预应力精轧螺纹钢筋断裂原因

Fracture reasons of prestressed finish rolled screw-thread steel bars

某快速路悬臂结构的多根预应力精轧螺纹钢筋在张拉锚固完成后出现断裂现象。采用宏观观察、化学成分分析、微观分析、力学性能测试等方法分析了钢筋断裂的原因。结果表明:钢筋近表面处的组织为回火马氏体,使钢筋表面对应力腐蚀较为敏感,且在安装钢筋后未对其采取有效保护措施,导致表面出现腐蚀坑;钢筋对中性不良,使钢筋在张拉后受到额外的剪切应力,在拉应力和剪切应力的作用下,最终导致钢筋断裂。

Several prestressed finish rolled screw-thread steel bars of a cantilever structure of an expressway fractured after the completion of tensioning and anchoring.The causes of steel bar fracture were analyzed by macroscopic observation,chemical composition analysis,micro analysis and mechanical property test.The results show that the microstructure near the surface of the steel bar was tempered martensite,which made the surface of the steel bar more sensitive to stress corrosion,and the steel bar did not take effective protection measures after installation,resulting in corrosion pits on the surface.The steel bar was not neutral,so that the steel bar was subjected to additional shear stress after tension.Under the action of tensile stress and shear stress,the steel bar was finally broken.