Dome roof

[fjodor]

Hopefully tank experts can help me here. I'm not API designer (I use ASME and EN) but I got a project to check and thought I could learn something new in process.
A tank is API 650 19m diameter with dome roof. Dome roof as I can see has radial and circumferental structers (rafters and girders) though sketch is awful. I'm also reading API 650 and what I read it says: self supported cone roof and self supp.dome,umbrella roof and supported cone roof, nothing about supported dome roof? Am I missing something?

 

[MJCronin]

The terms "umbrella roof" and "dome roof" are used interchangeably.....IMHO

MJCronin
Sr. Process Engineer

 

[JStephen]

Usually, the motivation to make a dome roof is to make it self-supporting. API may not address structurally-supported dome roofs, but I don't think it prohibits them, either. It is also possible to construct stiffened domes, without columns, and that may be what you are describing. In some cases, the stiffeners may be for erection only, and not required for stability of the completed roof.

 

[fjodor]

THX, It's true API doesn't prohibit other designs as well (read that later), my last question would then be: what are ways of calculating thoose designs? FEA?

 

[RudiHub]

@fjodor
Design of Dome roof can be done manually, however nowadays most designers use FEM packages like ANSYS. if loads on roof are distributed evenly (or uneven distribution is not major), you can divide the the hypothetical sphere into equal wedges, minim one or two pair of rafters and their connecting girders and roof plate should be part of Model. Then analyze loads and stresses for this wedge. You can consider results with reasonable margin acceptable for the whole dome.
In case of special load on roof like big nozzles and uneven/undistributed piping loads or platform which are concentrated on specific points, whether a total model of roof with singular loads should be considered OR those specific points can be analyzed separately and results and conclusion to be combined with Wedge model. so, you may need some reinforcement for large nozzles or pedestal of platform, ...

 

[IFRs]

If it's an aluminum dome roof, check API 650 Annex G