hello
this problem seems very sophisticated at first look and i did go through it yet
if the question was to allow some stiffness on the joint from 'mst_azi_house_to_elev_be', to 'slv_bears_to_azi_house',
if it was me i would do the following (as a quick answer)
1- create a node at a convenient place between 'mst_azi_house_to_elev_be', and 'slv_bears_to_azi_house', at mesh time, (if there is not)
2- create a POI1 on that node in code_aster
3- assign it a K_TR_D_N type of element
4- assign the required properties of stiffness
(could assign damping properties as well)
5- define a LIAISON_SOLIDE between that point and 'mst_azi_house_to_elev_be', and another one between that point and and 'slv_bears_to_azi_house',
the problem would be even simpler if there was a line element modeling the axis of rotation
note than refining the mesh would not help to take care of the joint stiffness and this mesh seems to me quite refined for a modal analysis
one further note as a convention mesh file in ASTER format have an extension .mail, .msh is for Gmsh mesh file
EDIT
i looked at the mesh i understand that to 'slv_bears_to_azi_house', is a node
so my first answer must be interpreted with that in mind
and also 'mst_azi_house_to_elev_be', seems fairly distorted
