Slenderness limit for GFRP reinforced concrete columns based on axial force ratio

Abstract

Concrete columns reinforced with fiber-reinforced polymer (FRP) bars have been of great interest in recent years. The distinct properties of FRP bars, such as linear stress–strain behavior and low modulus of elasticity in comparison to steel bars, make the study of FRP reinforced concrete (FRP-RC) columns of importance, especially with regard to the effect of slenderness. This work presents a numerical method for second-order analysis and examines the slenderness limit of glass FRP bars reinforced concrete (GFRP-RC) columns based on two criteria: a reduction in moment capacity at constant load and a reduction in load capacity at constant eccentricity. In the literature, only limited contributions have been made on the slenderness limit of FRP-RC columns, usually based on the latter criterion, whereas there is a lack of literature regarding the slenderness limit of FRP-RC columns based on the former criterion, which is also the slenderness limit criterion of Eurocode 2 (EC2-04) for steel-reinforced concrete (steel-RC) columns. This work may assist in the development of Eurocode provisions, national annexures and guidelines for the design of GFRP-RC concrete columns. A detailed sensitivity analysis was conducted with parameters including the modulus of elasticity of the GFRP bar, percentage of reinforcement, compressive strength of concrete and axial force ratio to examine the variation of slenderness limit for GFRP-RC columns. The axial force ratio is observed to be an important parameter to estimate the slenderness limit from the sensitivity analysis. Variation of slenderness limit for GFRP-RC columns with axial force ratio is observed to be different and the value of slenderness limit is lower compared to the steel-RC columns. Two Equations, which take into account the variation due to the axial force ratio, are proposed to estimate the slenderness limit for GFRP-RC columns.