锈蚀先张预应力混凝土构件传递长度研究

Research on Transfer Length of Pretensioned Prestressed Concrete Members Under Corrosion

锈蚀影响下先张预应力混凝土(PC)构件预应力传递长度评估对此类结构性能评价至关重要。首先基于厚壁圆筒理论,分析了预应力放张引起的端部混凝土开裂及传递界面受力特征。然后,考虑钢绞线七丝横截面锈胀特征,将初始放张开裂与锈胀开裂相结合,分析锈蚀影响下传递长度范围内混凝土二次开裂特征,得到传递长度范围内钢绞线侵蚀深度、锈蚀率与界面锈胀位移关系,并考虑开裂混凝土抗拉软化,推导传递长度内开裂混凝土及箍筋共同约束下钢绞线径向压应力计算模型,求得黏结应力分布。最后,基于黏结应力与预应力平衡关系,求得钢绞线与混凝土应变分布,确定锈胀开裂下预应力传递长度。将试验与理论结果对比表明所提出的方法可合理预测先张PC构件在不同锈蚀位置、锈蚀程度下的传递长度发展规律。

The evaluation of prestress transfer length of corroded pretensioned prestressed concrete(PC)members plays a significant role in assessing the performance of these structures.Firstly,the concrete cracking at member end and mechanical characteristics at the transfer interface caused by prestress releasing were analyzed based on the thickwalled cylinder model.Then,considering the rust expansion characteristics of seven-wire cross-section of steel strands,the further cracking characteristics of concrete along the transfer length under corrosion were analyzed by combining initial releasing cracking and corrosion-induced cracking,the relations between corrosion depth,corrosion loss and interfacial rust expansion displacement were established along the transfer length,considering the tensile softening of cracked concrete,the radial confining stress model of strands under the combined confinement of cracked concrete and stirrups was derived along the transfer length,then the bond stress distribution was obtained.Finally,based on the equilibrium relations between bond stress and prestress,the strain distribution of steel strands and concrete was obtained,and the prestress transfer length under corrosion-induced concrete cracking was determined.The comparison between analytical and experimental results showed that this method could reasonably predict the development laws of transfer length of corroded pretensioned PC members with various corrosion locations and degrees.