Improving seismic performance of deficient reinforced concrete columns using carbon fiber-reinforced polymers

Reinforced concrete columns lacking transverse reinforcing steel do not possess necessary ductility to dissipate seismic energy during a major earthquake. The study reported herein investigates the use of carbon fiber-reinforced polymer (CFRP) wrapping as a method of retrofitting nonductile square reinforced concrete columns with low strength concrete and plain bars. Five specimens representative of transverse steel deficient flexure dominated columns in existing buildings were tested under lateral cyclic displacement excursions and constant axial load. The main parameters under investigation were the number of layers of CFRP wrap and presence and absence of the axial load on the column during strengthening. It was found that upon CFRP retrofit, deficient columns were able to withstand larger deformation demands without strength degradation. The test results were also compared with the results obtained from the analytical study that was conducted using a simple plastic hinge model considering the effects of FRP confinement and slip of plain bars. A good agreement between analytical and experimental results was observed.