Reinforced Concrete Column Damage Index on Cracking and Spalling

试件为悬臂式足尺模型钢筋混凝土柱，截面为50x50&lt；cm^2；剪跨比(A/D)为2.2。柱顶由一对高强度钢杆和两个液压中心孔油压千斤顶承受轴向载荷，由半自动压控液压泵驱动。使用了两个轴向负荷值。LC-1、LC-2、LC-3和LC-4的一个轴向载荷约为75T(FC/6)，LC-5的另一个轴向载荷约为130T(FC/4)。利用手动液压油压千斤顶对试件进行了反向循环横向载荷试验。在残余挠度为零的加载阶段，用纤维笔在50 cm宽的透明塑料薄板上跟踪混凝土剥落区的裂缝形态和轮廓。混凝土剥落区的裂缝和轮廓被分成几个小的线段。用平板数字化仪测得这些线段的数字化数据。在计算机显示器上绘制裂缝图或混凝土剥落图后，用微型机计算出裂缝面积比和混凝土剥落面积比。对于位移延性(D.D.)，荷载-挠度曲线的曲线是非常稳定的。裂缝和混凝土剥落的数量随着D.D.的增加而增加。混凝土剥落面积比受轴压影响较大，而裂缝面积比受轴压影响较小。

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.