Debonding evolution in nonlinear FRP-retrofitted RC beams with cohesive interface

A novel semi-analytical formulation of the governing equations of an FRP retrofitted reinforced concrete beam under bending, based on the concept of moment-curvature, is presented and it is applied to compute the complete nonlinear load-deflection curve, FRP-concrete interfacial shear stress, the FRP laminate strain and the debonding load of statically determinate RC beams retrofitted by an adhesively bonded FRP laminate. The beam may be subjected to any loading, including uniformly distributed or discrete point load(s). The governing equations satisfy the equilibrium and strain compatibility requirements of the beam but slip at the FRP-concrete interface is permitted. A novel procedure for constructing the full nonlinear moment-curvature relationship of beams undergoing interfacial slip is presented in detail, but it is shown that practically a trilinear relationship is satisfactory for obtaining an accurate estimate of the beam deflection and stresses. The robustness and accuracy of the method are demonstrated by analyzing several beams tested by other researchers under uniformly distributed load or four-point bending, with remarkably close agreement between the experimental and corresponding computed values.