Residual Flexural Behavior of PBO FRCM-Strengthened Reinforced Concrete Beams after Exposure to Elevated Temperatures

The residual flexural behavior of reinforced concrete (RC) beams strengthened with a fabric-reinforced cementitious matrix (FRCM) composite system after exposure to elevated temperatures was analyzed and discussed in the paper. Ten RC beams, two unstrengthened and eight strengthened with a polypara-phenylene-benzo-bisthiazole (PBO) FRCM system, were tested at ambient temperature (20°C) under three-point bending after being exposed to temperatures of 100°C, 200°C, and 300°C. Test results were analyzed in terms of failure modes, failure loads, load–deflection curves, strain, stress distributions, and ductility. The obtained results evidenced that the load-bearing capacity of the strengthened beams remained roughly constant for temperatures ranging from 20°C to 200°C (from 13% to 23% higher than that of the unstrengthened beams). On the other hand, the collapse of PBO FRCM-strengthened beams exposed to a temperature of 300°C occurred for load values that were, on average, 12% lower than those of strengthened beams at room temperature. The effects of exposure to elevated temperatures on the PBO FRCM-to-concrete debonding were also discussed. A semiempirical model based on the experimental results was defined to estimate the residual debonding strain of the composite system as a function of temperature. The accuracy of the proposed model as well as those of some different analytical procedures available in the literature was assessed through a comparison with experimental results.