Introduction. This article presents the results of an experimental determination of the creep coefficient of glass-composite pressure pipes using long-term testing over 10,000 hours in accordance with GOST R 55077-2012. The relevance of the study is driven by the requirements of current Russian construction legislation: under the Town Planning Code of the Russian Federation and SP 35.13330.2020, the normative service life of pipeline structures is not less than 50 years, which necessitates mandatory substantiation of the long-term mechanical properties of the material. The aim of the present work is the experimental determination of the moisture creep coefficient for a control specimen of a continuous-winding glass-composite pipe and the prediction of creep coefficients over a 50-year horizon Materials and methods. The objects of study were segments of glass-composite pressure pipes of grade Dy 1000 0.6 10000, manufactured by continuous filament winding of glass roving onto a cylindrical mandrel. The control formulation contained no plasticizer; the modified formulations incorporated additives PolyPlast M, Polyplex, and Clearstrength XT100 at dosages of 10, 15, and 20% by binder mass. Long-term specific ring stiffness under creep conditions was tested in accordance with GOST R 55077-2012 (GOST 34644-2020). Specimens were placed horizontally and fully submerged in water (temperature 23±2 °C, pH = 7±2), then loaded with a diametral compressive force maintained constant throughout the entire test period of 10,000 hours. Ring deflection was measured at specified time intervals. Two specimens were tested for each formulation and the results were averaged. Results. For the control formulation of pipe grade Dy 1000 0.6 10000, the mean moisture creep coefficient αavg = 0.74 over a 50-year horizon was determined by regression analysis in logarithmic coordinates. To predict the behaviour of nine modified formulations containing plasticizers PolyPlast M, Polyplex, and Clearstrength XT100 at dosages of 10, 15, and 20%, the theoretical framework of A.A. Askadsky's molecular-kinetic theory was applied, based on the Boltzmann–Volterra integral equation with relaxation kernel T₁(τ). The method was verified against the control specimen: the coefficient of determination R² = 0.97, and the deviation between calculated and experimental load values does not exceed 0.28%. Predicted creep coefficients α₅₀ and long-term specific ring stiffness S50 were computed for all modified formulations. Conclusion. All investigated formulations satisfy S₅₀ > 5000 N/m² and comply with the 50-year normative service life requirements under current Russian legislation. The Askadsky method yields a more conservative prediction compared to the GOST method — from −3.4% to −18.4%

The influence of supramolecular structures on the optical characteristics of polymers is considered. Studies of fluorine-containing acrylic polymers with fluorine-containing electro-optical chromophores in the side chain have shown that they should have a fibrillar supramolecular structure. The preservation of the fibrillar structure determines the technical condi-tions (temperature range) for the operation of high-speed integrated optical modulators and switches. The polymers con-sidered in the work were divided into three types according to the degree of polarization kp: polymers for which kp1 = 1.39; polymers with kp2 = <1.17>; polymers with kp3 = 1.003. To calculate nonlinear optical characteristics, the Jepsen equation was used. The possibility of calculating the polarizability of a polymer x from experimental values of the dielec-tric constant εexp is shown. The approach being developed can be used in medicine and biology to analyze the functioning of neurons (tubulin protein) and identify the causes of age-related changes in human memory. The latter is due to plastici-zation of tubulin and disruption of its fibrillar structure over time at brain temperature.

