If you need to open a ProStructures file created with MicroStation platform with ProStructures running on the AutoCAD platform, you need to convert the file.
The opposite also applies (AutoCAD to MicroStation). Even if MicroStation can open DWG files, these would not contain the intelligent data.
Lets pretend we want to go from MicroStation to AutoCAD's version of ProStrcutures.
1) Open original file in ProStructures for MicroStation
2) Select Export from ProStructures pull down menu
3) Press Chose all
4) Type-in name of export file and make sure "Save as type" is set to "ProSteel exchange data"
5) Select all elements that need to be transfered and accept
Once the creation of the export file is finished you can go to the ProStrcutures version under AutoCAD
6) Make sure you are in an empty dwg file in the same measurement units as the MicroStation file you exported from
7) Select Import from ProStructures pull down menu
8) Set "Files of type" to "ProSteel exchange data" and browse to the location where the export file was stored and select it. Then press open
9) Select all elements that you want to import and accept.
10) Zoom extents and see your structure.