Investigation of fire resistance of steel structures covering a warehouse building under different temperature conditions

Introduction. In the process of designing warehouse buildings, taking into account the adopted design decisions, it is required to assess the compliance of the actual fire resistance limits of building structures with the required fire resistance limits. The fire resistance limits of the (actual) building structures are determined under the influence of a “standard” temperature regime, the use of which can lead to both laying an overestimated fire resistance margin in a project and underestimating the thermal effect in a “real” fire. Aims and purposes. The purpose of the study is to assess the convergence of the “standard” temperature regime and possible “real” temperature regimes of fires in modern warehouse buildings, as well as the correspondence of actual fire resistance limits to the effects of “real” fires. To achieve this goal, the following tasks were solved: mathematical modeling of the development of a “real” fire by the field method in a warehouse building at different fire loads was carried out, as well as modeling of heating of the supporting structures of the coating according to the standard temperature regime and the “real” temperature conditions of the fire obtained during the simulation; the required fire resistance limits of the bearing building structures of the coating are determined through the equivalent duration of the fire. Methods. A storage building of a standard form with dimensions of 12×12×6.5 m was chosen as the object of the study. The building has a 4×4 meter gate in the amount of 2 pieces and an entrance door of 1×2 meter size. Within the walls of the building are 32 windows measuring 0.7×1 meter. Coverage — an impassable flat roof over metal trusses. The parameters of the fire load during mathematical modeling were taken according to the reference data of Yu.A. Koshmarov 12 types of typical fire load stored in warehouse buildings are considered. For mathematical modeling of “real” temperature fires, the “Fire Dynamics Simulator” (FDS) software package was used, which implements a field (differential) mathematical model. For mathematical modeling of the heating process of steel building structures, the finite-difference method for solving the Fourier heat equation with external and internal nonlinearity was used, implemented in the ANSYS Mechanical software package. results and discussion. The results of modeling in the FDS software package show that the temperature impact on the structure according to the standard temperature regime for fire loads: cables+wires, industrial oil, ethyl alcohol was less, which indicates an underestimation of the thermal impact on the structure. The results of modeling the heating of structures showed that the heating time of the coating truss is up to 400–700 °C for fire loads: cables+wires, industrial oil, ethyl alcohol less than the time obtained from standard tests, which indicates an initial underestimation of the actual fire resistance of steel structures of the coating when designing warehouse buildings. Conclusions. The assumption that the thermal impact of the standard temperature regime on the steel structures of modern warehouse complexes was underestimated was confirmed for 3 of the 12 fire loads considered, namely: cables+wires, industrial oil, ethyl alcohol.