"Вестник МГСУ"

In view of providing durability of constructions, the urgent problem is studying dynamic processes in loaded rod structures occurring in the process of sudden local defects formation, such as breakage of support bonds, partial destruction, transverse and longitudinal cracks etc., which are united under general term "beyond design impacts". To date, a number of problems related to this topic are solved: the problem of dynamic loadings at sudden formation of transverse cracks, the problem of partial tie breaks in the bearings, partial destruction and longitudinal lamination of compound bars. In the paper the authors propose a method of determining the spectrum of natural frequencies of flexural vibrations of a rod system with this type of injury. The results are to be used for modal analysis of forced vibrations of a beam with a defect of longitudinal lamination, depending on its level.

Finite element method shows the influence of the joining area and the relative value of linearly distributed mass along the angular coordinate and concentrated mass on natural oscillations and forms of a closed, circular cylindrical shell. We defined the ranges of concentrated and linearly distributed mass, added to a shell. The variation of the concentrated mass contact area markedly affects the lower frequency of the "shell-mass" system, in this connection, reducing the area of the shell leads to a marked decrease of the lowest split natural frequencies. The greatest of split natural frequencies decreases markedly with the increasing of contact area. More complex (mixed) oscillation modes of the "shell-mass" are detected. Dependence of the geometric characteristics of the shell with a concentrated mass of the lower split natural frequencies lower tone of oscillations, thus, revealing the dependence of frequencies on the length of the sheath. Linear contact area variation of the added mass and the circular coordinate has little effect on the oscillation frequency of the "shell-mass" system.

Periodic two- and three-dimensional structural models designated for rectangular-plan buildings are considered in the article. Expressions for identification of natural frequencies designated for unloaded and loaded two-dimensional structural models, as well as non-free three-dimensional structural models of multistoried buildings are provided in the article.

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.