Real nonlinear diagrams of reinforcement and concrete deformation form the basis of the modern diagrammatic method for calculating reinforced concrete structures. This method allows for the most accurate consideration of the physico-mechanical and rheological properties of reinforced concrete under various modes of force loading of constructions. To extend the diagrammatic method to the calculation of reinforced concrete structures under the combined action of loads and elevated temperatures, a significant adjustment of the deformation diagrams of reinforcement and concrete is necessary. This article discusses the transition from reinforcement deformation diagrams at normal temperature to deformation diagrams under the combined action of force and temperature influences up to +500°C. At the same time, the basic physical and mechanical characteristics of the diagrams change depending on the values of the heating temperature. Changes in these characteristics are considered for two types of reinforcement – without yield point and with yield point. The results obtained provide the basis for constructing a method for calculating reinforced concrete structures under the combined action of loads and various heating modes.

A calculation model for determining level distance between cracks in reinforced concrete structures. The model is based on the generalization of the known in the F.G. Thomas hypothesis known in the theory of cracks in reinforced concrete and its generalization by V.I. Kolchunov in relation to the improved theory of deformation of reinforced concrete with cracks. The essence of the proposed generalization is that the stress state in concrete and reinforcement in the vicinity of the crack and in the area between the cracks is determined taking into account the deformation effect, which consists in the fact that at brittle fracture of the stretched concrete matrix the deformation of the crack banks is restrained by the reaction of the reinforcement bar, and the crack profile is nonlinearly curved. As a result, the relative mutual displacements of concrete and reinforcement and the level distance between cracks are determined by integrating the distribution diagrams of concrete and reinforcement strains at different locations in the block by two adjacent cracks.

Using the obtained analytical relationships for the calculation of the level distance between cracks, numerical investigations are carried out to determine the distance between cracks and the crack opening width. The obtained results are compared with the available test results of reinforced concrete structures, as well as with the results of calculation according to the methods of Russian and foreign standards. It is shown that the calculation dependences of the proposed model fully reflect the qualitative picture of the multilevel crack formation process obtained experimentally, when at discrete decrease of the crack spacing inversely proportional to the change of bending moments there is an increase in the crack opening width.

Analytical method of definition of surface considerably simplifies the following operation of design of curvilinear shell structures and shells in comparison with other methods of definition. Having used the universality of superellipses which form the family of close plane curves that are symmetrical relatively two coordinate axes, one can assume them as a three of curves of the main frame of a design surface. The three of different surfaces with identical main framework will be obtained as a result of plane-and-parallel translation of every of three superellipses along another director ellipse under condition of going of the mobile superellipse through symmetrical points of the third superellipse of the main framework. This method of formation of the surfaces gained wide distribution in many branches of building, technics, and science. In a paper, all known surfaces with main frames of three superellipses are described and illustrated by twenty-nine figures. More than nine tens of them were brought out. Some surfaces were taken as middle surfaces of thin building shells. Their stress-strain state was determined by FEM. The presented results and a list of references containing 32 names will help to find new directions in research of surfaces and shells of this type that have some advantages.

The object of research is the behavior of statically indeterminate frames under the influence of temperature. The purpose of this work is to suggest a simple algorithm for the analysis of framed structures by using the original idea of the loop resultant method. This basic loop is generated by splitting the given structure into statically indeterminate loops instead of the conventional approach of treating the redundant forces in the whole structure. The current approach allows to simplify the calculation, thanks for using the loop compatibility conditions and by dealing with the primary unknowns for each basic loop. The advantage of this presented approach is in simple structure of a system flexibility matrix: the location of zero and non-zero blocks depend only on the numbering of loops. Different types of flexibility matrices of the element-rods are established; it is shown how to build the compatibility matrix for any loops with or without hinges; and the simple algorithm of the loop resultant method is developed. Some numerical examples are performed to describe the presented algorithm in more detail.

