K bucling factor for truss 3

[Mohamed Maher]

Dear all

I want to get the k factor for the attached truss by using sap 2000
The model consisting from column and trusses arround it..and repeated .the covering is fabric but not shown in the model

Kindly find in the attached photo from the model

Thanks,
Maher

 

[Mohamed Maher]

BA
I'll try to answer your questions
1.BA member is stopped and other member similar to it continue to the other edge truss

2.No relation between member BC and the column

3.point D is intersection of two trusses .no relation between point D and the column


4.point f lateral prevented from movement ..no or that part of our question if bracing will prevent buckling or not

5.yes all trusses held to point E.

6.in my opinion there is to chance for trusses rotation as each truss loaded by force parallel to its plan.

7. I'll provide top view tommorow hopefully.

 

[centondollar]

The eigenvalue buckling analysis will not give the answer as a critical buckling length and "k" factor. The lengths of members are determined before the calculation is run. Are you sure that you understand what you are doing? You should speak to someone senior in your company who knows structural stability analysis.

 

[Mohamed Maher]

@centon
It will give if you add axial load to the truss only by 1 ton and remove all the loads from the model then from the first mode shape factor you multiply the factor by the actual max force in the truss under the actual load..that will give you the critical buckling load then from eular equation you can get the critical buckling length then compare it to the actual length .. so you can get the real K.

Then add this k to the real actual model.
That what I get from searches.

 

[centondollar]

"That what I get from searches."
And it is incorrect. Talk to your supervisor about this.

The Euler buckling formula applies to one column, while an eigenvalue buckling analysis of a frame gives as an answer the buckling multiplier for the whole frame - all member stiffnesses and axial loads (those can exist at many supports) are accounted for in such an analysis.

Furthermore, the Euler buckling formula requires you to define the effective buckling length - which depends on boundary conditions - before you can compute the critical buckling load. It cannot be used in the way you describe even for an axially centrically loaded, perfectly straight column supported at two ends.

 

[Settingsun]

It will give if you add axial load to the truss only by 1 ton and remove all the loads from the model

You run the buckling analysis with the actual design loads on all members, not nominal loading on a single member.

Agent666 replied to your other post but modestly didn't link to his webpage on the subject.

https://engineervsheep.com/tag/buckling-analysis/