Deformation Diagrams Research Articles

The influence of anisotropy on the character of hardening in additive high-strength alloys

The purpose of this work is to establish the dependence of the coefficients of planar anisotropy on the intensity of localized deformations in various loading ranges of transverse and longitudinal sections of samples of heat-resistant powder alloy Inconel 718 manufactured using SLM technology. The role of technological anisotropy of samples characteristic of SLM technology and its effect on the hardening of Inconel 718 alloy products is evaluated. Methods. To achieve this goal, the deformation diagrams of Inconel 718 powder alloy samples manufactured using SLM technology, measured during their stretching according to GOST 11701-84, were analyzed. Flat samples with a dividing grid applied to their surface were subjected to loading. During the tests, localized deformation of the samples in different sections was determined by measuring the geometry of the images of the dividing grid. A specially developed photo and video recording technology was used to capture these images. Results. The statistical analysis of the type and parameters of the deformation diagrams made it possible to determine the nature of changes in the intensity of stresses and deformations of the samples of the studied material. The linear character of its tensile hardening in the region of small values of strain intensity and the power-law character of hardening in the range of strain intensity from 0.03 to 0.17 were established. Conclusion. A significant effect of the technological anisotropy of Inconel 718 heat-resistant powder alloy samples obtained using SLM technology on the intensity of deformations is shown. The necessity of taking this fact into account in the development of technological processes for the production of responsible products from the studied material has been revealed.

Analysis of spectra of external impacts, reactions to them and limit states under the non-stationary modes of loading

It is noted that under real operating conditions of technical systems the so-called non-stationary loading in which external loadings increase or decrease arbitrarily is realized most often. At the same time final ratios between strains and stresses are of practical interest to engineering calculations. It is shown that for simple cyclic loadings the state equations in final ratios which are based on the theory of small elastic-plastic strains can be used. In this case the existence of the uniform generalized deformation diagram assuming a final relation between the corresponding components of stresses and strains both for initial and cyclic stages of deformation is essential for the analysis of considered conditions of a non-stationary cyclic loading. The analysis of conditions of achieving limit states at all stages of the life cycle the criteria base and the system of the computation equations become more complicated and more saturated by the factors taken into account and among them first external and internal impacts of natural, technogenic, anthropogenous origin, load from these impacts, and the reactions of installations to such impacts and loads as well. At the same time a set of criteria defining a limit state is presented in the form of a functional dependence characterizing a set of force and deformation parameters of the state of technical system on the one hand, and, on the other hand, a complex of criterion characteristics of constructional materials taking into account their change during operation. The most important step of determining conditions for achievement of the limit state causing fracture is establishing the critical parts that determine risks of emergency and catastrophic situations in which processes of local and main fractures are initiated. In this case transition of the operated installation from design area to the area of initiation of refusals, accidents and disasters occurs when the parameters of damage, defectiveness and risk reach their critical values.

To justification of concrete strength criterion at biaxial compression

Introduction. Numerous experimental data from Russian and foreign researchers indicate that the classical plasticity hypotheses do not take into account the different resistance to uniaxial tension and compression, the influence of the spherical tensor. At the same time, experiments show that the ultimate resistance depends on the type of stress state, and hydrostatic pressure increases the strength and plasticity of solids. Aim. To establish the dependence of the influence of the second component of stresses during biaxial compression of concrete on the parameters of the complete diagrams of deformation of the material σbR and εbR it is necessary to describe these diagrams, and to construct a closed curve on the plane of the main stresses (concrete strength criterion). Materials and methods. Based on the experimental materials of foreign and domestic researchers, including the experiments of the authors of the article, methods of mechanics of deformed solids, limit curves and a closed curve on the plane of the main stresses in the form of a chain line forming the smallest area strength surface in the form of a catenoid are proposed. Results. The article provides an analysis of the known strength criteria from the point of view of their geometric interpretation in the stress space. It is shown that these studies relate mainly to metals and metal structures, and for the design of reinforced concrete and steel-concrete structures in a complex stress state, it is necessary to develop an appropriate criterion for the strength of concrete. Conclusions. As a result, the proposed limit curves and the surface (material strength criterion) on the plane of main stresses in the form of a catenoid accurately reflect the behavior of concrete under conditions of uniform and uneven flat stress state, and the equation of the surface in the form of a catenoid is a generalization of the equations of limit curves for each of the three types of flat stress state. At the same time, there is no overestimation of strength in the "compression – compression" area in this case.

