Interaction diagrams of reinforced concrete sections in fire: A yield design approach

• Interaction diagrams of reinforced concrete section in fire conditions are derived.
• The yield design approach provides a quick and straightforward method.
• Predictions at ambient temperature are compared with Eurocode-based calculations.
• Predictions in fire conditions are compared with available experimental results.

Based upon the yield design (or limit analysis) theory, a straightforward computational procedure allowing to determine the interaction diagrams relating to combined axial and bending loadings of reinforced concrete sections in fire, is presented in this paper. It is shown in particular how both the lower and upper bound methods, leading to the exact determination of such interaction diagrams, can be easily implemented, where the local degradation of the material strength capacities as a function of temperature increase represents a key feature of the analysis. Such theoretical predictions prove to be in quite good agreement with both Eurocode-based calculations at ambient temperature and available experimental results in the case of fire-loaded reinforced concrete beams.