锈蚀影响下预应力筋与混凝土界面行为及构件承载力研究

Adverse environment leads easily to the corrosion of strands in Prestressed Concrete (PC) bridges. This will deteriorate the interface behavior between the strand and concrete. Structural safety and durability would be affected. However, very few studies have been performed for this problem. The existed pre-tensioned concrete bridges are chosen as the research background in this proposal. The features in the proposal is that the study focuses on the strand corrosion-induced concrete cracking, the bond behavior, stress transfer deterioration, and the degradation of the structural carrying capacity induced by the coupling effects of these factors. Both the experimental tests and theory analysis will be adopted. The main tasks include: ①The accumulation and development of corrosion rust within the interface between strand and concrete under the effect of prestressed force, the mechanism and the prediction model of concrete cracking induced by strand corrosion. ②The degradation of bond performance, the mechanism of stress transfer, and the calculation models for the stress transfer and anchorage length of strand under the effect of corrosion and cracking. ③The spatial distribution characteristics and the quantization method for the strain compatibility between corroded strand and concrete. ④The prediction methods for the deformation and carrying capacity of corroded pre-tensioned concrete bridge members. The spatial distribution characteristics of corrosion, the local stiffness degradation and the anchorage failure will be involved. This work will provide some scientific evidences for improving the existed assessment theory and guiding the repair and reinforcement decision-making of existed PC bridges.

不利环境极易导致混凝土桥梁中预应力钢绞线的锈蚀，引起钢绞线和混凝土界面行为退化，进而威胁结构安全，而相关研究十分缺乏。本项目以既有先张预应力混凝土桥梁为工程背景，特色在于关注锈蚀和预应力共同作用下钢绞线与混凝土界面间开裂、粘结和应力传递行为改变、结构承载力退化问题，联合试验和理论开展研究，内容包括：①研究预应力作用下钢绞线与混凝土界面间锈蚀产物累积和发展过程，揭示预应力混凝土胀裂机理，建立锈胀开裂预测模型；②探究锈蚀/胀裂下钢绞线与混凝土粘结力退化规律，揭示锈蚀对界面间预应力传递的影响机理，建立预应力传递和锚固长度计算模型；③明确锈蚀粘结退化影响下钢绞线与混凝土间不协调变形空间分布特征，提出不协调变形量化方法；④考虑锈蚀空间分布、局部刚度退化、锚固失效等影响，发展锈蚀桥梁构件变形和承载力计算方法。研究成果将有益于完善既有预应力混凝土桥梁评估理论，提升维修加固决策能力。

不利环境易导致钢绞线锈蚀，造成钢绞线和混凝土界面行为退化，威胁先张预应力混凝土结构服役安全。因此，研究锈蚀影响下预应力筋与混凝土界面行为，建立构件承载力计算方法具有重要的理论和应用价值。.针对锈蚀先张预应力混凝土构件性能退化问题，开展了不同应力状态下混凝土锈胀开裂、锈胀开裂试件粘结拉拔、锈蚀混凝土构件弯拔等系列试验，建立了预应力混凝土保护层锈胀开裂、锈蚀钢绞线粘结-滑移模型，提出了锈蚀钢绞线应力传递长度计算方法，提出了锈蚀粘结退化下钢绞线与混凝土界面间不协调变形量化方法，建立了锈蚀先张预应力混凝土构件承载力计算模型。.结合试验、理论研究，取得了如下成果：(1)预应力会加快混凝土锈胀开裂，当预应力达到75%钢绞线抗拉强度时，保护层开裂临界时间降低了22%，裂缝扩展速率增加了9%。(2)轻微的锈蚀(小于6.24%)对钢绞线和混凝土之间的粘结性能具有促进作用；进一步地锈蚀会引起粘结强度和粘结刚度的退化，尤其是当锈蚀率大于9.26%或者锈胀裂缝宽度大于0.67mm时，粘结退化尤为明显。(3)锈蚀粘结退化引起的不协调变形受锈蚀率、加载水平等影响。轻微锈蚀对不协调变形具有很小的影响直到锈蚀率超过某一临界值。此后，锈蚀率越大，不协调变形出现时的荷载水平越低，破坏时的不协调变形越明显。(4)锈蚀率较低时，粘结退化对抗弯承载力影响较小；当锈蚀率大于12.0%时，粘结退化对抗弯承载力影响较大，并随着锈蚀率的增加逐渐明显，承载力计算时应予以考虑。.项目组经过4年刻苦攻关，在学术期刊、会议上共发表论文20篇，其中SCI收录论文15篇，获得2018年湖南省技术发明一等奖、2019年中国公路学会科学技术一等奖各1项，培养博士研究生4人、硕士研究生8名。研究成果完善了既有预应力混凝土桥梁评估理论，提升了维修加固决策能力。