"Вестник МГСУ"

The authors draw attention to possible problems in the process of construction and operation of monolithic frame buildings, construction of which is now widespread. It is known that cracks can often appear in the facade and side walls. The size of the cracks can exceed the allowable limits and repair does not lead to their complete elimination. Also cracks significantly mar the appearance of a building. Thus, the relevance of this study lies not only in fuller understanding of the operation of walls, but also in the ability to prevent undesirable effects.The authors calculated temperature effects for boundary walls of the building blocks made of heavy concrete. The original dimensions of the walls conformed to a grid of columns for the majority of residential and public buildings.The stress-and-strain state of the walls in case of temperature changes is observed in detail, including the transition from sub-zero to above-zero temperatures within the same section (wall). It was revealed that the temperature variations within the established limits may cause stress-and-strain state in the walls, in which the temperature tensile stresses can exceed the tensile strength of materials. The article contains effective means of reducing thermal strains, which can prevent temperature and shrinkage cracking.

Masonry is a complex multicomponent composite composed of dissimilar materials (brick / stone and mortar). The process of masonry deformation under load depends on the mechanical characteristics of the basic composite materials, as well as of the parameters belonging to the elements, which define the link between brick and mortar being the structural elements. The paper provides an analysis of the experimental study results of masonry behaviour in two-dimensional stress state at primary stresses of opposite signs; identifies the mechanisms of masonry failure that are in compliance with the conditions of stress state. The work shows the key role that structural elements play in the formation of masonry failure processes. On the basis of failure mechanisms educed from the experiments, there was developed a discrete model of masonry. The processes and the corresponding strength criteria, which play a key role in the implementation of plastic deformation phase, have been detected. It has been shown that the plastic deformation of masonry under biaxial stresses occurs in case of the physical linear behavior of the basic materials (brick and mortar). It has been also substantiated that the plastic properties of masonry under biaxial stresses are determined by the processes occurring at the contact interaction nodes between brick and mortar in bed and cross joints. The values of the plasticity coefficients for masonry depending on the mechanical properties of a brick, a mortar and adhesive strength in their interaction have been obtained basing on the results of the performed numerical investigations.

The article reveals comparative results of experimental model studies of the dynamical characteristics of containment shells used for their calculation and construction as well as actual calculation of dynamic characteristics and the results of actual full-scale investigations executed after 40 years of their operation. This comparison of present-day calculations and full-scale researches showed their agreement with the previous investigations performed on physical models of containment shells.The dynamic analysis of the facilities on the base of physical models were widely used in the 70's of the 20th century, when the computers were still in the initial level of development. The results of these model studies were used to justify the strength of critical structures, including nuclear power plants (NPPs), some of which have already worked for over 40 years. The current investigation gives the opportunity to compare the results of the previous model studies with the present calculations of NPP protective containments (shells) and the field studies results. The field investigations were carried out on the reactor containment of VVER-1000 reactor for the 1st unit of Kalinin NPP.1. Model studies of the dynamic characteristics on the physical model base. In order to provide dynamic model studies in the laboratory it is necessary to solve the following problems: 1) to fulfill certain similarity conditions, which provide unambiguous recalculation of the results to the full-scale structures; 2) to determine the scale of the model and its production material, which is related to the structure and characteristics of the vibration-testing machine (shaker), the transitional fixing devices for the model, special vibrators for dynamic loads, etc. The particular attention should be paid to the registration, processing and analysis of dynamic parameters, taking into account quality changes, which have recently occurred in the measurement technique. The model studies were carried out on a series of geometrically similar models of the protective containments fabricated under special technology of gypsum (1:100 scale) and plexiglas (1:200 scale). The models were mounted on a specially designed shaker. Harmonic oscillations with continuous frequency scanning were set up to the testers and resonant vibration frequency was recorded. Then the shell vibration mode was defined at these frequencies using small-sized mobile vibrometer. The frequencies of natural oscillations were recounted for correlation on similarity conditions.2. The study (investigation) of the dynamic characteristics of the protective containment on the base of mathematical model. The model is built in ANSYS calculation software complex and is structurally similar to the physical model, but without built elements and elastic foundation (i.e, the adopted conditions are similar to the physical model). The problem is solved in three-dimensional setting, all elements are made of three-dimensional elements (of solid type). The comparison of the experiment results on physical models and field studies is given in the Table.