"Вестник МГСУ"

The basic problem of structural mechanics, namely the problem of pile shock loading sunk in a foundation, has been examined in an axisymmetric approach within defining relations for irreversible deformations offered earlier in the space of deformations. As a model of the theory of plasticity, the Mises model generalized by the authors has been accepted, the use of which solves a nonstationary system of nine two-dimensional equations with various entry and boundary conditions. Enlightened attitudes use approximate engineering approaches which allow estimating the behavior of a pile-foundation system. A solution is constructed mainly with the use of the theory of linear-elastic continuum. However they do not enable to consider various peculiarities of deformation behavior of soils and pile materials and to give an appropriate detailed picture of a system mode of deformation. Mechanical peculiarities of the behavior of foundation and pile materials discovered recently demand more enlightened attitudes to analyze a mode of deformation in a pile-foundation system considering both plasticity and fracture. The offered approach enables to give a complete picture of a mode of deformation in a pile-foundation system at any time and a picture of occurrence and development of plasticity and fracture zones.

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.

Criteria of plasticity and durability derivative of standard indicators of plasticity (δ, ψ) and durability (σ
_0,2, σ
_B) are offered. Criteria К
_δψ and К
_s follow from the equation of relative indicators of durability and plasticity. The purpose of the researches is the establishment of interrelation of derivative criteria with the Page indicator. The values of derivative criteria were defined for steels 50X and 50XH after processing by cold, and also for steels 50G2 and 38HGN after sorbitizing. It was established that the sum of the offered derivative criteria of plasticity and durability С
_к considered for the steels is almost equal to unit and corresponds to a square root of relative durability and plasticity criterion C
^0,5. Both criteria testify to two-unity opposite processes of deformation and resistance to deformation. By means of the equations for S
_к and С it is possible to calculate an indicator of uniform plastic deformation of σ
_р and through it to estimate synergetic criteria - true tension and specific energy of deformation and destruction of metal materials. On the basis of the received results the expressions for assessing the uniform and concentrated components of plastic deformation are established. The preference of the dependence of uniform relative lengthening from a cubic root of criterion К
_δψ, and also to work of the criteria of relative lengthening and relative durability is given. The advantage of the formulas consists in simplicity and efficiency of calculation, in ensuring necessary accuracy of calculation of the size δ
_р for the subsequent calculation of structural and power (synergetic) criteria of reliability of metals.

The authors draw attention to possible problems in the process of construction and operation of monolithic frame buildings, construction of which is now widespread. It is known that cracks can often appear in the facade and side walls. The size of the cracks can exceed the allowable limits and repair does not lead to their complete elimination. Also cracks significantly mar the appearance of a building. Thus, the relevance of this study lies not only in fuller understanding of the operation of walls, but also in the ability to prevent undesirable effects.The authors calculated temperature effects for boundary walls of the building blocks made of heavy concrete. The original dimensions of the walls conformed to a grid of columns for the majority of residential and public buildings.The stress-and-strain state of the walls in case of temperature changes is observed in detail, including the transition from sub-zero to above-zero temperatures within the same section (wall). It was revealed that the temperature variations within the established limits may cause stress-and-strain state in the walls, in which the temperature tensile stresses can exceed the tensile strength of materials. The article contains effective means of reducing thermal strains, which can prevent temperature and shrinkage cracking.

In the article, the authors describe the principal findings of the experimental study of destruction of spatial frames made of closed-profile steel rods. Six samples of frames were tested through the application of a kinematic loading scheme. Values of forces, displacements and deformations were measured over the time. Each sample was brought to the state when the load reached its maximal value. Thereafter, the load intensity was reduced to 0.6...0.7 of its maximal value. It was identified that the destruction of rods in the event of combined stress was similar to the formation of plastic hinges in the course of regular bending. In some cases, cracks were formed in the zones of plastic hinges. This process did not cause complete destruction of frames.
Destruction-related conditions were also assessed by the quasi-rigidity method implemented in STARK ES 2009 software package. The input data were used to perform failure, bending and torsion tests of steel pipes. The experiments and calculations have proven that in this case the process of destruction can be considered in accordance with the limit equilibrium method by taking account of formation of spatial plastic hinges. The quasi-rigidity method can be employed to identify the maximal load that the frames can bear.

Corrosive actions generate degradation of the bearing capacity of reinforced concrete elements of buildings and structures during their operation. Chemical corrosion occupies significant place among this actions. As a result of chemical reactions we evidence the change of mechanical characteristics of concrete and steel. In this paper the investigation of the problem is based on rheological equation of concrete state. In case of one-side contact of concrete with the environment layerwise chemical corrosive damages were educes. The author estimated the influence rate of chemical corrosive damages of concrete on its resistance. The dissipation of energy in compressed zone of corrosive-damaged beam is estimated. This estimation is related to the logarithmic decrement of damping under corrosional damages. The author considers. In the process of resistance of a structural element with a degrading module of total deformations equilibrium is only possible in case of increasing deformations and flexures. Account for this fact is important in the estimation of bearing capacity with the help of deformation criteria.

