Factory Fabrication and Segmental Hoisting Technology for Long-span U-shaped Steel Box Girders

To address the challenges in the fabrication of long-span U-shaped steel box girders on urban congested road sections, such as difficult control of welding deformation, limited space for on-site hoisting, and low efficiency of temporary support systems, this paper takes the Fangcun Avenue South Expressway Project as the background and conducts a systematic study on the production and installation technologies of U-shaped steel box girders. The study proposes and implements a longitudinal and transverse segmented fabrication process, combined with a rapidly assembled and disassembled adjustable standard modular temporary support system, forming a construction method that integrates factory-based high-precision assembly with on-site segmented hoisting.In the manufacturing stage, a rigid anti-deformation jig and symmetrical welding process are adopted to control welding deformation within 3 mm, which is more than 40% lower than that of traditional processes (typically 5 mm~8 mm). In the installation stage, an integrated hoisting process incorporating segmented closure, symmetrical welding, and graded unloading is employed, achieving a hoisting efficiency improvement of approximately 40%, a 50% reduction in support assembly and disassembly time, a maximum hoisting weight reduced from 60 t (conventional process) to 43.3 t (a 28% reduction), a single-segment installation positioning accuracy of ±2 mm, and a maximum settlement of only 8.4 mm after unloading, all of which meet the design and specification requirements.After the application of this technology, the project was completed and opened to traffic 30 days ahead of schedule, effectively alleviating the surrounding traffic pressure and achieving significant social benefits. This study establishes a high-efficiency construction technology system for long-span U-shaped steel box girders integrating “precision manufacturing, modular support, and integrated hoisting.” The system demonstrates significant advancements in adaptability to rapid modular construction of temporary supports, and whole-process precision control, providing an important reference for similar prefabricated bridge projects.