The bridge is supported by two legs supported on the ground track or on the foundation of the jib crane. It has a ground track, which can be made by railway vehicles or other ground vehicles. The rotating lifting device is mounted on a gantry crane on the door frame. The four legs of the portal frame constitute four "door holes" that can be used by rail vehicles and other vehicles. The portal crane is mostly on the ground or the crane track on the building. The "zigzag" crane is a semi - door crane with one side of its orbit on the ground and the other on a higher ground than the ground.
