海蚀环境钢筋混凝土梁桥损伤监测与安全评价

Durability of reinforced concrete (RC) bridge degenerates severely in marine environment. Corrosion of reinforcing bar is one of the most important reasons for durability deterioration which threatens the service safety of bridge and cause enormous losses to national economy. Therefore, the damage monitoring and safety assessment for RC Girder Bridge in marine environment are proposed in the proposal. Firstly, a new method of monitoring corrosion of reinforcing bars in situ is proposed based on prestressed self-balancing principle. The mechanism is the fact that the increase of bond stress between concrete and prestressed reinforcing bar due to corrosion can be obtained by detecting the strain variation of measuring points in self-balancing system. The mathematical models between degree of corrosion and strain of measuring points are established as the foundation of corrosion monitoring of reinforcing bars. Further, the in situ monitoring corrosion sensor is designed and the performance of monitoring corrosion sensor is verified by accelerated corrosion experiment. Secondly, the correlations of accelerated corrosion experiment and natural marine environment are established by using corrosion kinetics. The equivalence and applicability of accelerated corrosion experiment are discussed in this proposal. In order to ensure equal probability of corrosion initiation of different RC member of the Girder Bridge, the new durability design principle of RC Girder Bridge is proposed considering different service environment and different cross-section shape of RC members. Also, the discrete Markov chain model is used to describe the corrosion states of reinforcing bars. The transition probability function of the Markov stochastic process is updated by the data of monitoring corrosion. Thirdly, a multi-parameter Weibull model is proposed to describe the strength of corroded prestressing steel strand. Based on the multi-parameter Weibull model, Monte Carlo method is used to simulate the bearing capacity model of corroded strand bundle. The sensitive parameters and their control values are extracted to describe the deterioration process of bearing capacities of RC members. Further, the time-dependent models of bearing capacities are established. The failure criteria of corroded RC Girder Bridge are studied by using Life-Quality Index considering the failure lost, importance, location, type of the bridge. Finally, the reliability theory and multi-objective optimization are used to build safety assessment model of Girder Bridge. The RC Girder Bridge is considered as a weakest-link system which is composed by the important members. The weakest-link system reliability index is calculated to assess the safety of RC Girder Bridge. The optimum inspection and repair strategy and remaining service life are discussed thoroughly. The ultimate goals of this proposal are to establish the durability and safety assessment system of RC Girder Bridge in marine environment.

海蚀环境钢筋锈蚀严重威胁我国近海混凝土桥梁的服役安全，给国民经济带来巨大损失。本项目以海蚀环境为背景，以钢筋混凝土梁桥为研究对象，从锈蚀监测着手研究锈蚀演化与锈后性能并最终形成安全评价方法。提出基于预应力自平衡体系的钢筋锈蚀监测方法，构建锈蚀程度与体系内各测点应变的数学模型，设计锈蚀监测传感器。从腐蚀动力学角度建立人工气候与真实环境在时间域上的相关关系，研究人工气候的等效模型，并通过钢筋锈蚀监测数据验证该模型，提出海蚀环境梁桥结构等概率耐久性设计方法，基于锈蚀监测数据构建钢筋锈蚀状态Markov链随机模型。研究表征锈蚀钢绞线强度的多参数Weibull模型并建立锈蚀钢绞线束承载力模型；建立基于锈蚀监测的钢筋混凝土梁桥构件承载力时变模型及其失效准则，基于最弱联体系可靠度并采用多目标优化准则研究锈蚀钢筋混凝土梁桥的最优维修决策与剩余寿命预测，建立海蚀环境钢筋混凝土梁桥损伤监测与服役安全评价体系。

钢筋、钢绞线锈蚀严重威胁我国沿海钢筋混凝土桥梁的服役安全，给国民经济带来巨大损失。本项目系统开展海蚀环境钢筋混凝土梁桥耐久性损伤监测与安全评价研究。首先，提出基于预应力自平衡体系平面应力状态应力集中的原位锈蚀监测新方法，通过点蚀导致的应力集中，锈蚀监测传感元件局部应变突变实现锈蚀监测，应变测点越靠近锈蚀监测面、蚀坑形状越尖锐、敏感栅长越短、敏感栅中心距越小时锈蚀监测越敏感，通过在保护层不同深度布设锈蚀监测传感元件，采用Bayesian理论依次更新钢筋位置的初始锈蚀与锈蚀风险，提高锈蚀监测的可靠性。其次，考虑阻滞及胶凝材料吸附作用，计算暴露区域、保护层厚度、配合比、温湿度条件、临界浓度及角部二维扩展对钢筋初锈时间的影响，将敏感参数视为随机变量构造Kriging代理模型，采用Monte Carlo模拟钢筋初锈时间的概率分布，根据设计使用期内暴露区域及钢筋所处位置的锈蚀风险，设计不同保护层厚度使不同部位的钢筋具有相同的初锈时间且超越概率相同，系统地建立海蚀环境钢筋混凝土结构等概率耐久性设计方法。最后，确定锈蚀钢筋、钢绞线剩余疲劳寿命是海蚀环境钢筋混凝土梁桥失效的关键控制因素，构建考虑锈蚀程度影响的钢筋、钢绞线疲劳寿命预测统一多参数Weibull模型及钢绞线束疲劳寿命预测模型，钢绞线、钢绞线束疲劳寿命随着锈蚀程度增加而迅速减小，低应力幅条件下钢绞线、钢绞线束疲劳寿命随着锈蚀程度的增加降低更多，随着锈蚀程度的增加，指定疲劳寿命下钢绞线的许用应力幅迅速降低。通过锈蚀监测、初锈时间模拟及传感元件布设，实现初始锈蚀与锈蚀风险的监测及更新，形成海蚀环境钢筋混凝土结构等概率耐久性设计方法，考虑锈蚀后剩余疲劳寿命控制梁桥的服役安全，构建锈蚀钢筋、钢绞线疲劳寿命预测模型，以10%断丝率作为锈蚀钢绞线束疲劳寿命终止条件，系统地形成海蚀环境钢筋混凝土梁桥损伤监测与服役安全评价体系，对新建桥梁耐久性设计及在役桥梁剩余寿命评价具有重要的指导价值。