New button.
Free button and select
Ty to fix the channel in the enforced Y direction.
Duplicate button. Notice that the selection of three edges of the beam opposite to the side with the holes is retained.
Free button and select
Tx to fix the channel in the enforced X direction.
Constrain the same nodes/surfaces/curves in the direction of the enforced displacement/rotations. It is important that only the nodes that have the enforced displacement are constrained in the direction of the displacement. All other constraints will be treated as actual boundary conditions.
In the next steps we will apply loads.