Dynamic testing of reinforced concrete beams damaged and repaired with CFRP sheets

A procedure for assessing stiffness variations due to damaging and retrofitting of reinforced concrete beams is presented in this paper. This procedure is based on modal analysis and testing. Two beams were subjected to cyclic loading at increasing load levels, in order to induce in them increasing cracking patterns. The beams were then retrofitted by externally bonded carbon fiber reinforced polymer sheets. Modal tests were carried out after each loading–unloading cycle. A theoretical model was developed, in order to simulate the behavior of the beams in each situation. This model is based on the concepts of fracture mechanics to evaluate the stiffness of cracked beam elements, with and without external strengthening. The theoretical results are in good agreement with the experimental ones. The research suggests that dynamic testing can be used to obtain useful information about the effectiveness of the strengthening system.