As long as you don't have doors and windows that need to be cut through in plan, changing the View Range should do the job.
To do so -
1) type VR

2) make sure that the correct levels are associated for top and bottom of view range (1 and 3)
3) make sure that the cut plane is cutting through the feature that you wish to show in plan (2)
If there are no doors and windows (or other features) to complicate matters, a Plan Region will also do what you want. This has the advantage of not changing the view range for the entire view
1) View>>Plan Views>>Plan Region
2) you will be prompted to create a boundary - that will be your beam. Sketch and accept as usual
3) you will be prompted to set up the View Range for that boundary
Rina Sahay
Autodesk Expert Elite
Revit Architecture Certified Professional
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