Retrofit of square concrete columns with carbon fiber-reinforced polymer for seismic resistance

Reinforced concrete columns lacking sufficient lateral steel do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. This paper investigates the prospect of strengthening deficient and repairing damaged square columns with carbon fiber-reinforced polymer (CFRP) jackets. Eight specimens representative of members in buildings and bridges constructed before 1971 consisted of a 305 x 305 x 1473 mm column connected to a 508 x 762 x 813 nun stub. Each 900 kg specimen was tested under lateral cyclic displacement excursions and simultaneous constant axial load to simulate seismic forces. Results indicate that added confinement with CFRP at critical locations enhanced ductility, energy dissipation capacity, and strength of all substandard members. A positive relationship prevailed between favorable behavior and increasing reinforcement layers while improvements realized through CFRP repair declined as damage level prior to retrofit increased. Appropriately strengthened specimens also exceeded the performance of comparable columns with adequate seismic lateral reinforcement.