Linear releases and instability problems

[mdf_ourense]

Hi, first of all, excuse me if my english is not completely correct.

I'm trying to calculate a timber structure of a house made of cross laminated timber panels (my first project with Robot and my first FEM project too), and one of the caracteristics in this type of constructions, is the non-existent transmission of bending moments through the joints of the panels, so I have to define linear releases in every single edge between panels, and here comes the problem. When I calculate without linear releases everithing is OK (so I guess that the geometry is correct, altough I can't assure it 100%), but when I define the releases, instabilities show up. Sometimes an instability type 3 appears in one node, then I change the releases between the edges where the node is, and sometimes the instability turns into type 2 or other times the node with the instability type 3 appears in another edge or even this new node doesn't exist .

Of course I've defined releases as shown in this post http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Panels-with-Linear-Releases-Create-Isolated-... trying to define the release only in one of the panels and not defining releases in free edges, but there are many edges where three or more panels come togheter to a common edge. In these cases, I always leave one edge of one of these panels without releasing.

Could it be a meshing problem caused by the additional nodes created by the releases? I've changed the settings as Rafal explains here http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Structure-verification/m-p/3334787 (comment #3), but the result is the same, instabilities come up.

Am I doing something wrong? Any advice to solve this? Should I just ignore the instability?

I would like to attach the file with the model so you can figure out what is wrong with it, but it seems to be too much big to be uploaded (3.8 Mb), so if someone tells me an e-mail adress i will send the file.

Thanks in advance. Regards.

[Rafal.Gaweda]

use www.filemail.com or www.wetransfer.com or any other similar service, then send us link to this file.

[mdf_ourense]

Mediafire link to my file: http://www.mediafire.com/?l62u2ywdfsb6ray

[Rafal.Gaweda · Accepted solution]

In this case instability type 3 is caused by big differences between max and min elements on stiffeness matrix diagonal. (the values can be checked in calculation report).

Can be neglected.

[mdf_ourense]

OK, I'll ignore the warning, thaks for your help. Problem solved.

Regards.