大跨P.C.箱梁桥施工期合龙段底板开裂破坏机理

Failure mechanism of closure segment bottom slab cracks of long-span P.C. box girders during construction

针对大跨预应力混凝土箱梁桥对称悬臂浇筑施工过程中合龙段底板开裂破坏问题,对其开裂破坏机理和相应防治对策进行了研究.将合龙段底板开裂破坏特征划分为局部崩裂破坏、整体撕裂破坏、整体崩裂破坏等3种典型破坏特征,结合3个典型破坏案例,进行全结构空间实体单元施工全过程仿真分析.研究结果表明:底板局部崩裂破坏属于混凝土斜截面受剪破坏,底板整体撕裂破坏属于混凝土受拉破坏,底板整体崩裂破坏属于混凝土徐变受压破坏.根据典型破坏特征对应破坏机理的分析结果,在防治对策上提出了减小作用效应和提高结构抗力2种主要应对措施,在构造措施上建议增加底板横向箍筋以提高底板三向应力状态下的承载能力.

The failure mechanism and prevention countermeasures of the closure segment bottom slab cracks of long-span P. C. box girders during symmetric cantilever construction were investigated. The destruction styles of the closure segment bottom slab were classified as local bursting, global tearing and global bursting. Based on three classic destruction examples, a whole structural construction simulation analysis with spatial solid elements was conducted. The analysis results show that local bursting belongs to shear destruction, and global tearing belongs to tension destruction with global bursting caused by creep compression. Two countermeasures of reducing action effects and improving structural capacity were proposed. As a constitution solution, transverse stirrup for bottom slab was suggested to enhance the carrying capacity under three-dimensional stress.