Fracture mechanics approach to geometrically nonlinear debonding problems in RC beams strengthened with composite materials

The geometrically nonlinear debonding mechanism in reinforced concrete beams strengthened with externally bonded FRP strips is analytically investigated. The paper focuses on cases in which various loading scenarios yield compressive stresses in the bonded strip. Under these conditions, the FRP strip tends to buckle, and, in turn, to trigger and accelerate the unstable growth of the debonded region. A high order geometrically nonlinear model of the strengthened beam is developed and combined with the fracture mechanics concept of the energy release rate to provide a quantitative criterion for the initiation, propagation, and stability or instability of the debonding growth process. Numerical results that demonstrate the capabilities of the proposed modeling approach and throw light on some of the physical phenomena associated with the structural response of the strengthened beam are presented. The analysis reveals the response through the loading process and through the debonding growth process, highlights the localized effects near the debonded region, quantifies its tendency to grow, and describes the stability characteristics of the debonding mode of failure. A summary and conclusions are included in the sequel.