预应力效应对小箱梁纵向开裂影响分析

Analysis of effect of prestress effect on longitudinal cracks of small box girder

公路装配式预应力混凝土小箱梁纵向开裂问题较为普遍,纵向裂缝会严重影响结构安全及耐久性能,甚至降低桥梁结构承载力。本文以30 m装配式小箱梁为分析对象,根据后张法预应力对小箱梁梁体的作用机理,采用有限元软件ANSYS并基于等效荷载法,对预应力钢束张拉过程作用于小箱梁梁体的端部锚固力、曲线段径向力、管道偏差力等3种荷载引起的梁体竖向应力进行仿真分析。结果表明:端部锚固力引起的混凝土局部承压区竖向拉应力最大,达到1.503 MPa,发生在距梁端1.5 m附近截面;曲线段径向力引起的梁体竖向拉应力较小,可忽略其对纵向开裂的影响;在规范允许的施工误差范围±1 cm内,管道偏差力引起的梁体竖向拉应力介于0.610~3.250 MPa之间,可能导致梁体纵向开裂。

The longitudinal cracking problem of prestressed concrete small box girder assembled in highway is common.The longitudinal cracking will seriously affect the structural safety and durability,and even reduce the bearing capacity of bridge structure.A 30 m prefabricated small box girder is taken as the object of analysis.According to the action mechanism of post-tension-method prestressing on the small box girder,the finite element software ANSYS based on the equivalent load method is used to simulate and analyze the vertical stress of the small box girder caused by three kinds of loads:the end anchorage force,radial force of curve section and pipeline deviation force.The results show that the vertical tensile stress caused by the end anchorage is 1.503 MPa,which occurs at the section about 1.5 m away from the end of the beam.The vertical tensile stress caused by the radial force of the curve section is small,and its effect on the longitudinal cracking can be ignored.Within the allowable construction error range of±1 cm,the vertical tensile stress of beam body caused by pipeline deviation force ranges from 0.610 MPa to 3.250 MPa,which may lead to longitudinal cracking of beam body.