Abstract: This paper focuses on the longitudinal cracks that occur in the web of variable cross-section box beams during the cantilever construction of long-span prestressed concrete continuous girder bridges. Based on detailed on-site observation data and phased treatment practices, a systematic analysis of the causes and countermeasures is conducted. The crack characteristics are manifested as oblique extension along the direction of the prestressed ducts, with a length of approximately 2 meters, a width of up to 2 mm, and a depth of about 5 cm. The research reveals that the causes have distinct phased features: in the early stage, it is attributed to the non-uniform stress and material segregation during the concrete pouring period; in the later stage, it is mainly due to the improper prestress tension sequence and insufficient anti-crack reserve of the structure. Through the implementation of targeted measures (increasing the stiffness of the hanging basket, optimizing the concrete pouring process, enhancing the structural reinforcement, and adjusting the tension sequence), the crack defects are successfully eliminated. This study provides important theoretical basis and practical references for the quality control of similar bridge construction.

Key words: variable cross-section box beam, hanging basket construction, longitudinal cracks, prestress tension, anti-crack design, construction control

摘要： 针对大跨径预应力混凝土连续梁桥挂篮悬臂施工中变截面箱梁腹板出现的纵向裂缝问题,文中基于现场观测数据与分阶段治理实践,进行系统性成因分析与对策研究。裂缝特征表现为沿预应力管道方向斜向延伸、长度约2m、宽度达2mm、深度约5cm。研究揭示其成因具有显著的阶段性特征:早期归因于混凝土浇筑期的非均匀受力与材料离析,后期则主要源于预应力张拉次序不当与结构抗裂储备不足。通过实施针对性措施(增加挂篮刚度、优化混凝土浇筑工艺、增强构造配筋、调整张拉次序),成功消除了裂缝病害。此研究为同类桥梁施工质量控制提供了重要的理论依据与实践参考。

关键词: 变截面箱梁, 挂篮施工, 纵向裂缝, 预应力张拉, 抗裂设计, 施工控制