Stress-strain State Of Structures Research Articles

High performance modeling of the stress-strain state of thin-walled shell structures with the use of deep learning

Computer modeling is one of the most common approaches to the analysis of thin-walled shell structures stress-strain state analysis. It requires considerable time costs and high-performance hardware, especially when it is necessary to conduct a comparative analysis of various shell configurations. In this paper, we propose the use of deep learning methods to improve performance of this process. The purpose of work is to develop methods for high-performance computer simulation of thin-walled shell structures using deep neural networks, allowing to take into account geometric and physical properties of the structure as well as the load applied to it. A training approach and deep neural network architecture were developed to perform computer modeling of the stress-strain state of the shell. To form a training dataset, a computational experiment was carried out to simulate 3904 different configurations of doubly curved shallow shells that differ in linear dimensions, curvature radii, and materials used. Based on this dataset, 30 deep neural networks with different architectures were trained. To determine the optimal architecture in terms of modeling accuracy, mean absolute percentage error with clipping near-zero samples was calculated for each of the neural networks based on the test dataset. A network has been developed that allows calculating the stress-strain state of different shell configurations under an arbitrary uniformly distributed load. This is the first solution in the field of shell neural network modeling that allows us to vary the applied load, geometric and physical parameters of the shell and obtain calculation results at an arbitrary point of its middle surface. Performance measurements were carried out which show that the developed neural network allows simulating the stress-strain state of a shell structure 2117 times faster compared to the duration of solving the same problem by classical simulation. The modeling error using the network is at an acceptable level. An original architecture of a neural network for modeling the stress-strain state of shells was proposed which, through minor modifications, can be adapted for high-performance modeling of other building structure types. In accordance with the described architecture, a deep neural network was trained which reduces the computation time by several orders of magnitude. The results obtained are of high practical importance for researchers in the field of thin-walled shells modeling since they allow us to significantly reduce the time costs associated with conducting computational experiments. One of the possible applications for developed solution is prototyping of various shell configurations. Once prototyping is complete, the most efficient shell configurations can be explored in detail using classical computer simulation techniques.

Problems on Controlling the Stress State of Large-Sized Structures Being Consecutively Constructed of Materials with Rheological Properties

The presented study uses the mathematical theory of growing bodies to describe from the view point of continuum mechanics the processes of consecutive construction of large-sized arched structures based on flat foundations with taking into account the synchronous gravity action on the structure and to detect some ways of possible technological controlling these structures stress-strain state by a proper choice of the pace of structural material elements layerwise adding and of the values of pre-stretching stresses being set in the material elements. The structure material is implied to have rheological properties of creeping and aging what is decisively for the adoption of mentioned influence factors in control problems under consideration. The results of numeral calculations are given for specific material and process characteristics to illustrate the examples of successful stress controlling in thin-walled structures being constructed.

SIMPLIFIED MODEL FOR DETERMINING THE STRESS-STRAIN STATE IN MASSIVE MONOLITHIC FOUNDATION SLABS DURING CONSTRUCTION

The article proposes the simplified method for determining stresses in massive monolithic foundation slabs arising from the heat release of concrete during the hardening process. The proposed technique makes it possible to reduce a three-dimensional problem to a one-dimensional one based on the features of the distribution of stresses and strains in the structures under consideration, identified during finite element modeling in a three-dimensional setting. The resulting resolving equations take into account the creep and shrinkage of concrete, the coefficient of reinforcement of the structure. The strength and deformation characteristics of concrete are assumed as functions of the degree of maturity of the concrete, which in turn is determined by the time and temperature of curing. Approbation of the developed model is carried out by comparison with the calculation in a three-dimensional setting in the ANSYS software package. The influence of creep and contraction shrinkage of concrete, the degree of concrete maturity and the coefficient of reinforcement on the stress-strain state of structures is investigated.

