Axially compressed circular steel tube confined concrete columns have been parametrically analyzed through numerical simulation with the general aim to confirm the effectiveness of concrete confinement and quantitatively estimate it. Numerical models have been assembled using SIMULIA Abaqus finite element analysis commercial software and its relevant tools, in particular Abaqus/Explicit module, the general contact algorithm, and the concrete damaged plasticity model. The limit states of the first group and corresponding failure mechanisms have been defined for the considered columns and investigated, qualitatively and quantitatively, with regard to their dependence onto column structural scheme, steel tube thickness and concrete grade. Totally, 33 different cases have been simulated and analyzed.
This study investigates an experimental-analytical approach to improving the accuracy of calculating the nominal composition of heavy concrete using a database of test protocols from NEFU (2015–2025). Particular attention is paid to working with low-quality aggregates – sand with a fineness modulus below 1.4. Significant discrepancies between the calculated and actual concrete compositions were identified, reaching up to ±250 kg/m³. A corrective coefficient linking the cement-to-water ratio (C/W) with the proportion of aggregates is proposed. Its application reduced the error to ±60–150 kg/m³ and improved the convergence of results to 1.5% without loss of strength. It is shown that the strength of concrete incorporating very fine sand (fineness modulus ≤ 1.4) exhibits higher sensitivity to variations in the C/W ratio within a narrow range of 1.3–2.7. The discrepancy between calculated and actual concrete density varies widely, leading to material overconsumption and reducing the reliability of computational mix design methods. An empirical relationship has been established linking the key variable mix parameters (water-cement ratio and aggregate proportion), which can be used as a correction factor. Without the coefficient, the deviation range was 1.8–5.0%, while with its application it ranged from –0.6% to 1.5% without deterioration of concrete mixture properties or physical and mechanical characteristics.
It is noted that the curing of cement composites is impossible without effects and is a reaction to them. In this case, the forces of the resulting resistance, according to the laws of thermodynamics, are aimed at weakening the impact. Experimental prerequisites and arguments are given that by choosing the time, intensity and duration of aggressive action on cement composites during their curing, it is possible to obtain more impact-resistant or ordered and durable structures of the material. The creation of conditions for the hardening of cement composites using liquid aggressive media leads to the formation of a dense inert layer on their surface, more adapted to the effects of this type. Using temperature and humidity influences, freezing and thawing, and loads, more durable composites were obtained. Thus, the curing of cement composites using time- and intensity-determined harsh temperature and humidity conditions, freezing and thawing, aggressive liquids, and loads makes it possible to obtain more durable or resistant structures of the material to specific destructive factors.
A series of large-eddy simulations (LES) was performed to investigate the effects of computational domain size and grid resolution on flow prediction within an idealized urban street canyon. Three streamwise domain lengths were examined in combination with coarse, medium, and fine grid resolutions. The building height, H, was kept constant, and the canyon aspect ratio (street width to building height) was set to unity. Flow statistics were evaluated at the central canyon of each configuration and compared with available wind-tunnel data.The LES results indicate that the simulated mean velocity profiles agree well with experimental measurements for all cases. Both domain size and grid resolution exhibited minimal influence on the mean velocity components, suggesting that mean flow within a street canyon can be reliably predicted using a relatively small computational domain when combined with medium or fine grid resolutions. This offers a computationally efficient option for mean flow analysis. In contrast, turbulence statistics were found to be more sensitive to grid resolution than to domain size. Fine grid resolution significantly improved the prediction of velocity fluctuations and momentum transport, whereas smaller domains tended to produce less consistent turbulence results. Consequently, while small or medium domains may be suitable for mean flow assessment, they are not recommended for detailed turbulence analysis.Overall, this study highlights the importance of balancing domain size and grid resolution to obtain reliable LES results while minimizing computational cost, providing practical guidance for CFD–LES studies of urban street canyon flows.
