Theoretical and experimental studies

The author derives the equation of planar vibrations of rigid structure resting on kinematical pendulum supports with planar bottom (after A.M. Kurzanov). Both support and the surface below are assumed rigid; no sliding assumed. One of the coefficients in the equation (i.e. coordinate of the rotation center) proves to be piece-wise constant. The equation is of the hyperbolic type with parametric terms. Even linearization of this equation does not bring it to the conventional equation of the SDOF oscillator. Principal difference is that the free vibration period depends on the amplitude. The equation is checked for free and forced vibrations. Similar problem is for the seismic response of the unanchored items. For the further research the experimental data about damping are of great importance: both for rotation and the gap closing.

The paper presents a method of using the reduction factor to ensure the stability of monolithic reinforced concrete bearing structures to progressive collapse.

Studies have established the values of the reduction factor based on the accepted value of the relative deformation corresponding to the formation of an admissible zone of "destruction" of the support section of the overlap under the action of transverse forces, as the main criterion for asessing the stress-strain state of monolithic reinforced concrete structures for the failure mode of a vertical supporting structure.

The accepted deformation criteria for a special limiting state correctly reflect the conditions for the formation of an admissible amount of damage to elements of bearing reinforced concrete systems.

The reduction factor (K₁) obtained in the framework of the research performed is the most important deformation characteristic of the special limiting state of monolithic reinforced concrete bearing systems of buildings and structures for an emergency design situation associated with the failure of a local structural element.

Linear-spectral method (LSM) is still the common method for the seismic design analysis. "One-component one-mode" responses, obtained by static analysis in the conventional variant of LSM, are combined twice: first for different modes but for each single excitation component separately, then for the different excitation components. In the alternative LSM variant presented in the Russian code SP 14.13330, first one chooses the "most dangerous" direction of the one-component excitation for each mode; then calculates the "one-mode" response for this excitation, and finally these responses are combined. In both cases the combination is performed using the complete quadratic combination (CQC) rule. Different documents suggest different formulae for the correlation coefficients. In the paper different formulae are compared to each other. The goal is to limit the number of calculated coefficients and decrease the amount of calculations.

The article is devoted to issues related to the probabilistic justification of the safety of nuclear power plants (NPP) when a high-speed military aircraft falls. The random parameters are the recurrence of falls and the direction of the aircraft's trajectory. The conservative value of the recurrence of falls, given in the IAEA documents, was used, which ensures a high degree of NPP safety. The aircraft approach is assumed to be equally probable from either side. The trajectory slope is specified taking into account the IAEA documents and statistics of aviation accidents.

          The aircraft impact load is applied to one of the structures, therefore the impact probability must be determined independently for each of them. It is proportional to the equivalent area of the building structure, depending on its size, shape, position in space and in relation to other structures. Expressions are given for the equivalent areas of structures of various shapes, typical for NPP. It is shown that if the aircraft crash is unintentional (accident), then with the usual dimensions of structures, the probability of an impact in them is less than the value, starting from which, according to Russian standards, it must be taken into account in the design basis of the NPP, i.e. it can be ignored. Dependencies are given for calculating the probability of an aircraft strike in the case of a deliberately organized accident (terrorist attack), in which the aircraft will surely fall on the territory of “Nuclear Island” of the NPP.

          The procedure for setting the design loads on the building structures of a NPP in the case of a deliberate aircraft fall based on the allowed probability of their realization is described. It is shown that this method of setting the loads makes it possible to substantiate their significant reduction, which leads to a reduction in the cost of the NPP while guaranteeing its safety. A probabilistic assessment of structures safety of existing NPP in the event of an aircraft impact is discussed.

The general characteristics of the structural system of a full-assembly frame of "H" elements for the construction of residential buildings are described. "H" element is a hybrid of two columns, each is one storey high, join to monolith with the joist. The junction of the columns is located in the middle of the floor height. These elements are assembled to structural cells with longitudinal, transverse or cross-arrangement of bearing frames. Joints of columns with joist are rigid. The overall spatial stability of the frame is provided by the layout of the frame elements, as well as the use of various kinds of connections. Slabs are prefabricated. Connections of "H" elements are made by the ties with the use of screw reinforcing bars. 

In engineering approaches to calculating the seismic resistance of underground structures, in particular pipelines, it is important to find experimentally the forces of interaction with the ground, as this frees us from the need to solve a difficult dynamic problem for the ground (elastic or having more complex mechanical properties). In this work inaccuracies are corrected and further development of the known from literature theory of quasistatic experiment for determining the coefficient of longitudinal interaction of soil and underground pipeline in seismic problems is given. It is shown that only the second approximation for the named coefficient in the expansion with a small parameter, equal to the ratio of the length of the pipe sample to the length of the seismic wave, takes into account the longitudinal deformation of the pipe; the first approximation corresponds to the experiment with an absolutely rigid pipe.

The article considers the initial Cauchy problem for a fractional differential equation with a variable coefficient and its numerical solution is applicable in the problem of developing an oil well to determine the pressure change with increasing distance from the well. The parameter of the proposed mathematical model for a specific well was identified based on experimental data. The parameter of the mathematical model was determined by solving the problem of approximating empirical data using the least squares method.