Standardization of Testing Method for Tension Softening Diagrams of Concrete through Inverse Analysis and Applications

在这项研究中，我们打算在与国内外研究人员讨论的基础上，建立一种确定混凝土拉伸软化图的测试方法。利用测定的拉伸软化图对钢纤维混凝土和再生骨料混凝土的性能进行了评价。JSCE混凝土委员会尺寸效应小组委员会(主任委员：K.Rokugo)的报告中提出了由混凝土梁试件的试验荷载-位移曲线准确确定拉伸软化图的有限元逆分析程序。指出了梁试件的形状和尺寸以及位移测量的较佳条件。此外，还展示了用于稳定测量荷载-位移曲线的加载装置的实例。1998年10月在岐阜市举办了关于建立荷载-位移曲线及其应用测试方法的国际研讨会。研讨会一致认为，拉伸软化图的适用性较好。对于其他断裂力学参数，应根据应用情况对图解进行简化。建议日本RILEM和日本的JCI成立一个测试方法标准化的技术委员会，对不同纤维种类、不同纤维含量、不同砂浆基质强度的钢纤维混凝土的性能评价是有效的。指出当纤维体积含量小于2%时，图谱的形状与试件尺寸无关。通过拉伸软化图的形状可以很好地区分再生骨料混凝土的弯曲断裂行为。

In this study, we intended to establish a testing method for determination of tension softening diagrams of concrete based on discussions with researchers in the world. We evaluated the properties of steel fiber reinforced concrete and recycled aggregate concrete using the determined tension softening diagrams. In addition, the bond properties of concrete were also evaluated through the diagrams.The program of Finite Element Inverse Analysis for the accurate determination of the tension softening diagrams from experimental load- displacement curves of concrete beam specimens has been proposed in the report of the subcommittee on size effect (chairman : K.Rokugo) under JSCE concrete committee. The preferable conditions for the shape and size of beam specimens and for the measurements of displacement were indicated. An example of the loading apparatus for the stable measurement of load- displacement curves was also shown.The international workshop on the establishment of testing methods for the diagrams and applications was held in Gifu in October 1998. It was agreed in the workshop that the applicability of the tension softening diagrams is superior. to other fracture mechanics parameters and that the simplification of the diagrams should be taken depending on the applications. It was recommended that a technical committee on the standardization of the testing methods for the diagrams should be made in RILEM as well as JCI in Japan.It was found in this study that the diagrams were effective for the performance evaluation of steel fiber reinforced concrete differing in sorts of fibers, fiber contents and mortar matrix strength. It was pointed out that the shape of the diagrams did not depend on the specimen sizes, when the fiber content was less than 2 % by volume. The flexural fracture behavior of recycled aggregate concrete could be well distinguished through the shapes of the tension softening diagrams.