In recent years, the demand for repair and strengthening of concrete structures has been increasing due to aging infrastructure, increased service loads, changes in functional use, design deficiencies, updates in building codes, and environmental deterioration. To address these challenges, Fiber-Reinforced Polymer (FRP) composites have emerged as a popular and efficient method for strengthening concrete structures. Due to their light weight, high strength, durability against corrosion, and ease of installation, FRP composites are considered an efficient and reliable option for strengthening both reinforced and prestressed concrete elements. However, despite these advantages, FRP systems are thermally sensitive. At elevated temperatures, the polymer matrix and adhesive bonds deteriorate rapidly, leading to a significant reduction in strength, stiffness, and bond capacity. This vulnerability limits the performance of FRP-strengthened members under fire conditions. As a result, the application of FRP systems in prestressed concrete beams remains limited due to the lack of comprehensive design guidelines and experimental data related to fire exposure.To address this limitation, a rational approach is proposed for evaluating the fire resistance of FRP-strengthened prestressed concrete (PC) beams. This approach expands on conventional fire design principles for PC beams, while incorporating the effects of FRP reinforcement and fire insulation into strength calculations under fire exposure. Simplified equations are utilized to evaluate the cross-sectional temperature distribution in fire exposed FRP-strengthened PC beams, considering both uninsulated and insulated scenarios. These cross-sectional temperature profiles are then utilized to evaluate the reduction in strength of concrete, prestressing steel, and FRP based on their temperature-dependent mechanical properties. The moment capacity of the FRP-strengthened PC beams is determined at various fire exposure durations by applying force equilibrium and strain compatibility principles. The proposed approach is validated by comparing analysis results with available fire test data from FRP-strengthened reinforced concrete (RC) beams. The results show that, without supplementary fire insulation, FRP-strengthened PC beams experience a significant reduction in moment capacity early into fire exposure and can experience failure in 75 min. In contrast, with adequate fire insulation, these beams retain a substantial portion of their load-bearing capacity for up to 3 hours during fire exposure.
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