The main method for assessing the seismic resistance of buildings in the standards of most countries is the linear-spectral method. This method allows for the calculation of the spatial model of a building for seismic load in the elastic range without resorting to direct integration of the equations of motion. Nonlinear characteristics of reinforced concrete structure materials are usually considered integrally using the reduction factor. However, the values of this factor in the Russian standards are not sufficiently substantiated, as the later studies show. To determine the coefficient of permissible damage (reduction factor), six reinforced concrete frames were considered, with different parameters such as span length, number of spans, and number of floors. The design parameters of beams and columns (section sizes, reinforcement, etc.) were preliminarily selected based on the calculation using the linear-spectral method. In the second stage, numerical modeling was carried out in the OpenSEES PC to implement the pushover analysis procedure. Then, the coefficient of permissible damage was estimated by processing the capacity curves obtained on the basis of nonlinear static calculation. The value of the sought coefficients is practically not affected by the number of stores of the frame; however, with an increase in the number of spans, the coefficient K1 increases, which is explained by a decrease in the plasticity of the system. On average, for the frames under consideration, the coefficient K1 was 0.526, which is 1.5 times greater than the coefficient proposed in modern Russian standards, K1 = 0.35. The results obtained on the basis of pushover analysis are compared with the coefficients K1 determined through the values of the average degree of damage (d) of the buildings according to the modified seismic scale MMSK-86. For various types of reinforced concrete frame buildings, K1 = 0.51 was obtained. It is recommended that the coefficient K1 for reinforced concrete frame buildings should be increased to a value of at least K1 = 0.5 in the Russian standard.

Each building and structure are a complex technical system with predetermined technical parameters that must be monitored throughout the entire life cycle. The purpose of the study is to develop a methodology for quantitatively assessing the technical condition of load-bearing systems of buildings to improve their structural safety and operational suitability. The dependence of the actual wear of a building on the period of natural oscillations is determined based on the theory of predicting the risk of an accident, which allows determining an increase in the period of natural oscillations of load-bearing systems of buildings to assess the category of their technical condition. The limits of increase of the period of natural vibrations of bearing systems of buildings are defined. They allow quantitatively estimate the category of the technical condition (0-4% - normative technical condition, from 5-10% - serviceable, from 11-49% - limited serviceable, 50-95% and higher - emergency).

The purpose of the presented study is to determine and mathematically model the reliability of a steel truss with different variants of local failures of rod elements due to corrosion processes. In order to achieve a quantitative reliability assessment, the truss structure is considered as a combination of subsystems containing relatively small groups of rod components. Numerical calculations of truss structures taking into account the influence of corrosion have been carried out. It is shown that the components of the truss system can change their state by different schemes. The transition from one state to another depends on the level of stress state, which is caused by corrosion effects. It is easier to visualize this in a binary system. The probability of failure-free performance of rod components over the operating time can be written in vector form. By the matrix analysis method, failure states and functional states can be determined. As an example, a 5-bar structural system of a metal staircase type truss is considered.

The consequences of destructive earthquakes show that the problem of analyzing the response of reinforced concrete frames under seismic loads after a fire is relevant. The calculation models used for individual elements and buildings as a whole must take into account the nonlinear properties of concrete and reinforcement. In the spectral calculation method, the nonlinear properties of materials are taken into account by introducing a reduction coefficient to the elastic spectrum. When determining the reduction coefficient, a common deformation criterion is based on the use of the plasticity coefficient. The seismic resistance of a three-span, five-story reinforced concrete frame under four different fire exposure options is considered. The residual strength and stiffness of frame elements after a fire is assessed by performing a thermal engineering calculation in the SOLIDWORKS software for a standard fire. For the central sections of the elements, the highest temperatures were obtained after heating—during the cooling stage. The reduction coefficient is estimated by performing a nonlinear static analysis of reinforced concrete frames in OpenSees and constructing load-bearing capacity curves. Fracture patterns and damage levels in plastic hinges are analyzed. Based on the numerical modeling of reinforced concrete frames after exposure to fire, it was revealed that the most dangerous scenario is the occurrence of a fire on the first floor of the building. Based on the obtained plasticity coefficients, reduction coefficients were determined in the range of 2.62 to 2.44. The influence of fire on the permissible damage coefficient of a reinforced concrete frame is assessed using the coefficient φK—the coefficient of additional damage after a fire, which is equal to the ratio of the reduction coefficients for the control and fire-damaged frames. Depending on the percentage of damaged structures on the first floor, the following values were obtained: 50% or less—φK = 1.09; 100%—φK = 1.17. The obtained coefficients are recommended to be used when assessing the seismic resistance of a reinforced concrete frame after a local fire.

