Rational structure is of box construction (As per IS - 800 Bridge Girder structural calculation) adequately designed and reinforced by stiffening ribs. It is connected with bridge trolley, which is moved by motors, coupled up with speed reducers. The crab carriage is in steel section. It comprises of special crane duty motor, connected to speedreducers and is coupled to a grooved steel drum. Electromagnetic brakes are used to control the smooth lifting of weight. AC drive is also provided (on demand) for smooth operation of long travel.