The purpose of this work is to study the effect of synthetic polysaccharides on the structure formation and properties of lime coatings. Information is provided on the influence of synthetic polysaccharides on the structure formation of lime coatings. It has been shown that due to the water-retaining effect of the additive, more favorable conditions are created for lime carbonation. Using X-ray phase and thermographic analysis, optical and infrared spectroscopy, the presence of inter- and intracrystalline organic compounds was established, which modify the (nano)structure of newly formed calcite crystals and increase the strength of lime coatings.
The problem of controlling temperature stresses and preventing early cracking in massive monolithic foundation slabs at the stage of their hardening is considered. Existing methods often fail to account for the lag in concrete strength growth relative to the development of temperature gradients, which can lead to dangerous tensile stresses. The objective of the study is to develop a method for optimizing curing conditions aimed at minimizing tensile stress to strength ratio as an objective function. The method is based on combined numerical modeling of heat transfer and stress-strain problems, taking into account the kinetics of heat generation and concrete strength gain. The variable parameters were a coefficient determining the kinetics of concrete heat generation and the heat transfer coefficient from the upper surface of the slab. The interior point method, pattern search and particle swarm optimization were used to solve the optimization problem. Calculation results for various slab thicknesses and climatic conditions showed that to minimize the risk of cracking, it is necessary to reduce the heat transfer coefficient on the upper surface of the slab to 2.5–4.7 W/(m² °C), and to use normal- and rapid-hardening concrete rather than slow-hardening concrete. This is explained by the lag in tensile strength growth behind the development of temperature differences in slow-hardening concrete. Optimization reduced tensile stress levels by 2.2–3.3 times compared to standard conditions, making it possible to concretize slabs up to 3 m thick without the use of artificial cooling systems.
A mathematical model of thermomechanical deformation is presented for a shell with positive Gaussian curvature, made of an orthotropic composite that develops induced anisotropy during loading. The general formulation of the boundary value problems, as substantiated in a number of studies, is carried out in an uncoupled setting. The occurrence of a temperature gradient is assumed to be one-dimensional, normal to the shell surfaces. Small temperature gradients are assumed, allowing the problem to be solved in a quasi-static manner. To account for the effect of induced heterogeneity—manifested as the dependence of the deformation-strength properties of composites on the nature of the stress state—state equations formulated by one of the authors in the principal material axes of normalized tensor space are used. The developed model is implemented for the thermomechanical analysis of a single-layer shell with positive Gaussian curvature. The main solution parameters are compared with results obtained from similar problems using tested models for the theory of deformation of orthotropic materials with differing resistance proposed by other authors, as well as from the equations of orthotropic linear elasticity theory neglecting differing resistance.
Проблема автоматизированной диагностики дефектов строительных конструкций обусловлена высокой трудоемкостью и субъективностью визуальных обследований. В статье предложен прототип системы компьютерного зрения на основе архитектуры с облегченным блоком извлечения визуальных признаков (энкодером), предназначенный для бинарной семантической сегментации трещин на изображениях строительных поверхностей. Новое предложение заключается в адаптации указанной архитектуры к задаче выделения тонких протяженных объектов на неоднородном фоне с применением комбинированной функции потерь, объединяющей бинарную кросс‑энтропию и коэффициент Дайса. Приведены математическая постановка задачи, формальное описание модифицированного критерия оптимизации, методика подготовки данных с учетом артефактов JPEG‑сжатия, а также результаты вычислительных экспериментов. Полученные в работе на независимой тестовой выборке метрики значения коэффициента Дайса и индекса Жаккара (IoU) подтверждают работоспособность предложенного подхода и определяют направления дальнейшего совершенствования технологии.
