Effecto of Elevated Temperatures on the Flexural Behavior of FRP Bars

In recent years, fiber reinforced polymer (FRP) bars have become one of the promising reinforcing materials in concrete structures, however, elevated temperatures can severely affect their performance. Within this study, different types of FRP bars were subjected to elevated temperatures (100–300 °C) and then tested in flexure to investigate their flexure strength and tensile modulus. One type of carbon FRP (CFRP) bars and three types of glass FRP (GFRP) bars were tested in this study. The bars were tested using two testing scenarios. In the first scenario, the bars were tested immediately after exposure to temperature. In the second testing scenario, the specimens were kept to cool down before testing. Test results showed that significant reductions in the flexural strength and modulus were recorded at temperature levels higher than the glass transition temperature (Tg). The flexural strength and modulus decreased as the temperature level increased. The results also revealed that larger diameter bars showed lower residual flexure strength and modulus than smaller diameter bars after exposure to elevated temperatures. The immediately tested specimens showed higher losses compared to bars tested after cooling. All types of GFRP bars showed comparable results. The flexural strength losses ranged between 29 and 37% after exposure to 200 and ranged between 39 and 60% after exposure to 300 ℃. The tested CFRP bars showed similar flexural strengths compared to the tested GFRP bars; however, they showed lower residual flexural modulus.