Mixed structure and buckling length

[Romanich]

Hello guys!

Let me demonstrate simple example: steel frame without concrete columns and with concrete columns.

Also, for columns 1 and 4 we used Auto method, for columns 3 and 6 - Internal Bracing option.

 In first model, for steel columns 1 and 3 we have buckling coefficient equal 2.

In second model, for steel column 4 we have buckling coefficient equal 100, for steel column 6 buckling coefficient equal 1.

[Pawel.Pulak]

Hi Roman,

I see that you try to test this feature "to extremes" 🙂

Automatic buckling length in case of columns is dedicated to columns defined as single members between beams of different floors. Using it for part of column exceeds somehow the main goal of this feature.

The similar situation for using buckling type with internal bracings when there are no internal bracings.

The behavior for column 4 seems reasonable - because there are no adjoining beams (top beam has pinned release) according to SNiP code n and p coefficients are zero so mi coefficient (for instance formula (70,a)) is infinite. Robot is giving it equal to 100 instead of infinite one.

In case of buckling type with internal bracings Robot is not so smart. I will forward it to developers to check whether any improvement is possible there.

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[Romanich]

Hi Pawel,

Robot is giving it equal to 100 instead of infinite one.

Yes, but according to SNiP in this case we must use mi coefficient equal 3.

Thank you for your attention  and we will wait for a response from the developers.

[Pawel.Pulak]

Hi Roman,

your remark is related to formula (167) of Приложение 6 of SNiP II-23-81

Приложение 6  of SNiP II-23-81 concerning buckling lengths of multi-segment columns is not implemented in Robot in any schemas calculating buckling length. It is not implemented in automatic buckling length too. So formula (167) related to top segments of such columns is not supported too.

For such columns it is necessary to manually define buckling lengths using tables from the code to calculate buckling length coefficients.

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Regards,