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# overturning stability for a fixed roof tank

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## overturning stability for a fixed roof tank

(OP)
Hi all,

I am going to calculate the OVERTURNING STABILITY for a fixed rood storage tank (supported roof).
In section 5.11.2 (API 650, edition 11), we see:

MDL = moment about the shell-to-bottom joint from the weight of the shell and roof supported by the shell

can anyone tell me how I assume the weight of roof supported bye the shell?

we have roof plates and roof structures ( rafter+girders+column).

Thanks all

Replies continue below

### RE: overturning stability for a fixed roof tank

Normally, you're designing the roof structure along with the rest of the tank, so you pull those numbers off your roof structure design.

If you know the geometry, figure the loading on each rafter is equal to the spacing between rafters (which varies along the length) times the plate weight plus the rafter weight, and treat the rafter as a simply-supported beam with trapezoidal loading.

If you're checking for stability, try doing the calculation without including the roof weight.  If it passes like that, it won't matter what the roof weight is.

### RE: overturning stability for a fixed roof tank

(OP)
JSteph

I got it. but I think i have to calculate the detail information of rafter, girder and column.

many thanks again

### RE: overturning stability for a fixed roof tank

Hello fellow I sum 50% of the last rafter (support for the shell) and weight of roof plate support for this rafter.

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