Model order reduction with line bodies

[h.g.roubos]

I have the following model created. Is it build up from line bodies with different crossections assigned. In mechanical, different joints are created between line bodies as part of the structure is welded(fixed) and part of the structure is a truss structure with pinned(hinged) connections. Static structural and modal analysis were performed and work without problems. 
Now, I want to reduce the model to obtain the stiffness and mass matrix from the reduced model. The interface points to reduce to will be the center axis and endpoints of each boom. Using the substructure generation analysis seems unsuitable as it gives the warning: ' Only Fixed joints and Bushing formulation joints are allowed for a joint in substructure generation.'

Is there a way to overcome this error or a different way of obtaining a reduced model for stiffness and mass matrix?

Thanks in advance, any help is appreciated! 

[peteroznewman]

Open the line body geometry in Spaceclaim and use the Share button on the Workbench tab to create shared topology. That will weld all beam and truss bodies into one structure so you won't need any joints.

In Mechanical, the default assignment is BEAM elements.  Select all the truss line bodies and put them in a named selection. Then select them and assign the type to LINK elements.  LINK180 elements have pinned ends because they have no rotational DOF.  Select all the truss line bodies again and assign a Mesh Sizing control to use exactly one element on each body otherwise you will create an unwanted mechanism.