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

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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