ASSESSMENT OF THE FIRE RESISTANCE OF BUILDINGS FROM FIREPROOF REINFORCED CONCRETE BUILDING STRUCTURES

Abstract

The paper developed a computer model of the thermal and stress-strain state of a three-story car parking building, which consists of fire-resistant structures, taking into account: thermophysical characteristics of fire-resistant coatings, thermophysical and mechanical properties of the materials that make up the structure, nonlinear laws of deformation of the model materials, mechanical properties of materials at high temperature and force. Modeling of non-stationary heating of a reinforced concrete parking column with a square cross-section, dimensions 0.5×0.5×3 m under the conditions of exposure to a standard fire for 150 minutes was carried out. At the same time, it was found that the temperature on the reinforcing rods reaches 853 °C, which is sufficient to ensure the fire resistance of R150 at the given calculated forces in the column, and the mosaic of movements along the Z axis was not significant and amounted to 1.1 mm. The maximum reinforcement area was 5.55 cm2. When ensuring R180 fire resistance at the given calculated forces in the column, the temperature at the corner reinforcing bars reached 914 °С and the program calculated additional reinforcement. This indicates that the existing reinforcement is not enough to ensure the fire resistance of R180 at the given design forces in the column, so the maximum area of the reinforcement as a result of the calculation by the program increased to 58.7 cm2 (10 times more than the initial one). Measures to increase the fire resistance limits of structures, consisting in the use of fire-resistant coatings with scientifically based parameters, are proposed. The thickness of the passive fire-resistant coating, the coefficient of thermal conductivity, the specific heat capacity, which must be ensured when evaluating the fire resistance of a fire-resistant reinforced concrete column and increasing the limits of fire resistance to 180 minutes, are substantiated. Numerical calculations of non-stationary heating of a fire-protected reinforced concrete column of a parking lot (coating thickness 11 mm) under the conditions of exposure to a standard fire for 180 minutes revealed that the temperature on the reinforcing rods reached 213 °C, which is 4 times less than the heating of an unprotected column. Keywords: fire resistance, fire-resistant reinforced concrete structures, fire-resistant coating, thermophysical characteristics.