Active Control over Failure of RC Members by Application of Interrelation between Artificial Pre-Crack and Non-Orthogonal Crack

1)为了弄清混凝土构件人工预裂与剪力引起的剪切裂缝之间的相互关系，进行了一系列试验。在单调荷载和循环荷载作用下，人工预裂阻止了新的分担裂缝的扩展，从而提高了钢筋混凝土构件的承载力和延性。反之，当预裂裂缝与新裂缝夹角小于30°时，构件的承载能力会因沿预裂纹处形成新裂缝而降低。2)采用非正交弥散裂纹模型作为本构模型来处理具有交点的非正交裂纹。通过与试验结果的对比，验证了所提出的模型能够很好地预测相互作用的裂缝行为。3)基于试验事实和分析方法，研究了嵌入塑料板的混凝土构件作为模拟预裂构件的抗剪性能。4)通过钢筋混凝土板结构在多向荷载作用下的试验，验证了所提出的非正交裂纹模型的准确性。结果表明，以22.5°相交角为阈值的活动裂纹法能够很好地预测非正交裂纹之间的相互关系。此外，还验证了该模型在高强混凝土和高强钢筋组成的结构中的适用性。5)由于假定温度应力是预裂的引入来源，因此通过试验阐明了高温下预埋钢在混凝土中的拉-刚性能。所表现出的特征被纳入结构数值分析系统。

1) In order to clarify the interrelation between artificial pre-crack induced in concrete member and shear crack caused by shear force, a series of experiments was performed. Under both monotonic and cyclic loading, the artificial pre-creak prevented propagation of new share crack and then the capacity and ductility of RC member increased. On the contrary, when the angle between pre-crack and new crack because less than 30 degree, the capacity of member was decreased owing to the new crack formed along the pre-crack.2) Non-orthogonal smeared crack model of enhancing active crack method was adopted as a constitutive law to deal with non-orthogonal cracks with intersection. Comparinson with the experimental results verified that the proposed model could well predict the behavior of cracks with mutual interaction.3) Shear behavior of concrete members with embedded plastic plates, as devices to emulate pre-cracks, was studied based on both experimental facts and analytical approach. As a result, proposed joint element had a beneficial effect on modeling consecutive plates.4) The accuracy of the proposed non-orthogonal crack model was verified with experiments of RC plate structures under multi-directional loading. The result showed that active-crack method, which defined Intersection angle of 22.5 degrees as a threshold, could well predict interrelation between non-orthogonal cracks. In addition, the application of the model for structures that consist of high strength concrete and high strength reinforcing bars was proven.5) Because thermal stress was assumed as an introduction source of pre-cracks, the tension-stiffness behavior of embedded steel in concrete under high temperature was clarified experimentally. The manifested characteristics were incorporated into the structural numerical analysis system.