In recent years, the use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has become a promising technology in strengthening of reinforced concrete (RC) structures. When used in buildings, FRP strengthened RC members have to satisfy fire resistance requirements specified in codes and standards. Due to sensitivity of FRP to high temperatures, FRP strengthened RC members usually exhibit relatively low fire resistance. However, NSM FRP strengthening is considered to possess higher fire resistance than traditional externally bonded FRP strengthening. But there are no specific studies on fire response of NSM FRP strengthened RC members. Therefore, experimental and numerical studies were carried out for developing a fundamental understanding on the behavior of NSM FRP strengthened RC beams under fire conditions. To develop test data on fire response of NSM FRP strengthened members, experimental studies were undertaken at both material level and structural level. As part of material property characterization, extensive high temperature property tests were carried out for evaluating strength, bond, and thermal expansion properties of NSM FRP over a wide temperature range. As part of structural characterization, fire resistance tests were conducted on four NSM FRP strengthened concrete T-beams. Results from these fire tests show that with proper design and configuration, NSM FRP strengthened RC beam can achieve more than three hours of fire resistance, even without fire insulation. As part of numerical studies, a numerical model was developed for tracing the fire response of NSM FRP strengthened RC beams. The model is based on a macroscopic finite element approach and utilizes moment-curvature relationships to trace the response of beam from pre-loading stage to failure under fire conditions. The model accounts for high temperature properties of constituent materials, various strain components, and fire induced bond degradation. The numerical model was validated using test data generated on various NSM FRP strengthened RC beams at both ambient and fire conditions.The validated model was further applied to conduct a set of parametric studies to quantify the influence of critical factors on fire response of NSM FRP strengthened RC beams. Results from the studies indicate that type of strengthening, reinforcement ratio of FRP to steel, load level, axial restraint, fire scenario and fire insulation have significant influence on fire resistance of NSM FRP strengthened RC beams. Other factors such as location of NSM FRP and concrete strength have moderate influence on the fire response. Results from fire experiments and parametric studies were utilized to develop a rational methodology for evaluating the fire resistance of FRP strengthened RC beams. As the first step of this methodology, a set of simplified equations were derived to predict cross sectional temperatures in an FRP strengthened RC beam exposed to fire. Then moment capacity of the strengthened beam is evaluated utilizing an approach similar to that at room temperature but incorporated with temperature dependant strength properties of concrete, steel and FRP. Finally the fire resistance of FRP strengthened RC beam can be determined as the time when external load exceeds moment capacity. This approach facilitates a quick and reliable access on fire resistance of FRP strengthened RC beams, and thus it is attractive for incorporation in design codes and standards.
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