In this work, we studied stress variations of loading histories on polypropylene fiber reinforced concrete beams during flexure. A new experimental system was created to collect the stress-time curves at 100 kHz sampling rate to reveal temporal profiles of stress drops in high resolution. Concrete beams prepared at the early age of seven days with different fiber volume fractions were loaded at various rates during four-point bending tests. Stress drops induced by interactions between polypropylene fibers and cementitious matrices or matrix cracking were modeled as avalanches along the time history. We used the mean field model to predict statistics and dynamics of avalanches occurred inside polypropylene fiber reinforced concrete beams during flexure. Good agreement was obtained between measurements and predicted power law exponents and scaling functions from the mean field model. Two types of avalanches were observed for polypropylene fiber reinforced beams during flexure, i.e., small avalanches collapsed onto the scaling regime and large avalanches beyond the regime. Maximum stress drop rates of small avalanches were on the order of kPa/s, whereas maximum stress drop rates of large avalanches could reach the order of MPa/s. Observations of different avalanches revealed insights into the essential failure evolved during flexure concrete beams, i.e., small avalanches with limited plastic deformation and large avalanches with extended incubation periods. Findings from this study could help measure the evolved damage of concrete structural members under service loads, which provide valuable hints to improve the durability of reinforced concrete structures.

在这项工作中，我们研究了聚丙烯纤维增强混凝土梁在挠曲过程中荷载历史的应力变化。创建了一个新的实验系统，以100 kHz采样率收集应力-时间曲线，以高分辨率显示应力下降的时间分布。在四天弯曲试验期间，以不同的速率加载在7天初期制备的具有不同纤维体积分数的混凝土梁。由聚丙烯纤维与水泥基体之间的相互作用或基体开裂引起的应力降被建模为沿时间历史的雪崩。我们使用平均场模型来预测聚丙烯纤维增强混凝土梁在弯曲过程中发生的雪崩的统计数据和动力学。根据平均场模型，测量值与预测的幂律指数和比例函数之间取得了良好的一致性。聚丙烯纤维增强梁在弯曲过程中观察到两种类型的雪崩，即小雪崩塌陷到结垢状态，大雪崩超出该状态。小雪崩的最大应力下降率约为kPa / s，而大雪崩的最大应力下降率可达MPa / s。对不同雪崩的观察揭示了对弯曲混凝土梁过程中发生的基本破坏的见解，例如，具有有限塑性变形的小雪崩和具有较长保温时间的大雪崩。这项研究的发现可以帮助衡量混凝土结构构件在使用载荷下的演化损伤，