3D model problems

[Anonymous]

Hi,

I am working on 3D model of a steel structure. No matter how I model the releases, the program always tells me there are  instabilities type 1 2 or 3.

Would you please show me how can I model my roof truss to work only with normal forces, the X bracers on the roof too and the purlins - to be simply supported (by the nodes of the truss). All that without giving me warning for instabilities.

PS: There are some elements missing because the model is in very early stage. That my occur in other instabilities problems. I just need to understand the principle of 3D modeling in RSAP to model elements like those I asked for.

Please forgive my poor English.

Thankyouinadvanceforyourtimeshared!

http://www.4shared.com/rar/eXvDzWvq/Ramka_3D_3D.html?

[Rafal.Gaweda]

Bottom chord of these trusses are instable either due to excessive releases on bars or missing bracings \ stiffeners.

Example - red bars below added.

[Anonymous]

Thank you for your example. But is it possible to do it just with appropriate bar releases, because I don't need that many elements between the joints of my bottom chord.

To be exact my question, is there some kind of a rule for releases in 3D model like the one in 2D model - node with N number bar elements joining it, there must be N-1 releases.

I hope I explained my problem right.

Thank your for your time!

[Rafal.Gaweda]

It is not that simple.

It depends on released dofs, not on general number of releases in node.

[Rafal.Gaweda · Accepted solution]

Thank you for your example. But is it possible to do it just with appropriate bar releases, 

Take a look at LCS of bars and released dofs.

Maybe like that:

[Anonymous]

Thank you for your post, now I will try your suggestion.

[Anonymous]

Now after I try your proposition, I see everything works just fine, thank you very much! I have one type 3 instability, but despite it, all the results from my test loads are all what I expected.