Experimental and analytical study on unidirectional and off-axis GFRP rebars in concrete

The results of bond and tensile strength investigations of hollow glass-fiber reinforced polymer (GFRP) composite rebars are presented. GFRP rebars with similar geometry but different microstructures were evaluated. Bond characteristics of on-and off-axis specimens, in terms of maximum sustained load, bond strength and stress, concrete compressive strength and initial bond stress are reported. Two different procedures for evaluating the bond strength were used. The results of the well-known pullout tests are compared to these obtained by a newly developed test method. Based on the test results of this study, it appears that the compressive strength of concrete has minor influence on bond strength and stress performance of the composite reinforcement investigated herein. The bond between concrete and reinforcement is controlled by the geometry of the rebar, embedment length, and the clear cover provided by the concrete. In order to confirm the experimental results, a computer simulation of the rebar's behavior was performed. Stresses and strains were computed for each layer of both rebars structures. The theoretical analysis predicts the experimental results. The unidirectional bars exhibited higher longitudinal stresses in all three simulated loading schemes. The off-axis rebars showed higher transverse strains and stresses. The results of this study suggest that the microstructure of the composite bars is a significant factor influencing the bond performance. The specimens reinforced with unidirectional glass fibers showed higher bond strength than off-axis fiber-reinforced specimens. (C) 2000 Elsevier Science Ltd. All rights reserved.