NSM GFRP Strengthening of Reinforced Concrete Beams after Exposure to Fire: Experiments and Theoretical Model

Abstract

The effectiveness of near-surface mounted glass fiber–reinforced polymer (NSM GFRP) retrofitting of reinforced concrete (RC) beams after exposure to fire is investigated in this study both experimentally and analytically. Experiments were performed on nine RC beams: one beam was not exposed to fire (control specimen) and eight beams were divided into two groups exposed to fire for 30 and 60 min. In each group, one beam was not retrofitted, whereas the other three beams were retrofitted using NSM GFRP. After retrofitting, all beams were loaded until failure. The experimental results confirmed that the retrofitting technique effectively recovered the strengths of postfire RC beams. The failure mode of the GFRP retrofitted beams was the peeling-off of concrete cover, whereas that of the control and unretrofitted postfire beams was flexural failure via the yielding of tension steel. The NSM GFRP retrofitting fully recovered or significantly increased the yield and ultimate strengths of postfire RC beams by up to 39%. The yield deflection capacity of the NSM GFRP retrofitted postfire beams was much higher than that of the control beam; however, the ultimate deflection capacity of these beams significantly decreased. Consequently, the GFRP retrofitted postfire beams were of low ductility because of the peeling-off of the concrete cover. NSM GFRP retrofitting slightly improved but did not completely recover the yield stiffness reduced by fire, whereas it increased the plastic stiffness significantly by up to threefold. An analytical model for estimating the yield moment of postfire RC beams without/with NSM GFRP retrofitting was proposed, considering the very limited information, for example, fire duration obtained from actual fire events. The practicality and reasonable accuracy of the proposed model render it beneficial for structural engineers.