Effects of Steel-fibers on the Degradation of High-Performance Concrete subjected to Fatigue Loading - Testing and Modeling

目前还没有关于高性能混凝土和超高性能混凝土在疲劳荷载作用下劣化的系统研究。这一点对于钢纤维改性高性能混凝土和超高性能混凝土在多级和顺序加载下尤其适用。此外，数值方法和模型通常使用文献中的实验数据进行校准，由于实验和数值模型之间缺乏协调，因此不能进行全面的校准。因此，本项目旨在利用多尺度方法和相场理论来测试、描述和模拟钢纤维改性高性能混凝土和超高性能混凝土在疲劳荷载下的包括损伤累积在内的持续劣化过程。疲劳载荷除单级疲劳外，还包括多阶段疲劳载荷。研究中使用了两种高性能混凝土(SPP2020标准混凝土)。采用高强混凝土和超高强混凝土，高强混凝土采用钩端钢纤维，纤维含量在23 kg/m³至115 kg/m³之间，超高强混凝土采用光滑的高强短纤维，纤维含量分别为57 kg/m³和115 kg/m³。为了对损伤演变进行实验和数值分析，在第一个供资期间进行了广泛的静态纤维拔出试验以及静态和循环弯曲拉伸试验和循环压缩试验，并根据损伤指标描述了退化情况。这些指标包括裂纹张开发展、剩余刚度发展和损伤能量耗散。实验和数值模拟的紧密结合使得模型和材料描述的校准和验证成为可能。在第二个资助期，将补充高循环多阶段加载序列，考虑弯曲和压缩疲劳载荷下的序列效应。对于室内试验，现有的仿真模型在效率方面得到了进一步的发展，特别是在高循环载荷领域。为此，开发、校准和验证了基于特定测试的循环跳跃方法，以模拟和预测在高循环负荷下的退化。基于计划工作计划中的步骤，在实验虚拟实验室的意义上对实验和建模的交互作用进行了评估和优化。在这个实验室的帮助下，未来将有可能在几个试验的基础上对高性能混凝土的疲劳性能进行数值评估。

Systematic investigations of the deterioration of high- (HPC) and ultra-high-performance concrete (UHPC) subjected to fatigue loading are currently not available. This holds especially true for steel-fiber modified HPC and UHPC subjected to multi-level and sequence loadings. Furthermore, numerical approaches and models are often calibrated using experimental data from literature, which does not allow a comprehensive calibration due to lacking coordination between experiments and numerical models.Therefore, this project aims at testing, describing and modelling the ongoing deterioration including damage accumulation of steel-fiber modified HPC and UHPC subjected to fatigue loading, using multiscale approaches and phase-field theory. In addition to single-stage fatigue loads and the fatigue loads include multi-stage collectives. Two high-performance concretes (reference concretes of the SPP2020) are used for the investigations. A high-strength concrete with hooked-end steel fibres with fibre contents of 23 kg/m³ to 115 kg/m³ and an ultra-high-strength concrete with smooth, high-strength short steel fibres and fibre contents of 57 kg/m³ and 115 kg/m³ are used. For the experimental and numerical analysis of the damage evolution, extensive static fibre pull-out tests as well as static and cyclic bending tensile tests and cyclic compression tests were carried out in the first funding period and the degradation was described based on damage indicators. These indicators include crack opening development, residual stiffness development and energy dissipated into damage. The close collaboration between experiment and numerical simulation enabled calibration and validation of the models and material descriptions.In the second funding period, the experiments will be supplemented by high cyclic multi-stage loading sequences, taking into account sequence effects under flexural and compressive fatigue loading. For the in silico tests, the already existing simulation models are further developed with regard to efficiency, especially in the area of high cyclic loads. For this purpose, cycle jump approaches are developed, calibrated and validated on the basis of specific tests to model and predict degradation at high cycle loadings. Based on the procedure in the planned work program, the interaction of experiments and modelling is evaluated and optimized in the sense of an experimental virtual lab. With the help of this lab, it will be possible in future to numerically evaluate the fatigue behaviour of high-performance concretes based on few tests.