Amnesia editor - Object Collisions?

[TheGreatCthulhu]

The problem is that the surface of the beam is uneven - but you can use two beams instead of just one. Just add them to each side of the stairs, giving the impression that it's actually 1 connected beam. If the player can see the underside of the stairs, you can improvise some structures to hide the fact that the beam is lacking, or maybe use a 3rd beam, scaled down or something (although I suspect that would be ugly). EDIT: Unless, I just realised, the beam protrudes everywhere, not just at the stairs?

You can also give the floor some thickness, so that the upper side of the beam can be hidden between the upside and the underside of the floor.
In the end, you can open the dae file in a 3D modeling program, modify the beam, and save it as a separate model for your custom story, if you know your way around 3D apps.