I'm afraid that I don't use Vectorworks, so I don't know of any direct import option. However, you have answered your own question by saying you export to 3ds. A 3ds file HAS to be triangulated, because the format does not support quads. Therefore it's bound to come into vectorworks as triangulated...unles VW has an import option (like SketchUp) in which you can choose to have all triangulations removed from coplanar faces. You would be better using obj format as a go-between....if VW can import obj files...because it will not triangulate.