How to cut bottom part of a curved beam?

[honza.cink]

Is there a way to cut bottom part of a curved beam like the one in my picture?

Beam I have problem with

I tried the cope method, it did a good job except the top beam is touching the other one from the side and that is not the intension. 

Cope

So I tried cutting geometry with a reference plane but it always remove the wrong part.

Reference plane

[ToanDN · Accepted solution]

One way is splitting the beam and you can cut them with a ref plane.

Another way is create a horizontal beam, disallow join, and cope.  Then hide that beam some how.