Experimental Study on the Shear Transfer Resistance of Uncracked Concrete Interfaces Reinforced with GFRP

The shear transfer capacity of initially uncracked concrete push-off specimens reinforced with glass-fiber-reinforced polymer (GFRP) stirrups is experimentally evaluated and presented in this paper. The specimens were cast monolithically using the same concrete mix and tested under monotonic loading conditions until failure. The test matrix included eight specimens with GFRP clamping reinforcement crossing the shear transfer plane, three specimens with steel clamping reinforcement, and one control specimen without clamping reinforcement. The test variables were the type (steel and GFRP) and the amount of clamping reinforcement, with reinforcement ratios ranging from 0.28% to 1.9%. The variation in GFRP reinforcement ratio was achieved either by changing the number of clamping stirrups crossing the shear transfer plane while maintaining the same bar size, or by varying the bar size while keeping the number of stirrups constant. The test results showed that increasing the clamping reinforcement ratio led to higher ultimate and residual shear transfer strengths. However, this trend was not observed for the cracking strength of the specimens. The results also indicated that GFRP-reinforced specimens exhibited lower strength compared with those reinforced with steel reinforcement due to the lower modulus of elasticity of GFRP. The ultimate interface shear strength of the GFRP-reinforced specimens ranged from 5.69 to 9.13 MPa, compared with 6.55 to 10.96 MPa for the steel-reinforced specimens. All reinforced specimens exhibited a similar mode of failure, characterized by shear failure along the interface plane. The analyzed results demonstrated that the stiffness of the clamping stirrups is a key parameter affecting the interface shear behavior. However, it should not be considered the sole governing factor, as the stirrup distribution and bar diameter also influenced the shear behavior. The shear transfer capacities of the GFRP-reinforced specimens were predicted using the AASHTO LRFD, CSA S6, and Vega and others models and compared with the experimental results. The comparison showed notable differences in the accuracy, conservatism, and consistency of the three models in predicting the experimental shear resistance.