Ductility improvement of existing RC columns strengthened with CFRP

Existing reinforced concrete (RC) columns, designed according to obsolete standards, often show premature failures due to longitudinal bars buckling or loss of bond when subjected to horizontal cyclic loads. This kind of failure modes significantly reduces the deformation capacity and the relevant ductility of existing RC columns and leads to poor performances during seismic events. In order to improve the seismic performance of existing RC columns, the effectiveness of external confinement with carbon fiber reinforcement polymers (CFRP) was investigated in this work. Four square RC columns with deformed bars, designed according to obsolete standards, were strengthened in the plastic hinge region with one and two plies of uniaxial CFRP sheets. The columns were tested under horizontal cyclic load combined with a constant compressive axial load. The performance of strengthened columns has been compared with an unstrengthened control column. The test results have been analyzed and compared in terms of failure modes and ductility improvement. Particular attention has been focused on the strain distribution recorded on the CFRP strips; the strain profiles along the crosssection perimeter in case of axial load and bending moment interaction are presented and discussed at different drift levels.