Analytical modeling of moment-curvature behavior of steel and CFRP RC circular confined columns

This paper reports on the results of an experimental investigations and theoretical models of concrete filled fiber-reinforced polymer (FRP) tube (CFFT) columns reinforced with steel and carbon-FRP (CFRP) bars under concentric and eccentric compressive loads. The experimental test parameters were the type of the internal reinforcement (CFRP versus steel) and eccentricity to diameter ratios. It was found that the CFRP reinforced CFFT columns successfully maintained the axial load capacities under different eccentricities as compared with the steel reinforced CFFT columns. However, the strength and behavior of the steel and CFRP CFFT test specimens were mainly affected by the eccentric loading. The average compressive strength of CFFT columns was reduced by 42-75% with increasing the e/D ratio from 10 to 40%. Theoretical models using two approaches to predict the axial-moment interaction diagrams and moment curvature relationships were developed and validated through comparison with the experimental results. A nonlinear moment-curvature (M-phi) response was observed regardless the type of reinforcement and the applied eccentricity ratio. Furthermore, a comprehensive parametric study was performed to investigate the influence of different design variables on the moment capacity by creating numerous moment curvature relationships.