Thank you very much sir for your detailed response, this is very helpfull for me. 

Seams are screwed together in my assembly, if i am using shell bodies which one option i should use fixed joint or Beam connection to hold these parts. I tried both( on just two plate connected by bolt) but result are very different in both cases, for beam connection i have referred your youtube video which was for solid parts (thanks for this also). With beam joint,  two plates are rotating about beam in one of the mode shape. More important point here when using beam joint the plate are rotating in apposite directions which they should not.  Also if i need use solid bolt (for accuracy) then using this with shell enclosure means there will be actual a edge -surface contact for bolt shank and enclosure. What we can do this for situation.


fig. Beam Connection

Fig. Mode shape result with beam connection


Fixed Joint

Mode shape for fixed joint