normal modes - singularity

[davideaka]

Hello, everyone!
I am carrying out the study of the free response of a structure with a beam (4 floors), modeled with curves 1d, with elements rbeam2.
The base is framed, while in knots at the lines that meet, I used mpc type rbe2.
the first 4 fashion deformed that I get are clearly wrong, due (I believe) to the singularity of the spc (I found matchings looking for the topic "mechanism" in the quick reference); the other deformed (from the fifth onwards) are congruent with what obtained from experimentation.
I tried to use rjoints and meshare structure piece by piece but without improvements.
How do I eliminate these singularities? I fear that in that frequency range there are proper ways that the fem model does not detect.
Thank you guys!
Good evening!

 

[Onda]

I don't know the rbeam2 elements. Maybe cbeams?
However between element and element you must have the knots in common. elimnate the mpc2 and make an equivalence with size large enough to eliminate the knots.
a model of the basic genre should not have rbe2

 

[davideaka]

thanks for the answer first of all.
the structure is fixed with screws, so if you do equivalence I should consider it as framed.
I have already done an analysis with equivalence and in fact I have no problem.
I used the mpc to get as close as possible to the real situation (hinge type files).

p.s. not rbeam2 but rbe2 (I thought it was a subscription)

 

[Onda]

If you want to shape hinges you have to put between the matching knots of the cbush elements with high stiffness (the bolt) in the degree of freedom held by the bolt and rigidity nothing in the degree of freedom not held. Obviously you have to put the knots and elements in the appropriate reference system.

As for the term (errate) rbeam2 you used it to describe beams and not joints.

 

[davideaka]

Thank you very much