Flexular torsional buckling length

[TSOFA]

Hi all,

I have this steel tower and I want to evaluate the torsional buckling length to be between the stores (i.e. 3.21m). I tried all the different ways to enter this length (buckling member length (rear or coefficient)/ buckling length coeff- see green circles). The result was the same, the flexular torsional buckling is the whole height of the column (i.e. 12.86m instead of 3.22m). How I can overcome this, I don't want to intersect the column and the beams of the stories.

Can I see graphically the buckling or torsional lenghts of the structure somehow?

[Stephane.kapetanovic]

hi @TSOFA 

https://help.autodesk.com/view/RSAPRO/2024/ENU/?guid=GUID-EDA2A9FE-C5C5-4A07-A883-3B3A83B492DE

choose internal bracing instead of applying a buckling length

Best Regards

[TSOFA]

Thanks for your answer. I did that but didn't work... it's strange...

[Stephane.kapetanovic]

hi @TSOFA 

i can only see one setting on your screenshot, have you set buckling in both directions? the lateral buckling too?

you also have two sections for the colums, did you create superbars?

what is the nature of the releases of the braces, do they act favorably on the torsion ?

I-sections are susceptible to torsional buckling for low inertia buckling lengths lesser than the buckling length by torsion

Best Regards

↓ here is an example where flexural-torsional buckling is predominant/ Nb, Rd, TF < Min {Ny, b, Rd ; Nz, b, Rd} 

[umut.akparlar]

Hi,

Please check which member to show at internal bracing window bracing detection preview.

You shared a calc report for member 3 at your initial post but internal bracing window is showing bracings for member 1. 

[Stephane.kapetanovic]

hi @umut.akparlar 

my explanation in message 2 prepares to use the checkbox for internal points by comparison with the lengths defined in message 1 to favor a case where flexural-torsional buckling should be considered. As explained in 4, sections are sensitive to torsional buckling for low inertia buckling lengths less than the torsional buckling length. The choice of a particular element is not relevant at msg 2 stage. I finally chose a u-shaped section rather than an i, to highlight a case where flexural-torsional buckling is calculated. 

The answers did not apply to the same model or even the same case, but they shared a common concern about the effective consideration of flexural-torsional buckling verification. It’s more a matter of substance than form.

After that, it's always possible to modify the view, though it's not always necessary to do so in a threaded discussion. 

Best Regards