Use the Cut Geometry tool to cut a structural member with a plane.
For example, use Cut Geometry to cut a column to a certain height, or to stop a beam at a wall.
To cut a beam at a wall
 Geometry panel
Geometry panel Cut drop-down
Cut drop-down
 (Cut Geometry).
 (Cut Geometry). If you move the wall or the beam, the cut will persist at the wall unless the beam is no longer joined with the wall.