Evaluating the fire response of concrete beams strengthened with near-surface-mounted FRP reinforcement

This paper presents an approach for evaluating the fire response of reinforced concrete (RC) beams strengthened with near-surface-mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. The model is based on a macroscopic finite-element approach and is capable of tracing the response of NSM FRP-strengthened RC beam from the preloading stage to collapse under a specified fire exposure and loading conditions. The model accounts for high-temperature properties of constitutive materials, realistic load and boundary conditions, and temperature-induced bond degradation at the FRP-concrete interface. The validity of the model is established by comparing predictions from the model with measured data from tests at both ambient and fire conditions. The validated model was applied to carry out numerical studies to compare the fire response of concrete beams with different types of strengthening systems and insulation layouts. Results from numerical studies indicate that a concrete beam strengthened with NSM FRP reinforcement yields slightly lower fire resistance as compared to a conventional RC beam but achieves higher fire resistance than that of externally bonded FRP. It is also shown that appropriate location of a NSM FRP reinforcement and insulation scheme can increase the fire resistance of concrete beams strengthened with NSM FRP reinforcement.