Sec. VIII Div. 2, Part 5.4 Buckling

[LS_SMS]

Folks, I am looking at 2023 ASME Sec. VIII, Div. 2, Part 5.4.2 for the Method A Buckling Analysis. I plan to use the ANSYS eigenvalue buckling solver to perform the work. Here are some excerpts from the code...

This method is intended for use on independent individual components (e.g., heads, cylinders, and cones) assessed in isolation.

Separate eigenvalues shall be extracted for each component in the assembly, λ_component,k.

If assessing multiple components simultaneously in one assembly, each component’s loads shall be multiplied by its dominating eigenvalue, β_{b component,k} = λ_component,k.

I see a common theme about "assessing individual components." If I have a simple pressure vessel, one cylinder with two hemispherical heads, how do I assess all three of those components in isolation? I'm confused on how one would do this in FEA software. In FEA, I would normally model all three together so that the load path through the structure was accurately captured. And if the vessel has nozzles and appurtenances, it seems like this procedure could get pretty agonizing with a slew of separate components. I'm curious to hear some feedback.

 

[TGS4]

You will evaluate each component separately. That means that you will end up requesting a relatively large number of eigenvalues, so that you can get the lowest eigenvalue for each component. And then proceed accordingly.

 

[LS_SMS]

Does that insinuate that each piece of the vessel should be run in the FEA separately (e.g., top head separate from the bottom head separate from the shell)? Or should the FEA analyze the entire vessel at the same time?

 

[TGS4]

The latter. You need to consider the interaction of the various components.

 

[LS_SMS]

Can you elaborate on this statement in Step 2 of the procedure?

If assessing multiple components simultaneously in one assembly, each component’s loads shall be multiplied by its dominating eigenvalue, β_b component,k = λ_component,k.

My understanding is that if the top head's eigenvalue is 2, the bottom head's eigenvalue is 2.5, and the cylinder's eigenvalue is 3, I need to run a single elastic stress analysis having all three components present, but each having a different load. So for example, if the pressure is 100 psi, I need to run the analysis with 200 psi on the top head, 250 psi on the bottom head, and 300 psi on the cylinder, all at the same time in the same analysis. Is my interpretation correct?

 

[TGS4]

Correct

 

[r6155]

The concept is the same as that of hand-made calculations.