基于细观尺度时变模型的大跨度PC梁桥长期下挠开裂耦合分析

Long-term excessive deflection and concrete cracking of large-span prestressed concrete (PC) bridges are the dilemmas disturbing bridge engineers. Until now, there is still no effective numerical model yielding satisfactory predictions, compared to real measurements. This project devotes to enhancing the prediction in terms of PC bridge’s coupled long-term deflection and concrete cracking. At the beginning, through detailed RVE modelling of the concrete at meso-scale, we endeavour to reveal the mechanisms of time-dependent behaviors, including creep damage, and the influences originated from temperature and humidity cycling. These time-dependent behaviors are frequently witnessed in PC bridges but unfortunately ignored in current concrete time-dependent models in practice. Subsequently, the experiment will be deliberatively prepared to quantitively study the coupled phenomenon between the web cracking and deflection of the PC girder, and this phenomenon will further be realized through cohesive crack model. Finally, this project will build the multiscale constitutive law embracing the numerous potential influencing factors, including concrete creep and shrinkage, damage and cracking, prestressing loss, construction discrepancy, vehicle overloading, cyclic temperature and humidity, etc. Multiscale finite element method (FE2) is employed in the potential cracking regions at the web, to realistically capture their macro-scale responses from meso-scale behaviors. The probabilistic study will be performed, considering the uncertainties of these factors. In a word, this project will to great extent reveal the mechanism leading to excessive deflection and cracking of large-span PC bridges and provide suggestions to alleviate these illnesses.

大跨度PC梁桥长期持续“下挠-开裂”一直是困扰工程界的难题，并且现有预测结果与实测结果差距较大。本课题致力于揭示PC梁桥长期“下挠-开裂”的机理。首先，通过混凝土细观等效体积元（RVE）精细化分析，对当前时变模型中未能考虑的混凝土损伤、温度和湿度反复作用的影响展开研究。接着，通过试验量化PC梁腹板开裂和下挠的关系，并通过内聚裂纹模型实现“下挠-开裂”耦合分析。在此基础上，试图构建多因素作用的多尺度材料本构，包括混凝土徐变收缩、损伤开裂、预应力损失、施工误差、车辆超载、温度和湿度周期性变化等因素。在腹板易开裂区采用“细观-宏观”的多尺度有限元法（FE2），从而准确的模拟腹板开裂敏感区域的宏观响应。最后，开展多因素随机作用的PC梁桥长期“下挠-开裂”分析。预期本课题可揭示大跨度PC梁桥长期持续“下挠-开裂”机理，并为减轻此类病害提供理论依据和合理建议。

针对多跨连续梁桥长期下挠、预应力损失等问题，通过理论分析、有限元模拟、模型试验等方法，充分挖掘利用桥梁健康监测系统大数据，考虑多龄期混凝土徐变、空间效应等因素，对多跨刚构-连续桥梁应力演变、下挠过程、预应力退化等进行全过程演算，探究长期下挠-开裂机理，掌握桥梁运营期真实服役状态，并对连续刚构梁桥体外束加固方法关键技术进行分析。通过以上研究的开展，掌握刚构-连续梁桥长期开裂下挠耦合机理，有利于刚构-连续梁桥体外束加固关键技术的推广与应用，对多跨预应力混凝土连续刚构桥梁的安全运营与改扩建需求提供技术保障，具有深远的工程应用意义和经济社会价值。