Behavior of compressed reinforced concrete columns under thermodynamic influences taking into account increased concrete deformability

The behaviour of compressed reinforced concrete columns has been of great importance for the stability and safety of the entire structure. Therefore, the identification of additional resources that increase the load-carrying capacity of such structures under thermodynamic influences is the goal for solving this problem. The combined effect of dynamic loadings and high temperatures on the compressed element has its own specificity, expressed in the reduction of dynamic hardening coefficient, which is of no small importance for the actual evaluation of the resistance of buildings to progressive fracturing. In some cases, concrete is under volumetric compression, and therefore has increased strength and deformation properties, which can be expressed in greater fire resistance. A correct assessment of the effect of the combined factor of impacts on the compressed element, taking into account the revealed properties of limited concrete, is an actual scientific problem that solves issues related to ensuring the safety and reliability of building and structure's operation. The article presents analytical calculations of reinforced concrete elements for fire impacts in conditions of volumetric compression of concrete, thanks to the presence of spiral, annular reinforcement, using experimental data. The article gives the calculation of a reinforced concrete column of a high-rise building taking into account the increased deformability of concrete in normal conditions and in conditions of fire impacts. Dynamic calculation of the column in fire conditions shows that taking into account the increased deformation properties of concrete leads to an extension of the time of formation of cracks; the operating time of the element increases in the elastically plastic and in the plastic stages. Calculations show that, under fire impacts, the increase in the concrete deformability affects the opening angle of the plastic hinge, which in turn leads to a change in the nature of the element fracture. To assess the fire resistance of reinforced concrete columns under dynamic influences, a loading varying in time with respect to a linearly increasing function was adopted. Calculations show that taking into account the properties of limited concrete when calculating structural elements for thermodynamic influences leads to an increase in fire resistance of structures by an average of 25-30%.