STUDY OF THE FIRE RESISTANCE OF A REINFORCED CONCRETE SLAB
Abstract
The work presents an algorithm for carrying out a refined method of calculating the fire resistance of a reinforced concrete ribbed slab modeled according to the design type PR 63-15 when using the finite element method. The parameters of the Drucker–Prager theory of concrete strength were used in the calculations. The finite-element model consisted of more than 13,000 finite elements of hexahedral shape.
To solve the thermal problem, the thermophysical characteristics of concrete and steel reinforcement were used, which correspond to the temperature dependences recommended by the second part of Eurocode 2. To reproduce the heat exchange during the influence of the standard temperature regime of the fire, an unsteady two-dimensional quasi-linear equation of thermal conductivity is used, assuming that the stress-strain state does not affect the temperature distribution. Boundary conditions of the IIIrd kind are given, which is also recommended for the second part of Eurocode 2. The results of the temperature distribution in the simulated reinforced concrete ribbed slab during 60 min are obtained. The temperature indicators were used in solving the compatible thermomechanical problem of evaluating the fire resistance of the studied reinforced concrete ribbed slab at 50%, 70% and 100% load level from the maximum. The fire resistance of the board was evaluated according to the limit state of the loss of load-bearing capacity (R) without taking into account the formation of cracks or through defects. The maximum stresses in the concrete of the studied structure, which are formed during deformations at different load levels, are observed in the upper part of the longitudinal ribs and exceed 30 MPa, which is critical for concrete with such compressive strength.
Based on the results of the research, a regularity was determined that establishes the relationship between fire resistance indicators and the level of applied mechanical load.
