The mathematical model of the stress-strain ratio of compressed concrete at elevated temperatures for composite structures described in Eurocode EN 1994-1-2:2005 Eurocode 4 divided in two stages: Stage 1 -represents the ascending branch and is defined by two parameters: compressive strength fc,θ and corresponding deformations εcu,θ, stage II -the descending branch which is accepted for numerical methods. The design practice showed deficiencies in the provisions on models of deformation diagrams

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... given in Eurocode 2. Part 1-2 General provisions. were reflected in the national standards in the process of harmonization. A technique for determining the refined diagrams "σc,θ -εc,θ" was developed for the design of composite reinforced concrete structures in case of fire. Diagram parameter values were adjusted for concretes based on silicate filler at high temperatures, the mathematical stress-strain model of the concrete under compression and high temperatures was specified.