The research into the heating effect of secondary steel structures, having no fire proofing, on the fire resistance of fireproof steel beams

Introduction. The international practice of passive fire protection design, as well as some manufactures of fireproofing products recommend to apply fire proofing substances not only to the main element, whose fire resistance limit is standardized, but also to the elements that do not fall under any fire resistance standards. Various support brackets, pipeline supports (hereinafter — PS), etc. can serve as examples. They are not considered as bearing elements according to SP (Construction Regulations) 2.13130.2020, although they are connected to the structures that have fireproofing applied. It is recommended to apply fireproofing substances to such PS within the range of, at least, 450 mm from the point of attachment to the fireproof structure when the area of the PS cross section exceeds 3,000 mm². No “supplementary” fireproofing is required by the Russian design and fire protection regulations.
The subject of research. A change in the fire resistance limit of steel i-girders, caused by the PS heating, depends on the area of the PS cross section and the location of the point of its attachment.
The goal. The goal of the research is to analyze the effect, produced by the area of the cross section and the point of attachment, on the fire resistance limit of fireproof steel i-girders in the course of heating.
Materials and methods. ANSYS Workbench 2020 R2 (student version) was applied to perform the numerical simulation.
Results. The simulation has shown that the PS, having no fireproofing, influences the fire resistance limit of fireproof structures.
Conclusions. Currently available methods of analysis of the fire resistance of steel structures take no account of the fire resistance limit reduction, caused by the heating of the PS that has no fireproofing. The numerical simulation has shown that the fire proofing design must take account of the potential reduction in the fire resistance limit of fireproof structures, exposed to the heated PS that has no fire proofing. The further verification of the effect, produced by the PS, that has no fireproofing, on the time to the limit state of a fireproof steel i-girder requires fire tests and supplementary investigations to evaluate the influence of the PS on the heating of vertical fireproof constructions, including the case of the hydrocarbon fire mode.

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