"Вестник МГСУ"

The article is a brief review of the research of stress-strain state of a structure that represents a hemispherical geodetic dome exposed to the dead load. Double-contour geodetic domes composed of plates and rods are the subject of the research. The process of their design has two stages: (a) design of geometric models of geodetic domes and (b) analysis of the domes.The author demonstrates that the first stage can be implemented through the employment of the library of ArchiCAD objects. Supplementary research is needed to have the second stage implemented. The objective of this research is to present the results of the research using computeraided methods of metal structures modeling.The article presents a study of the stress-strain state of a construction with a geodetic dome (shell) of the system “R” (classification of prof. G.N. Pavlov). The purpose of the paper is to present the results of numerical modeling in PATRAN/NASTRAN system in the form of approximate formulas. Approximate formulas are presented for calculation of global maximum of stress in second contour.

In this article the operation of a continuous double-span beam with hybrid reinforcement, steel and composite reinforcement under the action of concentrated forces is considered. The nature of stress-strain state of structures is investigated with the help of computer modeling using a three-dimensional model. Five models of beams with different characteristics were studied. According to the results of numerical studies the data on the distribution of stresses and displacements in continuous beams was provided. The dependence of the stress-strain state on increasing the percentage of the top re- inforcement (composite) of fittings and change in the concrete class is determined and presented in the article. Currently, the interest in the use of composite reinforcement as a working reinforcement of concrete structures in Russia has increased significantly, which is reflected in the increase of the number of scientific and practical publications devoted to the study of the properties and use of composite materials in construction, as well as emerging draft documents for design of such structures. One of the proposals for basalt reinforcement application is to use it in bending elements with combined reinforcement. For theoretical justification of the proposed nature of reinforcement and improvement of the calculation method the authors conduct a study of stress-strain state of continuous beams with the use of modern computing systems. The software program LIRA is most often used compared to other programs representing strain-stress state analysis of concrete structures.

The authors have applied the method of boundary equations to resolve the problem of numerical calculation of the stress-strain state of arbitrary boundaries of excavation works in fractures massifs, if subjected to various impacts.
Benchmarking of the results have proven that the proposed model based on the method of boundary integral equations may be used to identify the concentrated stresses that the loose excavation boundaries in fractured massifs are exposed to.
The authors have developed an algorithm and a calculation pattern through the application of the method of boundary integral equations to calculate the values of stresses concentrated around arbitrary shape openings under impacts of various origins.
Any limiting process, namely, if or and any results are in line with the isotropic medium.
The proposed algorithm and calculation pattern may be used to research the concentrated stresses alongside the boundaries of hydrotechnical engineering facilities.

Subject: one of the promising trends in the development of structural mechanics is the development of methods for solving problems in the theory of elasticity for bodies with continuous inhomogeneity of any deformation characteristics: these methods make it possible to use the strength of the material most fully. In this paper, we consider the two-dimensional problem for the case when a vertical, locally distributed load acts on the hemisphere and the inhomogeneity is caused by the influence of the temperature field. Research objectives: derive governing system of equations in spherical coordinates for determination of the stress state of the radially inhomogeneous hemispherical shell under locally distributed vertical load. Materials and methods: as a mechanical model, we chose a thick-walled reinforced concrete shell (hemisphere) with inner and outer radii a and b, respectively, b > a. The shell’s parameters are a = 3.3 m, b = 4.5 m, Poisson’s ratio ν = 0.16; the load parameters are f = 10MPa - vertical localized load distributed over the outer face, θ0 = 30°, temperature on the internal surface of the shell Ta = 500 °C, temperature on the external surface of the shell Tb = 0 °C. The resulting boundary-value problem (a system of differential equations with variable coefficients) is solved using the Maple software package. Results: maximal compressive stresses σr with allowance for material inhomogeneity are reduced by 10 % compared with the case when the inhomogeneity is ignored. But it is not so important compared with a 3-fold decrease in the tensile stress σθ on the inner surface and a 2-fold reduction in the tensile stress σθ on the outer surface of the hemisphere as concretes generally have a tensile strength substantially smaller than the compressive strength. Conclusions: the method presented in this article makes it possible to reduce the deformation characteristics of the material, i.e. it leads to a reduction in stresses, which allows us to reduce the thickness of the reinforced concrete shell, and also more rationally distribute the reinforcement across the cross-section, increase the maximum values of the mechanical loads.

