Mechanical behaviors of RAC columns confined by steel-reinforced ECC shell under eccentric compression

Recycled aggregate concrete (RAC) typically exhibits higher porosity and lower strength than natural aggregate concrete (NAC) due to the existence of residual mortar layers and initial micro-cracks. To enhance the performance of RAC, this study presented an innovative ECC-RAC composite square column (ECC-RAC-CSC) and its eccentric compression behaviors with various eccentric distance ( e ), ECC shell thickness ( t ), stirrup spacing ( d ), and interface connection form ( I f ). The results showed that the e was the main factor affecting the eccentric compression behaviors, followed by t and d , while the influence of I f was relatively small. As e increased, the failure mode of ECC-RAC-CSCs gradually transitioned from compression-ductile failure to tension-controlled failure, and the bearing capacity was significantly decreased. Both bearing capacity and deformability enhanced with increasing t or decreasing d . Under high eccentricity, a distinct post-peak stable stage was observed in semi-precast ECC-RAC-CSCs with a wet connection form, indicating superior deformability. Furthermore, the bearing capacity of ECC-RAC-CSCs was calculated through the cross-section layer-by-layer method and simplified method. On this basis, a modified strength model was developed to predict the bearing capacity of ECC-RAC composite columns under eccentric compression, considering the confinement of ECC shell and stirrups. The model was verified through comparing the predicted values with experimental values, and the errors between them were within 7%.