An experimental study of the mechanical properties of fibre reinforced polymer (FRP) and steel reinforcing bars at elevated temperatures

This paper presents the results of an experimental study of the mechanical properties of FRP reinforcement bars, used as internal reinforcement in concrete structures, at elevated temperatures. Two types of FRP bars namely: carbon fibre reinforced polyester (CFRP) bars of 9.5 mm diameter and glass fibre reinforced polyester (GFRP) bars of 9.5 mm and 12.7 mm diameter were used in the study. For comparison, conventional steel reinforcement bars of 10 mm and 15 mm diameter were also tested. Results from the experimental study show that the stress-strain relationships of FRP bars remained almost linear at elevated temperatures until failure. However, there was a gradual reduction in the failure strength of FRP bars at elevated temperatures, at an almost linear rate to zero at about 500 °C. Their elastic modulus remained almost unchanged until 300-400 °C. After this temperature, there was a sharp drop in the elastic modulus. These properties can be used as input in computer programs for modelling the fire behaviour of concrete structural members reinforced with FRP bars.