Diagnostics of thin-walled structures of complex geometry and structure

The main stages of the birth of thin-walled structures, changes in their relative thickness and mass of a unit area are given; ways of creating perfect thin-walled structures are indicated. The problems arising during the operation of thin-walled structures of complex geometry, as well as approaches and methods of their calculation are noted. To ensure trouble-free operation of a thin-walled structure with a thin-layer coating, under load and exposed to physical fields and environments, it is necessary to correctly diagnose the condition of structural elements. The spline variant of the finite element method in two-dimensional (SV FEM-2) and three-dimensional (SV FEM-3) productions is noted, as well as the synthesis of these variants - SV FEM-2 + SV FEM-3. The combination of the idea of parametrization of the entire domain and approximation of the desired variables within the element by Hermitian cubic splines makes it possible to obtain high-precision consistent finite elements. The developed variants of the finite element method make it possible to evaluate the stress-strain state of structures of complex geometry, including the calculation of multilayer, thin-walled structures with coating and local defects, as well as to take into account specific surface properties other than those of the main array. Studies of stress concentration near local depressions are considered. Two-dimensional experimental and theoretical methods are noted for evaluating the stiffness properties and adhesion of thin-walled, thin-layer and composite structural elements of complex structure, which, along with a distributed complex structure, may have distributed defects. The developments were used in solving specific tasks of a number of enterprises.

Stress-deformed state of the shell with a small initial deflection under the action of the end load

Purpose of work. Construction of method for calculating the stress-strain state of cylindrical shell with small initial deflection, to which an end load is applied, using the method of characteristics. Comparison of the calculation results of the obtained model with the works of other authors in this area.
 Research methods. For the calculation, the equations of motion of the Timoshenko type shell were used, taking into account both the shear deformation and inertia of rotation, and some nonlinear terms, to which the method of characteristics was applied. To obtain the equations of shell motion, the Hamilton-Ostrogradsky variational principle was used.
 Results method is proposed for calculating the stress-strain state of a cylindrical shell with a small initial deflection using characteristics. Comparative analysis of the calculation results with research in this area by other authors, which showed the effectiveness of the proposed method.
 Scientific novelty. The equations of the classical theory of shells, based on the Kirchhoff-Love hypotheses, which do not take into account the shear deformation and inertia of rotation, as well as linear equations of the Timoshenko type, have become widespread. In this work, a model of the stress-strain state of an axisymmetric shell with small initial deflections is constructed, taking into account both shear deformation and rotational inertia, and some nonlinear terms.
 Practical value. The proposed method can be used to calculate the stress-strain state of structures in which thin shells are present as elements, taking into account small initial deflection. This method makes it possible to study the influence of the characteristics of the initial deflection on the stress-strain state of the entire structure.

The role of parameters of foundation structures in the formation of a stress-strain state of the foundations of the building

Requirements for the reliability and cost-effectiveness of rational foundation structures determine the performance of calculations taking into account the interaction of the loadbearing structures of the building with the soil base. Computer modeling makes it possible to perform such calculations and obtain the stress-strain state of the structures of the building and the soil base.
 Numerical modeling of the interaction of a building with a soil massif makes it possible to study the influence of all components of the system "soil base - foundation - building". At the same time, during numerical modeling it is possible to consider different options for the location of elements in the plan, different geometric dimensions of the elements and their properties. The results of the interaction calculations of the building with the soil base make it possible to choose the best option for foundation structures, which is cost-effective and ensures reliable operation of the building.
 In this study, the search for rational parameters of the foundation structures of the building was performed by numerical modeling of the joint work of the elements of the system "soil base - foundation - building". The study was performed on the example of a 16-storey frame building.
 A study of the influence of the parameters of the pile foundation on the stress-strain state of the foundation structures and bearing elements of the frame of the building:
 -The influence of the piles location in the plan is considered. The process of redistribution of forces in piles depending on the amount and location within the contour of the building is investigated. Deformation assessment is performed.
 -The optimal pile length has been searched. The relationship between the length of piles and deformations, their load-bearing capacity and quantity has been studied. The distribution of piles according to the coefficient of use of their bearing capacity has been obtained.
 -A study of the influence of the stiffness of the foundation pile cap on the redistribution of stresses and strains in the structures of the building. The relationship between the thickness of the pile cap and the percentage of reinforcement elements of the frame of the building has been obtained.
 It is confirmed by the results of the research that the use of numerical modeling of the interaction of the pile foundation with the soil base allows to obtain a quantitative assessment of the stress-strain state. It becomes possible to search for rational parameters at the design stage of foundation structures.

