Using four-point flexure test to investigate effects of temperature and bar size on the tensile properties of GFRP bars

Glass fibre reinforced polymer (GFRP) bars have been increasingly used in structures due to their advantages However, the effect of temperature variation is likely to degrade their mechanical behavior. In this experimental study, the tensile strength and modulus of elasticity of four types of GFRP bars with different diameters at 20 °C under four-point flexure test are initially investigated and their results are compared with those of a direct tensile test. Then, the tensile strength of GFRP bars with different diameters is obtained in low and high temperatures (-40 to 80 °C) using four-point flexure test. The experimental results indicate that the tensile strength variation of GFRP bars with different diameters obtained from four-point flexure test are slightly different from those obtained using direct tensile test. Furthermore, the highest reduction in tensile strength under flexure test occurred at -40 °C for most diameters. The obtained tensile strength from four-point flexure test, on average, reduced about 21, 31 and 38% at temperatures of 0, -20, and -40 °C and 11, 20 and 29% at temperatures of 40, 60, and 80 °C, respectively. In addition, the contribution of each parameter (bar diameter and temperature) was examined using a probability model, including the Analysis of variance. Models show that the bar diameter has significant effect on the GFRP bars’ tensile strength variations when subjected to temperature fluctuations. Finally, by applying the non-linear regression analysis, an equation has been developed to determine the tensile strength of GFRP bars with different diameters at different temperatures.