Shear Behavior in Fracture Process Zone of Concrete

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Most cracks in concrete structures are initiated first by the largest principle stress, and propagate under subsequent shear and transverse compression or tension. 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 shear behavior in cracked concrete. The shear tests on specimens containing narrow cracks (fracture process zone introduced by the tensile test in displacement control) have been carried out maintaining either normal displacement or load across the crack surface constant. The relation of normal and shear stresses to crack opening and sliding displacements was discussed and distinguished by the boundary conditions of the normal direction across the crack surface. Several expressions which give shear retention factor, β, and relations between shear displacement and normal load in cracks have been derived based on biaxial test results.