Evaluating Shear Stiffness and Crack for Reinforced Concrete Columns under combined states of stress

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The prestress in concrete structures is aimed generally at controlling the flexural cracks by the arrangement of tendons in an axial direction of the member. On the other hand, in order to delay initiating a shear crack and to reduce its width, experimental studies were conducted on the reinforced concrete(RC) columns laterally prestressed by the shear reinforcements. The test results have indicated that the performance in shear behaviors can be improved by the active confinement. The three dimensional finite element(FEM) analyses were also performed on RC columns to investigate the mechanics of the lateral confinement using the equivalent confining pressure and the degree of as a measure to evaluate active confinement and shear damage quantitatively. These studies have revealed that an increase in resistance against shear failure as well as shear cracking with increasing prestress in the shear reinforcements could be explained by the triaxial state of stress in the core concrete. The … More following study is to investigate how the lateral prestress in RC columns would affect the shear crack behaviors. The flexure-shear tests have been performed on two columns which are laterally prestressed(LPRC) and not prestressed(RC). Three strain gauges were glued on each of shear reinforcements and the widths of every shear crack over shear reinforcements were measured using two digital microscopes. The close relationship between the width of shear cracks and the distributed strain in reinforcements has been proven by evaluating the crack width from the gauges on reinforcements. With increasing lateral pressure, shear crack strength and ultimate shear strength have increased proportionally, shear crack patterns have changed appreciably, and the widths of cracks have decreased drastically. The FEM analyses can predict the difference between the shear strengths of RC columns and LPRC columns with a fair degree of precision. Furthermore, the FEM analyses using smeared crack model cannot evaluate a localized crack accurately but can provide valuable information about the total damage in the overall depth of a specimen. Less