Effect of steel-FRP ratio and FRP wrapping layers on tensile properties of glass FRP-wrapped ribbed steel reinforcing bars

One of the many alternative methods developed to address the corrosion problem of steel reinforcements is the use of hybrid reinforcement composed of a fiber-reinforced polymer (FRP)-wrapped ribbed steel reinforcing bars. However, the number of layers and thickness of the FRP wraps on the ribbed steel core affect the mechanical properties of the glass FRP (GFRP)-steel hybrid reinforcement. In this study, in order to increase the ductility of the hybrid reinforcements, 27 types of hybrid bars were produced by wrapping E-glass fibers at an angle around the steel reinforcement using the filament winding method. The effects of steel reinforcement diameter (8, 10 and 12 mm), steel-FRP ratio and number of glass fiber layers (one, two and three layers) on the tensile properties of hybrid reinforcement were investigated. The experimental results on hybrid bars were compared to the respective values of the plain GFRP and carbon FRP (CFRP) reinforcing bars as well as the results on hybrid bars in the literature. In addition, a theoretical stress-strain model was proposed for the GFRP-wrapped steel reinforcing bar. The study showed that increasing the FRP ratio in the hybrid reinforcement increased the ductility of the reinforcement, although the yielding stress was reduced. The strain of glass-wrapped ribbed steel reinforcements under maximum stress varied between 4.14 and 6.22%. The energy absorption capacity of the GFRP-wrapped reinforcement was observed to be higher than that of the plain GFRP, CFRP and the other hybrid bars. In addition, the developed theoretical model was found to be compatible with the experimental results.