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Vertical stiffener to resist buckling

Vertical stiffener to resist buckling

Vertical stiffener to resist buckling

Here is the situation:

API 650 (new construction) open top clarifier tank (98' diameter x 35' tall)
There is a complex platform and walk way that is supported by the shell and a center tower structure
In one area of the shell, additional aeration boxes are also being supported. This is putting about 17,000 lbs in 4 places, in addition to other loads.
Total shell loading in a 45° section of the shell is about 75,000 lbs.
I have run FEA on the shell and it will not carry the loads. I am seeing local buckling failure (not global) about 2 feet above the first and second ring joint. This is the location where I have a thickness change from 0.475" to 0.335".
All rings above the 1st shell course are 0.335"

Possible solutions I have thought of:
1. Column support the aeration boxes by adding columns inside the tank.
2. Add vertical stiffeners on the outside of the shell. I would stop these about 1 foot below the 1st to 2nd shell course seam.
3. Call Ghostbusters

What is the communities thoughts about option 2. It is certainly the easiest solution to this problem. I have lots of internals to miss or rearrange if we go with option 1.
I am concerned that the vertical stiffener may not let the shell grow with the liquid load. My gut tells me that as long as I do not tie it into the bottom, it should move just fine...but need a second opinion.

RE: Vertical stiffener to resist buckling

Either solution could be used. There may be weld-spacing restrictions on the stiffeners in API-650. A solution that didn't require FEM would be preferable if other things were equal.

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