Engineering method for calculating the temperature field in the cross-section of hollow-core reinforced concrete slabs under a standard fire

Purpose. To develop an engineering methodology for calculating the temperature field in the cross-section of hollow-core reinforced concrete slabs (150–250 mm thick) with symmetrically located (relative to the center of gravity) closed circular hollows (40 to 60 % volume) under unilateral standard fire exposure. This methodology is based on adapting a simplified solution to the nonlinear heat conduction equation for solid slabs using correction factors obtained through numerical modeling and taking into account the cross-sectional geometry, point coordinates, and heating duration. Methods. Numerical modeling of heating of reinforced concrete slabs during a standard fire using the finite element method based on the design of a full factorial experiment. This study summarizes the modeling results and analyzes the influence of the geometric parameters of cross-section of the hollow-core slabs and the duration of standard fire exposure on the temperature field generated within the slabs. An existing methodology for calculating the temperature field in solid slabs exposed to a standard fire is adapted for application to hollow-core slabs. Findings. The influence of the geometric parameters of hollow-core reinforced concrete slabs (thickness, volume of enclosed circular cavities) on the temperature field dynamics in the cross-section (at a depth of up to 0.3 of the structure's thickness) under unilateral standard fire exposure lasting from 30 to 180 minutes was determined. A regression equation was derived for determining the khol coefficient, which accounts for the temperature increment at a given distance from the heated surface in hollow-core slabs compared to their solid counterparts under unilateral standard fire exposure. An engineering methodology for assessing the temperature field in hollow-core reinforced concrete slabs (150–250 mm thick with a volume of enclosed circular hollows of 40–60 %) under standard fire exposure was developed. Application field of research. The research results can be used by specialists on design, expert, and scientific organizations to solve simplified heat engineering problems of fire resistance for hollow-core reinforced concrete slabs, as well as to improve existing regulatory legal acts.