Experimental study of the tensile behaviour of GFRP reinforcing bars at elevated temperatures

Understanding and quantifying the behaviour of glass fibre reinforced polymer (GFRP) bars when exposed to elevated temperatures is of great importance to predict the fire resistance of GFRP-reinforced concrete structural members. However, the experimental results available about the tensile properties of GFRP bars at elevated temperatures still do not cover a sufficiently wide range of temperatures likely to be attained during a fire incident. In fact, very few data has been reported for temperatures above the decomposition temperature of the polymeric resin, and the reduction of the tensile strength and elastic modulus of GFRP bars above 500 degrees C still remains largely unknown. This paper presents an experimental and analytical study about the tensile behaviour of GFRP bars exposed to elevated temperatures up to 715 degrees C. Tensile tests were performed at different elevated temperatures, under steady-state conditions, on four different types of GFRP bars provided by different manufacturers. The degradation of their tensile strength and elastic modulus with increasing temperatures was assessed and compared with data available in the literature. Such data was then used to propose analytical models describing the reduction of the tensile properties of GFRP bars with temperature. The results obtained show that the tensile strength is considerably more degraded with temperature than the elastic modulus, especially during the glass transition and after the decomposition of the resin. At 715 degrees C, after full decomposition of the resin, the tensile strength was reduced to 4% of the value at ambient temperature, while the remaining elastic modulus was still 66%.