Calculation proving primary bottom & shell are not overstressed

[miltiadis]

I'm working on a project concerning design of a double bottom tank according to API 650 11th.eddition and with reference to I.4.1 i want to verify that the primary bottom and shell are not overstressed.Any ideas how i must proceed with the calculation?

 

[khardy]

Depends on how you intend to support the primary bottom. Also, how large is the tank?

 

[JoeTank]

I.4.1 states that it should be "evaluated"... which may be done by calculation or comparison to existing installations (with successful service for which the analysis has already been performed). It was not intended that each and every tank be analyzed. If an analysis is to be performed it is too complex for simple hand calcs. Normally an FEA technique is used that accounts for a plastic moment at the shell-to-bottom joint.

Joe Tank

 

[miltiadis]

Thank you for your reply.The primary bottom is to be separated with wire fabric and with shell support ring at the tank perimeter as shown in figure I-5 of API.The tank diameter is 21.72m(71.2ft)/volume:4000m3. Joe tank you are right the code states ''evaluation'' but the purchaser of the tank requires calculation to be performed for overstress. I've found a book that specifies a method for analyzing the rotation and the stresses at the shell-to-bottom joint but i'm not sure if this is the calculation that the code requires.

 

[JoeTank]

miltiadis,
Sounds like you are on right track. What is the reference you describe and is it possi ble to obtain a copy of said paper?

Joe Tank

 

[miltiadis]

The book is titled ''Guide to Storage Tanks and Equipment'' by Bob Long & Bob Gardner.You can preview this book at the attached url (at pages 47-48 there is a reference for stresses at the joint).I would like to hear your opinion...

 

[JoeTank]

miltiadis,
It is difficult to read the pages, but from what I can see thus far the proceddure is somewhat similar to others I have used. Does it account for the plastic range or is it limited to an elastic analysis?

Joe Tank