The evaluation of actual fire resistance limits of steel structures exposed to real fire loading

Introduction. The fire resistance limits of load-bearing and enclosing structures can be identified using the method of heat-and-mass transfer calculation in case of fire. The multifactorial nature and nonlinearity of the problem makes the application of this method complicated. If necessary, the temperature regime, demonstrating the conditions of real fire, can be applied. In this work, actual fire resistance limits of metal structures of a thermal power station are calculated. Goals and objectives. The co-authors attempt to identify the actual fire resistance limits of bearing metal structures in case of the most dangerous fire development scenario. Methods. Taking into account the complexity of space-planning solutions of a building, the field-focused calculation method was selected. This method is applicable to premises, featuring complex geometric shape, where one geometric dimension is much larger than the others. Non-stationary three-dimensional differential equations of mass, momentum and energy conservation are solved for the gas medium inside a room (the Reynolds type of Navier–Stokes equations), as well as the components of the gas medium and the optical density of smoke. A heat transfer equation is solved to determine the temperature distribution inside the building structure for a one-dimensional case. The fire resistance limit of the building structure is identified as the moment in time following the start of fire, when the temperature in, at least, one point of the structure reaches a critical value. Results and discussion. Calculation results show that in case of the most dangerous fire development scenario, within 15 minutes as of the start of fire, maximum temperatures of load-bearing metal structures are far below the critical temperature of 500 °C. Conclusions. Load-bearing metal structures in an engine room, that has steam turbines, don't need fire protection.