Seismic response analysis of reinforced concrete columns considering shear effects

Cyclic loading tests of 6 short columns were conducted. The shearing and bending responses were separated. Analysis results indicated that the shear stiffness of a shear critical column degraded rapidly following the development of shear cracking. The skeleton curve of the shearing response entered the descending branch as the peak shear force was reached. The shear hysteresis shows the characteristics of pinching effect and stiffness degradation. Before the peak shear force is reached, the bending response and the shearing response occur simultaneously. After the peak shear force, if the shear failure is detected, the bending response will not further develop while the shearing response will increase rapidly, and the vice versa for the two responses if the flexural failure occurs. For columns with lower shear strength than the flexural strength, shear failure will be detected as the shear force reached the initial shear strength. For columns with higher shear strength than the flexural strength, the shear strength of the column at plastic hinge zone will decrease with the development of bending deformation and the shear failure will be detected as the shear strength degrades to the value lower than the flexural bearing capacity. A shear spring representing the in-plane shear action was then introduced into the multi-spring model for the seismic analysis of reinforced concrete columns. The load-carrying mechanism of a column was decomposed into bending mechanism and shearing mechanism which were connected in series. Comparing the calculated results with the test results, it was found that the modified multi-spring model provided a good estimation of the seismic behavior of shear-critical columns under earthquakes. The multi-spring model ignoring the shear action overestimates the ductility, energy dissipation and shear strength of the shear critical columns and leads to unsafe evaluation results.