The primary objective of the research is the synergetic reliability of perlite-reduced structural steel 09G2FB exposed to various thermal and mechanical treatments. In the aftermath of the above exposure, the steel in question has proved to assume a set of strength-related and plastic mechanical properties (σσδ and ψ).
On the basis of the above, an equation is formed\[{{{\sigma }_{\Tau }}}/{{{\sigma }_{\Beta }}+{\delta }/{\Psi }\;=}\;={{\left[ {\left( 1+{{\delta }_{}} \right)}/{\left( 1+{{\delta }_{\Rho }} \right)}\; \right]}^{{1}/{\Psi }\;}},\] and its solution in respect of the uniform component ${{\delta }_{\text{P}}}$ is used to generate the expression \[{{\delta }_{\Rho }}={{\left[ {\left( 1+\delta \right)}/{{{}^{\Psi }}}\; \right]}^{0,5}}-1\]and, hence \[{{\Psi }_{\Rho }}={{{\delta }_{\Rho }}}/{\left( 1+{{\delta }_{\Rho }} \right)}\;.\] To use the synergy criteria, the following expression is applied: \[{{S}_{\Beta }}={{{\sigma }_{\Beta }}}/{\left( 1-{{\Psi }_{\Rho }} \right)}\;,{{S}_{\operatorname{K}}}={{\sigma }_{\Beta }}\left[ {1+\Psi }/{\left( 1-{{\Psi }_{\Rho }} \right)}\; \right],\] as well as the following expression of specific uniform and a specific limit energy :
\[{{W}_{\Rho }}=0,5\left( {{\sigma }_{\Tau }}+{{S}_{B}} \right)\ln \left[ {1}/{\left( 1-{{\Psi }_{\Rho }} \right)}\; \right],{{W}_{C}}=0,5\left( {{\sigma }_{\Tau }}+{{S}_{K}} \right)\ln \left[ {1}/{\left( 1-\Psi \right)}\; \right].\]
\[{{K}_{}}={{{W}_{C}}}/{{{S}_{T}}}\;,G={{{W}_{}}}/{{{W}_{C}},}\;{{K}_{a}}={{{W}_{C}}}/{{{A}_{C}}}\;,\]where static viscosity is calculated according to:\[{{}_{}}=0,5\left( {{S}_{\operatorname{K}}}-{{\sigma }_{\Tau }} \right)\ln \left[ {1}/{\left( 1-\Psi \right)}\; \right].\]
The secondary objective of the project is the identification of the steel brittleness threshold to assure controlled rolling and application of the above steel in construction.

The author proposes original grounds for the classification of the full range of soil masses as a supplement to the classification of soils provided in GOST 25100—2011. The author proposes four classes of soil masses, each class having several types and sub-types of soils. The classification will improve the accuracy of engineering and geological surveys and computer models of the geological environment developed for the purpose of design of buildings and structures. The author offers a classification of soils to identify the geological environment comprising one or more types of soil which are genetically and structurally distinct. Any soil mass type differs by its origin, and, as a consequence, its internal geological structure, stress-strain state and inherent geological processes. Any genetically isolated type of soils a specific program of research, both in terms of methods and in terms of density testing in the point of sampling. The behavior of rock masses together with the engineering structure is pre-determined by the properties of the rock, its relative position (geological structure), a network of cracks and other weakening factors, and the natural state of stress. The fracture network is of paramount importance. Cracks are characterized by direction, length, width, surface roughness of walls, and a distance between parallel cracks.

The most typical types of crane substructures destruction are wear of crane rails, details of its fixation, deformation of crane beams, settlement or tilting of the columns. At technical examination of buildings and structures with crane rails their planned-high-altitude position is determined. There exist a list of methods for determining the crane rails’ planned-high-altitude position, each of them has its disadvantage, expressed in the final result - the real position of crane rails. While estimating their position from the ground, i.e. mounting transit on the ground, and indicating devices above, there is an inaccuracy on the rails, which is caused by different moments of indications fixation, both on the plan and hightwise. The authors carried out observations of the position of craneways both on the plan and heightwise for determining the reason of craneways bearing structures’ deformations and the period of their influence of railtrack state. The results of these observations are analyzed and presented. The authors present their suggestions on advancing the crane operation, which will increase its operation life.

Introduction. The possibility of determining the relative deformations of fine-grained concretes based on sulfate-resistant cement was formulated by testing samples of gypsum-cement-sand mixture in distilled water in accordance with the requirements of the Vietnamese standard TCVN 6068:2004. Objective - to determine the deformations of fine-grained concrete because of sulfate-resistant Portland cement in accordance with the requirements of the TCVN 6068:2004 standard to assess its resistance to corrosion in an aggressive sulfate medium. Materials and methods. To obtain a gypsum-cement-sand mixture, a finely disintegrating binder was used, consisting of sulfate-resistant Portland cement of the type CEM I CC 42.5 N produced by the “Tam Diep” plant with the addition of natural gypsum produced by the company “Dinh Vu”. Quartz sand was used as fine aggregate. All raw materials used were native to Vietnam. Grinding fineness, normal cement density, setting time, the uniformity of the volume change and the activity of sulfate-resistant Portland cement were determined according to GOST 30744-2001; deformations of samples from gypsum-cement-sand mixtures - according to the Vietnamese standard TCVN 6068:2004. Results. Investigated the relative increase in the volume of samples of gypsum-cement-sand mixture based on sulfate-resistant Portland cement and natural gypsum as a result of their testing in distilled water according to the standard TCVN 6068:2004. Conclusions. Found that the average value of the relative deformation of the prism samples of concrete as a result of a 14-day test in distilled water was 0.037 %, which is within the acceptable value of 0.04 % in accordance with the requirements of the Vietnamese standard TCVN 6067:2004. Therefore, sulfate-resistant Portland cement type CEM I CC 42.5 N produced by the “Tam Diep” plant is a promising material as a binder for the preparation of corrosion-resistant concrete. The increase in the mean values of the relative deformations of the gypsum-cement-sand prism specimens after the 28-day and 60-day of testing, compared to the results of the 14-day test, can be explained by a slightly increased content of tricalcium aluminate in the studied cement.