Mechanical behaviors of prefabricated ECC shell‐reinforced RAC composite square columns under axial compression

The corrosion of steel reinforcements and deterioration of mechanical properties are two major concerns in the application of recycled aggregate concrete (RAC). This study introduced a steel‐reinforced engineered cementitious composite (ECC) shell into RAC columns and proposed an innovative steel‐reinforced ECC‐RAC composite square column (ECC‐RAC‐CSC). Subsequently, the axial compressive behavior of ECC‐RAC‐CSCs was investigated based on key design parameters, including the recycled coarse aggregate substitution ratio ( r ), ECC shell thickness ( t ), stirrup spacing ( d ), and interface connection form ( I f ). Besides, a modified model for predicting the bearing capacity of ECC‐RAC‐CSCs was developed and verified, which was applied to the numerical simulation analysis of ECC‐RAC‐CSCs. On this basis, the numerical parametric study was carried out to further validate the effectiveness and accuracy of the modified model. The results indicated that the axial compressive performance of RAC columns ( r = 100%) was slightly lower than that of conventional natural aggregate concrete columns. The steel‐reinforced ECC shell effectively resisted lateral expansion deformation and provided confinement to the core RAC, thereby enhancing the carrying capacity and ductility of the ECC‐RAC‐CSCs. Moreover, the increased t improved both the carrying capacity and ductility, whereas the increases in r and d had a negative impact. The proposed model, considering the additional confinement effect of the steel‐reinforced ECC shell, could provide accurate predictions of the carrying capacity and ductility of ECC‐RAC‐CSCs.