Axial-flexural performance of columns reinforced by steel-FRP composite bars and FRP ties

The ductile and corrosion-resistant steel-FRP composite bar (SFCB) is a promising longitudinal reinforcement for marine engineering in harsh environments. However, the study about the axial-flexural performance of longitudinal SFCBs reinforced concrete columns, especially combined with corrosion-resistant FRP ties, is very limited. The lack of valuable experimental observations and design methods seriously limits its design and application. Here, 15 square concrete member specimens with different reinforcement types are tested under concentric compression, eccentric compression, and pure flexural loading, to investigate the effect of longitudinal SFCB and FRP tie on the axial-flexural behavior of columns. Results show that the yielding characteristic of longitudinal SFCB leads to two representative failure modes (tension-controlled and compression-controlled failure). Using equal-stiffness SFCB to replace steel bar contributes to a better axial-flexural behavior of columns, including the same failure mode, similar deformation, and higher load capacity. Furthermore, a theoretical model that considers the unique constitutive relationship of SFCB and confinement conditions of different ties is developed to predict the failure modes and axial-flexural capacity of columns, showing great accuracy. These findings provide a valuable experimental basis and safe design tactics for this corrosion-resistant and ductile hybrid reinforcement scheme of marine infrastructure.

Automated summary

This study investigated the use of longitudinal steel-FRP composite bars (SFCBs) with corrosion-resistant FRP ties in marine engineering. The results showed that using SFCBs instead of steel bars improved the axial-flexural behavior of columns, including the same failure mode, similar deformation, and higher load capacity. Additionally, a theoretical model considering the characteristics of different ties was developed to predict the failure modes and axial-flexural capacity of columns.