buckling load 5

You haven't much to say, but my guess is that you have not properly "constrained" your model. If you have "Hinged" both ends of the model then you probably have model that isn't tied down sufficently and your model is "bombing". Try doing a simple uniform column bucking problem from a textbook. David R. Dearth, P.E.
Applied Analysis & Technology
E-mail "AppliedAT@aol.com"

I am trying to do same thing.
I want to run a buckling analysis on a column, having hinged support at both the ends & axially loaded compression) at one end and I want to find Critical load (Fcr) for this condition. Which is theoratically equal to (E*I*(PI/Leff)^2) and in PM/Str. it is equal to F*Buckling Load Factor (B.L.F.).
Please guide me, how & which constraints & loads, i apply to solve this problem.

Assuming you've used Mechanica's shell idealization, and that your column is a tall plate, the bottom edge of the plate should be constrained in all translation dof and 2 rotation dof. Rotation about the edge should be free. The top edge should be constrained in 2 dof (translation allowed in the compression direction) and 2 rotation dof (rotation allowed about the edge). I've asssumed that the load is compressive on the top edge of the plate.

If you're using solids, I think you'll need to create a line on the top surface and the bottom surface, and apply the above constraints to these lines. Otherwise you can't get a hinged condition - if you constrain the 3 trans dof on the bottom surface, you have also constrained all 3 rotation dof.

Also, you can go to the knowledge base on the ptc website, search under 1. suggested technique, 2. mechanica, 3. buckling, there will be a document titled "suggested technique for buckling analysis" -- tutorial for doing buckling analysis on a coke can.

Hope this helps...

lawson,
In my case I have a pipe shell column. I modeled it hinged/hinged as you suggested and applied the load at the top. The static analysis went ok but when I tried to run the buckling analysis I got a fatal error. Any thoughts why?
Thanks!
Rainier

Follow up to my thread: I was able to complete the run on my pipe shell model but it did not converge within 10%.
My shell idealization blf = 12.3. As a check, I tried modeling it as a beam idealization, and it went through without any problem. My beam idealization blf = 6.3. The shell/beam idealization blf ratio = 2 is quite large. Any idea why is this so? (The blf=6.3 is also what I get by hand calculation using the AISC greenbook)
Thanks again!

Rainier,
How many elements are in the model? Sometimes mechanica creates really coarse meshes and it's necessary to adjust the autogem settings and/or add some fixed points to force it to create more elements. Is this it, or should I give it some more thought?