Effect of Concrete Strength on the Interface Shear Performance of GFRP Headed-End Bars

Glass fiber–reinforced polymer (GFRP) headed-end bars were evaluated as shear friction reinforcement for interface shear transfer across concrete cold joints. Fourteen large-scale double L-shaped push-off specimens were constructed and tested under monotonic axial loading using two different concrete strengths (35 and 55 MPa) and five GFRP reinforcement ratios (0.33%–1.00%), together with steel-reinforced and unreinforced controls. It was observed that headed-end GFRP connectors enhanced postpeak stability through improved anchorage and sustained dowel action, whereas higher concrete strength increased peak resistance but promoted larger postpeak drops at low reinforcement ratios. Comparisons with current design provisions and models from the literature indicated that strength-based approaches that mobilize FRP tensile strength can overestimate capacity, whereas formulations using constant cohesion and/or overly conservative strain limits can substantially underestimate capacity. A strain-limited, concrete strength–dependent formulation was therefore proposed by adopting a GFRP strain of 0.003 and a cohesion expression as a function of concrete compressive strength. The proposed model provided improved capacity predictions and reduced scatter relative to the compared formulations for GFRP-reinforced concrete interface shear transfer.