What Is a Gantry Crane?
A Gantry Crane, also known as a bridge crane, is a crane in which the girder is supported by legs and travels along rails installed on the ground or elevated on a framework.
The alternative term for it is “gantry crane.” Unlike overhead cranes that travel along runways provided on both sides of the building walls, the structure of a Gantry Crane is significantly different.
Gantry Cranes are suitable for factories or outdoor environments where the building structure is weak, and loads cannot be placed on it. The crane is defined as a device that lifts and lowers loads (excluding manual labor) using power and horizontally transports them (may involve manual labor).
Gantry Cranes typically operate electrically for hoisting, lateral movement, and travel.
Uses of Gantry Crane
Gantry cranes are utilized in various settings, including manufacturing, warehouses, logistics, shipyards, and docks, for the following purposes:
- Transporting long and heavy materials like steel beams.
- Handling heavy loads.
- Moving containers.
Structure of Gantry Crane
A Gantry Crane features a bridge-like steel frame structure.
1. Girders
These are structures that support the hoist and trolley, also known as girders. To ensure strength for supporting its weight and minimizing deflection when subjected to a load, various girder shapes such as box girders, I-beam girders, and plate girders are used based on the span and load requirements.
2. Legs
Girder and leg attachments, known as rigid legs, are designed to withstand horizontal forces during operation, and since they are often installed outdoors, they are built rigidly to withstand wind and seismic forces. One leg called a fixed leg, is made more robust to resist horizontal forces during operation, while the other, which may be subject to deflection due to the load, is comparatively slender. This leg is often attached to the girder using a pin structure and is called a pivoting leg.
3. Saddle
The saddle of a Gantry Crane supports the girders and legs and houses the wheels needed for the crane to travel. Structurally, it often consists of a box-type structure where steel plates are joined with channels (U-shaped steel).
4. Trolley (Hoisting Device)
The hoisting device, mounted under the crane boom, is used for lifting and lowering loads. It typically has cables or wire ropes attached, allowing it to hoist suspended loads. The power source is commonly electric or hydraulic.
There are two main types of hoisting devices: hoist type and crab trolley type. The hoist type combines an electric motor, reduction gear, brake, and the drum of the hoisting section. Wire rope and chain types are available. The configuration includes top-running and under-hung styles.
The crab trolley type integrates the hoisting and lateral-travel mechanisms into a single unit, running on double rails. This type is mainly used for heavy loads and high-speed operations.
5. Rigging
Hooks and rigging devices are used to lift loads with a crane. Attached to the hoisting machine, they facilitate the lifting of loads. In many cases, the maximum load capacity of the crane is indicated on these components.
Various rigging devices are used based on the application, but hooks are commonly employed. Other types include bucket-type, magnet-type, etc.
In Gantry Cranes used in ports, container spreaders are employed to handle the loading and unloading of containers.
Types of Gantry Crane
Gantry Cranes come in various types, including:
1. Hoist-type gantry Crane
This type of Gantry Crane utilizes a hoist in the hoisting device. It is cost-effective as it allows the use of pre-manufactured hoists.
2. Crab Trolley-Type Gantry Crane
This Gantry Crane employs a crab trolley that includes both the hoisting and lateral travel mechanisms. It is chosen for larger cranes. While robust and easy to maintain, it is individually designed based on installation space and capacity requirements, making it more expensive than the hoist type.