PV-Elite flat bottom tank

[Europeeng]

Hi,

Is it possible to analyse a vertical vessel/tank without skirt in PV-Elite? I want to analyse a vertical vessel with flat bottom and bolted connection to a concrete base according 13445.

 

[JStephen]

Generally, flat bottom tanks use a relatively thin steel bottom supported by grade, and this type of construction is not addressed in the ASME pressure vessel codes. If you try to apply ASME, that flat bottom will get treated like a blind flange with unreasonable results. Can't say about 13445, but if it's a vessel code, you'll likely have the same issue.
Depending on interior pressure (if any) and application, these tanks would normally be designed by API-650, API-620, AWWA D100, NFPA 22, etc.

 

[dig1]

It really doesn’t work for what you want. I’ve tried a long time ago. JStephen is correct. Would EN 14015 be more appropriate? If the tank is pressurized to any extent the shell to bottom joint and anchorage needs to be looked at in detail.

 

[Europeeng]

dig1, yes I use the EN 14015 for tanks but i want to solve this with PV-elite. Is it possible to design a vertical vessel in PV without bottom skirt, and use the reaction forces to calculate the support in detail? Loads will esentially be, Nozzle loads, wind loads, pressure and water filling.

 

[dig1]

Europeeng,

I don't think it can be done correctly. The flat head, as has been mentioned earlier, will not be calculated correct so it will show as failing under internal pressure. You could build the model w/ a welded flat on the bottom and then attach a shell and use lugs on the shell. Unless you can add a false load somewhere, the contents will resist the uplift because they are being carried through the flat to the shell and then the lugs; this is wrong for what you want to model so your reactions will be incorrect.

I'm going to use API Standard 650 as a comparison; I'm not as familiar w/ EN 14015 so these comments may not apply. In the event of seismic loads for a partially filled tank, unless you manually enter the impulsive and convective forces and their locations the seismic loads be what is required. Typically, the API standards have higher allowable tensile stress values than ASME Section VIII, Div. 1; you can make custom materials to overcome this fairly easily.

If this were an API 650 tank then I would either obtain software TANK by Hexagon (I'm not really a big fan of it because I think it is not straight forward to use but it would get you the design)or AMETank as it covers EN 14015. Preferably write spreadsheet(s)or MathCad to do the work.

My personal opinion is that I would not be pleased if someone sent me a flat bottom tank in PVElite w/o some good rationale and show how it can work properly. I understand you are trying to use software you have to design something. I'd much rather see the appropriate standard equations written out and then verify it.

 

[CuMo]

See API 650 as mentioned above.
You can also look into Formulas for Stress and strain by Roark & Young - formulas for circular plates of constant thickness - Uniformly distributed pressure from r0 to a. Edge fixed.

What you have to be aware of and codes don't address is potential rotation in the shell at the base corner. Which could increase the maximum deflection of the bottom if it has no additional external support.