Low cycle fracture resistance of the superalloy at single- and two-frequency modes of loading

Fatigue and long static damages to the majority of high-loaded units develop under repeated stresses and strains of large amplitudes in elastic and elastoplastic regions at a low number of the main cycles and superimposition of dynamic stresses of significantly smaller value with higher frequencies which results in the so-called two-frequency modes of loading. It is shown that in the region of elevated and high temperatures, which determine the manifestation of temperature and time effects in the material, parameters of the rate and duration of deformation which enter the basic equation for determination of the fatigue life through the frequency and time of loading become the most significant parameters determining the fracture process. The results of theoretical and experimental study carried out on nickel superalloy specimens under a hard mode of loading and high temperatures have shown that estimation of the strength and fatigue life in this case for the single-frequency and two-frequency modes of loading can be performed on the basis of the analysis of strain parameters and diagrams of cyclic elastoplastic deformation using the deformation-kinetic criterion of summation of damages accumulated in the material. A decrease in the fatigue life under two-frequency mode of loading and the possibility of estimating it using the specified criterion and corresponding dependences with the introduction of the parameters of frequency/amplitude ratios of the strains (both full and that imposed on the main process) is experimentally proved. The calculated dependences include the parameters of temperature conditions, frequency and duration of loading which allows (when assessing damage from low-frequency and high-frequency components of cyclic strains) taking into account the effects of cyclicity and time of loading, as well as the existence of a variable coefficient of the asymmetry of high-frequency cycles of the two-frequency mode during high-temperature cyclic elastoplastic deformation.

MODERN APPROACHES TO THE USE OF COMPOSITE MATERIALS IN CONSTRUCTION

A review of the literature on scientific approaches in the development of composite materials and building structures made of composites is carried out. When creating and manufacturing traditional and new composite materials, for example, by additive manufacturing, and when creating structures and structures in engineering calculations, new techniques, finite element computational software systems, and neural network technologies are used, which are used in the creation of modern metal and composite materials, analysis of mechanical characteristics of materials, forecasting loads on the structure, optimization of structures and calculation of their construction characteristics. The distinctive features of modern composite materials are shown. The main types of composite materials are considered: talc, diatomite, calcium carbonate, gibbsite, barium sulfate, feldspar, nepheline, aragonite, calcium carbonate, wool, silk, cotton, linen, jute, wood pulp, asbestos, fiberglass, metal fibers, quartz fibers, basalt fibers, polyamide fibers, polyester fibers, polyvinyl alcohol fibers, carbon fibers, viscose fibers. The physical and mechanical characteristics of composite materials (based on epoxy, aluminum, carbon, magnesium, and nickel matrices) and traditional (steel, aluminum, brick, concrete) building materials are presented. The disadvantages of such composite materials as carbon fiber, fiberglass, organoplastics, textolite, carbon concrete, and polystyrene concrete are presented. Deformation diagrams of some types of fibers for composite materials are considered: high-modulus carbon fibers, high-strength carbon fibers, aramid fibers, glass fibers, and basalt fibers. The advantages of the system of external reinforcement of building structures with composite materials are described. Examples of reinforcement of building structures are considered: reinforced concrete reinforcement; reinforcement of floor slabs; reinforcement of columns; and reinforcement of brick walls.

