If you want to extract the centerline of a column then simply follow these 5 steps below.
1. Select the Physical Structural Model
2. Extract the Geometry using the "Element.Geometry" node
3. Place vertices at all column locations
4. Covert all the vertices to points
5. Add the "LineByBestFitThroughtPoints" node to extract the centerline of the column
The image below summarizes this process
Note that all these nodes shown will create only one curve via the analytical model and also it extracts the centerline of MEP Piping, and Ducts. If you want to do that then simply select the MEP system family instead of the Structural Column family and enjoy!