Behaviour of strengthened RC beams with CFRP and GSM sheets under cyclic loading

This study investigates the structural behaviour of reinforced concrete (RC) beams subjected to cyclic loading. Four beam configurations were tested: a control beam (C) and beams externally strengthened with carbon fiber-reinforced polymer (CFRP) sheets, steel mesh sheets bonded with epoxy (SME), and steel mesh sheets bonded with mortar (SMM). The experimental program adhered to the evaluation criteria outlined by ACI437R-03. Although the tested beams satisfied the repeatability limit specified by the committee, the deviation from linearity and permanency limits could not be satisfied. The performance of the beams was also evaluated in terms of load-deflection behaviour, stiffness degradation, energy dissipation, and brittleness. The hysteresis loops of the tested beams revealed significant differences in energy dissipation. Strengthened beams exhibited larger hysteresis loop areas, reflecting their enhanced energy absorption and dissipation capacity. In contrast, the control beam demonstrated smaller and narrower loops. The SMM beam consistently outperformed other configurations, achieving the highest flexural load-carrying capacity and dissipation energy. Post-cyclic monotonic loading tests further evaluated the residual behaviour of the beams. The percentage increase in flexural strength ranged from 38 to 51 % compared to the control unstrengthened beam. Therefore, it is concluded that strengthening significantly improves the behaviour of RC beams under cyclic loading.