Section VIII, Div 2 Part 5 Design by analysis. Protection against buckling clarification 1

[flakyman]

Hi,
I am performing buckling analysis of a vessel according to Part 5.4. The design load factor to be achieved is calculated from a capacity reduction factor. I am specifically looking at ellipsoidal head. The capacity reduction factor mentioned in the section 5.4.1.3 is only for ellipsoidal head with external pressure. Following are the two questions in this regard.

1) What about the buckling of the ellipsoidal head knuckle. Is there a different capacity reduction factor for the head knuckles which are in danger of buckling under internal pressure?
2) I believe the capacity reduction factor is for a complete collapse of the head. How should local buckling be treated e.g local buckling due to nozzle loads. Is the same capacity reduction factor valid for local buckling.

Any insight into these issues are greatly appreciated.

Thanks and Regards,

Jaspreet Hothi P. Eng

 

[TGS4]

1) that is not specifically addressed by the capacity reduction factor.
2) that is not specifically addressed by the capacity reduction factor.

In my opinion, this is one of the biggest issues with the elastic/eigenvalue buckling analysis. Between that and the inherent issues with eigenvalue buckling, I only recommend using Option 3 - the elastic-plastic buckling analysis method.

 

[flakyman]

Thanks TGS4,

For Option 3. It says to explicitly consider the imperfections. Can you please give some insight into what exactly are these imperfections? Are they talking about manufacturing imperfections or imperfections induced by loads? I am planning to load up the model with the nozzle loads and perform a linear static analysis and then use this deformed model to perform the collapse analysis.

Thanks,

Jaspreet Hothi

 

[TGS4]

The intent is that you have sufficient perturbation to initiate a buckling-type failure should it be prone to occur. Sometimes a nozzle load may be sufficient. Other times, an out-of-roundness may be required. Sometimes the geometry is such that it is inherently a perturbation. The situation we want to avoid is that of a perfect geometry - without an imperfection or perturbation it just won't buckle.