What Is An Under Notched Crane Beam?
Often double beam cranes main beams will be under notched. This is because with double girder cranes the hoists runs on the top of the beams. Most factories have pitched roofs and the hoist cannot get full travel left and right.
The combat this the cranes beams (yellow RAL 1007 in the image below) are under notched; that is cut away below the gantry rails (white rails in the picture below) to allow a larger hoist envelope on the side hook approach.
Single girder cranes do not have this problem as the hoist runs underneath the beam.
Below is a picture of an overhead crane in a traditionally pitched industrial factory roof. That said the pitch of the roof isn’t in the centre as it usually is.