The effect of crack rate on the tensile stress–crack width relation of fibre reinforced concrete is studied experimentally, using the three-point bending test, where the post-peak flexural response of the material is determined over a range of loading rates covering 5 orders of magnitude. The tetralinear stress–crack opening (σ–w) relations are subsequently obtained from inverse analyses. Concretes with hooked-ended steel fibres at different dosages and with polypropylene fibres have been studied. The results show that the tensile strength is reduced and the initial drop in cohesive stresses is less steep at slower loading rates, with the changes being more significant in concretes with lower toughness. Numerical analysis shows that the fracture process zone at crack initiation extends further as the loading becomes slower. The variation in the σ–w relation with crack rate has been modelled empirically based on the rate-dependence of the concrete matrix and the tensile strength of the FRC. The general variation of flexural toughness with the loading rate has also been identified, reflecting the moderating influence due to steel fibres, especially at higher dosages.

中文翻译：

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准静态状态下纤维增强混凝土拉伸行为的速率相关性

使用三点弯曲试验，通过实验研究了裂纹速率对纤维增强混凝土拉伸应力-裂纹宽度关系的影响，其中在覆盖 5 个数量级的加载速率范围内确定了材料的峰值后弯曲响应量级。随后从逆向分析中获得四线应力-裂纹张开 (σ-w) 关系。已经研究了具有不同剂量的钩端钢纤维和聚丙烯纤维的混凝土。结果表明，在较慢的加载速率下，抗拉强度降低，内聚应力的初始下降幅度较小，而在韧性较低的混凝土中，这种变化更为显着。数值分析表明，随着加载速度变慢，裂纹萌生的断裂过程区进一步延伸。σ-w 关系随开裂速率的变化已根据混凝土基体的速率相关性和 FRC 的抗拉强度经验建模。弯曲韧性随加载速率的一般变化也已确定，这反映了钢纤维的缓和影响，尤其是在较高剂量下。