During the recent destructive earthquakes in Japan and other earthquake countries, a large number of brittle shear failure, flexural compression failure and crushing by high axial compression have been observed in reinforced concrete (R/C) rectangular columns in building structures as shown in Figs. 1, 2 and 3. On the contrary, if the R/C rectangular columns are confined laterally by steel plates (SP) or carbon fiber (CF) sheets, then brittle shear failure can be prevented and the column can develop its ultimate flexural moment capacity (Yoshimura [1], [2], [3]). Herein, in order to investigate the effectiveness of the seismic strengthening methods by using circular steel plate- or CF sheet-jackets for existing R/C rectangular columns, ten different columns with and without jacketing are tested under different constant high axial compression of 13.2MPa and 19.4MPa, and alternately repeated lateral forces. Results of the experiment indicate that the ultimate flexural strength and deformation capacity of the R/C rectangular columns which are confined laterally by the circular cross-sectional steel plate- and CF sheet-jacketing are quite effective, especially when the columns are subjected to high axial compression.
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