Effect of glass fiber-reinforced polymer reinforcement ratio on axial-flexural strength of reinforced concrete columns

A set of requirements parallel to those of ACI 318 has been proposed to generalize the design of reinforced concrete (RC) columns to include glass fiber-reinforced polymer (GFRP) bars in an anticipated GFRP-RC design code currently under preparation by ACI Committee 440. The prudent course of action prior to implementing such requirements, however, is to verify them with a comprehensive experimental study. In this study, 12 full-scale RC columns with a 405 x 405 mm (16 x 16 in.) cross section were designed, fabricated, and tested. The columns were reinforced with GFRP bars and ties. Three different longitudinal reinforcement ratios were investigated (1.0, 1.4, and 2.5%), resulting in three groups of four identical columns (similar reinforcement ratios) that were tested under four different levels of eccentricity. Experimental axial force-moment (P-M) interaction diagrams were constructed for each group. The effect of the longitudinal reinforcement ratio on strength, failure mode, deformation, and strain behavior is presented. A strain compatibility model has been developed, verified with experimental results, and used to provide a parametric study of the critical parameters affecting behavior. The parametric study covered a wide range of concrete strength and reinforcement ratios while considering or neglecting GFRP contribution in the compression zone. The resulting P-M interaction diagrams are presented and discussed.