1. Basic mechanics
There is a close relationship between the lifting capacity and span of the Double Girder Gantry Crane based on the principles of mechanics. From a mechanical point of view, the bridge structure of the crane can be simplified as a force model of the beam when bearing heavy objects. When the lifting capacity increases, the concentrated force acting on the bridge increases, and the bending moment and shear force generated on the bridge also increase accordingly. The span is an important factor affecting the stress condition of the bridge. The larger the span, the greater the bending moment generated under the same lifting capacity.
According to the bending moment calculation formula \(M=\frac{1}{8}QL^2\) in material mechanics (where \(M\) is the bending moment, \(Q\) is the concentrated force, i.e. the lifting capacity, and \(L\) is the span), it can be seen that the bending moment is proportional to the lifting capacity and the square of the span. This means that when the span increases, even if the lifting capacity remains unchanged, the bending moment borne by the bridge will increase significantly, and the strength and stiffness requirements of the bridge will be higher.
2. Considerations of structural design
In terms of structural design, in order to adapt to different combinations of lifting weights and spans, Double Girder Gantry Crane has corresponding design strategies. For small-span cranes, when the lifting weight is large, the double-beam structure of the bridge can adopt relatively small cross-sectional dimensions and lighter materials, because the smaller span makes the bending moment borne by the bridge relatively small. However, with the increase of span, in order to ensure that the bridge can safely carry the specified lifting weight, it is necessary to increase the cross-sectional dimensions of the double beams, improve the strength grade of the material, or change the structural form of the bridge, such as adding reinforcement ribs to improve the bearing capacity of the bridge.
At the same time, the design of the outrigger structure is also related to the lifting weight and span. Larger spans and lifting weights require more stable outriggers to support the bridge to prevent the bridge from excessive deformation or instability when subjected to force. The spacing, cross-sectional shape and material strength of the outriggers need to be optimized according to the lifting weight and span to ensure the stability of the entire crane structure.
3. Balance in practical applications
In practical applications, the relationship between lifting weight and span needs to be balanced by considering many factors. On the one hand, when choosing a crane, users need to determine the appropriate crane specifications based on the actual span of the work site and the maximum weight that needs to be lifted frequently. If you blindly pursue a large lifting capacity and ignore the impact of the span on the structure, it may cause the crane structure to be overstressed and cause safety hazards. On the other hand, during the design and production process, manufacturers will also develop a series of standard specifications of products based on the common lifting capacity and span requirements in the market, and through precise mechanical calculations and structural optimization, while ensuring safety, maximize the versatility and economy of the crane to meet the needs of different users.
