Railway box girders, as the core load-bearing components of railway bridge structures, their construction quality directly affects the safety, stability, and service life of railway lines. With the rapid development of high-speed railways and heavy-haul railways in China, higher requirements have been put forward for the structural precision, bearing capacity, and construction efficiency of box girders. However, railway box girder construction involves complex technological processes, from dimension control and component fabrication to painting and segment assembly, with each step facing numerous technical challenges. In-depth analysis and overcoming these difficulties are crucial to ensuring the quality of railway projects and promoting the upgrading of railway construction technology. This article focuses on the core difficulties in railway box girder construction, elaborates on their control points and countermeasures, providing references for practical construction.  

1. Control of Box Girder Dimensions

When controlling the dimensions of the box girder, it is necessary to ensure the matching degree of parameters such as length, width, and height. During construction, cutting should be carried out in accordance with the designed parameters of the upper and lower flange lengths. For the top plate, bottom plate, etc., the blanking width should be slightly larger than the designed width—specifically, both sides of the longitudinal baseline should be widened by approximately 1.5mm. In the process of box girder fabrication, construction personnel must strengthen the effective control of design data and pre-consider the deformation caused by lateral shrinkage under welding and constraint conditions.  

During blanking, the dimensions can be appropriately enlarged according to design requirements to reserve sufficient space for control. When assembling multi-segment box girders, temporary partitions can be set at the segment ports and removed after use. When matching the bottom plate and centerline, the height design must be completed in accordance with design requirements to ensure that the fabrication error is controlled within a reasonable range.  

2. Fabrication of Box Girders

The following points should be noted in box girder fabrication:  

- Fabrication of top and bottom plates: During fabrication, blanking correction should be prioritized for the top plate, bottom plate, and beveling positions. Attention must be paid to balance when lifting plates to avoid permanent deformation. After welding with a CO₂ automatic welding machine, reasonable correction should be performed.  

- **Fabrication of diaphragms**: Diaphragms should be cut semi-automatically for subsequent profiling operations, followed by special cutting of the main plate and large holes. When inspecting the platform, parameters such as flatness must be strictly controlled. In addition, during the assembly of vertical and horizontal ribs, a certain amount of shrinkage allowance should be reserved to ensure that the final supporting plates have room for adjustment. At the joint positions of plates, their edges must be fixed to the jig frame to avoid hidden dangers caused by loosening. During welding, welding deformation should be prevented to minimize the amount of post-welding trimming.  

3. Painting Process

In the painting process of box girders, sandblasting should be used for derusting to ensure that oil stains, oxidation, rust, and other impurities do not affect the final painting quality, thus guaranteeing the bonding strength between the coating and the sprayed surface. Then, full painting should be carried out by brushing, with the minimum film thickness exceeding 90% of the specified standard thickness. Finally, high-pressure airless spraying can be used in the topcoat process to ensure the neatness and aesthetics of the painting. After painting is completed, repair and inspection are required.  

4. Fabrication of Girder Segments

To shorten the construction period, before assembling the top plate, bottom plate, and girder segments, parts of the top plate and bottom plate should be pre-welded into hoisting blocks on the jig frame. During assembly, sample plates should be used to adjust and control the center distance of the weld U-ribs. To avoid welding deformation, construction personnel need to prefabricate anti-deformation before welding to improve flatness.  

During the welding of the bottom plate, the middle bottom plate should be placed on the jig frame, ensuring that its longitudinal and transverse baselines are aligned with those of the jig frame. Once confirmed correct, fixing construction can be carried out. In the bottom plate assembly stage, construction personnel must take the longitudinal and transverse baselines of the bottom plate as the standard, prioritize the assembly of the middle block, and weld the seams after the middle block is assembled. After welding, the side blocks and longitudinal diaphragms should be alternately assembled in a predetermined sequence. The flatness of the plates should be appropriately corrected, and the angle of the outer web should be controlled using a level. When assembling the middle top plate, attention should be paid to the top plate elevation, and the height of the box body should be controlled using a level, followed by optimization through grinding and repair.  

Conclusion

In summary, all links in railway box girder construction, including dimension control, component fabrication, painting process, and segment assembly, require precise control of technical details. Oversights in any link may affect the structural performance of the box girder and project progress. Construction teams must, in accordance with design requirements, adopt measures such as optimizing process parameters, strengthening process supervision, and prefabricating anti-deformation to address difficulties in each link, ensuring that the box girder quality meets standards. Only by strictly controlling the entire construction process can a solid foundation be laid for the safe operation of railway bridges, facilitating the high-quality construction of railway projects. In the future, with the application of new materials and technologies, railway box girder construction technology will continue to iterate and upgrade, providing stronger technical support for the development of China’s railway industry.