Axial compressive behavior and design of semi-precast steel reinforced concrete composite columns with permanent ECC formwork

This paper proposes an innovative semi-precast steel reinforced concrete (SRC) hybrid composite column, which incorporates a precast engineered cementitious composite (ECC) jacket as the permanent formwork for the infilled concrete. The ECC jacket enhances the column compressive resistance and provides superior post-peak ductility. To evaluate the compressive performance of the ECC-SRC composite column, an experimental program of six axially-loaded stub column specimens was conducted by varying the thickness of the ECC jacket, section size of structural steel and spacing of transverse reinforcing bars. The axial performance of the ECC-SRC column is evaluated in terms of failure characteristics, initial stiffness, load-carrying capacity, post-peak resistance and ductility, and the full range load-deformation response. The test results show that the ECC-SRC column exhibits improved compression capacity and ductility compared to conventional SRC columns. The assessment of compiled database also reveals the applicability of current design codes EN 1994-1-1 and JGJ 138-2016 in predicting the load-carrying capacity of ECC-SRC columns. Finally, based on the parametric study of the database, design suggestions are proposed to maximize the merits of ECC when employed in ECC-SRC columns.