This paper develops an advanced computational framework to investigate the nonlinear stability and imperfection sensitivity of hybrid three-layer timber beams, specifically composed of high-stiffness Birch faces and a relatively soft Pine core. By employing a rigorous variational energy formulation based on the principle of minimum total potential energy, the study explicitly models the complex interaction between flexural deformations and bending-induced membrane effects under large-scale initial geometric imperfections. A distinctive feature of the proposed model is the derivation of a mechanism-based energy index (η), which provides a robust mathematical criterion for identifying the transition from bending-dominated to membrane-activated structural regimes. The numerical implementation is executed via an efficient MATLAB-based algorithmic procedure, enabling a high-fidelity parametric exploration of imperfection amplitudes ranging from infinitesimal values to L/50. Comprehensive numerical results reveal that substantial geometric deviations lead to a significant "knock-down" effect on structural stability, with tangent stiffness degradation exceeding 60% in the pre-critical stage as the load increases. The analysis of shear stress gradients and interface slip distributions further highlights the susceptibility of hybrid members to local instability when membrane forces are activated. Furthermore, a topographical stability transition map is constructed to visualize the synergistic effects of interlayer slip stiffness and initial curvatures on the global buckling limits. The computational findings offer a robust theoretical basis for the safety-limit design of slender hybrid composite members in modern civil engineering applications, emphasizing the necessity of accounting for large-scale geometric nonlinearities in structural reliability assessments.
В статье представлены результаты экспериментального исследования характеристик высокопрочных самоуплотняющихся тяжелых и легких бетонов классов В60–В100 при различной относительной влажности окружающей среды. Цель работы заключалась в оценке влияния влажности среды на прочность, модуль упругости, деформации усадки и ползучести, меру ползучести и коэффициент ползучести высокопрочных самоуплотняющихся модифицированных бетонов. Испытания выполнялись по ГОСТ 24452 и ГОСТ 24544 в климатических камерах при относительной влажности воздуха 20, 60 и 90 % в течение 240 суток. Предложена формула для численного определения коэффициента ползучести, которую рекомендуется внести в ГОСТ 24544. Установлено, что снижение относительной влажности среды может приводить к увеличению деформаций ползучести более чем в 1,7 раза. Показано, что расчетная методика ГОСТ 24544 в ряде случаев завышает предельные деформации ползучести, причем в большей степени при повышении класса бетона и снижении влажности среды. Значения коэффициентов ползучести высокопрочных тяжелых и легких бетонов не превышают 1 и более чем в 2 раза ниже нормативных значений по СП 63.13330.2018 и EN 12390. Полученные результаты показали, что экспериментальное определение коэффициентов ползучести, позволит значительно повысить эффективность использования современных модифицированных бетонов при строительстве уникальных зданий и сооружений.
Above-ground storage tanks are significantly more vulnerable to damage from blast loading compared to bury or semi-buried concrete and steel tanks, primarily due to their exposed nature. To accurately assess the real behavior of above-ground tanks, it is essential to account for fluid-structure interaction (FSI) effects. Accordingly, in this study, 24 finite element models of cylindrical reinforced concrete tanks were developed in ABAQUS software and subjected to blast loading, incorporating FSI effects. The key variables considered include explosive mass, explosive distance, fluid fill level, tank wall height, and mesh size. The investigated responses encompass circumferential (hoop) stress and radial displacement. The design constraints were set as maximum allowable hoop stress (30MPa) and maximum displacement (20mm). The optimal tank was designed using C30 concrete and steel with a yield strength of 400 MPa. The tank dimensions were 15m in height and 33.85m in diameter. The explosive mass and explosive distance were set at 1000kg and 10m, respectively. The objective function was to minimize the tank weight while simultaneously satisfying the stress and displacement constraints. Using the Particle Swarm Optimization (PSO) algorithm, the minimum weight of the cylindrical reinforced concrete tank was determined to be 23933kN, which was achieved after approximately 25 iterations.
Modeling the transport and sedimentation of small particles of suspensions and colloids in porous rocks is an important problem in subsurface hydromechanics. Particles entrained in fluid are transported and retained in the rock pores. The filtration process is determined by the number and size of pores and is characterized by porosity—the ratio of the void volume to the total soil volume. In homogeneous materials, porosity can be considered constant. However, in practical problems describing filtration of suspended particles in multilayered and heterogeneous soils, the rock porosity is variable, and a constant-porosity model is inapplicable. A one-dimensional model of suspension and colloid filtration in a porous medium with nonuniform porosity is considered. The problem includes a mass balance equation accounting for variable porosity and a kinetic equation for sediment growth. The model describes the injection of a suspension or colloid of constant concentration into a porous medium containing pure water without suspended or sedimented particles. Unlike the case of uniform porosity, the transport velocity of suspended particles in pores is variable, and the boundary between the suspension and pure water, called the concentration front, is curved. Previously, such problems were solved only numerically. In this article, a system of filtration equations in a medium with variable porosity is solved analytically using the method of characteristics. An explicit formula is obtained for the curved front of suspended and sedimented particle concentrations, and exact analytical closed-form solutions are constructed ahead of and behind the front. An explicit solution is found for a model with a linear filtration function.
