus)? Or just for the Top Windgirder section modulus requirement?

Thank you for your help.

 

[JStephen]

I would assume the top wind girder is not counted as an intermediate wind girder.
I would assume that the actual diameter is used for the intermediate wind girder calculations, rather than the 200'.
Also, I believe the transformed height is the height below the top wind girder, so it wouldn't include the distance above that.