Interaction diagrams for reinforced concrete sections subjected to fire

Strength interaction diagrams are common tools for reinforced concrete (RC) cross-section analysis and design. They usually relate the ultimate values of the bending moments and axial force, allowing quick assessment of a cross-section’s strength. Under fire action, however, substantial changes occur on the behavior of the cross-section, and these diagrams become strongly dependent on the temperature field, which introduces thermal strains and modifies the stress–strain relationships. The purpose of this paper is to present an algorithm for the construction of strength interaction diagrams for arbitrary-shaped RC sections subjected to fire action. The diagrams are obtained by a stepwise variation of the deformed configuration, under assumptions of conventional ultimate strain values for concrete and steel. The procedure is illustrated by the construction of interaction diagrams for some RC sections subjected to different temperature distributions.