Subject: despite the accumulated experience in the construction of ground dams with anti-filtration elements from geosynthetic products, the response of geosynthetic products in the structure of ground dams have been little studied. It was not determined whether positive stretch values can arise in the polymeric anti-filtration elements and whether they can threaten integrity of anti-filtration elements. For this, studies of the stress-strain state are required. The recent results of investigations of the physico-mechanical properties of contacts of polymeric geomembranes with soils allow us to study the behavior of geosynthetic products in the structure of soil dams. One of the possible designs - a high ground seam with a zigzag geosynthetic diaphragm - has been studied here. Materials and methods: investigations of the stress-strain state of the seam were carried out using numerical simulation. Calculations were carried out for a wide range of physico-mechanical properties of the geomembrane and the contact of geomembrane with the soil. The modulus of linear deformation of the polymer material, the angle of internal friction, and the tangent stiffness of the contact were varied. Results: the results of studies of the analyzed seam designs have shown that, in the main, the stresses in the geomembrane are determined by the modulus of linear deformation of the polymer material. The higher the stiffness of geomembranes, the higher are the tensile stresses in them. The shear characteristics of the geomembrane-soil contact are also important. The lower the shear strength of the contact, the higher are the tensile stresses in the geomembrane. Conclusions: the most vulnerable point of the zigzag diaphragm is its upper anchors, because it is in them that the greatest tensile stresses occur. It is recommended to turn them to the bottom side. In the diaphragm of the considered structure, it is impossible to use a geomembrane made of polyethylene; it is necessary to use a geomembrane made of PVC.

Introduction. At present the urgent problem in hydraulic construction is establishing the causes of crack formation in seepage-control reinforced concrete faces at a number of rockfill dams. For solving this problem the studies are conducted of stress-strain state (SSS) of concrete-faced rockfill dams which are fulfilled by different methods. Materials and methods. Gives a review and analysis of the results of studies of stress-strain state of concrete-faced rockfill dams (CFRD) fulfilled by different authors over the last 15 years. The results of analytical, experimental and numerical studies are considered. Descriptions are given of the models used for simulation of non-linear character of rockfill deformation at numerical modeling of dam SSS. Results. Analysis showed that solving the problem of CFRD SSS causes a number of methodological difficulties. At present the only method permitting study of CFRD SSS is numerical modeling. The rest methods do not permit considering the impact of important factors on SSS. Large complications are caused by scarce knowledge of rockfill deformation properties in real dams. Conclusions. It was revealed that at present SSS of reinforced concrete faces has been studied insufficiently. The results of conducted studies do not give full and adequate understanding about operation conditions of reinforced concrete faces. Impact of various factors on the face SSS has not been studied. Besides, there are contradictions in the results of studies obtained by different authors. Differences in the results are based on objective and subjective reasons. A considerable obstruction for numerical studies is complicated modeling of rigid thin-walled reinforced concrete face behavior at large deformations inherent to rockfill. The obtained results of studies often do not permit conducting full analysis of SSS of concrete-faced rockfill dams.

