Introduction. Analytical solutions for problems of structural mechanics are not only an alternative approach to solving problems of strength, reliability and dynamics of structures, but also the possibility for simple performance evaluations and optimization of structures. Frequency analysis of planar trusses, most often used in construction and engineering, is an important part of the study of structures. Objectives - development of a three-parameter induction algorithm for deriving the analytical dependence of the natural oscillation frequencies of the truss on the number of panels. Materials and methods. A flat, statically definable truss with one additional external link and double braces has been considered. The inertia properties of the truss are modeled by point masses located in the nodes of the lower straight truss belt. Each mass is assumed to have only one vertical degree of freedom. The stiffness of all truss rods is assumed to be the same. The task is to obtain analytical dependences of the oscillation frequencies of the proposed truss model on the number of panels. The derivation of the desired formulas is performed by the method of induction in three stages - according to the numbers of rows and columns of the compliance matrix, calculated using the Maxwell - Mohr formula and the number of panels. To find common members of the obtained sequences of coefficients, an apparatus was used to compile and solve the recurrent equations of the Maple computer mathematics system. The task of determining frequencies has been reduced to the eigenvalue problem of a bisymmetric matrix. Results. For the elements of the compliance matrix, general formulas have been found, according to which the frequency equations are compiled and solved. It is shown that in the frequency spectra of trusses with different numbers of panels there is always one common frequency (middle frequency) located in the middle of the spectrum. An expression is found for the maximum value of the average oscillation frequency as a function of the height of the truss. Conclusions. The proposed truss scheme, despite its external static indeterminacy and the lattice, which does not allow for the calculation of forces by such methods as the method of cutting nodes and the cross section method, allows analytical solutions for the natural frequencies of loads in the nodes. The obtained formulas have a rather simple form, and some general properties, such as frequency coincidences for different numbers of panels and the presence of an analytically calculated maximum of the average frequency function of the truss height, make this solution convenient for practical structural evaluations.

Introduction. The article presents the results of a study to determine the influence of introduction method, type and concentration of plasticizing additives on the structure parameters and properties of gypsum stone obtained using gypsum cement treated in a vortex layer apparatus. Materials and methods. The G-5 BII gypsum cement was used for the investigation. The physicomechanical properties of the gypsum stone were determined in accordance with standard procedures, specific surface area was determined by air permeability, X-ray patterns were taken by means of the D2 Phaser diffractometer. Results. The data were obtained from 11 compositions of gypsum binder processed in the vortex layer apparatus and compared with a reference composition in the sense of the specific surface of the binder, mineralogical composition and physicomechanical characteristics of the gypsum stone. Conclusions. As a result of the investigation, it was revealed that the processing of the gypsum binder in the vortex layer apparatus leads to an increase in the specific surface up to 2 times. Modification of gypsum with MF superplasticizer significantly increases the ultimate compression strength (by 323 %) and bending strength (by 218 %) of the gypsum stone, as compared with the initial composition. Meanwhile the combined activation of gypsum with superplasticizers leads to a sharp decrease in strength and a significant slowdown in hydration. The greatest increase in the strength of the gypsum stone is observed when modifying activated gypsum. So, depending on the type of superplasticizer, the compression strength increases by 100 to 302 %, and bending strength by 86 to 218 %. Also this significantly reduces the gypsum stone overall porosity (down to 23 %) and softening coefficient (down to 51%).