On the reusable compressive behavior of multi-directional auxetic origami metamaterials

Origami metamaterials exhibit abnormal mechanical properties through artful structural design. To further explore the mechanical behavior of reentrant metamaterials, a multi-directional auxetic origami metamaterial (AOMM) was designed, and its negative Poisson’s ratio effect was analyzed through the diagram of load bearing and deformation. Theoretical models related to geometric parameters, relative density, folding rate, equivalent elasticity and load plateau were established to reveal the deformation transformation mechanism, and the influence of size parameters on the equivalent elastic constants was drawn. Using thermoplastic polyurethane (TPU) as the substrate, two types of multi-directional AOMMs were fabricated by 3D printing, and quasi-static compression experiments were performed. The results show that the TPU AOMMs has a reusable compressive capacity, whose compressive mechanical behaviors are mainly contributed by the buckling instability and large deformation of sidewall. There is a coupling effect between the cross connection boundaries, which results in the difference in mechanical properties of AOMM with different geometric sizes. The prediction results of relative density, load plateau and yield strain through equivalent theories approximate that of experimental results. Simultaneously, finite element analyses were conducted, which agrees well with the experiments. These foundings may provide reference for the design and application of novel auxetic or origami metamaterials.

Effect of aggregate type on strength and deformation properties of high-strength concrete during heating

Introduction. High-strength concrete is widely used in contemporary construction. Expanded introduction of high-strength concrete necessitates the need for studying its behavior at high temperatures (in case of fire) in order to ensure the required fire resistance of load-bearing reinforced concrete structures made of high-strength concrete in terms of fire safety of buildings and structures.Aim. To determine the effect of aggregate types on strength and deformation characteristics of high-strength B100 concrete when heated to temperatures from 100 °C to 800 °C with a step of 100 °C.Materials and methods. Laboratory tests of prism strength and elastic modulus of basalt and granite high-strength concrete were carried out on prism samples in a heated state according to standard methods using special heating equipment combined with laboratory pressure equipment.Results. The authors determined structure behavior factors of basalt and granite high-strength concrete during heating, specifying the decrease in compressive strength and elastic modulus. Deformation diagrams during axial compression of high-strength granite and basalt concretes under heating were drawn.Conclusions. The dynamics of reduction in strength and deformation properties is similar for granite and basalt high-strength concrete under heating and is specific for silicate aggregate concretes. The elastic moduli of basalt high-strength concrete are higher than those of granite high-strength concrete, both at 20 °C and when heated, thereby determining the dependence of high-strength concrete deformation properties on the types of aggregates. Deformation diagrams during the axial compression of high-strength granite and basalt concretes showed specific character: unilinear – when heated to temperatures of about 300–400 °C, bilinear – at higher heating temperatures, therefore differing from traditional ideas and theoretical recommendations.

BEARING CAPACITY OF BEAMS UNDER SHORT-TERM LOADS USING THE DIAGRAM OF CONCRETE DEFORMATION IN THE APPEARANCE OF THE FIFTH DEGREE POLYNOM

The theoretical determination of the load-bearing capacity of reinforced concrete beams under short-term loads using the concrete deformation diagram in the form of a fifth degree polynomial and its comparison with the results of experimental studies is considered. In the calculations of reinforced concrete structures using the deformation model of sections, the bending moments are calculated relative to the neutral line, which is located at a distance from the extreme fiber of the compressed concrete and limits its height. In the DBN of Ukraine, it is proposed to describe the concrete deformation diagram by a polynomial of the fifth degree or by a fractional-rational dependence, which was proposed and substantiated by the State Research Institute of Building Structures. Under these conditions, the theoretical bearing capacity of the reinforced concrete beam was obtained, which was also found experimentally. The authors conducted experimental studies of the load-bearing capacity of three series of beams of different types (three identical samples in each series): Series I - beams made of ordinary concrete; II series - steel-reinforced concrete beams; III series - beams of combined section, in which the lower (stretched) height zone is made of steel fiber concrete, and the upper (compressed) zone is made of ordinary concrete. Fiber, the total volume of which was 1%, was uniformly added to the composition of the concrete mass for the II and III series of samples during mixing. A comparison of the theoretical bearing capacity of a reinforced concrete beam with its value obtained experimentally shows that the theoretical value is quite significantly (1.36 times) higher than the experimental value.

