A model for predicting the properties of the constituents of a glass fibre rebar reinforced concrete beam at elevated temperatures simulating a fire test

This paper develops a series of expressions to predict the apparent strength and stiffness of composite rebars and the concrete matrix at elevated temperatures typical of those experienced in a standard fire test. Two methods of predicting the thermal distribution through the concrete beam at any time in a fire are compared: a semi empirical method based on experimental data and a finite element method using commercial software. The semi empirical method is found to provide the most accurate prediction and this is then used to generate expressions for the reduction in compression strength of the concrete. Expressions from earlier work, which predict the reduction in strength and stiffness of rebar with temperate are then used in combination with the calculated temperature profiles to generate equations predicting the reduction in strength and stiffness with time of the rebar encased in the concrete.