Shear Crack Behaviors and Shear Transfer Mechanism of RC Columns with High Strength Materials

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The configuration of a crack in a high-strength concrete more than 100 N/mm^2 is much smoother than that in normal-strength concrete. This smooth crack surface may lead different mechanical behaviors of RC members. To study the influence of the configuration of cracks and the confinement of shear reinforcement upon the shear behaviors of RC members, the shear tests were performed on cracked concrete specimens. The confining pressure is automatically applied on crack surfaces by a closed-loop servo system. The test results show that the shear behaviors in cracks are deeply affected by the configuration of cracks as well as reinforcement ratio (confining stiffness). The relations of normal and shear stresses to crack opening and shear displacements have been investigated on the basis of crack surfaces and normal constraints across the cracks.Experiments and 3-D FEM analyses were also performed on high-strength concrete columns laterally prestressed by the shear reinforcements to study the influence of the active confinement upon bond strength, shear strength and crack behaviors. The lateral prestress has been introduced in proportion to the strength of concrete, and the width of every crack over transverse reinforcements has been measured by a microscope. By increasing the lateral pressure as mentioned above, shear crack strength, bond strength and ultimate shear strength have increased significantly, however, the effectiveness of active confinement has been weakened with decreasing axial force ratio. The FEM analyses can evaluate the shear crack strength, bond strength and ultimate shear strength, and explain the effect of the active confinement on shear behaviors by evaluating the intensity of confinement in tri-axial state of stress with minor principal stress and equivalent confining pressure.