A method for determining the spectral relaxation functions of polymers under single stretching of micro samples

The principles of designing products made of the latest complex-structured polymer composite materials necessitate the need to take into account the large-scale structural effects determined by processes at the supramolecular and molecular levels of the polymer: relaxation, kinetic (breaking and recombination of chemical bonds), recrystallization of supramolecular structures, etc. The development of these processes is described by relaxation functions, which, in turn, can be calculated using the functions of relaxation time spectra. The purpose of the work was to develop a specialized equipment for testing micro-samples with a variable working part for uniaxial stretching along with the experimental technique and computational algorithms for processing the obtained measurement data, and experimental approbation of the developed approach to determining spectral relaxation functions. A method is proposed for estimating relaxation functions not at fixed stress levels within linear elasticity, at secant points of deformation diagrams, at fixed values of the linear elasticity modulus, but within an extended range of the sample deformation up to pre-rupture states. A set of test equipment designed for tensile tests of micro-samples with a thickness of the working part of 0.2 – 1.2 mm has been developed. The tooling can be installed on modern high-precision breaking machines. Tensile tests of polyethylene terephthalate micro-samples with a thickness of 50 and 175 μm were carried out taking into account the scale factor. A tensile test of micro-samples that are technologically stabilized by paper frames of a special shape is described. Diagrams illustrating the kinetics of changes in the spectral relaxation functions of oriented polyethylene terephthalate (PET) are constructed proceeding from the data of testing micro-samples with a constant strain rate. A method for using these diagrams in calculations of empirical relaxation time spectra is described. The results of testing micro-samples of polyethylene terephthalate are presented. Illustrative deformation diagrams of the studied polymer samples and calculated diagrams of functions of relaxation time spectra calculated according to the described method are given.

RESULTS OF MONITORING THE SETTLEMENT OF SILO FOUNDATIONS REINFORCED WITH SOIL-CEMENT ELEMENTS

During the first cycle of loading and in the subsequent process of steel silos operation to store grain, special attention goes to the observation of base settlement under silo foundations and their tilting. Traditionally, silo settlement tends to be monitored by geodetic measurements. To analyse the results of monitoring for the silos base settlement, we used the linearity changing of the base stiffness approach. The base stiffness is the ratio of the average pressure p (in kPa) under the foundation sole to the average settlement S (in mm). This approach relies on the following assumption: in the process of silo loading, thus gradually increasing the average pressure under the sole of the foundation, the modulus of deformation of the base soil gradually decreases, and the deformability of the base increases until the stresses in the soil mass under the foundation do not exceed the values of the calculated resistance and the development of plastic deformations begins. For grain storage elevator silos 10.1–10.12 located in the Khmelnytskyi region, we obtained the ratio of the average pressure p (in kPa) under the foundation sole to the average settlement S (in mm) during the geodetic monitoring, and then, we used it to construct the stiffness graphs of the silo base. The base stiffness indicators of silos 10.2 and 10.3 most closely match the calculated base stiffness. The specified values of base stiffness exceeding the measured ones by 3–5% are probably due to the higher calculated mechanical characteristics of the base reinforced with soil-cement elements. The rigidity of the silo base and the average pressure in the base under the foundations calculated based on geodetic measurement data are independent random variables, as evidenced by the graphs of the rigidity of the silo base 10.1–10.12. The study of the correlation between the specified random variables is of practical interest. The obtained value of the sample correlation coefficient r = –0.4687 indicates a negative correlation between the samples of the average pressure p (in kPa) under the foundation sole and the stiffness of the base (p / S, kPa/mm). The existence of negative correlation dependence has a clear physical meaning, such as when the pressure on the base increases, its stiffness decreases while increasing the deformability of the base, as confirmed by the results of silo geodetic monitoring. The calculated stiffness of the base decreases with increasing pressure due to the involvement of a greater depth of the compressible stratum, and, accordingly, the calculated deformability of the base increases. To determine the physical and mechanical properties of the base soil, the generally accepted pressure range during the tests does not exceed 250 kPa. A priori, this pressure range corresponds to the elastic section of the soil deformation diagram and the gradual decrease in mechanical characteristics. The average stresses under the foundations of the studied silos did not exceed 125 kPa. Therefore, the proposed method makes it possible to obtain not only quantitative conclusions – the magnitude of base settlement, but also to analyse qualitative indicators related to the stiffness characteristics (р / S, kPa/mm) of the base and to assess its deformation indicators acceptability. Keywords: foundation settlement, geodetic monitoring, reinforced concrete foundation, steel silo, base stiffness.