Cross-laminated timber (CLT) is a modern multilayer material with high load-bearing capacity, which allows the construction of multi-storey buildings made of wooden structures. In the present study, the relationship between the maximum deflection and natural vibration frequency in a 3- layer CLT panel at variable values of gaps in the central transverse layer under different boundary conditions was investigated. The study has been carried out by numerical methods in the SCAD++ computer complex using the finite element method (FEM). The result of the study is the verification of the identified fundamental regularity for a CLT panel with variable gaps in the central layer. This result contributes to the development of a vibration method for quality control of building structures using CLT with similar parameters and number of layers.

The reliability (safety) of the designed structures is ensured by using the design value of the bearing capacity, taking into account the uncertainty (variability, error) of the bearing capacity. Uncertainty is taken into account by means of a probabilistic model, which is represented as a distribution law with statistical parameters included in it. The most important and frequently used statistical parameters are the mean value and coefficient of variation.

Determining the coefficient of variation for the bearing capacity calculated on the basis of numerical models (computer modeling) is an important task, since existing classical methods cannot be applied. For this reason, the purpose of this article is to develop and study the accuracy of methods for determining the coefficient of variation of the bearing capacity calculated by computer modeling. The proposed method for determining the coefficient of variation is based on the decomposition of the function into a Taylor series, followed by the use of various numerical differentiation schemes. Verification was performed on generalized nonlinear models of load-bearing capacity, for which an exact solution can be obtained using the Monte Carlo method. The practical implementation of the proposed method is demonstrated on finite element models.As the results of the performed research, it is possible to identify the actual methods for determining the coefficient of variation of the bearing capacity calculated by computer modeling, and the values of the coefficients of variation for generalized models of the bearing capacity of thin-walled elements, taking into account the loss of local stability of the web and with the subsequent inclusion of the girder flanges in the work. The value of the coefficient of variation can be most accurately estimated using Taylor series expansion and numerical integration over 3 points, however, this method requires 2N+1 calculations, therefore it can be recommended only for individual verification tasks. As a practical method for estimating the coefficient of variation, Taylor series expansion and numerical integration by 2 points should be used (N+1 calculations are required).

Аrthquakes cause horizontal and vertical accelerations of the earth's surface, which can lead to the rotation and bending of structures. Columns, as elements of building structures, are subject to seismic forces, which can cause them to twist.

Additionally, one of the most serious threats to buildings and structures during earthquakes is the possibility of fires. Therefore, the issues of studying the stability of compressed metal elements with torsion under temperature effects are very important for seismic regions. The study presents methodologies for analytical and numerical calculations to determine the stability of compressed steel elements and compressed steel elements with torsion under temperature effects.

The calculation analysis is carried out based on numerical simulation methods in the software complex ANSYS Mechanical. A model of a steel column made of S355 steel, designed as a double T-beam, was developed as the test construction. A "Transient Thermal" module type was used for conducting the thermal analysis by applying temperature loading those changes over time to the heated surfaces. The heating of the column is performed according to the standard temperature curve of the gas environment in fire conditions. For analytical calculations, programs were developed for calculations in the PC Matlab. The algorithm for analytically calculating the loss of stability of a compressed element under temperature effects is based on determining the coefficient of reduction of the modulus of elasticity and the heating temperature corresponding to the selected intermediate value of the temperature coefficient of reduced yield strength.

Comparative graphs showing the change in critical temperature due to load action in numerical and analytical calculations, as well as diagrams depicting the decrease in critical force under temperature effects, are provided.

Methodologies for numerical and analytical calculations of the stability of a compressed element with torsion under fire exposure in ANSYS and Matlab have been developed.