Basing on the damaging statistics obtained during the on-site inspections of industrial multi-span building structures with under-crane secondary trusses which have continuous lower plinth, we simulated the scenario of the most likely damage development of under-crane secondary trusses.The first scenario is the development of cracks along the total cross section of plinth. In the process of calculations we defined a real deformation scheme of plinth of under-crane secondary trusses with damage and its stress condition.The second scenario is the destruction of a support or support mounting unit to the lower plinth of under-crane secondary trusses. The destruction of this kind can occur as a result of a crack in a support or as a result of destruction of high-strength fasteners of a support to plinth. We discovered that a system with such damage is geometrically unchanged; there is no possibility of sudden destruction of both the under-crane secondary trusses and the entire building frame.The third scenario is the upper plinth separation from one of the walls of lower plinth of under-crane secondary trusses.The scenario is developed to define the viability of under-crane secondary trusses as a result of cracks in the area of wall junction with the upper shelf of lower plinth, their further development and the appearance of discrete cracks developing into a backbone along the entire span length of under-crane secondary trusses.Based on the calculations of the stress strain state of under-crane secondary trusses with damages in the emergency nature in a separate span of the lower plinth and a truss member, we estimated the viability of structure. The analysis of viability limits makes it possible to find the measures of collapse preventing and avoid possible victims.

In the article the survey results of durability and crack resistance investigation of masonry are presented. The aim of the investigations is improving calculation methods of masonry and reinforced masonry. The relevancy of the problem is determined by the necessity of new efficient materials implementation. In accordance with scientific search methodology complex investigations were carried out, which includes gathering, analyzing and revising the existing data on the topic together with determining essential factors and their value rate. Within the framework of the investigations the features of masonry have been studied. The developed calculation method on the basis of the theory of resistance of anisotropic materials at the compression, which reflects the stress-strain state features and nature of destruction, allows to carry out an assessment of durability and crack resistance of the compressed members and structures made of masonry. The research results can be used at revising or updating the existing normative documents.

The proposed calculation method is specific in terms of determining the carrying capacity of eccentrically compressed concrete elements, in contrast to the calculation by error method, as in the existing regulations, where in the result of the calculation is not known what is the limit load the eccentric compression element can withstand. The proposed calculation method, the publication of which is expected in the next issue of the "Vestnik MGSU" the above mentioned shortcomings of the existing calculation methods, as well as the shortcomings listed in this article are eliminated, which results in the higher convergence of theoretical and experimental results of eccentrically compressed concrete elements strength and hence a high reliability of their operation.

Many Russian and foreign scientists studied in their works bearing capacity of reinforced concrete elements. The principal difference of the presented approaches from the traditional ones is that they lack the necessity of artificial sizing as improbable for simultaneous getting preset limit values of corresponding parameters. In our paper we evaluated the bending moment, giving rise to limit stress strain behavior of corroded reinforced concrete beams with corroded concrete and tensile reinforcement. In order to reduce and simplify calculations we consider single reinforcement and ignore tensile reinforcement resistance, and in order to emphasize the idea of the approach we assume noncorrosiveness. The results of concrete stress strain state analysis are more reliable.

The authors present their solution to the homogeneous boundary value problem of the theory of elasticity in the area of the cut boundary in the plane domain. The authors have derived the type of the stress-strain state in the small area of the peak of the cut area. The authors offer an asymptotic solution to the elastic homogeneous problem depending on intensity ratios as unknown constant values. The problem of research into the ratios of intensity is also relevant for the research into the stress-strain state of structures characterized by geometrical non-linearity of boundaries. In the article, the authors consider a plain problem of the theory of elasticity for a domain having an angular point (the case of concentrated forces in the vertex of an angle are not considered by the authors in this article). The authors consider a special case where the vertex angle is equal to 2π. The type of the stress-strain state derived for this case study coincides with the type of the stress-strain state considered in fracture mechanics. Identification of intensity ratios represents an independent problem of the stress-strain state in the area of the domain of the cut peak.

