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Description
This study presents a creep response model to investigate the long-term behavior of interfacial shear stresses induced by intermediate flexural cracks in reinforced concrete beams strengthened with externally bonded fiber-reinforced polymer (FRP) plates. A theoretical framework based on a bi-linear cohesive zone model is developed to describe intermediate crack-induced debonding. The proposed approach integrates both the initiation and propagation of debonding through time increments. The creep behavior of the RC beam, adhesive layer, and FRP plate is incorporated by considering the time-dependent mechanical properties of each component. The resulting time-dependent stress–deformation relationship caused by creep is described through a bond-slip law. Based on this concept, a new interfacial law is proposed that accounts for the time-dependent properties of all constituents of the strengthened beam system (concrete-FRP-interface). In the formulation, the total energy at the interface is assumed to remain constant during the creep response associated with intermediate cracking. The predictions obtained from the proposed model show good agreement with results reported in the literature, confirming its capability to capture the long-term interfacial behavior of FRP-strengthened RC beams. In addition, a parametric study is conducted to evaluate the influence of mechanical properties and thickness variations of the FRP plate, concrete substrate, and adhesive layer on interfacial debonding. The results indicate that creep significantly accelerates the debonding process over time. The softening zone develops rapidly, and the load-carrying capacity of the strengthened beam is progressively affected as time increases.