The Influence of the Level of Mechanical Load on the Fire Resistance Limit of a Reinforced Concrete Wall

Abstract

The work investigates the influence of the level of applied mechanical load on the fire resistance limit of a reinforced concrete wall under the conditions of a standard temperature fire regime. For this purpose, a geometric and finite element model of a wall fragment was developed, taking into account the joint operation of concrete and reinforcement. Numerical modeling was performed using temperature-dependent thermophysical and mechanical characteristics of materials in accordance with the provisions of EN 1992-1-2 in the ANSYS WB software package. At the first stage, a thermal calculation was carried out, the results of which established a significant unevenness of the temperature field in the cross-section of the structure and the formation of a temperature gradient between the heated and unheated surfaces. It was shown that the temperature in the area of ​​the reinforcement reaches values ​​​​over 600 ° C, which leads to a significant decrease in its mechanical characteristics. At the second stage, the static problem was solved for load levels from the bearing capacity μ = 0,2; 0,4; 0,6 and 0,8. It has been established that the limit state of the structure is determined not by the magnitude of the deformations, but by the achievement of critical compressive stresses in the concrete and the loss of convergence of the numerical solution. For load levels μ = 0,4; 0,6 and 0,8 loss of convergence is observed at 12 161 s, 7 506 s, and 5 021,5 s of fire action, respectively, while at μ = 0,2 the structure retains its load-bearing capacity throughout the entire calculation time. Based on the results obtained, a nonlinear dependence of the fire resistance limit on the level of mechanical load was established. The obtained dependence allows for the assessment of the fire resistance of a reinforced concrete wall 165 mm thick, taking into account the level of applied mechanical load, and to obtain results close to experimental, within the limits of the geometric and structural parameters adopted in the study, without conducting expensive tests or using complex numerical models.