In the article the finite elements were developed that allow to take into consideration the design features of structures and the specific deformation of reinforced concrete without complicating the design scheme. The results of flat structures calculation under different types of loading are presented.The flat finite elements, which are used today in most widespread software systems for the calculation of the majority of buildings and structures, have significant drawbacks due to the peculiarities of the finite element method computational model. The two major drawbacks are: first, stiffness characteristics are specified as for rectangular cross-section and, second, constant stiffness characteristics over the entire area of finite elements is presupposed.These drawbacks are particularly evident in the process of calculating reinforced concrete structures and they significantly complicate the support systems design of multi-storey buildings. The simplifications used by the calculators are dangerous, as it is practically impossible to evaluate the resulting inaccuracies.The calculation model of the finite element method can be represented as a collection of nodes connected in one system with the help of finite elements, which conditionally replace the corresponding parts of a structure.Elasticity theory problems are solved with the help of finite elements of the shells and spatial finite elements. Here the accuracy of the results increases with the increase in breakdown frequency, and one of the main criteria for evaluating the effectiveness of discrete models is their convergence: the worse is the convergence — the higher breakdown frequency is needed to achieve the required accuracy of homogeneous structures calculations.In order to consider the factors affecting the calculations accuracy without increasing the complexity of making the design scheme, it is advisable to arrange a more detailed structure discretization on the stage of developing computational model. This concept is implemented in the discrete-braced computational model, which supposes replacement of the structure sections by the discreet braces combined in nodal points. The main advantages of discrete-braced model are determined by the possibility of multilevel discretization of a structure, achieved in terms of geometrical dimensions and in terms of the direction of digital communication, components of the stressstrain state, stiffness characteristics of digital communications, variable along the longitudinal axis and changing layer by layer in cross section.The basic diagram of the discrete-braced model is: the calculated structure is conditionally replaced by a set of nodes located at the layout grid lines crossing and linked in pairs by the discrete braces, which limit the mutual displacement of the nodal points for all the considered degrees of freedom.The stiffness characteristics of braces are set independently for each brace and each type of deformation on the basis of geometrical and deformational characteristics of the construction sections replaced by braces.In order to determine these sections, conventional boundary lines are traced on the structure, that are located between the grid lines. It is believed that these lines demarcate the structure sections that influence the stiffness parameters of the neighboring connections of one direction. Thus each out-of-node structure point belongs simultaneously to two sections. Stress-strain state of the structure, stiffness characteristics of the braces along the X and Y axes are defined independently of one another. The distributed internal forces arising in front sections of the braces are brought to concentrated generalized forces transmitted through the nodes between the braces in both directions.In the general case, each node of the obtained flat system has six degrees of freedom — three linear and three angular. Generalized displacements inside connections are described by linear functions. Each connection resists six types of deformations — tension and compression, shear in plane of the structure, shear out of the plane, torsion, rotation (bending in plane) and bending out of the plane. In the process of braces deformation, the efforts relevant to deformations appear in them: axial force , two shear forces, torque and two bending moments, and the stress-strain states during deformation of braces in plane and out of plane of the structure are independent from one another.It is offered to determine stress-strain state of the obtained discrete braced-noded system using the method of shifts by means of composing and solving the system of 6n linear algebraic equations (n — the number of nodes ).The accuracy and convergence of the calculation results for discrete-braced model of structural homogeneous isotropic elements is not inferior, and in some cases exceeds the accuracy and convergence of the finite element method results. The use of discretebraced model provides additional opportunities, in particular for non-linear calculations of reinforced concrete structures, which can significantly simplify the numerical schemes used, and thus significantly reduce the calculation complexity.

In the article, the authors consider some classes of problems of geomechanics that are resolved through the application of SIMULIA ABAQUS software. The tasks associated with the assessment of the zone of influence of structures produced on surrounding buildings and structures in the dense urban environment, as well as the tectonic and physical simulation of rifts with the purpose of identification of deformations of the Earth surface and other defects of lithospheric plates. These seemingly different types of tasks can be grouped together on the basis of common characteristics due to the complexity of numerical modeling problems of geomechanics and geophysics. Non-linearity of physical processes, complexity of the geological structure and variable thickness of layers, bed thinning layers, lenses, as well as singular elements, make it hard to consolidate different elements (for example, engineering and geological elements and associated structures of buildings) in a single model. In this regard, software SIMULIA ABAQUS looks attractive, since it provides a highly advanced finite-element modeling technique, including a convenient hexahedral mesh generator, a wide range of models of elastic and plastic strain of materials, and the ability to work with certain geometric areas that interrelate through the mechanism of contacting surface pairs that have restrictions. It is noteworthy that the research also facilitates development of personal analytical methods designated for the assessment of physical and mechanical properties of heterogeneous materials as well as new solutions applicable in the vicinity of singular elements of the area that may be used in modeling together with ABAQUS software.