Introduction. The actual problem of improving the methods of experimental studies of the properties of fibre-reinforced concrete obtained using various types of fibre is considered in the article. As a result of the analysis of the technical literature, some shortcomings of the existing test methods of one of the most important characteristics of fibre-reinforced concrete, crack resistance, were revealed. The aim of this study is to develop methods for determining the fibre-reinforced concrete crack resistance parameters. Materials and methods. The GOST 29167 standard is used as a basis for the development of a new method and device. Regulations of this standard pursue an aim of obtaining the most informative data about the material by plotting the dependences of test specimen deflections on the applied loads and determining with their assistance the power and energy parameters of the crack resistance. The test samples are presented by fibre-reinforced fine concrete beams made using steel wire fibre of circular cross-section and wave profile. Diagrams of the dependences of sample deflections on applied loads were plotted in the course of the tests for tension in bending. Calculations of power and energy parameters of crack resistance were conducted. Results. The device and method of testing the fibre-reinforced concrete crack resistance are developed and proved. A comparative analysis of the results of tests of steel fibre concrete samples is made. Conclusions. The proposed device and method allow researching influence of the fibre reinforcement parameters on fibre-reinforced concrete crack resistance parameters quickly and with minimal labour expenditures for preparation and tests. Increased adequacy of the obtained data promotes building up new trends in research and rapid introduction of fibre-reinforced concrete in the construction industry. As a result of the analysis of the obtained data, it is established that the proposed device and method can be recommended for research of the influence of fibrous reinforcement parameters on the obtained fibre-reinforced concrete properties and accumulation of statistical data for the development and improvement of normative and technical documents.

Introduction. Domestic mineral natural-origin filler ‘wollastonite’, also known as calcium methyl silicate, is widely used as a base for wear-resisting epoxy antifriction materials. Due to anisodiametric shape of its particles, wollastonite functions as a micro reinforcement fibre enhancing adhesion strength and wear resistance of epoxy compositions, improving their antifriction properties, especially when organomodifying by quaternary ammonium salts. In this regard, the investigation of the impact of chemical composition of such surfactants as quaternary ammonium salts on the properties of epoxy compound materials presents utmost interest for researchers developing low-friction materials. Materials and methods. Epoxy diane resin ED-20 was hardened with aminoalkylphenol AF-2. Content of epoxy hardener was determined by equimolar ratio of epoxy groups to amine groups. Domestic wollastonite of the grade Miwoll 10-97 was used as filler, particle length to the diameter correlated as 15:1. The wollastonite surface was activated with surfactants belonging to domestically produced quaternary ammonium salts. Wear resistance of specimens was tested by means of the vertical optical caliper IZV-1. Friction coefficient was estimated with the assistance of the computer-automated frictional machine CSM Instruments Tribometer. Adhesion strength of glue joint was determined as per GOST 28840-90 standard. Two bars of sheet aluminium were used as glued surfaces as per GOST 14759-69 standard. Results. Reduction of wear of epoxy coatings when modified with micro reinforcing wollastonite can be explained by the increase of cross-linking degree of the polymer. The length of alkyl radical of quaternary ammonium salts used for wollastonite surface activation affects the intervals between the epoxy links. As the quaternary ammonium salt chain length is growing, wear of epoxy materials is reducing. Introduction of the wollastonite containing metallic oxides in the epoxy composites increases wear resistance and adhesion strength and reduces coating friction coefficients. Conclusions. Hardened with the AF-2 and filled with the wollastonite of the Miwoll 10-97 grade, the epoxy compound materials have enhanced wear resistance and adhesion strength and lower friction coefficient. The best result is observed when applying wollastonite modified with a surfactant belonging to the class of quaternary ammonium salts. The wollastonite can be used for practical purposes as a perspective reinforcing agent for epoxy materials with improved wear resistance, enhanced adhesion to metals and reduced friction coefficient.

Introduction. Wide introduction of fine concretes in the practice of monolithic building construction is limited by their low crack resistance due to considerable shrinkage. To reduce the shrinkage adverse effect on structure and properties of the fine concretes, it is suggested to use for their preparation composite binders, including expanding sulphoaluminate-based cements. Using the fine concrete with enhanced physical and technical properties improves produceability of construction, reduces labor input of concrete casting and allows building installations of complicated architectural forms. Material and methods. To study processes of fine concrete structure formation and properties, concrete mixes were prepared on the base of medium silica sand, dispersed ash entrainment and expanding additive. Activity of the ash entrainment increased at the expense of mechanical and chemical activation. Dispersity of the particles was monitored by means of laser granulometry. The composite binder was prepared by means of thorough homogenization of the basic CEM 42.5 Portland cement and different sorts of mineral aggregates, including an expanding additive based on calcium sulphoaluminate. Maturing conditions at a certain moisture content were simulated for every composition with subsequent evaluation of concrete performance. Results. Results of the study include effect of different mineral additives distinguishing in mineral composition, dispersivity and degree of hydraulic activity on shrinkage amount and kinetics, fine concrete porous structure parameters and strength. It is understood that amount of expansion has an effect on porous structure characteristics of the fine concrete and its strength performance. The study assessed an influence of maturing conditions on the various-composition fine concrete. A considerable influence of maintaining optimal moisture content during hydration on fine concrete technical properties is committed. Conclusions. It is understood that introduction of up to 10 % of expanding sulphoaluminate-based component in basic Portland cement allows to obtain fine concrete with enhanced crack resistance, impenetrability and longevity.

