The collapse simulation of underground reinforced concrete (RC) ducts surrounded by soil foundations in a fire is conducted using multi-scale finite element analysis. The underground RC ducts are found to be deteriorated by both long-term soil subsidence and creep and shrinkage of concrete. The long-term shear crack risk is clarified by site inspection of some underground RC ducts. To conduct the structural risk assessment, the multi-scale simulation is applied and its performance upgraded to 1000°C. The release of chemically bound water from hardened cement paste is developed in the scheme of micropore structural modelling. It is linked with the mesoscale thermodynamics of vapour and the mechanics of the solid skeleton, and its fracture is integrated with the macroscopic cracked concrete constitutive models. This framework is upgraded to include the spalling of concrete cover in the event of a fire, and the exposure of reinforcing bars to high temperatures during a fire is reproduced. As the moisture dynamics inside the micropores of concrete can be used to determine the creep and shrinkage of concrete, long-term RC deformation can also be consistently taken into account for its normal use.

中文翻译：

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基于模型的地下钢筋混凝土管道长期适用性和耐火性评估

使用多尺度有限元分析对火灾中被土壤基础包围的地下钢筋混凝土 (RC) 管道的倒塌模拟进行了模拟。发现地下 RC 管道因长期土壤沉降和混凝土的蠕变和收缩而恶化。通过对部分地下钢筋混凝土管道进行现场检查，明确了长期剪切裂纹风险。为了进行结构风险评估，应用了多尺度模拟并将其性能升级到 1000°C。在微孔结构建模方案中开发了硬化水泥浆中化学结合水的释放。它与蒸汽的中尺度热力学和固体骨架力学相联系，其断裂与宏观开裂混凝土本构模型相结合。该框架经过升级，包括发生火灾时混凝土覆盖层的剥落，并再现了火灾期间钢筋暴露在高温下的情况。由于混凝土微孔内的水分动力学可用于确定混凝土的徐变和收缩，因此在其正常使用时也可以始终如一地考虑长期RC变形。