Abstract:To investigate the effect of the near-surface mounted (NSM) technique using shape memory alloy (SMA) bars on the seismic performance of reinforced concrete columns, six reinforced concrete (RC) columns strengthened with near-surface mounted (NSM) shape memory alloy (SMA) bars were designed and fabricated to investigate the failure process and failure modes of SMA-reinforced concrete columns through low-cyclic reversed loading tests. The effect of SMA reinforcement ratios, axial compression ratio and CFRP wraps on the seismic performance of the columns, including hysteresis performance, displacement ductility, stiffness degradation, and energy dissipation capacity of those columns, were analyzed. Additionally, the curvature distribution of reinforced concrete columns strengthened with near-surface mounted SMA bars was analyzed based on the displacement field provided by the digital image correlation (DIC) method. Results indicated that the failure of concrete columns reinforced with SMA bars results from the yield of longitudinal tension reinforcement and concrete crushing at the column base, forming plastic hinges. This primarily exhibits a ductile failure mode. Under the same axial compression ratio, the load bearing capacity of the strengthened columns increased by 51.2% to 70.2% compared to ordinary RC column. Displacement ductility and the cumulative energy dissipation of the columns were also increased, significantly enhancing the seismic performance. As the amount of SMA reinforcement increased, the energy dissipation capacity, the length of the plastic hinges and the ultimate displacement of the strengthened columns greatly improved. The bearing capacity of the strengthened columns did not show a significant decrease before the drift ratio reached 1/50. As the axial compression ratio increased to 0.4, the peak load and energy dissipation capacity increased, while the ductility decreased significantly. The deformation performance and energy dissipation capacity of the columns wrapped with CFRP improved obviously. Additionally, based on the plane sections assumption, a theoretical calculation model that predicts the flexural bearing capacity of the SMA bar strengthened columns was established. The calculated results were in good agreement with the test results.