Shear Resisting Behavior of Reinforced Concrete Columns Under Biaxial Binding-Shear and Varying Axial Load

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The effects of axial stress ratio (eta), varying axial force, lateral loading direction (angle rheta) and concrete strength (sigma_B) on the shear resisting behavior of short square RC columns are experimentally investigated. The test results are summarized as follows :(1) The shear cracking load in the columns with high axial stress was a little higher value than the value obtained from the existing empirical formulae, and the diagonal cracks showed a tendency to become steeper with increase of axial stress.(2) The ultimate shear strength of short columns with sigma_B 600kgf/cm^2 increased in proportion to the sigma_B, regardless of the differences of angle rheta. However, the load carrying capacity after maximum load dropped rapidly. And also, the shear strength of columns with sigma_B 360kgf/cm^2 increased in proportion to the eta, within the range of eta 0.4.(3) The ultimate shear strength of short columns under biaxial bending-shear, within the range of sigma_B =300-600 kgf/cm^2, … More was similar to that of column loaded along the principal axis, and there was almost no need to consider the effect of rheta.(4) The ultimate shear strength of columns under varying axial load can be estimated by adopting the maximum axial load in the positive and negative loading.(5) It is possible to ensure the inelastic ductility and load carrying capacity after ultimate flexural load by increasing the amount of shear reinforcement, regardless of the differences of sigma_B and rheta. In this case, the ultimate flexural strength of columns can be estimated by use of the existing flexural strength equation.(6) All the test results in both positive and negative loading on ultimate shear strength of columns are in best agreement with the calculated value by the "Ultimate shear Design Equation" which is proposed by Kuramoto-Minami in 1990. In this case, the applicable limitation of sigma_B is changed from 420 to 600 kgf/cm^2. However, it is necessary to pay an attention that the calculated values obtained from the Design Equation proposed by the AIJ are overestimated to the test results for the short columns with lower axial stress or tensile axial stress. Less