Seismic retrofit for rectangular R/C columns by steel and CF jackets

During the recent destructive earthquakes, 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 Figures 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 (References 1, 2 and 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, four different columns with and without jacketing are tested under a constant axial compression and alternately repeated lateral forces. Results of the experiment indicate that the ultimate flexural strength and deformation capacity of the R/C rectangular columns are well improved if the rectangular column sections are confined laterally by circular steel plate- or CF sheet-jackets.