Experimental evidence of failure mode transition for reinforced concrete rectangular columns with corroded stirrup

Failure mode transition is paramount for reinforced concrete (RC) columns with corroded stirrup, affecting the seismic performance significantly. Previous experimental studies have overlooked investigations into the stirrup spacing and shear span ratio, both of which may exert significant impacts on the failure mode transition of corroded RC columns. To deal with this problem, this study investigates the effects of stirrup spacing and shear span ratio on the failure mode transition of corroded rectangular columns. A total of eight full-scale specimens with a cross-section of 300 mm × 450 mm were designed, including specimens with four different stirrup corrosion ratios, three different stirrup spacings, and three different shear span ratios. The failure modes of corroded columns were discussed by analyzing crack propagation, steel bar yielding and buckling, and actual stirrup corrosion ratios. The differences in seismic performance of corroded columns under different working conditions were examined by comparing and analyzing results of indicators including load capacity, ductility, and energy dissipation. The test results indicate that the failure mode transition occurs from flexural to shear when the corrosion ratio increases, stirrup spacing widens, and shear span ratio decreases. The stirrup corrosion ratio, stirrup spacing, and shear span ratio significantly influence the seismic performance of corroded columns. In the process of inducing the failure mode transition of RC columns, the increase of stirrup corrosion ratio and stirrup spacing significantly reduces the peak load capacity. Meanwhile, increasing the stirrup corrosion ratio, widening the stirrup spacing, and reducing the shear span ratio lead to a decline in the ductility and energy dissipation. Compared with the uncorroded column, the displacement ductility factor of the columns under three corrosion degrees decreases by 18.8 %, 5.2 %, and 15.8 % respectively. Their single-cycle energy dissipation at 3 % drift ratio has a decrease by 15.7 %, 33.4 %, and 63.1 % respectively. In addition, the cumulative energy dissipation capacity before the ultimate state exhibits a moderate decline when the shear span ratio decreases, whereas the single-cycle energy dissipation before the shear failure experiences a sudden increase. This experimental investigation is beneficial to understanding the complicated flexural and shear failure competition mechanism of corroded RC columns.