Experimental Assessment of Shear Transfer Capacity of GFRP Reinforcement Using the Push-Off Test

The interface shear transfer mechanism in concrete structures has been studied for several decades and its investigation has served as the basis for the provisions of current design specifications. However, most of the studies on interface shear transfer have used steel bars as interface shear reinforcement, with minimal experimental and analytical research conducted on glass fiber–reinforced polymer (GFRP) reinforcement. In this study, tests were conducted to quantify the contribution of GFRP rebars to interface shear transfer by using the push-off test. A total of 27 specimens were built and tested using a single concrete compressive strength of 36.5 MPa (5,300 psi); 9 of them included no reinforcement crossing the shear plane, 6 had steel stirrups, and 12 had GFRP stirrups with two quantities of reinforcement. Additionally, during the construction process, six of the specimens were built in two stages to simulate a cold joint condition at the interface. The experimental results showed that GFRP reinforcement contributes substantially to the interface shear strength with ultimate resistance values higher than the results from specimens without reinforcement. Furthermore, once the ultimate strength is reached, the GFRP reinforcement allows the specimen to deform and prevent sudden failure. As for the theoretical capacities estimated by current codes, the experimental tests for GFRP showed an overestimation in the calculation of these capacities. Therefore, the research findings will be helpful in the development and improvement of design guide specifications for concrete structures reinforced with GFRP stirrups where interface shear effects are significant.