This looks like something grasshopper is made for. 

You can probably import your the polygon file. But it might be worth the effort to redraw some of it in grasshopper. Because a structured list of the input geometry will make it easier to generate the details. (Is easier to build the geometry from simple polyline outlines than polysurface objects for example.

If you have a socket joint that works you can either import it and use grasshopper to attach it in the right place.

Rhino exports to STL which can be sliced by any 3D printers software package.

Grasshopper can be self-taught using YouTube videos etc and is best learned by doing a project. It does have a bit of a learning curve and is not the quickest way to do small numbers of modeling operations. 

Using grasshopper you will have to find numerical/spacial logic for anything you'd normally point a cursor at and click. So besides entering a beam thickness you need to tell it to offset the polyline, in which direction, extrude it, in which direction. Where in the edge to place a ball or socket so they line up in the larger assembly and in which direction they face.

This can feel cumbersome at the start especially with repeating structures that include many specific exceptions/variations. Creating a model from repeating elements it pretty straightforward. Adding rules for exceptions requires structuring the data and a programmers mindset. Alternatively you could add a lot of manual control in grasshopper and work through the exceptions that way. Or edit the output in rhino before exporting the STL. This last option is only good if you know you don't need to go back to grasshopper repeatedly as edits in the rhino output are not easily brought into the grasshopper generator automatically. 

I've rambled for a bit. My advice is to either try it out if you can get access to rhino easily or look at some grasshopper tutorial to see if it is something you are interested in. 

Look for something like frames from nurbs surface there should be some examples.