The previous article has detailed the key construction technologies of steel box girders for long-span highway bridges. As a core link to ensure the implementation of technologies and guarantee the safety, stability and service life of bridges, construction quality control is of great significance. This article focuses on key dimensions such as technical preparation, manufacturing quality and welding deformation control, and proposes targeted control measures to provide reference for practical construction.

1. Conduct Adequate Technical Preparation

For the construction of long-span continuous steel box girders in complex traffic environments, it is necessary to focus on formulating two core plans to ensure construction safety and quality.

(1) Special Construction Plan for Steel Box Girder Installation. Before installation, comprehensive planning shall be carried out with design documents as the core and in combination with the general construction organization design. The plan shall cover construction deployment, processes, key process guidance, quality inspection standards, safety guarantees and emergency plans. Clarify key contents such as transportation and hoisting parameters, assembly precision requirements and temporary support standards, refine inspection indicators such as raw material inspection, component processing and node assembly, and formulate protective measures for risk points such as hoisting and high-altitude operations. The plan can be implemented only after expert demonstration and approval.

(2) Special Traffic Diversion Plan. Most long-span bridges are located in busy traffic sections. The construction unit shall communicate with traffic management, road administration and other departments in advance to grasp the surrounding traffic flow, road network distribution and other conditions, and formulate a diversion plan in combination with the construction period and enclosure scope. The plan shall clarify traffic guidance routes, traffic sign and marking settings, personnel allocation and inspection mechanisms, and shall be publicized after approval by the traffic management department to reduce the impact of construction on citizens' travel.

2. Control Manufacturing Quality

The manufacturing quality of steel box girders directly determines the subsequent construction and structural performance, so it is necessary to strengthen the control of key links such as deflection calculation and formwork precision control.

First, accurately complete deflection calculation and pre-bending dimension determination. Technical personnel shall comprehensively analyze influencing factors such as traffic load, structural dead weight, welding deformation and temperature change, establish a model for accurate calculation through professional software, and determine pre-bending dimensions that take both stress rationality and construction feasibility into account. Ensure that the design alignment requirements are met after installation, and guarantee driving smoothness and structural stability.

Second, strictly control the precision of the formwork. According to the deflection calculation results and structural curvature, determine the precision parameters of the formwork such as elevation, plane position and verticality, and use the deflection distribution method combined with the parabola equation for detailed calculation to accurately locate the support points. During manufacturing, high-precision instruments such as total stations are used for real-time monitoring and adjustment, and the spacing between steel longitudinal and transverse beams is controlled within 2m to ensure rigidity. After the formwork installation is completed, a load preloading test shall be carried out to check the stability and bearing capacity.

3. Welding Deformation Control Process for Butt Joint of Steel Box Girder Plates

Welding deformation of steel box girder plate butt joints will directly affect the structural dimension precision and mechanical performance, so full-process control from pre-welding, welding to post-welding is required.

Three key points shall be controlled in pre-welding preparation: first, ensure that the welding materials match the main materials of the steel box girder, and they can be used only after passing chemical composition analysis and mechanical performance test upon entering the site; second, accurately process and clean the welding groove to ensure that the dimension is compliant and the surface is free of impurities; third, determine welding process parameters such as welding current, voltage and welding speed according to material characteristics, and conduct welding process qualification test if necessary to verify the rationality of the parameters.

During welding, adopt reasonable welding sequence and methods to control deformation. For long welds, segmented backstep welding and skip welding are used to reduce shrinkage deformation caused by concentrated welding heat; for welds of symmetrical structures, symmetrical welding is used to offset welding deformation; carbon dioxide gas shielded welding is preferred to reduce heat input. Arrange professional personnel for operation to avoid welding defects.

Timely detect deformation after welding. If the deviation exceeds the allowable limit, flame straightening or mechanical straightening shall be adopted. Strictly control the flame temperature and mechanical straightening force to avoid damaging the material or causing secondary deformation. Re-inspection shall be carried out after straightening to confirm compliance.

Conclusion

In summary, with the development of the construction industry, the construction scale and technical difficulty of long-span highway bridges have increased. The rational application of steel box girder assembly technology can improve the scientificity of construction plans and reduce the incidence of problems. Construction units must fully recognize the value of steel box girders and the importance of quality control, strictly follow relevant specifications and standards, strengthen the control of various links, and ensure construction safety and overall quality. At the same time, optimize control measures in combination with on-site actual conditions, accumulate construction experience, promote the improvement of steel box girder construction technology and quality control level, and provide guarantee for the high-quality development of highway transportation infrastructure.