FRP-to-concrete interface debonding: Experimental calibration of a capacity model

Externally Bonded FRP Reinforcement (EBR) has become a popular technique for Reinforced Concrete (RC) structures strengthening. Several theoretical models, based on the fracture mechanics, have been developed by researchers in the last years to estimate the debonding load of Fiber Reinforced Polymer (FRP) reinforcement applied on concrete surface. Theoretical fracture energy relationships generally include parameters calibrated with experimental data obtained by FRP-concrete bond test. The main available experimental FRP-concrete bond tests show that the most used test procedure is the Single Shear Test (SST) and the largest part of tests involved FRP sheets rather than plates. The results of 34 SST tests carried out by authors on both CFRP sheets (18) and plates (16) are reported and discussed in the present paper; a comparison between plates and sheets reinforcements in terms of debonding load is also given. Based on an enlarged database of FRP-concrete bond tests, a refined calibration of the experimental coefficient to be used in the design equations provided by CNR-DT200/2004 to compute fracture energy for EBR FRP strengthening has been performed; the calibration has been separately performed for sheets and plates in order to specifically take into account the influence of the type of reinforcement on fracture energy. Finally a comparison between experimental results and theoretical predictions provided by the re-calibrated CNR-DT200/2004 equation, fib bulletin 14 and ACI 440.2R-08 is reported.