topic Re: 3D model problems in Robot Structural Analysis Forum

3D model problems

Anonymous — Mon, 20 May 2013 17:42:00 GMT

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?

Re: 3D model problems

Rafal.Gaweda — Tue, 21 May 2013 07:40:56 GMT

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

Example - red bars below added.

Re: 3D model problems

Anonymous — Wed, 22 May 2013 20:56:44 GMT

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!

Re: 3D model problems

Rafal.Gaweda — Thu, 23 May 2013 09:20:20 GMT

It is not that simple.

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

Re: 3D model problems

Rafal.Gaweda — Thu, 23 May 2013 08:09:47 GMT

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:

Re: 3D model problems

Anonymous — Thu, 23 May 2013 09:01:02 GMT

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

Re: 3D model problems

Anonymous — Thu, 23 May 2013 22:24:26 GMT

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.