Buckling of functionally graded carbon nanotubes reinforced composite joined spherical-cylindrical-spherical thin-walled structure

Functionally graded carbon nanotubes reinforced composite joined spherical-cylindrical-spherical thin-walled structure under the actions of axial and lateral distributed loads is considered. The static buckling of this structure is analyzed numerically. The Ritz method is used to derive the governing equations of the joined thin-walled structure buckling. Higher-order shear deformation theory is applied to describe the structure stress-strain state. The continuity conditions of the spherical-cylinder junction are derived. The displacements projections are chosen in the special form to satisfy these continuity conditions. The dependences of the buckling axial load on the CNTs distributions, CNTs volume fractions are analyzed numerically.

РАСЧЕТ ЖЕЛЕЗОБЕТОННОЙ ПЛИТЫ ПЕРЕКРЫТИЯ ПРИ ВОЗДЕЙСТВИИ ПОВЫШЕННЫХ ТЕМПЕРАТУР ПОЖАРА

Розроблено методику чисельного дослідження напружено-деформованого стану залізобетонних конструкцій плит перекриттів з урахуванням нестаціонарних полів температур в арматурі і бетоні за стандартним температурним режимом і температурному режимі реальної пожежі. В рамках методики використовуються характеристики материлов, наведені в ДСТУ-Н Б EN 1992-1-2, а також вихідні дані, необхідні для застосування уточненого методу розрахунку. Ці дані встановлюються шляхом аналізу наявних в літературі експериментальних даних і характеристик матеріалів, наведених в Єврокодах. При оцінці вогнестійкості конструкцій уточненим методом розрахунку враховуються всі фактори, які справляють істотний вплив на напружено-деформований стан конструкції при пожежі. Визначають підвищення і поширення температури в конструкції в заданий момент часу (теплотехнічний розрахунок) і механічну поведінку конструкції (статичний розрахунок), при цьому враховується відповідний сценарій пожежі. Методика ілюструється на прикладі розрахунку на вогнестійкість залізобетонної плити перекриття. Проведено розрахунки з реалізацією пов'язаних термопрочностних завдань в програмному комплексі ANSYS. Проектування залізобетонної плити перекриття виконувалося в модулі Design Modeller програми ANSYS. Потім здійснювалися послідовно розрахунки в модулях TRANSIENT THERMAL і STATIC STRUCTURAL. Бетон і арматура моделюються об'ємними елементами. Підхід не вимагає прив'язки сітки кінцевих елементів до кроку арматури, що дозволяє застосовувати його до завдань з реальними розмірами. У прийнятій моделі бетону поверхня плинності складається з двох пересічних конічних поверхонь Друкера-Прагера. Результати розрахунків добре узгоджуються з представленими літературними експериментальними даними. Використання запропонованої методики дозволяє досить точно оцінити вогнестійкість залізобетонних конструкцій і прогнозувати їх напружено-деформований стан при пожежі.

Создание прототипа Smart-слоя для контроля напряжённо-деформированного состояния конструкций из полимерных композиционных материалов и оценка его технических характеристик

Создание прототипа Smart-слоя для контроля напряжённо-деформированного состояния конструкций из полимерных композиционных материалов и оценка его технических характеристик

The design criteria evaluation for the rigidity of the structure foundation with various models for moving the grillage and head wall

Taking into account the nonlinearity of the soil during geotechnical calculation, including modeling the base stiffness, makes it possible to correctly determine the structures’ stress-strain state (SSS), as well as to consider their work in the base – foundation – structure system.

