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.