Seismic Performance and Cumulative Damage Analysis of Concrete Columns Confined by High-Strength Stirrups

The damage index can quantify the damage degree of structures and components under earthquake, and provide an important theoretical basis for the post-seismic damage assessment and design of structures. For this reason, this paper conducted on the experiments of seismic performance and cumulative damage analysis about 15 concrete columns confined by high-strength stirrups. The test results showed that the stirrup did not yield at the peak point and the tensile stress of stirrup was 56%–91% of the yield strength. The stirrup could yield at the ultimate displacement but did not break. The concrete columns confined by high-strength stirrups showed good bearing capacity and deformation capacity in the whole loading process. For concrete columns confined by high-strength stirrups whose concrete grade is C50 and longitudinal reinforcement strength grade is HRB500, the comparison between calculated results of different damage models and test results showed that the Chai model could accurately predict the damage degree. For specimens with a shear-span ratio of 3, larger reinforcement ratio and stirrup ratio, the damage index calculated by Kunnath model was slightly smaller at the stage of minor damage and moderate failure. The Fu model could predict the damage degree of confined concrete columns at five stages, but the calculated values were greater than 1 and did not converge. Confined concrete columns with larger shearspan ratio would decrease the development rate of damage, and the increase in axial compression ratio would aggravate the damage degree of confined concrete columns. With high reinforcement ratio and stirrup ratio, the damage development rate was slower and the damage degree was relatively lower with the same cyclic times. In the stirrup design of confined concrete columns, the cumulative damage can be decreased and delayed based on a rational configuration of longitudinal rebar sand stirrups.