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What is a crane composed of?
Crane The traveling mechanism typically employs only four driving and idler wheels. When the lifting capacity is very large, additional wheels are usually added to reduce wheel pressure. When more than four wheels are used, a hinged balancing frame must be incorporated to ensure that the crane’s load is evenly distributed among all wheels.
The metal structure of a bridge consists of main girders and end girders, and is classified into two main types: single-girder bridges and double-girder bridges. A single-girder bridge comprises a single main girder and end girders on both sides of the midspan, whereas a double-girder bridge consists of two main girders and end girders.
The main girder is rigidly connected to the end girders, and wheel supports are mounted at both ends of the end girders to enable the bridge to run on an elevated platform. The main girder is welded to the track to provide a running path for the crane trolley. There are many structural types for such bridges, including box-girder structures, four-truss structures, and open-web truss structures.
Box-type structures can be classified into two types: on-orbit box-type double-girder, off-orbit box-type double-girder, and off-orbit box-type single-girder. The box girder is a widely used basic structural form. The main girder consists of upper and lower flange plates and vertical web plates on both sides. The trolley track is installed along the centerline of the upper flange plate. This design features a simple structure, easy fabrication, and suitability for mass production; however, it has a relatively large self-weight.
Eccentric box girders and their cross sections consist of upper and lower flange plates, as well as primary and secondary webs of unequal thickness. The trolley track is mounted on top of the primary web, allowing the short stiffening plates within the box section to be omitted. In particular, eccentric box girders can be replaced by wide-flange box girders, which have a lower self-weight but are more complex to fabricate. A four-truss structure is a closed-space structure composed of four planar trusses. Typically, a walking platform is laid on the upper horizontal truss plane, resulting in a light self-weight and high stiffness. However, compared with other structural forms, it has larger dimensions, more complex fabrication, and lower fatigue strength, hence its production volume is relatively small.
The open-web truss structure is similar to an external box girder for railway tracks, consisting of a closed configuration formed by four steel plates. With the exception of the main web, which is made of solid I-beams, the remaining three steel plates are cut into multiple openings according to design requirements, thereby creating an open-web truss without diagonal bracing. Walking decks are laid on the top and bottom transverse girders, and crane traveling mechanisms and electrical equipment are installed inside the bridge. This design features low self-weight and high overall stiffness, making it a widely used type in China.
Keywords:
Crane
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