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Elevated Temperature Performance of Concrete Beams Reinforced with FRP Bars



There is a strong case for fibre reinforced polymer (FRP) bars to be used in reinforced concrete (RC) construction, owing to numerous important benefits such as corrosion resistance and high tensile strength. However the limiting temperature for FRP reinforcement in case of fire is typically assumed to be defined by the FRP’s glass transition temperature (Tg); this can prevent FRP from being efficiently used in many structures that require fire resistance ratings. Tensile tests performed at the University of Edinburgh have demonstrated that FRP bars can retain considerable (>50%) tensile strength at temperatures above Tg, and due to their high ambient temperature strength the absolute strength values at a given temperature may be higher than for mild steel reinforcement in many cases. In certain applications it may therefore be reasonable to assume that the critical temperature for FRP bars is greater than Tg, provided that “cool” anchorage zones are maintained. To investigate these ideas, 32 small-scale RC beams were tested with either continuous or spliced FRP or steel reinforcement, at ambient temperature or under transient localised heating. The results confirm that cool anchorage is necessary for fire-safe use of FRP bars as internal reinforcement for concrete; the only alternative is to provide considerably larger concrete covers as compared with steel reinforcing bars. The performance of cool anchored FRP bars is demonstrated to be satisfactory under full service load with midspan bar temperatures typically exceeding 400°C. Residual tests on beams that did not fail during heating showed considerable strength retention in some cases.

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