Why the condition i1*i2-i12**2 => 0 for PBEAM is necessary

[Rashmikant Upadhyay]

Dear pyNastran Team,

Could you please tell me why such condition is set for the PBEAM which I think isn't correct depending upon the dimension and unit like a case below.

A Beam with a Area (A) = 330 mm^2

I1 = 99129.5 mm^4; I2 = 44310.49 mm^4;  I12 = 50738.73 mm^4

Now convert the dimension of the Beam into meter

A = 330e-6 m^2         I1= 9.91295e-8 m^4;  I2 = 4.431049e-8 m^4;  I12 = 5.073873e-8 m^4

It sure that in the second case, the above criteria will fail althought the beam is same. 

Please guide me if I am wrong. 

Thank you so much for your support. 

[Steven Doyle]

It is a positive definite eigenvalue check. Maybe I’m misunderstanding the requirement; but how would you get a negative principal inertia? I just ran the calc and it seems like it should pass in both unit systems.

Also, what section do you have?

Steve

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