Answer: Gantry cranes are a variation of bridge cranes. They are mainly used for loading and unloading operations of goods and bulk materials in outdoor yards and material yards. Its metal structure is like a gate-shaped frame, with two legs installed under the main beam, which can directly walk on the ground track, and the main beam can have cantilever beams at both ends. Gantry cranes have the characteristics of high site utilization rate, large operation range, wide adaptability, and strong versatility. In the stone industry, it is mainly used for lifting and unloading rough materials.
Structural Form Classification
I. According to the gantry structure form
　　Gantry cranes and cantilever gantry cranes
　　Gantry crane
　　1. Full gantry crane: The main beam has no overhang, and the trolley operates within the main span.
　　2. Half-gantry crane: The legs have a height difference, which can be determined according to the civil engineering requirements of the site.
Cantilever gantry crane
1. Double cantilever gantry crane: This is the most common type of structure, and its structural force and effective use of site area are reasonable.
2. Single cantilever gantry crane: This type of structure is often chosen due to site limitations.
II. According to the main beam structure form
1. Single-girder gantry crane
Single-girder gantry cranes have a simple structure, convenient manufacturing and installation, small self-weight, and the main beam is mostly an off-track box-shaped frame structure. Compared with double-girder gantry cranes, the overall rigidity is weaker. Therefore, when the lifting weight Q≤50t and the span S≤35m, this form can be adopted. Single-girder gantry cranes have two forms: L-shaped and C-shaped. The L-shaped one is convenient for manufacturing and installation, has good stress conditions, and has a smaller self-weight. However, the space through the legs for hoisting goods is relatively small. The C-shaped leg is made into an inclined or curved shape to have a larger lateral space so that the goods can pass through the legs smoothly.
2. Double-beam bridge crane
Double-beam bridge cranes have strong load-bearing capacity, large span, good overall stability, and many varieties, but their self-weight is larger than that of single-girder gantry cranes with the same lifting weight, and the cost is also higher. According to the different main beam structures, they can be divided into box beams and trusses. At present, box structures are generally used.
III. According to the application form
1. Ordinary gantry crane, track gantry crane
This type of crane mostly adopts box-type and truss-type structures, and is the most widely used. It can handle various finished goods and bulk materials, with a lifting weight of less than 100 tons and a span of 4 to 39 meters. The ordinary gantry crane using a grab has a higher work level. Ordinary gantry cranes mainly refer to hook, grab, electromagnetic, and hoist gantry cranes, and also include half-gantry cranes.
2. Hydropower station gantry crane
It is mainly used for lifting and opening and closing gates, and can also be used for installation operations. The lifting weight is 80 to 500 tons, the span is small, 8 to 16 meters; the lifting speed is low, 1 to 5 meters/minute. Although this type of crane does not often lift, the work is very heavy once used, so the work level should be appropriately improved.
3. Shipbuilding gantry crane
4. Container gantry crane
Used for assembling ship bodies on shipways, it often has two crane trolleys: one has two main hooks, running on the tracks on the flanges of the bridge; the other has one main hook and one auxiliary hook, running on the tracks on the lower flanges of the bridge, in order to turn over and lift large ship body sections. The lifting weight is generally 100 to 1500 tons; the span is up to 185 meters; the lifting speed is 2 to 15 meters/minute, and there is also a micro-movement speed of 0.1 to 0.5 meters/minute.