A nonlinear semi-analytical model for predicting debonding of FRP laminates from RC beams subjected to uniform or concentrated load

A semi-analytical model is developed to determine in FRP retrofitted reinforced concrete (RC) beams the interfacial shear and peeling stresses, the FRP laminate and the RC section strain and stresses at all loading stages up to failure. The FRP is assumed to be externally bonded to the beam but can undergo slip and relative vertical displacement at its interface with the concrete. The model is developed by satisfying the requirements of equilibrium and strain compatibility while concurrently allowing for interfacial deformations. FRP is treated as a linear elastic, steel as elasto-plastic strain hardening and concrete as fully nonlinear material in compression and tension, including tension stiffening. The governing equations are formulated as two second order differential equations with their dependent variables being the strain in the FRP and the relative normal displacement of the interface. The equations are solved for discrete states (uncracked, cracked, yielded) experienced by the RC section and their associated level of interfacial slip. The model results are compared with available experimental results for several beams retrofitted with carbon FRP or steel reinforced polymer (SRP) laminates subjected to either four point bending or simulated uniform load, with satisfactory agreement between them.