API650 Fixed Roof

[magmath76]

I am in the process of designing a 15.5 mitr dia 15.8 dia steel tank with conical roof. I am bit stuck on the roof design and much appreciated some one could help me with this.

1) I am not clear either to go for self supporting or cone with rafter suppoerted from the tank wall, as i could not see any guideline in API 650 what type to be used based on diameter etc
2) when I look at the rafter spacing calculation , I am confued on the calulcation of uniform pressure which referes to Appendix R as i am not clear on what combination is should be used.

Any help would be much appreciated.

 

[fegenbush]

The roof type is not dictated by the standard. It is up to the engineer to determine the appropriate roof design. For 15.8m, a self supported cone roof is unlikely to be economical in either design or fabrication/erection. Additionally, you may want to consider whether a center column to support the rafters is permissible.

The load cases in Appendix R are all to be considered. The value that used in the design is the most severe of the load combinations.

 

[magmath76]

Thanks