Analysis of the influence of girth weld strength matching on pipe deformation mode and failure pattern

A theory model with two kinds of material, which are used to describe the axis stress strain relationship of the pipe segment and girth weld joints, is proposed for the pipeline axial deformation analysis, and a pipeline deformation diagram is composed for the axis deformation combination within the pipeline design limit. According to the pipeline deformation diagram, it is found that the strength of the pipe segment at the design limit σbA plays a key role in the strength matching discussion. The pipeline axis deformation could be classified as three categories based on the yield strength σwY, ultimate tensile strength σwcritof the weld joints and the pipe design strength σbA, which are σwY>σbA, σwcrit≥σbA≥σwY and σbA>σwcrit. For σwY>σbA, the axis plastic deformation will distribute along the pipe segment and this is the ideal states for the pipeline. For σbA>σwcrit, the girth weld may fail as stress rupture with tensile strain as low as 0.003. For σwcrit≥σbA≥σwY, the weld joint may endure the plastic deformation, and the material properties of the weld joint may change, such as the toughness may decrease. Charpy-V impact test have shown that the toughness decreases 35 % for 2 % deformation for the weld joints welded by FCAW-S. In this scenario, the girth weld may break up as brittle fracture due to the toughness decrease. This model could be used to explain the girth weld failures, optimize the strength matching and control the risk, especially for the buried high strength pipeline of the high stress locations.

BEARING CAPACITY, DEFORMABILITY AND CRACK RESISTANCE OF A DAMAGED BEAM REINFORCED WITH FIBER CONCRETE IN THE COMPRESSED ZONE

The paper presents the results of the study of the load-bearing capacity, deformability and crack resistance of a damaged beam reinforced with fiber concrete in the compressed zone. A beam with 40% damage is considered. The research was conducted in two stages. At the first stage, tests of prisms and cubes made of concrete and fiber concrete were carried out, which showed that the introduction of steel fiber into the composition of concrete in the amount of 2% by volume increases the compressive strength by 15.3%. The initial modulus of elasticity of fiber concrete of the specified mixture is 38.0% higher than that of ordinary concrete of this composition. According to the results of experimental studies of prisms, a diagram of concrete deformation, the nature of changes in relative linear deformations of fiber concrete, as well as graphs showing a comparison of the nature of deformation of concrete and fiber concrete were constructed. At the second stage, the beam sample was tested on a specially designed stand. Before concreting, a foam insert was installed in the zone of planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete set to 70% strength, the liner was removed, and the formed cavity was filled with a 2% fiber concrete mixture. A beam with 40% cross-sectional damage in the mid-compression zone and a near-rectangular damage shape was found to have a load-bearing capacity of 92.0 kN, or 93.9% of the load-bearing capacity of an undamaged beam. Cracking started at the 4th loading stage, when the load value was 26.0kN, i.e. 28.3% of the bearing capacity of the damaged beam. At the same time, 5 cracks formed in the area of pure bending. At the fifth stage, two more cracks appeared. At the 8th and 9th loading stages, 4 more cracks formed. A total of 12 cracks were formed. The maximum final crack opening width was 0.6 mm. Thus, the strengthening of a beam with 40% damage in the compressed zone by the method considered in the work allows you to achieve its bearing capacity, which is 93.9% of the bearing capacity of an intact beam.

