Unanchored Tanks Uplift Criteria - API 650 12th Edition

[sajk14]

Hello all,

Looking at API 650 12th Edition............The uplift criteria for unanchored tanks has yet again been changed.

Clause 5.11.2.1 states that Unanchored tanks need to satisfy criteria:
1) 0.6Mw + Mpi < Mdl/1.5 + Mdlr
2) Mw + Fp(Mpi) < (Mdl + Mf )/2 + Mdlr
3) Mws + Fp(Mpi) < Mdl/1.5 + Mdlr

Clause 5.11.2.2 then follows on to say that unanchored tanks with supported cone roofs (i.e. where the roof plates are resting on and supported by an internal roof structure ) shall satisfy the following criteria:
Mws + Fp(Mpi) < Mdl/1.5 + Mdlr...note this is the exact same formula as criteria 3) shown above.

Am i therefore correct in making the following statements:

If you have a cone roof tank where the roof plates are supported by an internal structure or columns you only have to carry out uplift criteria calculation 3) and criterias 1) & 2) do not apply.

If you have any other type of roof such as Floating roof, Dome roof or a self supporting Cone roof you must carry out and satisfy uplift criteria calculations 1) 2) and 3).

Thanks

 

[mariog123]

The new rule allows the designer to ignore the uplift force on structurally supported conical roofs.
I cannot say it is something to be supported by engineering. Why ignore the vertical uplift on a supported cone roof, but not on a supported domed roof or self-supported dome roof? In addition, they maintained 5.10.2.3, "Structural Member Attachment: Roof plates of supported cone roofs shall not be attached to the supporting members unless otherwise approved by the Purchaser", hence the structural members have nothing to do with the wind uplift exerted to the roof plates.

That is, you have to follow the rules!

 

[mariog123]

In the previous post, when I written "uplift force" I referred to wind uplift, due to suction effect on roof.

 

[IFRs]

sajk14 and mariog123 are correct - uplift is not included for normal cone roof tanks. It is supported by experience.