The effects of high temperature on the mechanical properties of concrete have been investigated by many researchers [1-6]. Unfortunately, there is not a distinct method to verify flexural strength 1160 The 3rd ACF International Conference-ACF/VCA 2008 of concrete at high temperatures.t high temperatures, the differences between the results are not significant. This may be due to the fact that steel will be soft at high temperatures, so the effect of steel on Flexural Strength and prevention of crack opening is not significant.