Performance of Postfire Reinforced Concrete Beams Retrofitted with External Bonded and Near-Surface Mounted CFRP: Experiments and Analyses

Fire imposes negative effects on reinforced concrete (RC) members, shifting postfire structures onto dangerous situations. This study aims at carbon fiber-reinforced polymer (CFRP) retrofit of postfire RC beams to recover their mechanical properties, providing technical information for structural engineers in practice. Toward this aim, experiments were performed for 16 RC beams, which were divided into four groups exposed to 30, 45, 60, and 75 min of ISO 834 fire. After exposure to fire, these beams were strengthened by external bonded (EB) and near-surface mounted (NSM) techniques using a similar amount of CFRP for comparison. These specimens were then loaded until failure. The results are compared with one another and compared with control specimens. It is found that both EB and NSM CFRP retrofitted beams failed in the form of peeling off of concrete, whereas no rupture of CFRP was observed. CFRP retrofit significantly changes the behavior of postfire RC beams, being brittle or exhibiting low ductility. The effectiveness of EB and NSM CFRP techniques is similar and it decreases with the increase in fire duration. CFRP retrofit increases the yield load-carrying capacity by 27.5%-40.9% for 30-60-min postfire RC beams and recovers the yield load-carrying capacity for 75-min postfire RC beams. CFRP retrofit significantly increases the ultimate load-carrying capacity, whereas its increasing levels depend not only on the CFRP retrofit but also on the fire duration. Both CFRP retrofitting techniques successfully recovered the yield stiffness of postfire RC beams. The moment capacity of CFRP retrofitted postfire RC beams was theoretically analyzed, and a prediction model was proposed. The proposed model is simple, but it accurately predicts the moment capacity of retrofitted postfire beams; thus, it can be useful for structural engineers in practice.