This paper presents the flexural strength of precast three-layer reinforced concrete structures made from different types of concrete. The three-layer reinforced concrete structure consists of an outer layer of ordinary concrete with strength grades from B12.5 to B30 and an inner layer of lightweight polystyrene concrete. Experiments involving the fabrication of 150x150x150 mm concrete samples using two different materials – B25 normal concrete and B0.75 polystyrene concrete showed that when two layers are poured consecutively with a rest time of less than 2 hours, a contact layer forms between the two materials. This contact layer has a structure with decreasing density from the outer layer using normal concrete to the inner layer using lightweight concrete with low compressive strength. This paper proposes a method for calculating the flexural strength of precast three-layer reinforced concrete structures accounting for the continuous variation in the compressive strength of the contact layer. Calculation results for the load-bearing capacity of three-layer reinforced concrete beam specimens using traditional methods, proposed methods, and experiments have shown that considering the contact layer in the bending behavior of three-layer reinforced concrete beams yields results closer to experimental values than traditional methods. Increasing the thickness and characteristics of the contact layer increases the structure's load-bearing capacity by up to 1%. When the compressive strength of the outer concrete layer is increased from B15 to B25, the load-bearing capacity of the structural plate can increase by up to 59%. When the compressive strength of the inner concrete layer is increased from B5 to B15 while keeping the outer layer's concrete type unchanged, the load-bearing capacity of the three-layer structure can increase by up to 40.1%. The proposed method for calculating three-layer reinforced concrete structures with different materials, accounting for the material properties of the contact layer, accurately captures the phenomena observed during the practical fabrication of such structures.
In this paper, the influence of traveling waves arising from external action on the filtering process of aqueous solutions in the expanded loading layer is investigated. A three-dimensional dynamic generalized model of fluid motion in a porous medium under a nonlinear external influence is used as the primary mathematical model. A model describing traveling waves is obtained. Nine particular cases of this model with three types of nonlinearity process of filtering are examined: power, exponential, and logarithmic. The external influence is also selected power, exponential, and logarithmic. The particular models describe both expansion and contraction of the loading layer on the type of filtration nonlinearity, the type of external influence, and the traveling wave parameters. For filtering with the expanding loading layer we found the time at which maximum it's expansion is achieved. When the loading layer contaminates we found the time at which it will be destroyed.
This paper presents an analytical method for the calculation of compressed-bent reinforced concrete (RC) columns subjected to emergency transverse impact, characteristic of relevant anthropogenic hazards such as collisions with vehicles or other impacting objects. The proposed approach accounts for two primary failure mechanisms: flexural failure and diagonal shear failure, and enables the assessment of the ultimate horizontal load capacity, considering the dynamic strengthening of both concrete and reinforcement. The method is based on constructing ultimate capacity curves, which reflect the relationship between the maximum lateral force and the applied axial compressive force. It also introduces coefficients for the confinement of transverse deformations and parameters for the load intensity resisted by the transverse reinforcement. Particular attention is given to modeling the confinement effect on concrete, the influence of the pitch, diameter, and grade of the transverse reinforcement, and the potential for preventing progressive collapse. The proposed methodology serves as an effective tool for analyzing the robustness of buildings and structures under emergency mechanical impacts of anthropogenic origin. The developed approach can be applied in designing preventive measures to enhance column resistance against transverse impacts and contributes to the evaluation of the mechanical safety level of RC structures. This is especially important for columns with high slenderness and for elements with various types of initial or acquired damage.
