Seismic retrofit of corroded RC columns using textile reinforced UHTCC jackets and near-surface-mounted BFRP bars

Corroded reinforced concrete (RC) columns usually require retrofitting to ensure the seismic safety of engineering structures. This study employs an innovative combined strengthening system, comprising textile-reinforced ultra-high toughness cementitious composite (UHTCC) jackets and near-surface-mounted (NSM) BFRP (basalt fiber reinforced polymer) reinforcement, referred to as the TRU-NSM system. In this study, the seismic behavior of six corroded RC columns strengthened with the TRU-NSM system was investigated through cyclic lateral loading tests. The test variables included corrosion ratios, stirrup ratios, and axial load ratios. The experimental results indicated that the TRU jacket can effectively restrain shear deformation and concrete cracking in the plastic hinge zone, and all the strengthened specimens showed ductile flexural failure. When the corrosion ratio was below 13.59%, the seismic resistance of corroded columns can be effectively restored. Despite severe corrosion damage to the stirrups, the TRU jacket can still provide sufficient transverse confinement. With an increase in axial load ratio from 0.25 to 0.4, the ultimate load-bearing capacity of the strengthened columns increased by 1.12 times, but their deformation capacity was reduced to a great extent. Although the NSM reinforcement could enhance the peak load to some extent, early failure of the BFRP bars at a drift ratio of 3–5% resulted in a limited effect on their deformation and ductility. Furthermore, a numerical model that accounts for the slip effects of corroded reinforcement and BFRP bars was proposed to predict the hysteretic curves of TRU-NSM-strengthened corroded RC columns.