Theoretical study on the bond performance of embedded through-section reinforcing bar-to-concrete joints with localized debonding defects

Embedded through-section (ETS) technique represents an efficient solution for strengthening existing reinforced concrete (RC) members, where steel or fibre-reinforced polymer (FRP) bars are inserted into predrilled holes and bonded to the concrete via adhesive. Recent experimental and theoretical studies on ETS bond interfaces have found that debonding defects may occur, in certain scenarios, in the construction process induced by air voids, poor grouting or partially cured adhesives, which negatively influences the bond behavior. Currently, little is known about the influence of localized debonding defects on the performance of ETS reinforcement bar-to- concrete joints at present. Therefore, this work attempts to propose a new analytical model that allows for studying the influence of localized debonding defects on the bond behavior of the ETS system. A cohesive zone model (CZM) with a trilinear bond-slip law is used to describe the nonlinearity of ETS reinforcement-to-concrete interfaces. Experimental investigations were conducted on both FRP and steel bars bonded in concrete using different adhesive types, defect lengths, and bond lengths. The solution proposed emphasised the key difference between “short” and “long” joints: short joints were characterized by a softening behavior in the load-slip curve regardless of debonding defects, while long joints exhibited two peak loads followed by a snap-back behavior in the presence of localized debonding defects. The results showed that the analytical predictions were in agreement with the test data, both revealing degradations of the load capacity of the joint with the increase of the ratio (η) between the debonded and the bonded area, particularly for short bonded joints. However, less sensitivity to the location of debonding defects was observed with minimal changes in the load degradation of both long and short joints. This paper facilitates a better understanding of the interfacial behavior of ETS reinforcement-to-substrate bonded joints with debonding defects.