Justification of the Methodology for the Calculation Assessment of Fire Resistance of Reinforced Concrete Enclosing Structures of Cable Tunnels

Abstract

The purpose of this work was to develop and substantiate a methodology for calculating the fire resistance of reinforced concrete enclosing structures of cable tunnels, taking into account different cross-sectional sizes, aerodynamic parameters and fire load. The work uses the results of previous studies of temperature regimes of fire in cable tunnels, on the basis of which temperature curves were formed for different conditions of their operation. Using heat transfer models, the heating of reinforced concrete enclosing structures of different thicknesses was calculated. It was found that when using the real temperature regime of fire, the temperature on the unheated side of the structures does not exceed 400 °C, which is significantly lower compared to the standard temperature regime. It was shown that the use of the standard temperature curve leads to much more stringent conditions for heating the structures. The influence of the thickness of the enclosing structures on compliance with the requirements of fire resistance classes was determined. In particular, under standard temperature conditions, only structures with a thickness of 100 mm correspond to classes EI 30–EI 60, while taking into account the real temperature conditions, it is possible to substantiate the compliance of these classes for structures of smaller thickness. The developed methodology allows for a substantiated assessment of the fire resistance of reinforced concrete enclosing structures of cable tunnels without conducting full-scale tests, takes into account real conditions for fire development and can be used in the design and assessment of fire safety of building structures for various purposes.