基于CA的服役混凝土箱梁桥耐久性分析与寿命预测

Durability analysis and life prediction of concrete box girder bridge in service based on CA

为建立混凝土桥梁受碳化和氯离子侵蚀的耐久性模拟方法,文章基于Fick扩散定律,结合混凝土中二氧化碳和氯离子的扩散规律,构建了模拟碳化和氯离子侵蚀及其耦合的三维Von Neuman型元胞自动机(CA)模型及求解流程,建立以碳化和氯离子侵蚀为耐久性控制要素的可靠度寿命预测方法。以服役的三跨预应力混凝土箱梁桥为例,结合桥梁实测数据分析了箱梁截面上混凝土中氯离子质量分数和碳化深度的分布规律,进行了混凝土箱梁的耐久性使用寿命预测。结果表明,采用本文三维CA模型的碳化和氯离子侵蚀模拟结果与服役桥梁的实测结果吻合良好,服役箱梁跨中截面外侧的腹板与底板相交区域是最容易发生耐久性失效的部位,该部位氯离子质量分数、碳化深度分别是截面外侧箱底中心部位的1.8倍、1.5倍;该部位也是桥梁耐久性寿命的控制部位,在服役环境下该部位受碳化影响的寿命最短,服役寿命为90.2年。

In order to establish the durability simulation method of concrete bridges exposed to carbonation and chloride ion erosion,based on Fick's diffusion law and combined with the diffusion law of carbon dioxide and chloride ion in concrete,a 3D Von Neuman cellular automata(CA)model considering carbonation,chloride ion erosion and their coupling is proposed and the corresponding solution process is given.Furthermore,a reliability life prediction method governed by carbonation and chloride ion erosion is established.Based on a three-span prestressed concrete box girder bridge in service,the durability service life of concrete box girder is predicted,and the distribution law of chloride ion concentration and carbonation depth in concrete of the box girder section is analyzed in terms of the measured data of the real bridge.It is shown that the simulation results of carbonation and chloride ion erosion using the 3D CA model are in good agreement with the measured results of the service bridge.The intersection part between the web and the bottom plate on the outside of the mid-span section of the service box girder is the most prone to durability failure,and at the part the chloride ion concentration and carbonation depth are 1.8 times and 1.5 times those at the center of the box bottom on the outside of the section respectively.The intersection part is also the control part of the durability life of the bridge,and under the service environment of carbonization,the service life of this part,which is 90.2 years,is the shortest.