Behavior of Hybrid GFRP–Steel Reinforced Concrete Columns under Monotonic and Cyclic Lateral Loadings: Tests and Parametric Analysis

Abstract

In this study, eight hybrid glass fiber–reinforced polymer (GFRP)–steel-reinforced concrete (RC) columns were tested under a constant axial load and monotonic or cyclic lateral loads, followed by numerical analyses. These columns were divided into four groups based on the ratio of the GFRP area ( A f ) to the total reinforcement area ( A f + A s ), defined as ρ f/fs . The test results indicated that the 4%-drift cycles caused concrete crushing. The subsequent larger-amplitude cycles caused severe damage, degradation in stiffness and strength, and buckling of steel and/or GFRP bars. For columns with high ρ f/fs , the peak lateral load was reduced by up to 39.5% due to compression failure. An increase in ρ f/fs decreased stiffness and strength degradation while enhancing deformation capacity, recoverability, and postyield stiffness. As ρ f/fs increased from 0 to 1, the behavior transitioned from softening to hardening, and the absorbed energy decreased; however, the recovered energy increased. As ρ f/fs increased from 0 to 1, owing to the elastic behavior of GFRP bars, the ductility of GFRP–steel RC columns under monotonic loading increased from moderate to high. However, cyclic loading decreased the ductility by one level for columns with similar ρ f/fs and degraded stiffness by approximately 4% per cycle. The numerical analyses extended the findings to include different values of axial load ratio, concrete strength, steel strength, and ρ f/fs . The parametric study showed that, for the ultimate lateral load, ρ f/fs had a negative effect, while the axial load ratio, concrete strength, and steel strength had positive effects.