Introduction. The work relates to the scientific foundations of hydraulic and energy construction and is devoted to the study of laminar flows with coaxial oppositely-rotating layers. In the literature, such flows are called counter-vortex. In the turbulent range, counter-vortex flows are characterized by intensive mixing of the medium, which is widely used in the technologies of mixing non-natural and multi-phase media in thermal and atomic energy, in systems of mass- and heat transfer, in chemistry and microbiology, ecology, engine and rocket production. The aim of the theoretical study is to study the physical laws of the hydrodynamics of counter-vortex flows. Research methods. The theoretical Navier-Stokes equations and continuity equation are the basis of the theoretical model of the laminar counter-vortex flow. Results. Assuming the radial velocities are much less than the azimuthal and axial velocities and taking the Oseen approximation, the solution of the Navier - Stokes equations is obtained as Fourier - Bessel series or products of Fourier - Bessel series. In particular, the following were obtained: formulas for calculating the radial-longitudinal distributions of the normalized azimuthal, axial and radial velocities in the flow under study, the velocities are presented graphically in the form of radial profiles; equations for the calculation of current lines and viscous vortex fields, which are also presented in the form of graphs, were obtained. The two-layer and four-layer counter-vortex flows are considered. The analysis of the obtained theoretical results is performed. Conclusions. On the axis at the beginning of the active zone, the formation of a return flow with significant negative velocities is characteristic. This leads to the formation of a recirculation region, the mass exchange between which and the external flow is absent. Cascades of concentric vortexes of such high intensity that are not found in streams of a different nature are generated in the active zone. Calculation formulas include exp (-λ2x/Re) exponent multiplied by Reynolds number in degree b = 0 or b = -1, therefore increasing Reynolds number when b = 0 leads to proportional transfer of arbitrary characteristic counter-vortex flow down the pipe; and at b = -1, the bias of characteristic is accompanied by a proportional decrease in its scale.

ABSTRACT Introduction. The article considers results of research of reinforced-concrete face stress-deformation state depending on availability of the reinforcement. At some ultra-high reinforced-concrete faced rockfill dams (CFRD) the transversal (horizontal) cracks were developed in the seepage-control element. It is supposed that the cause of the crack formation is high values of tensile stresses. In this connection, opinions are expressed about the necessity of strengthening the face reinforcement. However, in accordance with the experience gained, in real dams the reinforcement, as a rule, is arranged in one row with reinforcement percentage 0.35 to 0.5 %. The urgent issue of CFRD studies is assessment of impact of the concrete face strengthened reinforcement on enhancement of its reliability. Materials and methods. The studies were conducted for different variants of rock fill deformation properties on the example of 100 m high rockfill dam. The reinforced concrete face was adopted to be wide (1 m thick). The reinforcement was adopted to be two-row one, with reinforcement percentage of 1.5 %. The study was conducted using the finite element method. The reinforcement was simulated using bar finite elements. Results. To reveal the role of reinforcement, analyses of the stress-deformation state were conducted for two cases. In one case it was assumed that reinforcement is absent and in the other case consideration was made for the face with steel reinforcement. Stresses in concrete and steel reinforcement were analysed. Stresses acting along the upstream slope were considered. Conclusions. It was revealed that due to the reinforcement of steel-bar reinforced concrete face it was impossible to provide decrease of tensile stresses in the face concrete down to the permissible level. Reinforcement may play a significant role in the face stress-deformation state only at the moment of forming transversal cracks in the face concrete, but such a case is inadmissible.

