removing part of steel tank

[duncs]

i have a steel tank to patch up. it is 8meters high and 8 meters diameter. i need to perform a calculation on how large a patch i can remove before the tank buckles.Does anyone have any ideas on how to go about this.

 

[JedClampett]

I would do it by trial and error. I would remove a section and figure out the section properties, Section Modulus and center of gravity. I would then a stress analysis of the remaining section, using the moment created by the dead load of the upper portion of the tank (above the cut) times the distance between the CG of the top section and the CG of the cut section. Combine stresses, axial and bending and compare to the plate allowable compression stress. Treat the plate as an unsupported section. I would limit the stresses to one half the AISC allowable.