Reinforced concrete (RC) infrastructure typically endures repeated subcritical loading throughout its operational lifespan, potentially compromising structural integrity. A realistic loading condition of these structures consists of constantly changing maximum and minimum load events. Characterizing the fatigue response of concrete proves challenging due to its heterogeneous and quasi-brittle nature, leading to varying fatigue lifetimes depending on the loading sequence. Understanding the impact of this so-called load sequence effect stands as a critical facet in ensuring structural longevity and reliability of current infrastructure. This paper offers insights into this phenomenon, focusing on unraveling the intricate behavior of plain concrete under multistage fatigue loading. Since the experimental investigation of the load sequence effect is highly complex due to the large scatter of test results, a newly developed, mode II test setup was employed. The advantage of this test setup resides in the precise specification of stress state and fracture zone. The systematic investigation of over 50 specimens elucidates the pronounced load sequence effect and provides insight into the underlying mechanisms. Based on these experimental results, a deformation-based incremental modeling approach was developed which considers the effect of loading sequence and provides not only the fatigue life but also the entire evolution of deformation. The experimental recalculation underscores the efficacy of this approach over the conventional Palmgren–Miner (P–M) rule.

中文翻译：

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对载荷序列效应的新见解：变幅 II 型疲劳载荷下普通高强混凝土的实验表征和增量建模

钢筋混凝土 (RC) 基础设施通常在其整个使用寿命期间承受重复的亚临界载荷，可能会损害结构完整性。这些结构的实际载荷条件包括不断变化的最大和最小载荷事件。由于混凝土的异质性和准脆性，表征混凝土的疲劳响应具有挑战性，导致疲劳寿命根据加载顺序而变化。了解这种所谓的负载顺序效应的影响是确保当前基础设施的结构寿命和可靠性的关键方面。本文深入探讨了这一现象，重点揭示了素混凝土在多级疲劳载荷下的复杂行为。由于测试结果分散性大，载荷序列效应的实验研究非常复杂，因此采用了新开发的模式 II 测试装置。该测试装置的优点在于应力状态和断裂区域的精确规范。对 50 多个样本的系统研究阐明了显着的载荷顺序效应，并提供了对潜在机制的深入了解。基于这些实验结果，开发了一种基于变形的增量建模方法，该方法考虑了加载顺序的影响，不仅提供了疲劳寿命，还提供了变形的整个演化过程。实验重新计算强调了该方法相对于传统 Palmgren-Miner (P-M) 规则的有效性。