The article covers the problem of applicability of finite-element and engineering methods to the development of a model of interaction between pipeline structures and the environment in the complex conditions with a view to the simulation and projection of exogenous geological processes, trustworthy assessment of their impacts on the pipeline, and the testing of varied calculation methodologies. Pipelining in the areas that have a severe continental climate and permafrost soils is accompanied by cryogenic and exogenous processes and developments. It may also involve the development of karst and/or thermokarst. The adverse effect of the natural environment is intensified by the anthropogenic impact produced onto the natural state of the area, causing destruction of forests and other vegetation, changing the ratio of soils in the course of the site planning, changing the conditions that impact the surface and underground waters, and causing the thawing of the bedding in the course of the energy carrier pumping, etc.
The aforementioned consequences are not covered by effective regulatory documents. The latter constitute general and incomplete recommendations in this respect. The appropriate mathematical description of physical processes in complex heterogeneous environments is a separate task to be addressed. The failure to consider the above consequences has repeatedly caused both minor damages (denudation of the pipeline, insulation stripping) and substantial accidents; the rectification of their consequences was utterly expensive. Pipelining produces a thermal impact on the environment; it may alter the mechanical properties of soils and de-frost the clay.
The stress of the pipeline is one of the principal factors that determines its strength and safety. The pipeline stress exposure caused by loads and impacts (self-weight, internal pressure, etc.) may be calculated in advance, and the accuracy of these calculations is sufficient for practical implementation. Stress and strain caused by other factors (groundwater supports, anchors, fixing elements) may only be identified on location. The impact of other factors (temperature, permafrost thawing, karst phenomena and landslides, etc.) may be identified as approximate values.

Results of the theoretical analysis of experimental diagrams of deformations of columns made of wood sawdust and concrete mixtures and of wood sawdust and gypsum mixtures exposed to uniaxial compression are provided in the paper.
The findings of the prototype testing include identification of the two areas of deformations: areas of elastic deformations and areas of intensive development of deformations. The first area of partial elastic deformations is characterized by the linear stress function, while the second area demonstrates that this relationship is nonlinear. Permanent deformations appear as of the startup of the loading process and disproportionate stress is demonstrated throughout the deformation process. However, in the first area (partial elastic deformations) residual deformations are so small that this area is considered as the area of "the area of incomplete elasticity".

The article describes the experimental methods of determining stress-strain state of elements and structures with a brief description of the essence of each method. The authors focus mostly on polarization-optical method for determining stresses in the translucent optical sensing models made of epoxy resins. Physical component of the method is described in the article and a simple diagram of a circular polariscope is presented, as well as an example of the resulting interference pattern in illuminated monochromatic light. A polariscope, in its most general definition, consists of two polarizers. The polarizers sandwich a material or object of interest, and allows one to view the changes of the polarity of light passing through the material or object. Since we are unable to perceive the polarity of light with the naked eye, we are forced to use polariscopes to view the changes in polarity caused by the temporary birefringence of our photoelastic materials. A polariscope is constructed of two polarizers, each set perpendicular to the path of light transmitted through the setup. The first polarizer is called the "polarizer", and the second polarizer is called the "analyzer". The method how the polarizer works is quite simple: unpolarized light enters the polariscope through the polarizer, which allows through only the light of its orientation. This light then passes through the material under observation, and experiences some change in polarity. Finally, this light reaches the analyzer, which, like the polarizer, only lets the light of its orientation through.

