The bond behavior of precured FRP strips and steel plates to concrete substrate was investigated in this research in terms of the load capacity, slip and strain distribution and debonding mechanism. Experimental single lap shear tests were performed and an experimental-analytical model was proposed to determine the bond strength of the FRP-bonded joints. Two strengthening methods, including externally bonded reinforcement (EBR) and externally bonded reinforcement on groove (EBROG), were compared. A two-dimensional digital image correlation (2D-DIC) system was utilized to measure the full-field deformations. Compared to the 90 mm effective bond length for the EBR method, the effective bond lengths for the EBROG method were equal to 145 and 160 mm for 5 5 and 5 10 mm groove cross sections, with 92% and 112% higher loads, respectively. In addition, the results showed that the EBROG method improved the bond resistance of steel-to-concrete joints, but it was not as efficient as it was for the FRP-to-concrete bonded joints. Furthermore, the crack propagation underneath the strip was assessed for the first time for the EBROG method, by using a side-view measurement.

Introduction

FRP composites have been accepted extensively for retrofitting and strengthening civil structures, i.e., buildings and bridges. Proper bond behavior between FRP and concrete is important for the strengthening efficiency. Usually, premature debonding happens before full capacity of the materials is achieved. Therefore, the bond behavior of FRP composites to concrete substrate has been studied over the past decades [1–۵]. Experimental, analytical, and numerical research works were performed to evaluate the effect of different parameters [6–۱۰]. Design equations were also proposed to predict bond behavior [1,11–۱۳]. Efforts have been made to postpone debonding, which achieves higher bond resistance. Among those efforts, the EBROG method was introduced as a substitute for the EBR method at Isfahan University of Technology (IUT) [14]. Flexural strengthening of concrete beams with FRP composites using the EBROG method demonstrated a high increase in the beam load capacity and postponed the debonding [14,15]. A comparison of the EBROG method with the conventional EBR technique in the axial/flexural retrofitting of columns, in the shear/flexural strengthening of reinforced concrete beams, and in the repair of beam-column joints was investigated through previous research works [16–۲۱].