Protecting existing underground structures in urban areas from adverse impacts caused by surface construction activities is a significant challenge, especially when applying the open-cut sequential excavation method. This paper proposes a simple analytical method to determine the deflection of the tunnel axis induced by the sequential excavation of the overlying excavation pit segments. The method is based on identifying the changes in soil stress at the tunnel cross-section during each construction stage, followed by using analytical techniques to determine the corresponding tunnel deflection. The tunnel-soil interaction is modeled by an Euler-Bernoulli beam on an elastic foundation represented by the Winkler model. Furthermore, the paper investigates the influence of segmental excavation length on the tunnel deflection. The results show that with excavation step lengths of 3.6 m, 7.2 m, and 14.4 m, the maximum tunnel deflection increases by 135% and 193%, respectively. These results provide a basis for optimizing construction methods, minimizing risks, and effectively protecting underground structures.
In the context of increasing wear and tear of utility pipelines, improving the quality of diagnostics of their technical condition, as well as improving the quality of control over construction and repair work, is of particular importance. Timely detection of defects and damage helps prevent emergency situations and negative socio-economic and environmental consequences. Traditional methods of visual and instrumental control have a number of disadvantages, in particular, high labor intensity, long information processing time, and insufficient accuracy. This problem can be solved by using computer vision to identify and classify damage, which will improve the quality of defect detection, reduce the likelihood of human error, and speed up the diagnostic process. However, different levels of readiness of the developed machine learning algorithms require additional research to confirm the effectiveness of their use in professional fields, for example, when inspecting structures, which justifies the relevance of this study. The object of the study was the YOLO family of computer vision models capable of identifying various classes of defects. The aim of the study was to train the YOLOv5, YOLOv8, and YOLO11 detection algorithms and to perform a comparative analysis of their speed and accuracy of data processing using weld defects as an example. The results of the experimental studies show that the use of the latest version of the model does not lead to significant improvements in the quality of defect detection compared to previous versions. The results presented in the work allow us to assess the feasibility of using the new YOLO11 model to detect defects in radiographic images. Based on the experiments, researchers using computer vision methods to control the quality of welds can make an informed decision about whether to use this model or use previous versions of the algorithms.
This article presents numerical modeling results of prognosed dynamic response for load-bearing structural elements of constructing business complex building to railway transport vibration excitation. The transport vibrations are measured on existing pile foundation heads. The obtained response vibration acceleration evaluated by its spectra in accordance with Russian sanitary normative document.
The main regional features of subsidence clay soils common in Mongolia are high porosity, low humidity and underfilling within the seasonal deep freezing due to their heaving and sublimation loosening. Using such soils as foundations for buildings and structures under conditions of increasing humidity is difficult at the design and construction stages, as well as during operation. This paper examines the results of analytical calculations to identify the dependence of a decrease in the physical and mechanical properties of subsidence soils on an increase in humidity and constructs the corresponding dependence graphs. Numerical modeling of the quantitative and qualitative assessment of the subsidence properties of sandy loam and loamy soils using the method of indirect signs and the probability of the formation of a subsidence process during soaking is also carried out.
In the process of designing buildings and structures, the issue arises of ensuring their mechanical safety under accidental loads. Furthermore, existing buildings and structures are often subjected to technogenic impacts that may lead to complete or partial failure of the structural system. To provide a quantitative characterization of the resistance of load-bearing structures to such factors, the concept of survivability has been introduced in the modern scientific literature. However, the formalization of survivability in the form of specific quantitative indicators remains a pressing and insufficiently explored problem for both steel and reinforced concrete structures. This study proposes a methodology for computing the probabilistic survivability index for frame structural systems. The calculation is based on a modified model of classical reliability theory, which assumes that the failure of the frame system occurs through the formation of a mechanism with a minimum number of plastic hinges. The assessment of structural failure or component degradation is performed on an energy basis using the J-integral. To analyze the scatter of random parameters, statistical modeling based on empirical data is employed. The article provides examples of survivability index calculations. Practical implementation of the proposed method has demonstrated its effectiveness, allowing it to be recommended for evaluating the mechanical safety of steel and reinforced concrete frame structures, including cases with increased responsibility requirements and specific robustness criteria against progressive collapse.