This article addresses a second-order differential equation containing a Gerasimov-Kaputo fractional differentiation operator of order less than two. The Neumann problem is formulated for this equation. A system of eigenfunctions and eigenvalues for the considered homogeneous boundary problem of the second kind is found. A conjugate boundary problem for the Gerasimov-Kaputo fractional derivative is introduced. A biorthogonal system is obtained that is orthogonal to the found system of eigenfunctions. Visualizations of the eigenfunction system, biorthogonal system, and an example of eigenvalue distribution on the real axis are provided.

A new approach to assessing the degree of damage to buildings during earthquakes using statistical modeling is proposed. Using the Monte Carlo method, synthetic databases with specified statistical characteristics of damageability of reinforced concrete frame buildings were obtained. After transforming the elements of these databases, new statistical characteristics of damageability were obtained with variation coefficient values less than 0.30. The research results can be used to determine the seismic load calculation through the permissible damage coefficient.

This paper is devoted to the spectral analysis of one class of integral operators, associated with the boundary-value problems for differential equations of fractional order. In particular, we show the positive definiteness of studying operators, which makes it possible to select areas in the complex plane where there are no eigenvalues for these operators.

Investigations carried out in recent years on the development of models and computer programs for predicting and analyzing the physical properties of polymers are described. The method for constructing diagrams of compatibility of water permeability and the glass transition temperature, density, the thermal expansion coefficient, the cohesion energy, etc. is analyzed. Computer synthesis of network polymers and the possibility of predicting the thermal expansion coefficient of materials based on polyvinyl chloride and the elastic modulus of composites with a number of aromatic polymers are considered. The effect of a solvent (plasticizer) on strength and viscosity is analyzed. Considerable attention is paid to the use of self-oscillations excited during deformation of polymer films in actuators of nanomechanical devices. The calculation of the viscosity of dispersions of spherical nanoparticles with an adsorption polymer layer in a polymer melt and in a low-molecular liquid is carried out. The principles of predicting the coefficients of molecular packing of amorphous-crystalline polymers and their solvents are stated, and the influence of the chemical structure of heat-resistant thermoplastics on friction against steel is also estimated.

Static calculations of experimental models in an elastic formulation were carried out, and the regularities connecting the dependences of forces in the calculated cross-section of punching out from the main structural parameters of contacting elements (reinforced concrete slabs and pylons) and from the used concrete class were revealed. This article concerns the safety issues of reinforced concrete slabs under punching with different ratios and combinations of pylon and slab thickness parameters, as well as concrete strength. The objectives of the research are consideration of the fracture pattern of reinforced concrete monolithic slabs due to punching shear; comparative analysis of modern normative calculation methods and flat reinforced concrete slabs due to static punching shear; finite element modelling and analysis of the punching shear calculation results for reinforced concrete floor slabs; and the force distribution over the area of the contacting elements-saw and floor slab. The practical significance of the results lies in the use of the obtained forces in the contacting elements for the calculation and design of reliable structures of beamless floor slabs.

The stress-optical coefficient C σ of copolymers based on cured epoxy resins has been calculated. Calculations were made for epoxy resins based on bisphenol A and aliphatic and aromatic diamines. The C σ values are in the range of 91.6÷103 weight percent. All calculations were carried out using the Cascade computer program (developed by INEOS RAS). The investigated structures of cured epoxy resins are obtained from industrial components. High C σ values make it possible to confidently use the mentioned network polymers in the photoelasticity method, from which models of full-scale building structures can be made.

In this study, we obtained a system of eigenfunctions and eigenvalues for the mixed homogeneous Sturm-Liouville problem of a second-order differential equation containing a fractional derivative operator. The fractional differentiation operator was considered according to two definitions: Gerasimov-Caputo and Riemann-Liouville-Visualizations of the system of eigenfunctions, the biorthogonal system, and the distribution of eigenvalues on the real axis were presented. The numerical behavior of eigenvalues was studied depending on the order of the fractional derivative for both definitions of the fractional derivative.

