Frame analysis problem

[na57zim12]

I am designing a ingot casting Machine. where three support (C120, 70x70x7, 40x10 Plate)  are weleded parallaly. means fully rigid  (in Pic). in the structure  i have four like this .  The roller chain move on 40x10 plate. 

Now when i enter in the frame analysis environment, these three support(C120, L50x50x8, 40x10 Plate) make rigid link only at two ends.so after applying the force on (40x10 plate),  when i do simulation, i get huge deflection as there are  only two rigid link at the  end.

if i increase the rigid link within these link mannualy, this delection will  surely decrease. but how many times will i do it ?

is there any system that will automatically keep these three supports (C120, L50x50x8, 40x10 Plate) as one rigid link.

i appreciate any help in this regards thank you

nazim

[na57zim12]

I am using inventor 2012 professional