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

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