Seismic upgrade with carbon fiber-reinforced polymer of columns containing lap-spliced reinforcing bars

Most reinforced concrete columns designed and constructed prior to 1970 may have inadequate seismic resistance. This study evaluates the effectiveness of carbon fiber-reinforced polymer (CFRP) jackets in the strengthening and repair of such columns under simulated earthquake loading. Six circular and 6 square columns were constructed and tested. The columns were 1.47 m (58 in.) long and had a 510 x 760 x 810 mm (20 x 30 x 32 in.) stub at one end with a construction joint at the interface and spliced longitudinal bars in the columns. The variables studied in this program included effect of the presence of lap splices, the effectiveness of CFRP in pre-earthquake strengthening and post-earthquake retrofitting of deficient columns, as well as effects of level of axial load, shape of column cross section, and transverse steel reinforcement details. Findings suggest that the CFRP retrofitting technique was effective in enhancing the seismic resistance of the columns and resulted in more stable hysteresis curves with lower stiffness and strength degradations compared with the unretrofitted columns. Ductility improvements in the square columns with lap splices as a result of CFRP retrofitting were significantly lower than that of comparable circular columns.