To explore the shear performance of glass fiber reinforced polymer (GFRP) bars in concrete after fire and high temperature, nine temperature conditions of 100°C, 150°C, 200°C, 300°C, 350°C, 400°C, 500°C, 650°C and 800°C were selected to treat the GFRP bars placed in concrete, and the horizontal shear tests were carried out on the obtained bar specimens. The method of predicting the horizontal shear strength of GFRP bars in concrete after exposure to high temperature was discussed using the results of this study and some existing tests. Test and analytical results show that within 300°C there is a hysteresis phenomenon in the surface temperature of GFRP bars in concrete. Their high temperature deterioration is significantly lower than that of the bare bars, as well as the shear strength degradation is also relatively slow. As the temperature exceeds 300°C and the concrete surface cracks continue to develop, the deterioration of embedded GFRP bars caused by high temperature gradually enlarges, meanwhile, the shear strength decreases sharply, which shows a similar degradation pattern to that of bare bars. At high temperature of 300°C which is close to the thermal decomposition temperature of resins, the shear strength retention rate of GFRP bars decreases linearly from 76.4% to 46.5% with the constant temperature time increasing from 1h to 3h. Based on the hyperbolic tangent function model, a prediction model for the horizontal shear strength of GFRP bars in concrete after high temperature was established and model’s predictions were in good agreement with test values. Finally, considering a shear strength retention factor of 0.7, the predictions of fire resistance time of GFRP bars with different cover thickness were proposed, which can provide some references for engineering application.
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