Vol 14, No 6 (2018)

Relevance. To ensure the safe operation of buildings and structures, it is necessary to more accurately determine the stress-strain state (SSS) of structural elements, to identify areas of stress concentration. The distribution of stresses in the region of the fastening bars in three-dimensional formulation is relatively little studied. In these areas, there may be significant stress concentrations that contribute to the occurrence and development of cracks and splits, which are a harbinger of destruction. The development of modern methods of calculation, software systems and the growth of computing capabilities allow refining the design scheme: to move from one-dimensional to two-dimensional calculation scheme, from two-dimensional to three-dimensional calculation scheme. All this makes it possible to more accurately assess the SSS of structural elements and structures, to identify areas of stress concentration, as well as to investigate the effect of the Poisson's ratio on the stress concentration. Methods of research. It is noted that cracks and breaks in the edges under the influence of longitudinal loads occur in the rods (racks) of square cross-section. Three-dimensional elements based on the spline version of the finite element method and the LIRA computational complex are used to estimate the stress-strain state. The spline finite element method, thanks to the synthesis of the idea of parametrization and the finite element method (FEM) with cubic approximation of all three required variables within each element, allows obtaining consistent three-dimensional finite elements. On the basis of the mentioned methods and complexes, numerical studies of the stress concentration in the bars of square and rectangular cross-sections fixed at one end and perceiving the tensile forces at the other end are performed. Conclusions. It is found that in the angular points of the cross section in the area of fastening of straight bars, perceiving axial tensile forces, there are stress concentrations. Away from the mounting area of the bar, the voltages are aligned. By increasing the Poisson's ratio, the stress concentration increases faster than at low values. The transition from a onedimensional design model to a two-dimensional one, and even more so to a three-dimensional model allows to determine the stress concentration, both in plan and in thickness. Information about the concentration of stresses in elements of structures will allow designers to more accurately design structures and facilities, and the operators to promptly identify the defective region.

Introduction and objectives. When calculating buildings and structures for special combinations of loads caused by the action of air shock waves, it is necessary to determine the main parameters of the actual load. The regulatory approach implemented in modern regulatory documents proposes the use of simplified calculation methods based on the use of equivalent static loads. The aim of the study is to obtain the basic parameters of air shock waves, as well as to consider the nature of the propagation of the shock wave front during an explosion on the ground and in the air, using numerical simulation. Materials and methods. To obtain the basic parameters of air shock waves, high-precision numerical methods implemented in the modern LS-DYNA software package are considered. To describe the explosion process, the LagrangianEulerian approach is used. Results. Isopoles and graphs of excess overpressure Δ Р ф over atmospheric pressure in an air shock wave were obtained when the epicenter of the explosion was located at ground level and in the air, as well as at a distance from the designed structure. Conclusions. The considered method of numerical simulation allows to obtain the main parameters of air shock waves, which can be used for further calculation of building structures.

Goal. The goal of this paper is to characterize the process of forming the frames of large-span metal domes during assembly process. The load-bearing structural schemes during the assembly of frames differ from those, adopted for their analysis and design. Due to this fact, initial internal forces appear in the structural elements of frameworks that are called assembly forces. Geometric schemes of dome frameworks and the principles of their formation are described for ribbed domes, ribbed domes with annular rings and lattice domes. It is shown how lattice dome frameworks are formed and why they are considered as spatial bar systems. Specific features of the structural solutions for single-layer and double-layer frameworks are described. It is noted that the technological scheme for the assembly of structures of large-span metal domes depends on the structural systems of frameworks and on the methods of their erection. A brief description is given of differrent methods for erecting frameworks of large-span metal domes and of the number of temporary supports and mechanisms used in this process. Review. Different methods of erection are illustrated with the examples of several well-known dome structures built in the world. The evaluation of the influence of each process on the behavior of structures during the installation is given. The nature of the work of individual structures and a frame is described for the process of erecting large-span metal domes. The emphasis was made on the significant differences in the nature of work of structural systems of dome frame-works with different ways of their installation. Research. Computer models of the lattice metal domes are made of steel I-bars with rigid connections at the joints. Additional models were created for incomplete frameworks to study alternative ways of erection. For each assembly model of the dome framework, computer analysis was performed for the action of its self-weight. Stresses in the structural members, obtained as a result of the analysis, were compared with the stresses in the corresponding elements of the design model of the framework under the self-weight. Conclusions. The conclusion is made that the stresses in the elements of frameworks of the large-span metal domes are unavoidable when they are erected. The necessity of compulsory analysis of frameworks for erection conditions in the design of large-span metal domes was noted.

Aims. Thin shells in the form of cylindroids are fourth-degree ruled shells for which few works are devoted. In this paper, their geometric modeling is worked out and their middle surface are plotted, using the software MathCAD. Their stress-strain state are instigated with two building material: reinforcement concert and qualitative steel. Methods. This linear investigation is done for fixed and hinged supports and for various thicknesses in the software SCAD. The numerical values of their maximum and minimum displacements of their middle surfaces are given. Based on these displacements, conclusions are made for the whole paper. Results. The linear analysis for reinforced concrete and metallic shells, computed using the software SCAD gives the numerical and graphical results that are presented. Conclusions. The investigations of the stress-strain state are done for shells with the shape of cylindroid with two directrices ellipses and cylindroid Frazer. For the same thickness, loading and span, the reinforced concrete shells has minimum displacements. For thickness, 20 cm the steel shells have the same maximum displacements. For the thickness 30 cm the maximum displacement is more in steel shells. It is more optimal to use reinforced concrete shells than the one in steel. A large span (till 30 m) shells can be designed with reinforced concrete.

Aims. The problem of differential equation construction characteristics and balances is being analyzed; and also the definitions of the planar wave rotational deformation travel time in the continuum, the mechanical character of which is described by the mathematical models geometrically nonlinear analogues in continuous body, the stress-strain stain of which is described by the undefined, basically, by the cross-connections between the first tensor invariant and the second invariant deviator of the stresses and nonlinear deformations. Methods. As an example let’s plot the specific speed of the transverse waves depending on the intensive rotational transverse deformation and the meanings of the material mechanical constants for the three mathematical models of the continuum: model 1 corresponds to the geometrically nonlinear analogue of the elasticity linear theory; model 2 corresponds to the geometrically nonlinear analogue of the small quantity elastoplastic strain theory; model 3 corresponds to geometrically nonlinear analogue of deformation theory of the loose medium plasticity. Conclusions. It is stated that in half-subspace the mechanical behavior of which is described by the deformation theory equations of the loose medium plasticity, the shock waves can appear in continuous boundary conditions.

The article presents the schematic diagrams and mathematical models of multi-barrel artillery systems designed for shooting and extraction of building elements from the ground, describes the results of numerical experiments carried out on the basis of the proposed mathematical models and allow to study the dynamics of multi-barrel building artillery systems during the shot. Mathematical forecasts on the depth of piles in the soil, the maximum pressure in the channels of the stems, the magnitude and speed of the guns rollback for different conditions of loading the stems and their technical characteristics are described. As a verification of the proposed mathematical models, the results of experiments for singlebarrel artillery guns, which are a special case of multi-barrel guns, are described.