When coordinating designs with Architectural, Structural, or Mechanical elements, the best format to receive their data is an IFC file.
If you need to export an IFC file, please see here: Write Infrastructure IFC
The IFC Express Reader currently supports IFC2x3, IFC4x1 and IFC4x3.
IFC Spatial Structure is not currently read in by the IFC Express Reader. However, if the IFC file is kept with the 12d Project the IFC Spatial Structure can be examined by the IFC Properties (BIM => Import => IFC Properties).
Reference Trimeshes
Reference trimeshes were only introduced in 12d Model 15 and are still under development.
BIM => Import => IFC => IFC Express Reader
When importing an IFC, most of the default settings on the IFC Express Reader panel can be left as-is. For information on some of the common settings, please see here;