Simple Truss Finite Element to Model FRCM Strengthened Specimens in Single Lap Shear Tests

A novel non-linear truss finite element specifically conceived to study an FRCM reinforcing package is presented. FRCM is modelled considering separately the central elastic fiber grid and the two upper and lower inelastic matrix layers; matrix and fiber are considered in a monoaxial state of stress, mutually exchanging shear stresses at the interface. The interface constitutive relationship assumed is trilinear with softening and residual strength; the element is thus constituted by three trusses (one elastic and two inelastic) linked with shear springs. The internal matrix layer exchanges also tangential stresses between reinforcement and substrate by means of elastic shear springs. The finite element is therefore characterized by 8 DOF, namely the longitudinal displacements of the three layers of the FRCM package plus that of the substrate, evaluated at the extremes of the element. The finite element performance is successfully validated against some available experimental datasets, relying into different FRCM strengthening packages bonded to rigid substrates and subjected to single lap shear tests.