Acoustic emission monitoring and numerical modeling of FRP delamination in RC beams with non-rectangular cross-section

A case study concerning both numerical modeling and in-situ monitoring of a retrofitted RC beam with non-rectangular cross-section is presented. Before retrofitting, non-destructive techniques, such as pull-out and impact tests, were used to estimate the mechanical parameters of concrete. At the same time, a long-term monitoring with the Acoustic Emission (AE) technique was carried out in order to investigate on creep effects and microcracking phenomena. Then, after a complete removal of the overload and retrofitting with FRP sheets, an in-situ loading test was performed. At that stage, the AE technique was again profitably used for the analysis of the cracking progression leading to FRP debonding. A numerical model of the structure is then proposed in the framework of the FE discretization with mechanical parameters estimated according to an inverse analysis on the monitored mechanical behavior of the structure before retrofitting. According to this model it is shown that, when the flexural inertia of the retrofitted beam is considerably higher than that of the unrepaired beam, snap-back instabilities can take place. Finally, considering the self-similarity between the acoustic emission phenomenon and seismicity, an analogy between the snap-back instability of the FRP delamination and that occurring during fault growth is proposed.