Influence of transient strain on fire resistance of concrete elements

Reinforced concrete (RC) elements generally have good fire-resistance ability. Knowledge of the temperature dependant material properties of concrete and steel bars is important for understanding of the fire-response of a RC structure. At high temperatures, the total strain of concrete is for a large extent influenced by load dependent strains, the so called transient strain and creep strain. Although these types of strain are not considered in simplified calculation procedures of concrete elements exposed to fire as provided in EN 1992-1-2, they may be of major importance for the development of deformation during heating. Based on the mechanical properties of concrete and steel bars at elevated temperatures as given in literature, a numerical model which includes transient strain and creep strain is proposed. The computational procedure consists of a coupled thermo-mechanical analysis, including the development of the temperature, the deflection and ultimate bending moment. The proposed approach is validated by experimental data from fire tests executed on simply supported slabs exposed to an ISO 834 fire load. The influence of transient train is analyzed by comparing the calculating results