Flexural Performance of RC Beams with Hybrid Combination of Conventional FRP and PET Laminates

Abstract

Externally bonded fiber-reinforced polymer (FRP) composites are widely used to strengthen reinforced concrete (RC) beams. However, due to composites' brittleness, strengthened beams usually fail by premature brittle debonding of the FRP laminates. Delaying this failure mode enhances the beams’ flexural capacity and ductility. This work aims to study the effect of balancing traditional high-strength FRPs with polyethylene terephthalate (PET-FRP) laminates. Unlike conventional FRPs, PET-FRP has a bilinear stress-strain relationship and ruptures at large strains exceeding 7%. However, it has lower elastic modulus and tensile strength than conventional FRPs. To compensate for this drawback, the effect of hybridizing carbon-FRP (CFRP) and glass-FRP (GFRP) with PET-FRP laminates is examined. In addition, to enhance the effectiveness of the strengthening systems and delay FRP debonding, the effect of anchoring using end U-wraps is explored. Twenty-seven RC beams, strengthened with different combinations of layers and stacking sequences of hybrid CFRP, GFRP, and PET-FRP laminates and with and without end U-wrap anchors, were tested to failure. The results of the strengthened anchored beams were compared to the un-anchored strengthened beams and un-strengthened control beams. Results showed that hybrid combinations of PET, CFRP, and GFRP laminates provided enhanced flexural performance over CFRP and GFRP-strengthened specimens. The enhancement depended on the number of strengthening sheets, type of FRPs, stacking sequence, and presence of anchors. The enhancement in the load-carrying capacity and ductility ranged from 23% to 70% and -17% to 92%, respectively. Results proved that side anchors effectively prevented premature failure due to debonding or delamination. The highest load-carrying capacity and ductility enhancement were exhibited by the PGP anchored specimen. The load-carrying capacity of the strengthened beams was predicted using the ACI 440.2R-17 and CEB-FIB design guidelines. It can be concluded that combining PET with CFRP and GFRP laminates could provide a robust strengthening system that enhances both the strength and ductility of RC beams in flexure.