INTEGRATED MONITORING OF ENGINEERING STRUCTURES

The article recommends the correct spelling of the names of monitoring systems based on semantic content and a logically consistent word order. Three components of the complex monitoring system of a high-rise building are considered, which complement each other, creating a general picture of the position and condition of the building, its load-bearing structures and the soil mass under it. Geotechnical monitoring, geodetic monitoring, and civil engineering monitoring are considered in unity. The tasks of each monitoring are shown and instruments and sensors that are used in modern automated monitoring systems are described.Geotechnical monitoring provides information about the condition and displacement of the soil base, which is located under the building under construction and around it, about the processes taking place inside the soil massif. Automated systems for geotechnical monitoring use downhole inclinometers, downhole extensometers, soil pressure sensors in combination with geodetic and civil engineering monitoring devices.Geodesic monitoring gives an idea of the spatial position of the building and its elements, as well as the plan-height and angular displacements of the supporting structures. Automated systems of geodetic monitoring use robotic total stations, levels, scanners, GNSS equipment in combination with instruments for civil engineering and geotechnical monitoring.Engineering and construction monitoring shows changes in the stress-strain state of structures and their elements and changes in their mutual position. Automated systems for engineering and construction monitoring use different types of sensors: deformations, displacements, vibrations, temperature, pressure, and others in combination with geodetic and geotechnical monitoring devices.

Studying of the wall cylindrical rigidity influence on the stress-strain state of the tank during local settlement

The article numerically researched the stress-strain state of the tank RVS-20000 at the settlement zone is located near the tank wall. A numerical model of the tank was developed in accordance with the actual geometric dimensions, taking into account all structural elements of the structure and the maximum operating loads. When modeling local settlement to account for the spatial work of the soil, the model of the Pasternak soil base was used. The stress-strain state calculation of the tank was performed at values of the radius of the drawdown zone from 1 to 10 m. The choice of this interval is due to the fact that in more than 92 % of cases, tanks with local bottom settlements fall within this range of values.The dependences of the maximum acting stresses in the wall of the internal combustion engine on the position of the inhomogeneity area in the soil base are established. The boundary of the zone of action of the edge effect from the tank wall is established. If the center of the heterogeneity area is located in this zone, it is necessary to conduct additional analysis of the tank metal structures stress-strain state when assigning the maximum settlement.

Reinforced concrete structures stress-strain state strengthen with composite materials

In recent years, innovative strengthening of reinforced concrete structures for industrial and civil use by external reinforcement based on carbon fiber has been widely used. However, there are only a few application examples of this amplification technology in the water treatment and sanitation facilities construction and rehabilitation. Based on experimental and practical data, composite amplification systems provide significant results both when working structures in normal conditions, and when they are in aggressive environments. Compared to conventional structural materials, carbon fiber-based composite materials have higher strength, significant fatigue resistance, high elastic modulus, chemical and thermal resistance.This article discusses the calculating method for strengthening reinforced concrete crossbars for coating the construction of an underground purified drinking water reservoir reinforced with composite materials. Based on the calculation methods, the reinforcing feasibility is substantiated. This work was carried out according to the results of a crossbars survey. In order to achieve these goals, a survey was made of the crossbars of the treated drinking water tank, the actual effective loads on the reinforced concrete crossbars were determined, the need to strengthen the examined structures according to the results of calibration calculations was determined, recommendations were developed to strengthen the examined structures of the reservoir construction. A survey of the structures of the structure, as well as an assessment of their technical condition, was carried out taking into account the requirements of current regulatory documents.

The civil structures bearing capacity assessment for 150 m high reinforced concrete ventilation pipe based on the field and numerical surveys

In the paper the results of the building structures bearing capacity assessment are presented for a reinforced concrete ventilation pipe with a height of 150 m under seismic effects and tornado loads, taking into account the results of full-scale dynamic and instrumental building structures surveys, based on the linear and nonlinear spatial design models numerical studies.
 This goal was achieved by solving the following tasks:
 
 the vibrodynamic surveys execution;
 the concrete structures strength determination by an ultrasonic method;
 development of linear and nonlinear spatial design models of the pipe;
 the calculations of class F3 tornado effects and intensities 6 (MDE) and 7 (above MDE) seismic impacts.
 