Introduction. The subject of the study is the study of technologies to ensure the reliability of sewage pumping stations (SPS), exploited in the Far North. One of the most important problems is the freezing of water in the SPS tanks, associated with the incorrect selection of the insulation of the SPS of new TPPs, as well as the deterioration of the insulation of the SPS under the influence of aggressive media on the old TPPs. As a solution, the article considers two main methods of internal heating: liquid and electric. Both methods were analyzed using the example of the Yakutsk State District Power Plant-2, where the disruption of the drainage system may lead to a station shutdown. Materials and methods. The purpose of the study was a comparative analysis and selection on the basis of a feasibility study of the most reliable method of heating the pumping unit of the Yakutsk State District Power Plant-2, exposed to low temperatures and, as a consequence, the freezing of wastewater in tanks. On the basis of field surveys and the processing of their results using mathematical statistics, the causes of the problem of water freezing in the SPS units at Yakutsk State District Power Plant-2 were studied and analyzed. Technological characteristics of the installed SPS were also analyzed, heat engineering calculations were performed, economic indicators were calculated, and further solutions to the problem under consideration were determined. Results. Analysis of the technical parameters and configuration of the SPS showed that the installed insulation and the heating system do not correspond to the territorial conditions in which this equipment is installed. To bring the SPS into working condition, two solutions for internal heating of tanks were developed and their comparative analysis was performed. Selected heating option with heating cable. This system has been successfully implemented and is operating normally. Conclusions. The results of the work can be used to repair thermal insulation and install a heating system for industrial pumping stations without using earthworks in the conditions of the Far North and on the territory of permafrost soils.

Introduction. When building residential, public and administrative buildings of various spatial structural designs (monolithic, precast-monolithic, precast, etc.), it is common practice to design self-sustaining (non-structural) outer walls within a storey. Developing and using new design and fabrication solutions of multilayer industrial-made wall panels in modern construction practice makes actual the issue of improving methods of their calculation in different stages of maintenance and under various sorts and combinations of loads and effects. However, there is an infinite variety of possible loading levels in practice and, therefore, the same variety of design approaches would be required. This is obviously unacceptable for engineering calculations, hence it is necessary to provide a monolithic matrix bond of layers, both technologically and structurally, which can provide a generalized approach to the calculation of multilayer enclosing structures in accordance with current design standards. Materials and methods. The article describes structural features of a multilayer wall panel made of structural concrete with the middle layer of concrete with low thermal conductivity and monolithic bond of layers. These features have an influence on creation of a design model and a calculation procedure in the stages of transportation, installation and maintenance. Results. The article has examined the structures described above in the sense of design parameters that provide their competitive advantages in strength and maintenance as compared with conventional mass-built enclosures. Conclusions. The studies demonstrate that when combining loads of force and non-force character, stresses in the considered structure do not exceed allowable values in all the stages what proves the prospects of using the multilayer panels with monolithic bond of layers for erection of various-purpose frame-panel buildings.

Introduction. Single-dipper hydraulic excavators are becoming widely used multifunctional machines. Upgrading the machine as a whole and its assemblies is an actual problem to be solved with the aim of reducing material consumption and increasing stability and throughput. The article presents results of computer simulation of the excavating part designed to reduce the weight of the equipment. These data can be used to improve the equipment of excavators when operating with non-standard excavating equipment of increased weight. Materials and methods. The excavating equipment of the Hitachi ZX270 excavator is taken as a prototype. Computer simulating and calculation of the excavating part is conducted using the T-FLEX software. The calculation is carried out for different modes of the excavator operation and for different orientations of the jig boom, dipper stick and dipper relative to each other: excavating with the entire width of the dipper, single-tooth excavating, swiveling the loaded excavator for unloading. The highest stresses arise in structural members in the considered calculation cases. The calculations are performed without accounting the oscillations occurring at transient operating modes and during locking. Results. The study determines a stress-deformed condition of the pseudotruss excavating part structures of the excavator with various lightened makes selected on the basis of computer simulation. Zones of the highest stresses and largest deformations are revealed as well as suggestions on their decrease are made. The research results are used to optimize the jig boom and dipper stick structures by the criterion of generated stress minimization. Conclusions. The obtained data and formulated recommendations are the basis for further detailed simulation of pseudotruss excavating part structures of excavators and other machines of various layouts and purposes.