help about the analysis of 7 pinned arch on autodesk robot structural

[sor2007]

Hi Arthu or Rafal, can you please help to sort out  the instability of  the problme i found when  analyising a 7 pinned arch(see attached   model and analysis and sketch). i released the joint  in a similar way  when I do analyze continoous beams with intermidate  hinges. but in the case the software  states   INSTABILITY OF TYPE  1 OR 3.  the   structure i m  anlyis is a  hub Spoke bas . the structural behaviour is similar to the one of a bicycle wheel.

 The source of  error may be:

 wrong release of Joints

 wrong type of Anlasis,ie. linear- non linear  analysis

Please give me  or correct my analyis.

Thank you very much

[t.sautierr]

I would model in one of these ways.

I think your model was unstable because it is 3D so your have to avoid global rotation around Y and then in some nodes to many releases.

Other point : you can't release all the bars in rotation when ending to a pinned support, at least one has to be not released in that dof.

One last point, except you have an horizontal bar to link both supports and avoid them from going in opposite direction, I would let the structure slide on one side to let it take it real deformed shape. (I put this also in the files as you can see the difference.)

[sor2007]

Hi T Sautier

Thank you very much for your explanation

I will do the analysis again