低周往复荷载下既有混凝土柱变形能力试验研究

基于我国89抗震规范中一、二、三(四)级混凝土框架柱的抗震措施，完成了以剪跨比、轴压比、加密区体积配箍率为基本设计参数的24个混凝土悬臂柱试件低周反复荷载(位移)试验。试验结果表明，高(一、二)抗震等级的试验柱表现为水平裂缝的形成和发展、最终压区混凝土压碎的弯曲型破坏，低(三、四)抗震等级的试验柱局部出现一定宽度的弯剪裂缝、最终为压区混凝土压碎的弯剪型破坏；试验柱的轴压比显著影响其滞回性能，侧向变形能力随轴压比的增大有降低趋势；轴压比和剪跨比相同时，柱位移延性系数随加密区体积配箍率的增大而增大；轴压比和配箍率相同时，大剪跨比(7.27)的试验柱位移延性总体上小于相对应的小剪跨比(5.0)柱位移延性；按Park能量法的屈服位移、承载力下降至85%的极限位移确定的位移延性系数，62.5%(15/24)的试件小于3.0，其最大值为3.86，最小值为2.27。对比已有试验结果发现，本文按89规范的加密区体积配箍率下限要求(0.6%~1.6%)的试验柱，位移延性系数偏小、极限变形能力不大。

Experiment on drift capacity of existing concrete columns under low cyclic reciprocating loading

Based on seismic measurements for different seismic grades in domestic 89 seismic code, twenty-four cantilever concrete columns considering aspect ratio, axial load level and volumetric ratio of stirrups were tested under cyclic loading. Test results showed that columns with high seismic grades (grades 1, 2) failed after occurrence and development of flexural cracks and crushing in compressive concrete zone, and the columns with low seismic grades (grade 3, 4) failed with some inclined cracks and concrete crushing. Axial load level can largely influence hysteretic performance of specimens. With high axial load level, the drift of columns decreased significantly. Under same aspect ratio and axial load level, ductility of columns was enhanced by more stirrup arranged in critical region. The ductility of columns with large aspect ratio (7.27) were normally smaller than that with small aspect ratio (5.0). Based on the yield displacement given by Park energy method, and defining the ultimate displacement when lateral load dropped to 85% of the peak value, 62.5% (15/24) of specimens has ductility less than 3.0, the maximum is 3.86 and minimum is 2.27. Compared with other test results, it showed that these specimens had small ductility coefficient and low drift capacity, which followed lower bound (0.6%~1.6%) of stirrup ratio in 89 seismic code.