Effect of Cyclic Loading upon Shear Behavior in Fracture Process Zone of Concrete

本实验研究的主要目的是获得断裂过程区在损伤后仍能传递应力的循环剪切响应，为非线性有限元分析积累必要的信息。由于混凝土结构中的混合模式加载是由于主拉应力和随后的主应力方向旋转而产生的裂缝的结果，因此试验方法要求首先在纯拉伸下产生小裂缝，然后在第二阶段施加剪切。为此，为了建立裂缝混凝土的循环剪切性能，研制了一种可由闭环伺服系统独立控制竖向和水平荷载以及位移的双轴试验装置。在本试验中，通过位移控制…中的拉伸试验，对含有窄裂纹的试件进行了循环剪切试验更多的是在保持裂纹面法向位移或载荷不变的边界条件下进行的。然而，在钢筋混凝土结构中，这种加载路径永远不会发生，因为裂缝宽度的任何增加都会导致跨越裂纹面的钢筋拉力增加，从而使围压同时增加。因此，还进行了剪切试验，以研究裂纹表面围压的影响。与其他方法不同的是，围压始终由裂缝宽度、配筋率、混凝土与钢筋之间滑移的约束长度、钢筋的屈服强度来估计，并通过闭环伺服系统自动施加在裂缝表面。根据裂纹面法向方向的各种边界条件，讨论了法向载荷和剪切载荷与裂纹张开和滑动位移的关系。较少

The primary purpose of this experimental investigation is to obtain the cyclic shear response in a fracture process zone that the stress can still be transferred in spite of the damage, and to accumulate the necessary information that applies to nonlinear finite element analysis. Since the mixed mode loading in concrete structures is a consequence of the presence of a crack due to principal tensile stresses and subsequent rotation of the principal stress direction, testing methods require that a small crack can be generated first under pure tension and that shear can be applied in a second stage. For that reason, a biaxial testing device, with which the vertical and horizontal load as well as displacement can be independently controlled by closed-loop servo systems, has been developed in order to establish the cyclic shear behavior in cracked concrete. In this experiment, the cyclic shear tests on specimens containing narrow cracks introduced by the tensile test in displacement control … More have been mainly carried out under the boundary conditions maintaining either normal displacement or load across the crack surface constant. However, in reinforced concrete structures, this loading path will never occur because any increasing of crack width causes an increase of tensile force in reinforcement crossing the crack planes and subsequently makes the confining pressures increase simultaneously. Therefore, the shear tests have been also carried out to study the effect of confining pressures across the crack surface. Unlike others, the confining pressure is all the time estimated by crack width, reinforcement ratio, constraint length relating to the slip between concrete and reinforcement, yield strength of reinforcement and automatically applied on the crack surfaces by closed-loop servo systems. The relation of normal and shear loads to crack opening and sliding displacements was discussed on the basis of the various boundary conditions of the normal direction across the crack surface. Less