Gantry cranes are overhead bridge cranes supported on ground tracks by legs on both sides. Structurally, they consist of a gantry, trolley running mechanism, hoist trolley, and electrical components. Some gantry cranes have legs only on one side, supported by buildings or trestles on the other, known as semi-gantry cranes. The components of a gantry crane include the upper bridge girder (including the main beam and end beam), legs, lower crossbeam, etc. To expand the crane's working range, the main beam can extend beyond the legs on one or both sides, forming a cantilever. Cranes with boom trolleys can also be used, expanding the working range through the boom's tilting and rotation.