IMPROVED THERMOMECHANICAL MODEL FOR PREDICTING THE BEHAVIOUR OF REINFORCED CONCRETE STRUCTURES UNDER FIRE AND EXPLOSION CONDITIONS

Abstract

The article presents the results of a study aimed at improving the thermomechanical model for predicting the behaviour of monolithic reinforced concrete structures when exposed to elevated fire temperatures and overpressure from a deflagration explosion. The relevance of the topic is due to the growing requirements for the reliability of modern buildings, especially critical infrastructure facilities, where the combination of thermal and dynamic loads creates particularly dangerous operating conditions. The model is implemented using the finite element method, which makes it possible to comprehensively take into account transient heat transfer, temperature-dependent material properties, and impulsive loads from explosions, described in the form of triangular and exponential functions. The dynamic behaviour of reinforced concrete structures is represented by the equation of motion, considering temperature-dependent stiffness, Rayleigh damping, and thermal deformations of both concrete and reinforcement. A comparative analysis of code-specified material properties and the results of full-scale tests was carried out. Significant differences were found in the curves describing the reduction in strength and initial modulus of elasticity when concrete is heated, as well as in the strength values of reinforcement of different grades. Based on experimental data, analytical and polynomial relationships were proposed that reproduce the actual behaviour of heavy concrete and lightweight expanded clay aggregate concrete at elevated temperatures, along with formulas for determining reduction factors for reinforcement strength. This ensures a significant improvement in the accuracy of predictions of the load-bearing capacity and deformability of reinforced concrete structures. The model can be used as a tool in methodologies for assessing the robustness of monolithic reinforced concrete buildings against progressive collapse caused by fire and explosion. At the same time, the limitations of the model are outlined: it does not take into account crack formation, creep, or the spatial effects of blast wave propagation. Directions for further research are identified, aimed at expanding the practical applicability of the model and improving methods for assessing the structural stability of buildings.