Answer:
First, you should check if there is a specific interface for the design program. If you use Revit or Tekla, direct interfaces are available. There is also the option to export to the DSTV format. This is also supported by many programs.
Of course, export to the *.dxf format is possible at any time. Since member structures are basically pure central axis models with information about the cross-section and material attached, you can only export the lines.
However, if you need a member as a 3D object, you can use the export into the Bentley ISM format. Please note that this requires the free Bentley Structural Synchronizer. You can find a link to this product at the end of this FAQ. The export can be easily run by clicking "File" – "Export."
Structural Synchronizer converts members into solid models. Then, a file with the *.ism.dgn extension is recorded. This format is supported by many design programs.