Seismic behaviour at ultimate limit state of reinforced concrete structures retrofitted with glass fiber reinforced polymer rebars

The use of Glass Fiber Reinforced Polymer (GFRP) bars in the framework of retrofitting Reinforced Concrete (RC) structures subjected to seismic action is an advanced technique that offers several benefits due to the material's unique properties. The resulting hybrid reinforcement, consisting of preexisting steel reinforcement in the inner part of the cross-section and additional GFRP bars embedded in the external jacketing, increases the load-bearing capacity while reducing the overall structural element's susceptibility to subsequent corrosion phenomena, saving future maintenance costs. Designers seeking to enhance the durability and safety of RC structures in seismic zones might considerably benefit from implementing hybrid reinforcing systems. The present study analyses a 2D RC multistorey frame as a case study. Two distinct retrofitting interventions are compared: a traditional jacketing, with steel reinforcement, and a GFRP jacketing. The structural behaviour is assessed by, first, computing the moment-curvature relationship of nonlinear plastic hinges, obtained by considering the different failure modes of hybrid reinforced concrete sections, which lead to different postyielding branches. Then, a pushover analysis is performed using a lumped plasticity approach to monitor the activation and evolution of plastic hinges, thus assessing the load-bearing capacity, ductility and energy dissipation of the frames.