Reinforced Concrete Column Damage Index on Cracking and Spalling

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The test specimen, a section 50x50 <cm^2> is a cantilever type full scale model of reinforced concrete column. The shear span ratio (A/D) was 2.2. The axial load was applied to the column-top with a pair of high strength steel rods and two hydraulic center hole oil jacks, which were driven by a semi-automatic pressure controlled hydraulic pump. The two axial load values were used. The one of the axial loads was about 75t(Fc/6) for LC-1, 2, 3 and 4. The other was about 130t(Fc/4) for LC-5. The test specimen was subjected to the reversed cyclic lateral load with the man-controlled hydraulic oil jacks. At the time the loading stage at which the residual deflection became zero, crack patterns and outlines of concrete spall off area were traced with a fiber tip pen on a transparent thin plastics sheet of 50cm width. Cracks and outlines of the concrete spall off area were divided into small linear segments. Digital data of those linear segments were obtained with a tablet digitizer. The crack area ratio and the concrete spall off area ratio were calculated with a micro-computer by counting up the number of ON-dots and OFF-dots, after making crack diagrams or the concrete spall off diagrams on the computer display. The loops of the load-deflection curves are very stable up to the displacement ductility (D.D.) of 10. The amount of cracks and concrete spall off increases as the D.D. increases. No crack can be found beyond the column-width height, if the D.D. is less than 1. The concrete spall off starts from the D.D. of 5. The concrete spall off area ratio is much affected by the value of the axial load, while the crack area ratio is slightly affected.