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Gantry cranes are a type of crane built atop a gantry, which is a structure used to straddle an object or workspace. They are also called portal cranes, the "portal" being the empty space straddled by the gantry.
The terms gantry crane and overhead crane (or bridge crane) are often used interchangeably, as both types of crane straddle their workload. The usual distinction drawn between the two is that with gantry cranes, the entire structure (including gantry) is usually wheeled (often on rails). By contrast, the supporting structure of an overhead crane is fixed in location, often in the form of the walls or ceiling of a building, to which is attached a movable hoist running overhead along a rail or beam (which may itself move). Further confusing the issue is that gantry cranes may also incorporate a movable beam-mounted hoist in addition to the entire structure being wheeled, and some overhead cranes are suspended from a freestanding gantry.
Gantry cranes can range from enormous "full" gantry cranes, capable of lifting some of the heaviest loads in the world, to small shop cranes, used for tasks such as lifting automobile engines out of vehicles.
A ship-to-shore rail mounted gantry crane is a specialised version of the gantry crane in which the horizontal gantry rails and their supporting beam are cantilevered out from between frame uprights spaced to suit the length of a standard freight container, so that the beam supporting the rails projects over a quayside and over the width of an adjacent ship allowing the hoist to lift containers from the quay and move out along the rails to place the containers on the ship. The uprights have wheels which run in tracks allowing the crane to move along the quay to position the containers at any point on the length of the ship.
The first quayside container gantry crane was developed in 1959 by Paceco, Inc. Paceco's name for their line of quayside cranes, "Portainer", has since become something of a genericised trademark, used to refer to any quayside container gantry crane.
Full gantry crane
"Full" gantry cranes (where the load remains beneath the gantry structure, supported from a beam) are well suited to lifting massive objects such as ships' engines, as the entire structure can resist the torque created by the load, and counterweights are generally not required. For example, Samson and Goliath, two full gantry cranes located in the Harland and Wolff shipyard in Belfast have spans of 140 metres and can lift loads of up to 840 tonnes to a height of 70 metres.
In 2008, the world's strongest gantry crane, Taisun, which can lift 20,000 metric tons, was installed in Yantai, China at the Yantai Raffles Shipyard. In 2012, a 22,000-ton capacity crane, the "Honghai Crane" was planned for construction in Qidong City, China..
Workstation gantry crane
Workstation gantry cranes are used to lift and transport smaller items around a working area in a factory or machine shop. Some workstation gantry cranes are equipped with an enclosed track, while others use an I-beam, or other extruded shapes, for the running surface. Most workstation gantry cranes are intended to be stationary when loaded, and mobile when unloaded. Workstation Gantry Cranes can be outfitted with either a Wire Rope hoist or a lower capacity Chain Hoist.
Rubber tyred gantry crane
Smaller gantry cranes are also available running on rubber tyres so that tracks are not needed. Rubber tyred gantry cranes are used in container terminals to straddle multiple lanes of rail/road and container storage; straddle carriers are used when moving individual containers or stacks.
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