Gantry cranes/Portal cranes are cranes which:

• Lift objects by a hoist which is fitted in a trolley. Hoisting system uses cables, winches and pulleys to lift and move containers by its lifting hook.
• Trolley (& hence the hoist) can move horizontally on a rail or pair of rails fitted under a horizontal supporting beam called jib or boom or bridge
• Supporting beam is supported by (vertical) uprights, usually with wheels at the foot of the uprights allowing the whole crane to traverse.

(A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium. The load is attached to the hoist by means of a lifting hook.)

Thus Gantry crane runs on a track at the floor level along the length of a  factory and can provide three axes of hook motion i.e. movement of whole crane along the length of the building,  trolley (& hence the hoist) movement across the width of the building & up /down movement of lifting hook. However, gantry cranes are also available running on rubber tyres so that tracks are not needed.

Gantry cranes are generally available in spans to 150 feet and capacities to 150 tons

Video: Gantry Crane at work

Some portal cranes may have only a fixed gantry, particularly when they are lifting loads such as railway cargoes that are already easily moved beneath them. Gantries can be either of Single Leg type or  Double Leg type.

Single Leg Gantry	Double Leg Gantry

Gantry Cranes usually span a smaller portion of the work area as compared to a bridge crane.

Gantry / Portal/Goliath Cranes are adapted to applications where overhead runways would be very long, costly to erect, and difficult to maintain in alignment. Where the installation is only temporary, a gantry crane can be moved to a new location with less trouble or expenses than an overhead crane and its runway. Also it is comparatively easy and inexpensive to extend the length of the runway and thus increase the working area of the crane. Most gantry crane installations are outdoors. The initial cost of a gantry crane, which may be double that of an overhead crane, must be equated against the additional cost of an overhead runway.

The gantry crane provides the same performance characteristics that an overhead bridge crane offers.

Two famous gantry cranes built in 1974 and 1969 respectively, were Samson and Goliath, in the largest dry dock in the world in Belfast, Northern Ireland. Each crane had a span of 140 metres and lifting capacity of 840 tonnes to a height of 70 metres, making a combined lifting capacity of over 1,600 tonnes! . The world's biggest 1600 t gantry crane was installed in Hyundai Heavy Industries Ulsan plant, South Korea in year 2009.