Calculation of the stress-strain state of layers of cross-ply laminate based on an experimental stress-strain curves under uniaxial tension

A method for calculating the stress-strain state of layers of cross-ply laminate based on an experimental deformation diagram under uniaxial tension is proposed. The essence of the method consists in solving a system of two equations describing the experimental curves σx = f(εx) and σx = f(εy), which allows determination of two unknown parameters related to the secant elastic characteristics of the material layers. The law of change in the remaining unknown parameters is set by assumptions regarding deformation of the polymer matrix composite and its layers during loading. To carry out the calculation, it is necessary to set the initial values of the elastic properties of the unidirectional material of the layers, which should be well consistent with the initial values of the elastic properties of the structure under study determined from the experiment. According to the developed algorithm, calculated dependences between average stresses, deformations and secant elastic properties of the layers of the structure are obtained (0°/90°/90°/0°) made of fiberglass E-Glass/MY750 using experimental data from the literature. Calculations carried out for three sets of initial values of the elastic properties of the material under study showed qualitatively identical results. The transverse tensile stress in the 90° layer reaches a maximum in the first half of the stress-strain diagram, and then decreases to zero. A similar stress in the 0° layer reaches a maximum at the failure point of the structure under study. It is revealed that the maximum calculated values of transverse stresses acting in layers 0° and 90° noticeably exceed the transverse tensile strength of the material specified in the literature. The longitudinal tensile stress in the 0° layer reaches a maximum at the failure point and corresponds to 95% of the value of the longitudinal tensile strength of the material. The longitudinal compressive stress in the 90° layer is at a low level throughout the deformation process of the structure under study. The results of this study can be recommended for developing models of the behavior of layers with cracks in the matrix when loading a polymer matrix composite.

Using the wavelet transform to process data from experimental studies of the discontinuous plastic deformation effect

Vast number of theoretical and experimental works has been devoted to the study of discontinuous plastic deformation (the Portevin-Le Chatelier effect), which manifests itself for most widely used alloys in certain ranges of both temperatures and strain rates. Due to the statistical nature of this phenomenon, difficulties arise in processing, qualitative analysis and quantitative comparison of test results and calculations. Using of statistical methods for these purposes makes it possible to get only some averaged characteristics of the obtained data (usually - moments of the first and second orders in amplitudes and frequencies). A possible alternative for processing of experimental and theoretical results of this effect research is wavelet analysis using. The results of experimental studies of the Portevin–Le Chatelier effect, realized during the deformation of thin-walled tubular specimens made of aluminum alloy AMg6M at certain strain rates at room temperature are presented. Diagrams of deformation under uniaxial tension, shear, proportional and disproportionate loading of specimens were obtained. The inhomogeneity of strain fields and their rates is shown, illustrating the manifestation of the Portevin – Le Chatelier effect under conditions of complex loading of thin-walled tubular specimens made of AMg6M alloy. A brief overview of existing methods and means of non-destructive testing is presented that make it possible to non-contactly record the spatial heterogeneity of plastic yielding. Some possibilities of using the wavelet transform to process certain types of non-monotonic stress-strain diagrams obtained for the specimens made of the aluminum alloy in question are discussed. Using wavelet analysis, a compact presentation of data from field experiments in the form of amplitude-frequency characteristics was obtained. The scalograms analysis of specimen loading diagrams was carried out.

