Simple model with in-parallel elasto-fragile trusses to characterize debonding on FRP-reinforced flat substrates

In many structural applications for masonry and rc strengthening, Fiber Reinforced Polymer (FRP) composites exhibit a typical mode II fracture behavior at the bond between substrate and strip when the latter is subjected to considerable tensile stresses. At structural level, the debonding mechanism is usually considered lumping the non-linearity at the interface. A variety of different models is already available to accurately study the debonding, but their utilization within a standard low-cost FE software is difficult, because of the limited gallery of nonlinear elements at disposal for the user. Among the most common elements available, the simplest one is the so-called cutoff bar, which is a truss behaving in an elastic-perfectly brittle way. The paper presents a recursive analytical approach to study debonding using a device constituted by several in-parallel cutoff bars. To closely fit existing analytical models’ response, it is shown that many in-series cutoff bars should be used. Due to the considerable number of elements required, such procedure is still hardily implementable, albeit theoretically applicable. For this reason, an identification procedure of a layer of trusses representing FRP and connected to the support with a layer constituted by two in-parallel cutoff bars is proposed. To do so, the selection of only two target points located on the actual global debonding curve is needed. Resultant mechanical properties of the cutoff bars allow to fit very closely the global behavior obtained through analytical approaches with an extremely simple discretization. The model is successfully validated against an already presented closed form procedure and applied on a set of experimental data available in the literature.