EFFECT OF UNBONDING OF MAIN REINFORCEMENTS AT PLASTIC HINGE REGION FOR ENHANCING DUCTILITY OF REINFORCED CONCRETE BRIDGE COLUMNS

This paper presents the effect of unbonding of main reinforcements at the plastic hinge region in a reinforced concrete single cantilevered bridge column. Five specimens with a rectangular section of 400mm×400mm were constructed by changing the height, in the plastic hinge region, where main reinforcements were unbonded fully or partially. It was found from a cyclic loading test that the unbonding results in uplifting of the base of columns in tension side, and this leads to the rocking motion in the columns. Axial strain in main reinforcements decreases by unbonding the main reinforcements, but the buckling of main reinforcements tend to be developed at only a short interval at the bottom. The ductility factor increases slightly with less amount of reduction of maximum restoring force, stiffness and energy dissipation.