Experimental and Numerical Study of Concrete Columns Reinforced with BFRP and Steel Bars under Eccentric Loading

Abstract

There is a limited understanding of the behavior of hybrid reinforced concrete (hybrid-RC) columns, incorporating both fiber-reinforced polymer (FRP) and steel bars, when subjected to eccentric compression loads. In this study, eccentric loading was performed on four hybrid-RC columns with inner-layer steel bars and ties and outer-layer basalt fiber–reinforced polymer (BFRP) bars and ties, along with one steel-RC column. The effects of spacing, surface treatment, and concrete cover of longitudinal BFRP bars were considered for the hybrid-RC columns. Subsequently, a finite-element model (FEM) was developed and validated using the experimental data. This FEM was then utilized to conduct a parametric study, exploring the effects of reinforcement ratio, ratio of ρs/ρf, eccentricity, and slenderness ratio. It was experimentally found that substituting the outer-layer steel bars in the steel-RC column with BFRP bars could improve the axial load capacity, although the stiffness and crack-resistance ability decreased. The numerical results indicated that, under larger eccentricities, hybrid-RC columns could more effectively utilize the high tensile strength of BFRP bars. Consequently, hybrid-RC columns exhibited higher cross-sectional strength and a slower reduction in axial load capacity as the slenderness ratio increased, compared to the steel-RC column. Furthermore, the slenderness limit for hybrid-RC columns was proposed based on the parametric analysis.