Analyzing the fire performance of concrete columns and slabs under loading and using options, preventing explosive spalling to ensure the pre-set fire resistance

Introduction. The authors focus on preventing the explosive spalling of concrete and the fireproofing of reinforced concrete structures. The relevance of this issue is explained by the insufficient number of fire tests of such structures under loading and thermal engineering calculations, needed for an objective analysis of testing results.

Goal and objectives. The authors analyze the results of a series of fire tests, involving concrete columns and slabs with and without polypropylene microfiber, if no fireproofing is applied, as well as the results of the same tests involving the same items fireproofed by plates or plaster.

Methods. The fire resistance of full-scale specimens of concrete was evaluated according to a standardized testing in a fire furnace under loading. It encompasses additional thermocouple measurements used to make a thermal engineering analysis. The analysis entailed both one- and two-dimensional problem formulations, methods and programmes for the numerical computation of non-stationary temperature fields in fireproof structures.

Results. New data, obtained in the course of the fire experiments, show the efficiency of the polypropylene microfiber used to prevent the explosive spalling of concrete. The fire resistance limit is R 120 and R 150 under constant static loading. The fire resistance limit of similar structures, fireproofed by PROSASK Firepanel plates or IGNIS LIGHT plaster, was demonstrated. The specimens show the efficiency of methods and programmes for the one- and two-dimensional numerical analysis of non-stationary temperature fields in fireproof structures. The calculation results are presented for various fireproofing options.

Conclusions. The testing results and their thermal analysis represent important items of information necessary to ensure the fire safety and the pre-set fire resistance of concrete structures under loading. They can also be used to outline the development pattern of this experimental and theoretical research project. The efficiency of thermal engineering calculations as a tool for evaluating fire protection parameters and the fire resistance of concrete structures is demonstrated, also as an option to reduce the number of expensive fire tests.

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