Modeling of the reinforced cast-in-place concrete slab heating at fire test as a part of the experimental frame building unit
Keywords:fire resistance, reinforced concrete monolithic slab, modeling, heating, calculation model, Ansys Workbench, temperature field, heat engineering calculation, brittle fracture of concrete, local damage to the protective layer of concrete
Purpose. Based on the results of previously conducted full-scale fire tests of an experimental frame building unit including reinforced cast-in-place concrete slab and reinforced precast centrifugal concrete tube columns to develop a calculation model and assess the temperatures during the slab heating at fire.
Methods. Numerical method for reinforced cast-in-place concrete slab heating using Ansys Workbench finite element analysis system. The analogy technique. The graphical method analysis. Assessment of temperature field distribution over the examined structure cross section. The heating results comparison analysis with the available experimental data.
Findings. An analysis of the damage to a reinforced concrete monolithic floor, obtained during full-scale fire tests, is presented. It has been established that on the side of the heated surface, the greatest damage was observed mainly on the surface layers of compressed concrete in the places of maximum compressive stresses, in the stretched zone the damage was insignificant. A computational model for the heating of a reinforced concrete floor has been developed, which made it possible to establish that the brittle fracture of concrete significantly affected the heating of the reinforcement. The average heating temperature of the working longitudinal reinforcement with a diameter of 10 mm with a protective layer of 20 mm at a temperature regime fixed in the central part of the floor fragment was 402 °C, in a local area with a protective layer of 13.5 mm – 486 °C The design temperature of the upper longitudinal reinforcement located in the support areas did not exceed 20 °C, and that of the unheated surface did not exceed 15 °C. The average temperatures in the calculated sections of the floor, as well as temperature diagrams along the height of the floor section, are obtained. The experimental average overlap temperature was 144 °C, which is 23 % lower than the calculated value (187 °C with a slab thickness of 200 mm), because the calculation did not take into account the decrease in temperature on the heated floor surface by the end of the experiment. The calculated average temperature of heating the cross-section of the floor with a thickness of 193.5 mm was 184 °C, with a thickness of 166.5 mm – 231 °C.
Application field of research. The results of the research can be used for fire resistance estimation of the reinforced concrete structures. It is planned to apply the obtained results to determine the load-bearing fire resistance function of the tested reinforced cast-in-place concrete slab.
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