Grasshopper

algorithmic modeling for Rhino

(Below topic was published on Karamba Group forum http://www.grasshopper3d.com/forum/topics/karamba-user-problems?gro..., but because of none answers I thought that someone else might know the solution)

 

Dear Karamba Users,

 

I have a problem with Buckling (Buckling length) Effect of elements. Does anyone knows the way how to examin elements (cross section) regarding buckling?

I`ve found that Karamba is showing some deformation via `Eigen Modes` (prntscreen : http://storage.ning.com/topology/rest/1.0/file/get/2654790511?profi...) but it seems that it`s a wrong direction.

 

I will be happy for any advise.

 

Best,

R.

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I am interested in the same issue too.

Any comments by developers?

in its cross section optimization component, karamba does a simplified buckling design on compression members, where it also looks at how it is connected to the rest of the structure. this is a first estimation of  member-buckling design using the euler-cases.

secondly, preventing local stability failures like web- or flange-crippling, you can simply avoid the usage of cross sections of type 2 to 4 by limiting the c/t - ratio to a value below 8,32 or 70, respectively. often, standard welded sections are of type 1 anyway, just be cafeful when defining cross sections yourself.

additionally, we are developing a component to determine the exact buckling lengths around a member's y- and z-axis seperatly, depending on the entire structure. this is for another reason at the moment (export to another FE-program to do acknowledged code checks), but possibly could make its way into the opti-cro-sec component ...!

if you use eigenmodes for buckling design, theoretically you first have to calculate ALL eigenmodes of the structure, scale their deformed shapes and then do another (second order??) analysis of all of them. by looking at the occuring stresses, you then get an idea of the buckling-safety. but there are analytical checks in the codes for this, and many FE-programs do have them built in. this is the way we go right now, why we develop the buckling-length module to export the lengths to those external programs ... etc.

Thank you for the reply Robert.

The cross section optimization component is not available in free version of karamba?

trial and pro only  ..

i know things like this prevent many people from using karamba ..

cause of this i would vote for a free version that allows all the cool features being used without limits by architects and designers, just restricting output of engineering results, export formats etc ..

Well 400 euros for one year is not that much. But it's too much for us out of the "standard" quality zone.

By the way, am I missing something or there is not Cross section optimization component, at karambaTRIAL 1.0.2 (32bit):

?

Did not succeed in finding the Cross section optimization component.
Is there a manual work around?

By using the Euler buckling formula:

?

This is a simple planar truss example I am trying to check for buckling:

For some reason RFEM gave much larger diameter (4.4cm) than Galapagos (2.5cm).
Am I doing something wrong?

Thank you.

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