Vol 19, No 3 (2023)

Based on a comprehensive analysis of the experimental studies from the standpoint of their convergence with the theoretical solutions, the computational models of resistance (CMR) of reinforced concrete are proposed. These models include CMR1 - modeling of normal cracks, CMR2 - modeling of inclined cracks, CMR3 - modeling of diagonal cracks, CMR4 - modeling of intersecting cracks in the wall, CMR4* - modeling of cracks in a flat slab, and CMR5 - modeling of spatial cracks in torsion with bending, CMR5* - modeling of spatial cracks in bending with transverse force. Also, a hierarchy of computational models of the second and third levels is proposed. The distribution of intensity of working reinforcement along the cross-section of the calculated element was obtained in an analytical form by creating closed equations of blocks, corresponding to the blocks of the reinforced concrete element under the condition of equality to zero of partial derivatives of the Lagrange function to determine the maximum crack opening width. It is considered the effect proposed by the author on the additional deformation impact of the reaction “concrete - reinforcement” from the discontinuity of concrete during the formation of the crack by means of a special model of the two-cantilever element of fracture mechanics. Hypotheses about the distribution of linear and angular deformations during cross-section with account of gradients of deformations caused by formation of cracks were formulated for a complex-stressed element subjected to torsion with bending. Crack opening is defined as mutual displacements of reinforcement and concrete, taking into account deformation. The consolidation of substructures in the building system is performed by the method of initial parameters.

The compaction of the snow base of the wintering complex under construction of the Russian Antarctic station “Vostok” is considered, which was required due to the unsuitability of the natural snow base for the perception of loads from the supports of the foundation of the wintering complex. Technical solutions were developed for snow base compaction on the basis of heating by solar radiation with the use of thermal mat and on the basis of snow vacuuming. The computational justification of the developed technical solutions was performed, which was carried out based on spatial finite element models using the computational software complex ANSYS. In this case, to substantiate the method of snow base compaction by solar radiation heating with the use of thermal mat, the calculated volume was analyzed, including the snow base zone, thermal mat and the space filled with air. When substantiating the method of snow base compaction by snow vacuuming, there was explored the calculation area for modeling the method of vacuuming for the hermetic volume of the excavation pit with immersed columns under the wintering complex foundation supports. The results of the of the calculated research have fully confirmed the assumptions laid down in the technical solutions for compaction of the wintering complex snow base by using of thermal mat and snow vacuuming.

The key factor of engineering structures made of concrete and reinforced concrete is insufficient frost resistance of concretes. It is important to identify the causes and prevent concrete damage caused by frost. The research provides the basic points of the developed physical and mathematical theory of cement concretes frost resistance. Under consideration are the processes occurring during cyclic freezing and thawing of concrete in a water-saturated state. The results of the performed theoretical and experimental studies are presented. The criterion of concrete frost resistance, which estimates the pore structure of concrete, was derived on the basis of the obtained results. The suggested criterion has a close correlative relation with the frost resistance of concrete. Using this interrelation, the method was proposed for accelerated determination of actual frost resistance of concrete, as well as the method of selection concretes' compositions for a specified design frost resistance of concretes. The methods of accelerated determination of concrete frost resistance, as well as ways to increase it, are described. The developed physical and mathematical model was used to carry out computational modeling for freezing of an extended concrete structure. This made it possible to determine the changes in humidity, temperature, and pressure in concrete during cyclic freezing and thawing at different distances from the surface of its freezing and also draw graphs of changes in these parameters. The recommendations on assignment of concrete design grades by frost resistance for various elements of concrete and reinforced concrete structures are given.

In Ecuador, about 95.9% of dwellings are built with masonry, however the local production of bricks does not meet technical standards and there is no scientific research on its geometric characterization and the technical state of their production. The geometric characterization of bricks is essential for the standardization of materials and constructions and allows the design of structures with a higher degree of accuracy. This research, conducted in 12 provinces of the 3 continental regions of the country, where 79% of the buildings are concentrated, studies for the first time the geometric characteristics of solid clay bricks in Ecuador. The results show that 67% of the brick production in Ecuador is artisanal and 98% of the factories do not comply with the technical standards for brick production. The authors present the characteristic dimensions of solid bricks produced in different regions of Ecuador. The results show a high variation in brick dimensions depending on the region, and even in a same province the dimensions depend on the factory, since its production does not comply with any standard. Ecuadorian standards regulating brick geometry need to be updated taking into account the real characteristics of the national brick production.