You are looking for weight supported by the tank roof or shell that adds to the overturning resistance. See section F.1.2 for the context. Basically structure that is supported by the tank bottom does not count because of the flexibility of the bottom plate. All else counts.

Thanks for the reply IFR, I presume you are referring to the equation for DLR?

So DLR would be the roof plates and attachments to the roof plates such as nozzles, dip hatches etc. as well as any attachments to the shell such as staircase, nozzles etc? I presumed it does not include the roof rafters as this is coverred under DLS.

From what you have stated above I would take it that DLS is then the weight of the shell and roof rafters but not shell attachemnts. Please advise?

Any comments on the other calculations?

I was not responding to the direct question, my bad.

Appendix F defines DLR and DLS as including the weights of the shell, the roof plate and structural components. It is silent on including appurtenances, stairways, nozzles, etc. It would be your judgment to include these but note that they act locally while the other weights are uniformly distributed. Failure tends to occurs locally, at the highest stressed place, where there is the least resisting weight.

In F.4.1 we are looking at maximum pressure determined by the ability of the roof-to-shell junction to resist inwards force that the roof plate would exert on it after the roof's self weight was exceeded by the internal pressure. In this case, logically only structure that was attached to the roof or supported by the roof would be considered, and that is how DLR is defined. Could you include nozzles, etc? I think not because they are not present everywhere and the lightest portion of the roof would lift first and locally stress the top joint to failure.

In F.4.2 we are looking at maximum pressure determined by uplift at the base of the shell so it includes DLS and DLR which together include shell, roof and structural supported by the shell or roof. Could you include the total weight of the tank and all it's appurtenances here? I don't really think so, for similar reasons as above, except the failure is at the corner weld instead of the top joint.

I hope this helps understand what I think the equations are being used for, but please note that these are my opinions only and your engineering judgment should be your best guide. The code can be read pretty literally most of the time, each word is important and there is no extraneous information to confuse the reader.