Experimental study on seismic behaviours of hybrid FRP-steel-reinforced ECC-concrete composite columns

Owing to the high strength, noncorrosive property, and linear stress strain relationship of fibre-reinforced polymers (FRPs), hybrid FRP-steel-reinforced concrete members exhibit higher strength, superior durability, and lesser residual deformation compared to steel-reinforced concrete members and higher ductility compared to FRP-reinforced concrete members. Hybrid-reinforced members have been widely used as flexural-dominated members rather than compression-dominated members owing to the poor compression performance of the FRP reinforcement. This paper proposes a novel approach for improving the seismic behaviour of such members through the use of high-ductility engineered cementitious composites (ECCs) in the plastic hinge zone. Numerous hybrid FRP steel-reinforced ECC concrete columns were tested under reversed cyclic loading. The effects of the matrix type, reinforcement type, axial force ratio, and reinforcement ratio on the seismic behaviours, including the failure mode, crack pattern, load-carrying capacity, residual deformation, ductility, and energy-dissipation capacity, of the columns were systematically investigated. The replacement of concrete with ECC in the plastic hinge zone efficiently eliminated the local buckling of the FRP bars and significantly improved the seismic performance of the column. Compared with the steel-reinforced ECC concrete composite column, the hybrid-reinforced composite column exhibited significantly less residual deformation and higher post-yielding stiffness. With an increase in the axial force ratio, the ultimate strength increased, while the deformation capacity decreased.