Generalized Deplanation Hypotheses for Linear and Angular Deformations in Reinforced Concrete Structures under Combined Torsion and Bending

Statement of the problem. The analysis of the deplanation hypothesis for linear and angular deformations in reinforced concrete in bending with torsion has been carried out. Results. A simple new method from the method of grids has been developed for complex functions under the combined action of bending and torsion. Diagrams of linear and angular deformities and a new hypotheses have been analyzed. Complex functions have been found to determine the linear and angular deformations, bending and torque moments in the compressed area of concrete. The author has found the projection coefficients of linear and angular deformations using diagrams of compressed concrete and main reinforcement. Deplanations from a special geometric figure of deformations in a complex function have been found. There are vectors of several triangles and gradients where the proportions of a hypotenuse, cathetuses and vectors have been derived. Conclusions. It is also important that similar relative values can be obtained for any vectors. A field of small squares have been plotted and jumps from lateral, normal and other cracks appear have been determined. Fillings of the deformation (stress) diagrams have been obtained for the analysis of the moments in bending with torsion using simple expressions or in a full form. The research on the complex function of linear and angular deformations and the approximation of a function from Timoshenko-Goodyear have been carried out. The error of the deformations value of using the complex function at the points under study is 2% and is 7% at any points of the cross section.

Static Analysis of Gear Periodic Symmetrical Structure Based On ANSYS

Gears are important components of transmission mechanisms, and it is crucial to analyze the stress and strain of gears using ANSYS to obtain their mechanical characteristics for product research and development in production. After establishing a mechanical model of gears based on material characteristics, define constraints and boundary critical conditions. Through analysis and solution, the deformation diagram and stress distribution diagram of the gear are obtained. Using the characteristic of periodic symmetry can simplify the analysis of the mechanical characteristics of gears, reduce the cycle time and cost of prototype development. Of course, this method can be applied to all similar institutional developments with this characteristic, which provides convenience for product design and improvement and saves cost.

Method for calculating compression resistance of reinforced masonry elements using deformation diagrams

Method for calculating compression resistance of reinforced masonry elements using deformation diagrams

Study of Bending of Beams Made of Material with a Nonlinear Deformation Diagram

Study of Bending of Beams Made of Material with a Nonlinear Deformation Diagram

РАСЧЕТНАЯ МОДЕЛЬ ДЕФОРМИРОВАНИЯ ГРУНТОВОГО ОСНОВАНИЯ ВЫСОТНОГО ЗДАНИЯ С УЧЕТОМ ПРЕДЫСТОРИИ ЗАГРУЖЕНИЯ

While designing high-rise buildings, it is necessary to take into account the influence of stages of their erection, this is the sequence of loading, on the change in physical-mechanical properties of soils. The calculation of deformations of subgrade is made with due regard for the change in soils properties comparing with the initial (natural) state. On the basis of the results of experimental studies, the authors substantiate the necessity for introducing the new parameter which makes it possible to characterize the mechanical condition of the soil at any stage of loading and can be used for creating calculation models. An analytical diagram of soil deformation in coordinates «σ1–ε1» for triaxial compression (where σ1 – vertical stresses (deviator), ε1 – linear deformations under the triaxial compression) is adopted as this parameter. The procedure for constructing transformed diagrams of the soil state under the long performance triaxial loading is described. The procedure obtained was approbated when calculating deformations of the foundation base of the high-rise building with due regard for the influence of staging of construction and rheological properties of soils on the change in the base rigidity and, as a result, on the redistribution of stresses among separate elements of the system “subgrade –foundation – upper part of the building.

Experimental Study of Longitudinal and Transverse Bending of Pipe Concrete Rods

The results of experimental studies of pipe-concrete rods during longitudinal and transverse bending tests, since these stress-strain states are of interest from the point of view of the operation of building structures, are presented. To carry out the experiments, several series of laboratory samples 700 mm long were made, which were steel pipes with a monolithic core made of fine-grained concrete. Diagrams of test installations are presented and methods for conducting experiments on axial compression with subsequent loss of stability and three-point bending with concentrated lateral load are described. Based on experimental data, deformation diagrams are constructed and compared with the deformation of a hollow steel pipe. It is noted that the presence of a concrete rod prevents premature loss of stability of the pipe wall during longitudinal bending, limits local deformations due to the curvature of sections during transverse bending, increases the elastic region of deformations, and also prevents the brittle nature of destruction, which is an important advantage in the design of buildings.