The main problem of reducing the reliability and durability of reinforced concrete structures is the corrosion of concrete and reinforcement of operated buildings and structures. Calculation of structures made of reinforced concrete, taking into account environmental influences, is complicated by the stochastic nature of the parameters of corrosion processes. The conducted studies are aimed at solving the problem of improving the methodology of the probabilistic approach to the calculation of corrosion-damaged reinforced concrete elements. The article considers a probabilistic assessment of reliability for the most common bent reinforced concrete elements, taking into account corrosive wear and the time factor. The modeling of the effect of corrosion processes on the stress-strain state of a reinforced concrete element was carried out using the concrete deformation diagram, which takes into account the decrease in strength characteristics with an increase in the concentration of an aggressive medium in concrete. The scheme of propagation of an aggressive environment in concrete is adopted according to the diffuse front method. Corrosion processes in reinforcement were taken into account by reducing the effective cross-sectional area of reinforcing bars. The change in the properties of steel (its embrittlement) with an increase in the concentration of an aggressive medium was not taken into account. Reinforcement corrosion was simulated after the incubation period, after the concentration of the aggressive medium on the surface of the reinforcing bars reached a critical value. The determination of the moment of the onset of the limit state in the element was carried out on the basis of a nonlinear deformation model at each point of the section of the element to achieve the maximum possible tensile or compression strains in concrete and reinforcement. To solve the problem of reliability assessment, the method of statistical modeling implemented in a specialized software package was used. To apply this method, according to previous studies, the probabilistic parameters of all random variables were taken: mathematical expectation and standard deviation. Based on the results of the reliability assessment, graphs of the decrease in the reliability of a bent reinforced concrete element from the time of exposure to an aggressive environment were obtained.

A model was proposed for constructing the diagrams of compatibility of the water permeability of polymers with their physical characteristics such as van der Waals volume, density, glass transition temperature, intense thermal degradation onset temperature, and cohesion energy. A computer program that allows constructing such diagrams in automatic mode was developed. It was shown that, for polycarbonates, there exist a huge number of structures with relatively low water permeability. The choice of structures with high water permeability is significantly limited. For substituted polystyrenes the number of structures with both high and low water permeability is limited. The reason is that the repeating units of polymers of this group are synthesized from two basic fragments, while those for the rest of the polymers, from five or more basic fragments.

The method for estimating the influence of polar groups on the temperature of the onset of the intense thermal degradation of polymers under heating is proposed. This estimate is based on the equation for calculating this value for the entire repeating link proposed earlier [1-4]. The method is computerized and is included as an integral part of the computer program "Cascade" (INEOS RAS). The calculated estimation is carried out for one of the structures of the rejected cycloaliphatic epoxy resin. The most "weak" group was the group –CO–. The temperature of the onset of intensive thermal degradation of this group is 547 K.

Introduction. The general corrosion model, made for reinforced concrete structures, must include the initiation of environmental influences such as carbonation, cracking and chloride ion penetration. It depends on the rate and degree of corrosion, corrosive effects in reduced areas, as well as the lower strength of bond between pre-stressed and unstressed reinforcement bars and concrete. The majority of earlier studies were focused on one-dimensional diffusion problems with an assumed constant corrosion rate. Materials and methods. In the aftermath of general corrosion, localized corrosion is accompanied by a release of hydrogen and alkaline water, chlorine ions. Crack propagation in reinforcement wires is calculated using the transient finite element software for chloride diffusion, which is time-dependent. Results. In most cases, the diffusion equation does not have a closed form solution, and therefore, the finite difference method can be used. The authors have shown that the corrosion rate decreases with time if current density has different water-cement ratios. If the water-cement ratio increases, the corrosion rate increases, as well. Conclusions. In a pre-stressed reinforced concrete beam, the corrosion of one bar affects the total corrosion of all bars and the reduction in the cross-sectional area of bars that does not exceed 15 %.