Reinforced Concrete Column Damage Index on Cracking and Spalling

试件截面为50x50 <cm^2>，为悬臂式钢筋混凝土柱全尺寸模型。剪跨比（A/D）为2.2。柱顶轴向载荷由一对高强度钢杆和两个中心孔液压千斤顶组成，由半自动压控液压泵驱动。采用两个轴向载荷值。LC-1、2、3、4的轴向载荷均约为75t（Fc/6）。另一个是LC-5约130吨（Fc/4）。在人工控制液压千斤顶的作用下，对试件进行了反向循环横向荷载试验。在残余挠度为零的加载阶段，用纤维尖笔在50cm宽的透明塑料薄板上描画混凝土剥落区裂缝形态和轮廓。混凝土剥落区的裂缝和轮廓被划分成小的线段。这些线段的数字数据是用平板数字化仪获得的。在计算机显示裂缝图或混凝土剥落图后，用微机计算裂缝面积比和混凝土剥落面积比，通过计算on -dot和off -dot的数量来计算裂缝面积比和混凝土剥落面积比。荷载-挠度曲线的回路非常稳定，位移延性达到10。裂缝和混凝土剥落的数量随着D.D.的增加而增加。当D.D.小于1时，在柱宽高度之外没有裂缝。混凝土剥落从5点开始。混凝土的剥落面积比受轴向荷载的影响较大，而裂缝面积比受轴向荷载的影响较小。

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.