Energy Based Method to Predict Temperature within Rectangular Concrete Sections

Abstract

In addition to the prescriptive method used in design, the fire resistance of reinforced concrete structures under various fire scenarios needs to be assessed by combined heat transfer and structural analysis. The available numerical simulations of heat transfer analysis are complicated techniques and require an expert user. To predict temperature within rectangular sections of normal concrete subjected to fire loads in two directions, the energy based method is proposed as an alternative method. The method is based on a pre-determined power function as the temperature profile, and conservation of energy: it can be implemented in a spreadsheet. The analysis of two dimensional heat transfer is approximated by superposition of one-dimensional solutions. Benchmarking against FEM analysis of various sections shows that an exponent 2.6 performs well to predict the temperature. By comparing the temperature prediction with the previous experimental and FEM results, the method is validated. The method is suitable for various monotonically increasing fire curves and various convection and radiation heat transfers. However, the method has its limitations; in particular the lowest temperature in the sections needs to remain less than 0.2 times the highest, or the energy estimated becomes inaccurate. Generally, the method can be used to approximately predict the temperature profile as well as the temperature at the reinforcing location: knowledge of these is necessary for fire safety design.