Basics of the advanced calculating method the fire resistance of the section of an eccentrically compressed reinforced concrete element

The paper considers the issue of some special features in fire resistance calculations of an eccentrically compressed reinforced concrete element and propose new approach for calculating the fire resistance, based on the advanced formula of the stress-strain diagram for concrete depending on temperature. It has been shown that due to the change of the temperature field during a fire a change in the strength and deformation characteristics of concrete and reinforcing steel occurs as well, which, accordingly, leads to a change in eccentricity over time, that is, the eccentricity value is variable and depends both on the internal characteristics of the element (class of concrete, reinforcement) and from external factors (type of fire, time, loading). Formulas for calculating the eccentricity of an eccentrically compressed rod reinforced concrete element for a specific fixed moment of time are presented. There are also given the coordinates of the cross-section core and the center of central compression. It is possible to obtain the dynamics of changes in the eccentricity of a compressed rod reinforced concrete element during the time of the fire by doing such calculations for certain moments of time.