K buckling factor for steel truss

[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

 

[Agent666]

Generally you'd need to run a bucking analysis to determine the critical effective length factor or the critical buckling load. And then use that result in accordance with the requirements in your design code. The critical buckling load is not the capacity, you still need to apply the relevant column curves to this value to account for second order effects that have not been modelled (imperfections, plasticity, etc)

You might be better separating out the various truss components into smaller models though, to isolate certain trusses with appropriate restraints to determine the critical buckling loads for each truss type.

Hard to really say the best approach as the exact arrangement and how the loads are applied and how the structure responds isn't too clear based on your photo and explanation.

https://engineervsheep.com

 

[Mohamed Maher]

The load is applied at the end of each truss.
You mean I can separate each individual truss in a separate model ..and I this separate model I make buckling analysis.

I get some examples how to make the k factor after determine critical load from the sap ..but what I don't know how I should put the supports in the model .

 

[centondollar]

You have already made a thread about this subject. To my knowledge, double posting is not recommended.

"You mean I can separate each individual truss in a separate model ..and I this separate model I make buckling analysis."
No. A frame (consisting of trusses and beams) buckling analysis requires you to model the frame and perform analysis using it.

PS. If you do not know what supports your model should have, you should not be modelling buckling - or anything else - in SAP2000. Have your colleague walk you through the calculation and review your university lecture notes regarding boundary conditions. This advice may sound blunt, but it is the only reasonable answer you will get to your questions. Structural engineering is a job that places a lot of responsibility (both moral and legal) on you, and fiddling around with software without understanding the fundamentals is not a good excuse in case something goes wrong and you have to answer for your design.

 

[Mohamed Maher]

First I post two posts as I didn't receive feed back on this thread so I double it after arround one day so may I get answer and I get but not to much useful till now.

The trsusses are free from end and top chord and bottom are hinged from column side ..I don't know what you mean by frame ..but I have truss not frame .. maybe you mean frame element.

You don't understand what I mean by support ..I mean how I should represent the out of plan support which support the truss ..as it's not totally hinge may be I should prevent only translation in the out of plane to getthe correct simulation for end condition.

For other supports any one can determine it
Thanks for your time

 

[Mohamed Maher]

I don't have drawings right now only the model ...first you told me its enough to consider the truss braced in the out of plan direction then I stated that I thought it should be contain cross bracing to prevent buckling so you edit your replay which was yes in the first replay to be that we have to see all..
then I get other valuable answers that even cross maybe not enough and we may need buckling analysis and that what I'm think about now... I believe that the picture of model is clear enough however any other picture from other view I can provide.

 

[Mohamed Maher]

by the way this is the first thread not the second !!
and I got recently the replay from Eng. Agent recently