In the previous article, we have detailed the complete construction process of curved steel box girder bridges—from the segmentation and fabrication of steel box girder segments, transportation and storage, erection of temporary supports, to hoisting and positioning, welding and connection, and construction of the bridge deck system. The orderly advancement of each step lays the foundation for ensuring bridge construction. However, to truly overcome core challenges brought by the curved structure, such as "complex alignment, special force conditions, and difficult precision control," it is inseparable from the support and breakthroughs of key technologies. These technologies not only determine the safety and efficiency of the construction process but also directly affect the structural stability and appearance compliance of the bridge after completion. This article will focus on the four core technologies in the construction of curved steel box girder bridges, and in-depth analyze the key points of welding, hoisting, alignment control, and temporary support design and construction, providing technical references for engineering practice.

1. Welding Technology

Welding technology is of crucial importance in the construction of curved steel box girder bridges. Due to the curved characteristics of steel box girders, the positions and angles of welding joints are more complex. First, it is necessary to accurately select welding materials and processes based on the steel material, thickness, and welding position. For example, for high-strength steel, low-hydrogen electrodes are often used to ensure the toughness and strength of the welds. During the welding process, welding parameters are strictly controlled. Excessively high welding current may lead to weld burn-through and deformation, while excessively low current may cause defects such as incomplete penetration; the voltage must match the current to ensure arc stability. At the same time, the welding speed is controlled to ensure the penetration depth and forming quality of the welds. Considering on-site environmental factors such as wind force and humidity, it is essential to take windproof, rainproof, and moisture-proof measures. In windy environments, wind shields are installed to avoid the interference of air flow on the welding arc. After welding, visual inspection is carried out in accordance with relevant standards to check for defects such as undercutting, blowholes, and cracks in the welds. Subsequently, non-destructive testing methods, such as ultrasonic testing and radiographic testing, are used to inspect the internal quality of the welds, ensuring that the welding quality meets the design requirements.

 2. Hoisting Technology

The hoisting of curved steel box girders is a highly challenging task. Since the girder body is curved, its center of gravity is difficult to determine, and the posture of the girder body needs to be accurately controlled during the hoisting process to meet the installation requirements. When selecting hoisting equipment, comprehensive consideration should be given to the weight, size, hoisting height of the steel box girders, and the site conditions of the construction site. Large floating cranes are suitable for bridge construction in water areas such as river-crossing and sea-crossing projects, with strong hoisting capacity and a wide operating range; while on land, large tower cranes or crawler cranes are more commonly used. Determining a reasonable hoisting plan is crucial. Before hoisting, the lifting point positions are determined through precise calculations to keep the steel box girders balanced during the hoisting process. Professional hoisting slings are used, and strict inspections are conducted on them to ensure their safety and reliability. During the hoisting process, advanced measuring instruments such as total stations and GPS are used to monitor the position and posture of the steel box girders in real time, compare and analyze them with the preset installation positions, and adjust deviations in a timely manner. At the same time, professional commanders are assigned to ensure the coordination of all hoisting links, and guarantee the accurate and safe positioning of the steel box girders.

3. Alignment Control Technology

Alignment control is a key technology to ensure the appearance and mechanical performance of curved steel box girder bridges. During the construction process of curved steel box girders, their alignment will change due to factors such as self-weight, construction load, and temperature variation. Before construction, an accurate structural analysis model is established, which takes into account the influence of various factors on the girder alignment, predicts the deformation of the girder body at each construction stage, and formulates a reasonable camber setting plan. During the construction process, advanced measurement methods, such as total station measurement and level measurement, are used to monitor the alignment of the girder body in real time. After the steel box girder segments are hoisted and positioned, the deviation between their actual position and the design position is measured in a timely manner, and the causes of the deviation are analyzed. If the deviation exceeds the allowable range, corresponding adjustment measures are taken. For example, methods such as adjusting the height of temporary supports and tensioning temporary cables are used to fine-tune the girder alignment. At the same time, the influence of temperature on the girder alignment is considered, and measurements and adjustments are carried out during periods of stable temperature. Throughout the construction process, the alignment control plan is continuously optimized to ensure that the alignment of the bridge after completion meets the design requirements, and guarantees the aesthetics and structural safety of the bridge.

4. Temporary Support Design and Construction Technology

As an important supporting structure for the construction of curved steel box girders, the rationality of the design and construction of temporary supports is directly related to construction safety and quality. When designing temporary supports, factors such as the bridge structure form, span, construction load, and geological conditions are fully considered. Based on mechanical principles, structural calculations are conducted on the supports to determine the arrangement form, member size, and connection method of the supports. Appropriate materials, such as steel pipes and section steel, are selected to ensure that the supports have sufficient strength, stiffness, and stability. During the construction process, the supports are erected in strict accordance with the design plan. The support foundation is treated to ensure that its bearing capacity meets the requirements. Precise measuring instruments are used to control the verticality and levelness of the supports, ensuring the erection accuracy of the supports. The connections of support joints must be firm and reliable; when welding or high-strength bolt connections are used, operations are carried out in strict accordance with relevant specifications. After the erection of the supports is completed, a comprehensive inspection and acceptance are conducted. To eliminate the inelastic deformation of the supports, preloading tests are usually required. The preloading load is applied according to a certain proportion of the design load. During the preloading process, the deformation of the supports is monitored; when the deformation is stable, the load is unloaded and the elevation of the supports is measured again, providing an accurate supporting platform for the hoisting of the steel box girders.

Conclusion

The above four key technologies are the core means to solve the construction difficulties of curved steel box girder bridges. The implementation quality of each technology is closely related to the overall construction effect of the bridge. As a professional bridge formwork manufacturer, we are well aware of the importance of "coordinated adaptation" between high-quality formwork and key construction technologies—whether it is the requirement for the precision of steel box girder segments in the welding process or the control of the forming size of the girder body in alignment control, we can customize high-precision and high-stability formwork plans according to your project technical parameters. At the same time, we provide full-process cooperation from the technical team to ensure seamless connection between the formwork and construction technologies, helping to overcome construction difficulties. In the next article, we will focus on "quality control in the construction of curved steel box girder bridges" and explain the key points of quality control in detail. Please stay tuned!