Brittle failure in FRP plate and sheet bonded beams

Analytical and numerical models are presented to simulate the failure of RC beams strengthened with FRP plates and flexible sheets. Different failure mechanisms, from ductile to brittle, can be simulated and verified. The proposed analytical model takes into account the influence of concrete confinement in the compression zone due to the presence of the stirrups and the tensile softening properties of concrete. This allows following more accurately the crack propagation and the failure mechanism of the flexural member. The numerical model is based on finite element analysis (FEA), follows the smeared crack approach, and uses standard elements available in a commercial package. Comparisons with experimental data obtained from strengthened RC beams tested in the laboratory are presented. Analytical and numerical models show good agreement with the experiments. It is shown that FRP type, thickness, and bonded length produce different types of failure ranging from FRP rupture to concrete shear failure. Particularly important is the characterization of the interface (FRP-concrete) mechanical properties, for which a simple test is proposed