Mechanical properties of RC combination columns configured with ECC jacket

Shaped steel-reinforced concrete (SRCC) is used in engineering applications because of its load resistance and energy absorption properties, but the lack of ductility limits its ability to improve seismic performance. A novel structure-SRCC configured with Engineered Cementitious Composites (ECC) jacket (ESRCC) is proposed for breaking through this limitation and improving the load-bearing capacity and ductility of SRCC. Then, the mechanism of the key design parameters of ESRCC (ECC jacket thickness, rebar ratio, hoop ratio and size of shaped steel) on the mechanical properties is systematically investigated on the basis of the finite element model, focusing on revealing the role of these variables on the failure modes, load-deflection curves and ductility. The results show that the rebar ratio and hoop ratio have a significant effect on the mechanical properties of ESRCC, and the ultimate load capacity is increased by 12.85% when both increase from 0 to 1.84% and 3.3%, respectively. The ECC jacket thickness has a limited impact and is not upgraded by more than 1.5%. The effect of shaped steel size is nonlinear, increasing the shaped steel size within a certain range can improve the load-bearing capacity of the ESRCC, but the ductility of the ESRCC will be degraded when the distance between the shaped steel flange and the concrete surface is reduced. Finally, a prediction formula for calculating the ultimate bearing capacity of ESRCC was proposed. This formula can be applied to ESRCC with varying ECC jacket thicknesses, and the predicted results show relatively small errors. The research provides theoretical support for selecting the optimal ECC jacket thickness in practical engineering applications.