Plastic Collapse and ratcheting assessment locations

[victor6397]

Hello, I'm trying to understand the rationale for limiting the evaluation of plastic collapse and ratcheting to basic structural elements, rather than transition elements or discontinuities.

I've been searching for info about this and haven't found a clear answer, at least to my limited knowledge of the subject.

For example, in WRC 429 "Discussion of Summary Recommendations" Part 7.1, we can read: "There are discontinuities where PL stresses exist but where they need not be evaluated because their design is established by Code rules".
Is that the reason? Should PL be checked for plastic collapse if those discontinuities have not been designed according to a Code?

In Recommendation 7.3 we also can read: "In structural elements, rotational and extensional deformation modes are possible, but these are not found in transition elements. Therefore, the (PL+Pb) and (P+Q) limits should be evaluated in all structural elements, but not in transition elements".
However, I cannot properly understand what It means.

Can someone give me an explanation or a recommendation of some papers or resources that can help me to understand this better?

Thanks in advance.

 

[TGS4]

The way that I like to think about it is as follows:

• The elastic stress limits were originally based on interaction equations (think Timoshenko thin shell theory)
• That basis originated prior to the advent of FEA
• In that approach, you would have the "structural" elements of a shell and head (for example) or a shell and nozzle
• These approaches never were able to calculate the stress levels in the transition elements
• At the advent of FEA, we were able to calculate vastly more stresses than the above-approach
• That was the impetus for the WRC 429 effort

This is well discussed in Recommendation 7.3.

The other aspect of not including SCLs in transition elements is that they are likely to fail the validity criteria.

You may need to go back to Timoshenko Thin Shell Theory for starters.