Due to the lower elastic modulus and higher tensile strength of glass fibre-reinforced polymer (GFRP) bars compared to steel, the design of GFRP-reinforced concrete (RC) flexural members is governed by serviceability limit states, including deflection and crack width. This study enhances understanding of the flexural and shear behaviour of concrete beams reinforced with GFRP bars through experimental and analytical work. The main objective is to elucidate the effect of GFRP bars and fibre reinforced concrete (FRC) on the flexural and shear response of concrete beams. This investigation evaluates existing design equations in North American standards, offering design recommendations for GFRP-FRC beams.
Accordingly, this research is divided into two main phases. Phase I, “Flexural and Serviceability Behaviour of GFRP-FRC Beams”, examines the impact of macro-synthetic fibres on the behaviour of 11 GFRP-RC beams. The study investigates the deflection equations outlined in the CSA S806-12 and ACI 440.11-22 standards, alongside assessing flexural capacity in accordance with ACI 544.4R-18. Furthermore, digital image correlation (DIC) was utilized to capture the crack propagation, crack width, and deflection up to failure, demonstrating its effectiveness over conventional contact instrumentations such as linear variable differential transducers (LVDTs) and potentiometers.
Phase II, titled “Shear Behaviour of GFRP-RC Beams”, utilizing 15 specimens, explores parameters including reinforcement ratio, stirrup type, stirrup reinforcement ratio, shear span to depth ratio, and fibre content. The study aims to establish the influence of these parameters on shear capacity, failure mode, and strain variation of stirrup and longitudinal rebar. The results indicated that ACI 440.11-22 and CSA S806-12 strain limits for GFRP stirrups are conservative, and a modified equation is proposed. Current GFRP design codes do not consider the effect of fibres on the shear capacity of GFRP-RC beams. Moreover, the design standard ACI 544.4R-18 for fibre-reinforced concrete, developed for members with steel reinforcement, tends to overestimate the shear capacity of FRP-FRC beams. An experimental database was utilized to assess the accuracy of GFRP design code provisions in determining the shear capacity of GFRP-RC beams. A modified equation is proposed to incorporate the effect of macro-synthetic fibres, validated through literature and current tested specimens.