Predicting the mechanical properties of E-glass fiber-reinforced polymer bars after exposure to elevated temperature

This paper presents the experimental investigations on the tensile, flexural, and shear performance of E-glass fiber-reinforced polymer (GFRP) bars after exposure to elevated temperatures from ambient to 500 degrees C. Two types of GFRP bars with nominal diameters of 12 mm and 16 mm were directly exposed to several target temperatures for 0.5 h, and their mechanical properties were tested after cooling. The experimental results showed that the GFRP bars gradually loosened, and their surface color darkened with the increasing exposure temperature. After experiencing high temperatures, the bars' tension, bending, and shear failure modes remained unchanged. However, their mechanical strengths showed a phased decline in three typical temperature ranges of 20 to 120 degrees C, 120 to 270 degrees C, and 270 to 420 degrees C. In addition, no significant tensile and flexural elastic modulus degradation was observed. The measured strengths were compared with the results of several existing prediction models. A simplified model was proposed to predict the residual strength of GFRP bars after high-temperature exposure. Based on fire safety requirements, a fire-resisting reduction factor, CF, was proposed to determine the design strength of GFRP bars used in concrete slabs. For GFRP bar-reinforced concrete slabs with a cover thickness of 60 mm, the suggested CF for tensile strength and the other two strengths should be 0.65 and 0.75, respectively, to achieve structural safety after 2-h fire disasters.