SCIENTIFIC SUBSTANTIATION OF THE METHOD OF CALCULATION ASSESSMENT OF THE CLASS OF FIRE RESISTANCE OF BUILDING STRUCTURES OF CABLE TUNNELS

Abstract

Cable tunnels differ in geometric configuration, type of cables laid in them, fire load and aerodynamic characteristics. This can lead to the fact that the temperature of the fire in such tunnels may differ from the standard and from each other. In this case, it is not possible to guarantee compliance of the limits of fire resistance of the tested structures with the current standards. In this work, the temperature regimes of heating reinforced concrete enclosing structures of different thickness (40 mm; 60 mm; 80 mm; 100 mm) of cable tunnel at constant values of specific heat of combustion of fire load, cross-sectional area of cable tunnel and horizontal air velocity component are calculated. The calculation of fire resistance of building structures of the wall of the cable tunnel fence with a thickness of: 40 mm; 60 mm; 80 mm; 100 mm is conducted. To perform a calculated assessment of the fire resistance of reinforcing concrete structures of cable tunnels using the proposed temperature regimes of the fire, the heating temperature of the fence at any time of the fire was determined. The obtained data shows that not all barriers will meet the requirements of fire resistance classes EI 30, EI 45 and EI 60. The advantages of the proposed approach have been proven, as it allows to justify much higher fire resistance classes for fences smaller than 80 mm. Based on the results of the work, the calculation algorithm is scientifically substantiated and verified, and the method of calculation assessment of the fire resistance class of building structures of cable tunnels based on mathematical modeling is developed on its basis. During the calculation, temperature distributions are constructed along the cross section of the cable tunnel fence at a time that corresponds to the required fire resistance class. If the temperature on the unheated side does not exceed 140 C, it can be concluded that it complies or does not comply with the required fire resistance class. In view of the conducted research, recommendations were proposed for the estimated assessment of fire resistance of reinforced concrete enclosing structures of cable tunnels. The developed technique is based on the following procedures