How is the "X span" on the "Buckling" page found?

[HyperSizer Moderator]

Questions submitted by HyperSizer user via email:

Hi Hypersizer,
I wanted to know how the “X span” on the “Buckling” page is found.  When I import an fem, some of the
span lengths do not match those in the model, they are smaller lengths.  I’m not sure what’s going on
and if you have any guidance.
 
What I’ve done is to update the “X span” to the lengths in the fem and then size the groups.  I take
the sections into nastran and perform a buckling analysis.  Is this approach ok or do you think I should
be doing something else….

[Phil]

I think the process you are using is correct.  You size in HyperSizer with panel buckling turned on and then do a check in Nastran for panel buckling as a double check, is that right? 
 
The automated buckling span calculation tries to get the correct spans from the FEM, but in some situations is may or may not get it right.  That is why we allow you to type your own buckling length in.  Remember that HyperSizer calculates buckling by creating an idealized rectangular panel so if you have something really complex shaped in the FEA, you have to make an engineering judgement about what is the correct buckling length so that the buckling of the idealized rectangle matches that of the actual geometry.
 
As far as how HyperSizer calculates the buckling lengths, the process is described in the Pro Users Manual in the Finite Element coupling reference, Page 121.  The section should be titled “Buckling Span Length Calculation”.
 
Let me know if you have more questions.
 
Phil