Vol 14, No 5 (2018)

The aim of work. To determine the dynamic stiffness at considering vertical and horizontal vibrations of embedded foundations on a conventional and pile base, the possibility of using formulas obtained within the framework of the wave model and SP 26.13330.2012 is considered. Solution technique. Depending on deepening changes, the natural-vibration frequencies of the system oscillations are calculated. The obtained results are compared with the experimental data obtained in a series of impulse dynamic loads performed on foundation models in semi-real conditions. The values of the transverse wave velocities were determined directly on the experimental range from the results of measurements. Results. It is determined that deepening leads to an increase in the frequencies of natural oscillations, both pile foundations and shallow foundations. Full penetration helps to increase natural-vibration frequencies. For horizontal oscillations more than 1.6 times, for vertical oscillations up to 1.4 times. The influence of deepening on shallow foundations is more significant. The advantage of the calculations results and their high agreement with the values obtained during the experiments in the framework of the wave model in comparison with the method from SP 26.13330.2012 is shown. It allows to reliably determining the amplitude-frequency characteristics of the foundations. The results determined in accordance with SP 26.13330.2012, have significantly lower values of the natural-vibration frequencies and do not fully take into account the influence of deepening. The maximum difference with the experimental data for vertical vibrations for a foundation on piles and for a shallow foundation is 33 %. In case of horizontal fluctuations, the maximum differences are from 20 % for a shallow foundation and up to 27 % for a pile foundation.

The aim of the work is to identify and analyze errors in the field of creep theory, where, as indicated by the leaders and authors of this theory, there is an “established consensus”. Here we are not talking about a different point of view or simplifications in standardization, since the elimination of the identified errors will significantly simplify the theory of longterm resistance of reinforced concrete. The analysis presented below is important not only for scientific theory, but also for the vast international practice of reinforced concrete construction. On the inconsistency of the theory of creep of reinforced concrete: this system arose and develops because of the construction of the theory on a set of erroneous principles, rules and unauthorized methods; it is aggravated by the numerous changes (random or deliberate) of the fundamental experimental properties of concrete; it is based on the inheritance of the principles of the inappropriate theory of Boltzmann elastic aftereffect. About the inconsistency of the theory of versatile and comprehensive evidence of: the presence of a system of gross mathematical errors; violations of the principles and rules of classical mechanics and Eurocodes; inconsistencies with wellknown experimental data; negative results of design practices, including world experience in designing unique structures by Ramboll institutions (UK). The main results were reported by the authors at the Sixth International Symposium on Life - Cycle Civil Engineering in Ghent (Belgium), IALCCE 2018, October 28-31.

Relevance. Basalt fibers are increasingly studied in structural applications due to its environmental friendliness, good mechanical properties, thermal and chemical resistance. The aim of work. Mass production of high-strength concrete in Russia is mostly associated with the use of organomineral modifiers of the MB series, which consist of composition microsilica, fly ash, hardening regulator and superplasticizer C-3 in various proportions. The purpose of the experimental research is to study the effect of basalt fibers in high-strength concrete. Solution technique. The research of physical and mechanical properties of basalt-fibered high-strength concrete was made on samples with detentions of 100×100×100 and 100×100×400 mm with the use of modifier MB10-30C. The compressive strength, the tensile strength at bending, the strength at axial tension, and the cracking moment in various periods of curing (after 7, 14, 28 and 60 days of curing) were determined under the research. Results. The research results show that the use of basalt fibers in high-strength concrete resulted in a decrease in the compressive strength about 18-20 %, however, enhance the tensile behavior about 42-48 %.

The aim of work. The work is devoted to the study of the propagation of axisymmetric longitudinal waves in a compound cylinder with initial torsion. Solution technique. The initial stresses in the cylinder are determined using the classical linear theory of elasticity. Methods for solving corresponding problems of intrinsic significance are proposed. Numerical results are given and their analysis is carried out. Results. It was found that the presence of initial torsion in cylinders does not exclude the appearance of an axisymmetric longitudinal and axisymmetric waves in a compound cylinder separately. It is found that, in the absence of initial torsion in the compound cylinder, there are intersection points between the dispersion curves corresponding to the modes of axially symmetric longitudinal and torsional waves. It is shown that in the case when initial torsion takes place on at least one cylinder, the axisymmetric longitudinal and torsional waves can not propagate separately, i.e. there is an interference between these two types of axisymmetric waves in a composite cylinder. Methods for solving the problem are developed and corresponding dispersion equations for a compound cylinder are obtained. Dispersion equations are solved and dispersion curves are obtained, an algorithm is developed for constructing these curves.

Subject . Analysis of applicability and effectiveness of various complexity level models in design of reinforcement of stretch elements by gluing on their surface high-strength fiber reinforced polymers (HSFRP). Research objectives. Determine the necessary level of complexity of the calculation model based on the comparison of calculation results obtained on models of various complexity within the elastic behavior of the reinforced element and analysis of features of its elastoplastic behavior in case of its overload. Materials and methods. Few relatively simple variants of HSFRP-reinforcement structures with application of four Finite Element Method (FEM) simulation models of varying complexity and an analytic approach. Plane and spatial Finite Element (FE) models with PC LIRA (SCAD) and FEMAP (NASTRAN) apply in considered series of numerical experiments. Comparative analysis of results of elastic FEM calculation based on various FE models with the results obtained using analytical expressions. A number of diagrams and tables represent the results of calculations. Nonlinear FEM analysis reveals some features of the reinforced elements response under extreme loads. Results. The effect of various factors on the bonded joint behavior observed, the equations and formulae for the analysis and design are applied, the analytical approach based numerical results well correspond with those obtained using FEM. A number of nonlinear FEM calculations discover some features of elastic-plastic response of joints. Conclusions. All the considered here FE models within the limits of elastic design are quite compatible mutually and with an approximate analytical approach as well. The least timeand effort-expensive for the stage of preliminary assessment of the various parameters effect on the glued joint behavior in the elastic design of the stretched elements reinforcement is an analytical approach allowing instantaneously obtain the resulting main components of stresses and forces in the components of joint to scroll through parameter values. FEM simulation for elastic calculation is expedient for verification of results. The simplified plain FEM simulation seems to be quite reliable here. In inelastic state of the reinforced element material yet, the features of its stress-strain distribution not observable in the elastic stage of its loading and requiring special attention and refined FEM simulation may dominate.

Relevancy. Most of the non-ferrous metal ores are produced by low-productivity and dangerous technology in conditions when high-performance technology cannot be used. The aim of many studies and this work is to find reserves for increasing productivity and safety in the development of such deposits through the use of hidden technology capabilities. The method of investigation is a comparison of the traditional version of ore breakage with new variants of ore breaking in the framework of an industrial field experiment with interpretation of the results obtained. Results. Quantitative values of the efficiency indices of ore breakage from drilling workings are obtained in comparison with the traditional version with the breakage of the ledges and the worked out space. It is proved that the application of the new technology, despite the laboriousness of penetrating the drilling workings, does not worsen the technical and economic performance of the design, radically improving the safety of work. The results obtained are approximated graphically. Conclusions. The indicators of the breakage from the drilling workings outstrip the traditional version of the breakage due to the previously unavailable features of the breakage and placement in the worked out space of the ore, saving the workers from the danger of being in the open worked-out space.