The study provides an analytical solution to the problem of dynamic buckling of an eccentrically compressed reinforced concrete element with eccentricities of axial force in two planes. It takes into account the initial stress-strain state formed by the preceding long-term loading with a service load. The object of the study is the columns of reinforced concrete frames of buildings and structures subjected to dynamic loading as a result of the initial local failure in the structural system. The study is based on the analytical method under the following assumptions and limitations: before the formation of cracks, the strain is consistent with the Bernoulli hypothesis; the projections of the deformed axis of the column are approximated by sinusoids; the influence of short-term loads and their variability on the formation of the stress-strain state of the column at the time of a special design situation is not taken into account; a piecewise linear law of variation in time is assumed for the load and initial deflections. A combination of viscoelastic model of aging material and modified Maxwell model with consideration of nonlinear elastic relations of stresses and conventionally instantaneous strains is utilized as a model of concrete under the considered regime loading. Validation of the adopted material model on the background of experimental data is performed.

The paper presents the solution of the problem of determining the stress-strain state of a reinforced concrete column taking into account the adopted material model under static-dynamic loading considering the influence of creep.

In Siberia the urban development along the railways and navigable rivers dominates totally. The problem of “transport-settlement” is considered on specific materials of the Angara-Yenisei macroregion of interzonal type. The construction of the North Siberian Railway will create an additional resource for improving the settlement structure of the Near North zone based on the idea of the "basic city - shift method", formed in Soviet times. The use of such forms of spatial organization of the Lower Angara region production facilities as clusters and the Middle Angara region as territories of advanced development is the characteristic of the innovative economy. This peculiarity will allow forming the framework of a settlement system founded on basic settlements formed from the existing cities.

Promising forms of transformation of the existing settlement structure of the Angara-Yenisei macroregion are proposed, which is based on the concept of forming interzonal systems providing for both external and internal centralized shift and expeditionary settlement in the north of the Irkutsk Region and the Krasnoyarsk Territory.

In the presented work, the unsteady-state temperature field in the single-layer brick building wall enclosing structure was investigated. To model the nonstationary temperature field of the building wall, the differential equation of thermal conductivity was solved by the finite difference method using an explicit difference scheme, taking into account boundary conditions of the third kind. The formula using to calculate the value of operational thermal conductivity at the known value of operational moisture of building materials is given.

For the calculations, single-layer enclosing brick structures with base thicknesses of 0.12 m, 0.25 m and 0.51 m in Moscow were adopted. The results of calculating temperatures in sections of enclosing structures over time at a thermal conductivity value selected in accordance with the regulatory document are presented. The time establishing stationary temperature field is presented. For brick walls, the time of the stationary state was determined when the outside air temperature is equal to the temperature of the coldest five-day period.

The increasing demands for the quality and reliability of concrete structures, particularly in tunnel construction, necessitate the development of modified concretes with enhanced operational characteristics. This study examines the modification of heavy concrete using a complex chemical additive, comprising a superplasticizer and a water-soluble polymer additive (Polidon-A). The research reveals that the activation process of metakaolin particles is insufficiently studied. Therefore, the investigations presented here, which aim to improve operational characteristics through the pre-treatment of metakaolin in an alkaline environment (pH=10) with a micro-reinforcing component (wollastonite), are highly relevant. The study's objective is to establish the positive effect of metakaolin activation with a complex modifier and a micro-reinforcing component on the modification of heavy concrete's structure to enhance its strength and hydrophysical properties.Object: Modified heavy concrete based on activated metakaolin with a complex modifier (superplasticizer + Polidon-A) and a micro-reinforcing component for concrete tunnel structures.

Research results: The study demonstrates the positive impact of complex modification on the properties of heavy concrete. This is achieved by reducing the cement content (binder) and replacing it with metakaolin, which is pre-activated in an alkaline environment (pH=10) with a modifier and wollastonite. This allows for an increase in strength and hydrophysical characteristics: the compressive strength at 28 days was 68.6 MPa, compared to 39.4 MPa for the control mixture; water absorption was 2.4%; and the waterproofing grade was W14. This makes it possible to use this composition in practice for the production of building products and structures with specified characteristics, operating under conditions of increased load and aggressive environment, in particular, for tunnel structures.