To the estimation of emergency bearing capacity of reinforced slabs in the case of fire

Introduction. The relevance of understanding the mechanisms of formation of the stress-strain state of reinforced concrete structures in fire conditions is noted. The need to take into account the design situation in which an emergency high-temperature effect is applied along the upper face of a reinforced concrete slab is highlighted. The connection between the performance of a reinforced concrete section heated along the upper face and the change in the payload during the development of a fire due to its burnout is indicated. The aim of the work is to obtain a calculation methodology that allows us to assess the dependence of structural failure on a changing payload and determine the reserves of the bearing capacity of the structural section.

Theoretical theses of research. There is given the analytical conclusion about the dependence of the forced loading value on the fire timing, its temperature and the lowest working combustion heat value within building. The conclusion about the analytical dependence is carried out using the equivalent of wood-pulp combustion to the forced loading.

Results and discussion. On the basis of the presented dependences there numerous calculations for an administrative building were carried out. Graphs showing the dependence of forced loading decrease on fire timing and its temperature are given. The calculation showed that in administrative buildings in 60 minutes after the fire starts the forced loading decrease on the bearing structures reaches not less than 420 H/m². Taking into account the above dependences, it was determined that the emergency bearing capacity of reinforced stabs is reached in 79 minutes considering the forced loading decrease changing in time compared with the constant load.

Conclusion. There was drawn a conclusion that while modeling a high temperature loading on the upper boarder of reinforced slab floors and coverings, it’s advisable to consider the decrease of forced loading because of its de­struction by fire. It will allow to include additional reserves of load bearing capacity of reinforced stabs in case of fire.

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