Energy-Based Temperature Profiles for Designing Fire Resistance of Concrete Sections

Abstract

While prescriptive methods are used in design, the fire resistance of a reinforced concrete structure can be assessed by combined heat transfer and structural analysis. However, available numerical codes to simulate heat transfer use complicated techniques. Furthermore, the available simplified methods are limited to a standard fire curve and are inaccurate when temperatures at the non-fire-exposed surface significantly exceed the initial normal temperature. To predict temperatures within ordinary concrete sections subjected to various fire curves, the energy-based method (EBM) was proposed as an alternative approach. It is based on a predetermined power function as the temperature profile, and energy is conserved. Benchmarking against finite element analysis (FEA) of one-dimensional heat transfer under a standard fire curve for sections with thickness of 10–50 cm and fire duration of 0.5–4 h showed that a power function with fitted exponent performs well as a generic temperature profile. Furthermore, simplified approximate solutions to two-dimensional heat transfer were created by superposing one-dimensional solutions. The EBM was validated by comparisons to FEA temperature results across various slab, beam and column models. On comparison to FEA models, when using the thermal properties based on Annex A of EN 1992-1-2, the average normalized absolute error of the EBM was 0.68% for the slab cases and 1.76% for the beam or column cases. Generally, this method predicts the temperature profiles with sufficient accuracy within concrete sections, as well as at their reinforcing locations. This method can facilitate the design for fire resistance of reinforced concrete members.