高应变率反复荷载下约束再生混凝土大尺度试件损伤力学行为研究

Aiming at the basic problems which are induced by the material rate-sensitivity and the damage evolution of recycled aggregate concrete (RAC), the early tentative research work has paved the way for study on mechanical performance of confined recycled aggregate concrete (CRAC) under dynamic monotonic loading, which is financially supported from Projects funded by China Postdoctoral Science Foundation through Grant Nos. 2014M550247 and 2015T80449. On the basis of the previous research work, these basic methods such as the theoretical analysis and the experimental study are combined and carried out to investigate and analyze thoroughly and systematically the mechanical behavior and constitutive relationship of CRAC at cyclic loading conditions with high strain. The development regularity of cracks and failure modes for CRAC under dynamic cyclic loading conditions are described and analyzed. The mechanical parameters such as the strength and the deformation are examined thoroughly to investigate the strain rate-sensitivity and confinement effect of CRAC under cyclic loading. Correspondingly, the empirical calculation formulas of the dynamic increase factors (DIF) on the strength and deformation are proposed, and the function models of the dynamic constraint factor on the strength and deformation are put forward. The influence of loading history for both monotonic and cyclic loads on CRAC behaviors such as the strength, the deformation, the crack propagation, and the complete curve of stress-strain relation are analyzed and compared. The variations for both unloading and reloading curves under dynamic cyclic loading are investigated deeply, the corresponding curve equations are proposed. The mechanism of damage evolution of CRAC at the process from initial loading to final failure under dynamic cyclic loading conditions is investigated, and the dynamic damage evolution equation is proposed. The dynamic increase factor, the dynamic constraint factor and the damage are coupled with the envelope curve, the normalized empirical formula for complete curve of dynamic damage constitutive relation of CRAC is proposed and established.

针对再生混凝土率敏感性和损伤演化等基础性问题，在前期研究工作中，对约束再生混凝土在动态单调荷载下的力学性能作了初步的探索性研究（中国博士后科学基金项目面上“一等资助”和特别资助）。在此基础上，采用理论分析和试验研究相结合的方法，将重点开展约束再生混凝土在高应变率反复荷载下的力学性能和本构关系研究。分析约束再生混凝土在动态反复荷载下的裂缝发展规律和破坏特征；研究高应变率反复荷载下约束再生混凝土的强度和变形性能，提出动态放大系数和约束因子计算公式；分析比较荷载史（反复和单调荷载）对约束混凝土性能的影响；研究卸载曲线和再加载曲线的变化规律，提出卸载曲线和再加载曲线方程；考察约束再生混凝土在受压荷载动态反复作用下的损伤演化过程，提出动态损伤演化方程。采用数据回归技术，提出受压荷载反复作用下统一化的约束再生混凝土动态损伤本构关系曲线经验公式。

基于约束再生混凝土系列动态试验研究和理论分析，揭示了再生粗骨料取代率、应变率效应和约束效应对再生混凝土各类受力构件破坏特征的影响规律。得出了再生混凝土比普通混凝土率敏感性更为显著的重要结论，在快速加载下 (应变率10-3/s～10-1/s)，再生混凝土抗压强度比普通混凝土抗压强度提高约10%，提出了再生混凝土动态因子模型 (DIF)；针对再生混凝土受力特点，同时考虑工程建造成本，在进行再生混凝土结构设计时，采用箍筋约束措施，将再生混凝土在强地震动下的结构延性系数提高了20%~25%，很大程度上弥补了再生混凝土材料脆性比普通混凝土脆性低的缺陷，给出了再生混凝土约束因子模型 (CIF)；创建了将应变率效应、箍筋约束效应和取代率影响耦合的再生混凝土率型本构关系模型；提出的再生混凝土率型本构关系模型应用于再生混凝土结构动力非线性分析，将在弹塑性阶段的预测误差控制在10%以内，在强非线性阶段的预测误差平均值降低到17%以下，很好的提高了数值预测与试验结果的吻合度。基于再生混凝土结构的抗震性能和损伤演化机理研究，确定了结构损伤阈值，优化了传统的结构损伤评估方法。