Structural reinforced concrete (RC) experiences cyclic loads during their service life, and in practice, the load amplitude can always change, which will lead to a mixed high and low-cycle fatigue failure. This paper aims to investigate the fatigue behaviors of RC beams under different load levels and more importantly, their sequential effects. Based on the path-dependent constitutive models, the structural degradation under different repeated loads are comprehensively investigated by numerical simulation of higher consistency with the reality. It is fairly indicated that a clear bi-linear character may exist in the so-called S-N diagram, of which the high-cycle fatigue failure is attributed to rupture of main reinforcement under tension, while the low-cycle fatigue failure is controlled by the concrete failure in flexural compression zone. A simple design method to consider mixed low and high cycle fatigue is proposed to quantify this bi-linear character. For the varying amplitude of cyclic loads, the high-to-low loading sequence may cause a shortened fatigue life. More interestingly, if a rather high heavy load (0.85 or 0.95 of the static capacity) is applied just once before ordinary fatigue loads (ex. 0.6), the deflection may significantly increase, while the stiffness and final fatigue life would be slightly reduced in view of nonlinear mechanics.

中文翻译：

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全幅变幅下钢筋混凝土梁高低周弯曲疲劳数值分析

结构钢筋混凝土（RC）在其使用寿命期间会承受循环载荷，在实际应用中，载荷幅值总是会发生变化，这将导致高低周混合疲劳失效。本文旨在研究 RC 梁在不同载荷水平下的疲劳行为，更重要的是，研究它们的连续效应。基于路径相关的本构模型，通过与实际具有更高一致性的数值模拟，综合研究了不同重复载荷下的结构退化。可以很好地表明，所谓的SN图中可能存在明显的双线性特征，其中高周疲劳破坏归因于受拉主筋断裂，而低周疲劳破坏受拉力控制。弯曲受压区混凝土破坏。提出了一种考虑混合低周和高周疲劳的简单设计方法来量化这种双线性特征。对于变化幅度的循环载荷，从高到低的加载顺序可能会导致疲劳寿命缩短。更有趣的是，如果在普通疲劳载荷（例如 0.6）之前仅施加一次相当高的重载荷（静承载力的 0.85 或 0.95），挠度可能会显着增加，而刚度和最终疲劳寿命会略微降低非线性力学的观点。