Experimental Study on Seismic Behavior of Resilient Circular Concrete Columns

In order to maintain the positive stiffness and small residual deformation of reinforced concrete columns when they are subjected to tremendous earthquakes that exceed the standard set by current codes, a method of using high-strength and low-bond non-prestressed steel strands as longitudinal reinforcement bars of columns is proposed. In order to verify the effectiveness of this method, horizontal low-frequency cyclic loading tests were performed on four circular reinforced concrete columns under a constant axial load, of which three were reinforced with the above-mentioned longitudinal steel strands (hereinafter referred to as ‘new type columns’) and one with normal-strength (NS) rebars. The effects of shear-span ratios and transverse confinement modes within the potential plastic hinge region on the seismic behavior of the new type columns were studied. The test results show that when the drift ratio of the new type columns with a shear-span ratio of 3 to 4 reaches 6%, it still maintains positive stiffness and the residual drift ratio is less than 2%. Compared with the concrete column reinforced with NS rebars, the lateral bearing capacity of the new type column was increased by 90% and the residual deformation was reduced by 73% at the drift ratio of 6%. Besides, the lateral bearing capacity of the new column can be further increased by 15% and the residual deformation can be further reduced by 21% by adding transverse confinement with bolted steel plates in the plastic hinge zone of the column (1.5D). Comparisons between the experimental and analytical results indicate that the flexural analysis based on Navier’s hypothesis is not suitable for prediction of the lateral bearing capacity of the concrete columns reinforced with steel strands due to the the obvious bond-slip effect of steel strands.