CONNECT Edition (10.08.00.XX Update 8)
In OpenPlant Modeler there is a feasibility to import solid model which would be in the form .stp format i.e STEP file. This Option would help user to import the solid model into the dgn and work further on it.
If above problem still persists, then please create a Service Request and contact the Bentley Product Advantage group. Please include a list of all relevant details to get in depth analysis for a solution or workaround