Rational Approach for Evaluating Fire Resistance of FRP-Strengthened Concrete Beams

This paper presents a rational approach for evaluating the fire resistance of reinforced concrete (RC) beams strengthened with different types of fiber-reinforced polymers (FRP). This approach is based on conventional fire design principles for RC beams, but incorporates the contribution of FRP and fire insulation in fire resistance calculations. Simplified equations are proposed for evaluating cross-sectional temperatures in fire-exposed FRP-strengthened RC beams with and without fire insulation. These temperatures are used to determine the loss of strength in steel, FRP, and concrete using temperature-dependent strength properties. Employing the strength in different materials, the moment capacity of FRP-strengthened beams is calculated, at any given fire exposure time, by applying force equilibrium and strain compatibility principles. At each time step, the limit state is applied to define the failure of an FRP-strengthened RC beam, and the time to failure is taken as the fire resistance of the beam. The validity of the proposed approach is established by comparing predicted fire response parameters with those obtained from fire resistance tests and detailed finite-element analyses. Further, the applicability of the proposed approach in practical situations is illustrated through a design example. Results from the proposed approach clearly indicate that a typical FRP-strengthened beam without supplemental fire insulation experiences a significant loss of moment capacity after approximately 20 min into fire exposure. However, a similar FRP-strengthened beam with supplemental fire insulation retains much of its moment capacity until 2 h into fire exposure.