1.1 本试验方法包括使用支撑在三个对称布置的枢轴上并承受中心点荷载的圆形面板，测定纤维增强混凝土的弯曲韧性，表示为裂纹后范围内的能量吸收。通过该方法测试的试样性能根据加载开始和中心挠度选定值之间吸收的能量进行量化。 1.2 当试样不符合目标厚度和直径时，只要尺寸不超出给定限制，本试验方法规定了结果的比例。 1.3 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.4 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 板状纤维增强混凝土结构构件的裂纹后行为由中心加载的圆形面板试样很好地表示，该试样简单地支撑在围绕其圆周对称布置的三个枢轴上。 这种试板在中心点荷载作用下会经历双轴弯曲，并表现出与以下因素相关的失效模式: 现场 结构的行为。承受中心点荷载的圆形面板的裂纹后性能可以由面板吸收的能量表示，直到指定的中心挠度。在本试验方法中，吸收到指定中心挠度的能量表示纤维增强混凝土在开裂后重新分布应力的能力。 注1: 在测试配置中使用三个枢轴点支架可在开裂之前确定平面外反应，但由于每个裂缝沿线的弯曲阻力分布未知，因此开裂后的支架反应不确定。 随着试验的进行，试样中的负载阻力机制也会发生变化，从主要的弯曲阻力开始，随着外加挠度的增加，逐渐发展到围绕中心的拉伸膜作用。吸收到指定中心挠度的能量与材料的韧性有关，但特定于此试样配置，因为它也由试样的支撑条件和尺寸决定。要指定的最合适中心挠度的选择取决于材料的预期应用。吸收的能量高达5 mm中心挠度，适用于要求材料在低变形水平下紧紧闭合裂缝的情况。 例如，可能需要保持水密性的地下土木结构（如铁路隧道）的最终衬砌。吸收高达40 mm的能量更适用于材料预计会发生严重变形的情况 现场 （例如，矿井隧道中的喷射混凝土衬砌和膨胀地面中的临时衬砌）。在需要中等变形水平性能的情况下，可以指定高达中心挠度中间值的能量吸收。 5.2 使用带有三个支架的圆形面板的动机是基于实验室中发现的批内重复性 3. 和现场经验。 4. 由于使用三个对称布置的支承枢轴而产生的故障模式的一致性，导致内部故障率较低- 一组面板吸收的能量在指定中心挠度范围内的批量变化。使用圆形面板也消除了制备喷射混凝土梁试样所需的锯切。 5.3 面板的标称尺寸为75 mm厚和800 mm直径。在本试验中，厚度对面板性能有很大影响，而直径变化对性能影响较小。 5. 提供了修正系数以说明实际测量的尺寸。 注2: 无论组成试样的混凝土中使用的骨料和纤维的特性如何，本试验中使用的面板试样的目标尺寸保持不变。如果混凝土中使用大骨料颗粒或长纤维，则裂缝后性能可能会受到尺寸和边界效应的影响。 本试验方法承认并接受了这些影响，因为实际结构中会出现尺寸效应和纤维排列问题，并且没有任何单个试样可以适合模拟所有尺寸的结构。与厚度大于100 mm的铸造纤维增强混凝土构件相比，本试验方法中显示的裂纹后行为存在差异。由于喷射混凝土产生的结构中纤维排列明显，并且喷射混凝土混合物中的最大骨料尺寸通常为10 mm，因此通过该方法测试的试样中的裂纹后行为更具代表性 现场 通过喷射而不是浇注混凝土产生的行为。

1.1 This test method covers the determination of flexural toughness of fiber-reinforced concrete expressed as energy absorption in the post-crack range using a round panel supported on three symmetrically arranged pivots and subjected to a central point load. The performance of specimens tested by this method is quantified in terms of the energy absorbed between the onset of loading and selected values of central deflection. 1.2 This test method provides for the scaling of results whenever specimens do not comply with the target thickness and diameter, as long as dimensions do not fall outside of given limits. 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 The post-crack behavior of plate-like, fiber-reinforced concrete structural members is well represented by a centrally loaded round panel test specimen that is simply supported on three pivots symmetrically arranged around its circumference. Such a test panel experiences bi-axial bending in response to a central point load and exhibits a mode of failure related to the in situ behavior of structures. The post-crack performance of round panels subject to a central point load can be represented by the energy absorbed by the panel up to a specified central deflection. In this test method, the energy absorbed up to a specified central deflection is taken to represent the ability of a fiber-reinforced concrete to redistribute stress following cracking. Note 1: The use of three pivoted point supports in the test configuration results in determinate out-of-plane reactions prior to cracking, however the support reactions are indeterminate after cracking due to the unknown distribution of flexural resistance along each crack. There is also a change in the load resistance mechanism in the specimen as the test proceeds, starting with predominantly flexural resistance and progressing to tensile membrane action around the center as the imposed deflection is increased. The energy absorbed up to a specified central deflection is related to the toughness of the material but is specific to this specimen configuration because it is also determined by the support conditions and size of the specimen. Selection of the most appropriate central deflection to specify depends on the intended application for the material. The energy absorbed up to 5 mm central deflection is applicable to situations in which the material is required to hold cracks tightly closed at low levels of deformation. Examples include final linings in underground civil structures such as railway tunnels that may be required to remain water-tight. The energy absorbed up to 40 mm is more applicable to situations in that the material is expected to suffer severe deformation in situ (for example, shotcrete linings in mine tunnels and temporary linings in swelling ground). Energy absorption up to intermediate values of central deflection can be specified in situations requiring performance at intermediate levels of deformation. 5.2 The motivation for use of a round panel with three supports is based on the within-batch repeatability found in laboratory 3 and field experience. 4 The consistency of the failure mode that arises through the use of three symmetrically arranged support pivots results in low within-batch variability in the energy absorbed by a set of panels up to a specified central deflection. The use of round panels also eliminates the sawing that is required to prepare shotcrete beam specimens. 5.3 The nominal dimensions of the panel are 75 mm in thickness and 800 mm in diameter. Thickness has been shown to strongly influence panel performance in this test, while variations in diameter have been shown to exert a minor influence on performance. 5 Correction factors are provided to account for actual measured dimensions. Note 2: The target dimensions of the panel specimen used in this test are held constant regardless of the characteristics of aggregate and fibers used in the concrete comprising the specimen. Post-crack performance may be influenced by size and boundary effects if large aggregate particles or long fibers are used in the concrete. These influences are acknowledged and accepted in this test method because issues of size effect and fiber alignment arise in actual structures and no single test specimen can suitably model structures of all sizes. Differences in post-crack behavior exhibited in this test method can be expected relative to cast fiber-reinforced concrete members thicker than 100 mm. Because fiber alignment is pronounced in structures produced by shotcreting, and the maximum aggregate size in shotcrete mixtures is typically 10 mm, post-crack behavior in specimens tested by this method are more representative of in situ behavior when they are produced by spraying rather than casting concrete.