Modeling singular solutions of the elasticity theory problems, which are determined by geometric factor - bird's mouth of the edge, make it necessary to analyze the solutions with some peculiarity, which are obtained experimentally with the help of photoelasticity method. In this article the peculiar stress-strain state is analyzed on the example of the known experimental solutions for a wedge under a concentrated force obtained by M. Frocht. Solution analysis for a wedge with a power-type peculiarity obtained experimentally by photoelasticity method, helps to detach a singular solution field, where fringe contour is not visible. Due to idealization of the boundary shape and loading technique, infinitely large stresses arise, which are obtained as a singular solution of the boundary problem in a planar domain. Comparison of theoretical and experimental solutions obtained for a wedge shows areas of overlap and areas of significant and insignificant differences as a result of the inability to experimentally apply the force to a single point.

The article presents the results of evaluation and prediction of reliability a building of the ship hull shop of Astrakhan sea plant under the action of complex combination of stresses. Basing on the values of geometric and stiffness characteristics, a computational model of the object of the study was built. The results were obtained in the course of realization of the method of limiting states, taking into account the random character of the current loads and the strength properties of the materials. Their reliability was confirmed by a multiple conduction of the searching algorithm of mathematical expectations and indicators of variations in the calculated parameters of building structures and operating loads. Numerical characteristics were determined by the results of two surveys of natural oscillations of the framework. During the study the authors evaluated stress-strain state of the building of the ship hull shop both taking into account seismic disturbances and their absence. The calculation of the perception of the seismic load was carried with choosing the earthquake model implementation by mapping the impact of the earthquake in the form of a set of random processes with defining spectra of the input and output. The presented results were obtained by the complex automation of calculating integrated indicators. Its components are: safety factor, depreciation rate of structures, reliability index and the residual resource of the framework. When predicting the durability of the research object the correlation dependencies are built in the form of: a fictitious function of generalized load; time function of stress; generalized function of the reserve coefficient; function of working capacity of the carcass structures; function of the reliability index. The developed algorithm for estimating the reliability of an industrial building can be adopted for use as a tool for further research. Its implementation allows accurately tracking the kinetics of the stress-strain state of individual elements and the overall framework of a particular object in the time of operation.

Earthquakes can be very strong and can lead to significant damages. Effect of earthquakes depend on seismic action characteristics (intensity, spectral composition, etc.), foundation soil properties in region of construction, design and construction quality. In seismically dangerous regions structural calculations the current design standards suppose the use of the coefficient K1, which takes account the non-linear work of construction material and the allowable damages of structures. Our research shows that a stiffening core fails in case of intensive earthquake if the walls are designed according to current design standards. Thus, plastic deformations do not occur and develop in the supporting elements at the beginning of the process, so the lowering coefficient K1 should be disregarded. As stiffening core is projected with account for the reduction factor K1, the existing reinforcement is not enough for standing the emerging stress and its failure happens followed by a redistribution of the stress to frame columns. The columns are also projected with account for the reduction factor K1 and are not able to take such an increase stress beyond design. There is destruction of column frame and complete collapse of the building. So seismic resistance of bearing structures is reduced several times. The approach to estimating K1 must be responsible, based on the latest scientific research, which sometimes could not be done according to the acting design standards.

An earthquake is a rapid highly nonlinear process. In effective normative documents there is a coefficient K1, which takes into account limit damage of building structures, i.e. non-linear work of building materials and structures during seismic load. Its value depends on the building constructive layout. However, because of the development of construction and new constructive solutions this coefficient should be defined according to design-basis justification. The article considers the five-storey building calculation on seismic impact by linear-spectral and direct dynamic methods. Our research shows that the coefficient K1 for this building is 0.4, which was calculated using nonlinear dynamic method. According to effective normative documents K1 is 0.25…0.3 for buildings of this type. Thus we get a lack of seismic stability of bearing structures by 1.5…2 times. In order to ensure the seismic safety of buildings and facilities, especially of unique objects, the coefficient K1 should be determined by calculations with sufficient scientific justification, particularly with the use of non-linear dynamic methods.