 Based on the results of vibrodynamic surveys, the actual dynamic parameters of the ventilation pipe structures were determined (vibration modes, prevailing periods and frequencies during principal modes vibrations). Based on the results of structures instrumental studies by ultrasonic method, the actual characteristics of concrete structures strength are determined. The obtained field data were used in the development of the facility spatial design models.
 To determine the bearing capacity of structures, the models calculations were performed using the LIRA CAD software package, which is a computer system for structural analysis and design.
 The calculations were performed for the class F3 tornado loads, as well as the intensities 6 and 7 seismic effects determined by the spectral method. Additionally, the bearing capacity of facility reinforced concrete structures was assessed under extreme loads (intensity 7 seismic impacts and class F3 tornado) taking into account the concrete and reinforcement plastic properties. The structures non-linear static analysis (Pushover analysis) applied in the standards of Ukraine, the European Union, the USA and other countries for the assessment of the operating structures seismic resistance was used.
 Based on the results of the research, the reinforced concrete ventilation pipe structures stress-strain state parameters under the considered seismic and tornado loads were obtained and the recommendations were prepared to reduce the possible consequences of an intensity 7 earthquake and a class F3 tornado.

The civil structures bearing capacity assessment for 150 m high reinforced concrete ventilation pipe based on the field and numerical surveys

In the paper the results of the building structures bearing capacity assessment are presented for a reinforced concrete ventilation pipe with a height of 150 m under seismic effects and tornado loads, taking into account the results of full-scale dynamic and instrumental building structures surveys, based on the linear and nonlinear spatial design models numerical studies.
 This goal was achieved by solving the following tasks:
 
 the vibrodynamic surveys execution;
 the concrete structures strength determination by an ultrasonic method;
 development of linear and nonlinear spatial design models of the pipe;
 the calculations of class F3 tornado effects and intensities 6 (MDE) and 7 (above MDE) seismic impacts.
 
 Based on the results of vibrodynamic surveys, the actual dynamic parameters of the ventilation pipe structures were determined (vibration modes, prevailing periods and frequencies during principal modes vibrations). Based on the results of structures instrumental studies by ultrasonic method, the actual characteristics of concrete structures strength are determined. The obtained field data were used in the development of the facility spatial design models.
 To determine the bearing capacity of structures, the models calculations were performed using the LIRA CAD software package, which is a computer system for structural analysis and design.
 The calculations were performed for the class F3 tornado loads, as well as the intensities 6 and 7 seismic effects determined by the spectral method. Additionally, the bearing capacity of facility reinforced concrete structures was assessed under extreme loads (intensity 7 seismic impacts and class F3 tornado) taking into account the concrete and reinforcement plastic properties. The structures non-linear static analysis (Pushover analysis) applied in the standards of Ukraine, the European Union, the USA and other countries for the assessment of the operating structures seismic resistance was used.
 Based on the results of the research, the reinforced concrete ventilation pipe structures stress-strain state parameters under the considered seismic and tornado loads were obtained and the recommendations were prepared to reduce the possible consequences of an intensity 7 earthquake and a class F3 tornado.

Stresses In Tendons Of Post-Tensioned Concrete Structures At Ultimate Limit State

Currently post-tensioned concrete structures, which are designed with bonded or unbonded tendons, are widely used in construction. The features of calculation of post-tensioned structures with unbonded tendons, which are contained in some other design codes, are considered. It is noted that the current design code for plain and reinforced concrete structures include the provisions for the calculation of post-tensioned concrete structures with bonded tendons. However, there are no recommendations for the calculation of post-tensioned concrete structures with unbonded tendons, taking into account the specific features of the stress-strain state of structures with such prestressing tendons. These features significantly affect both the ultimate moment resistance of structures and their deformations, usually in the unfavorable direction in comparison with structures in which the bonded tendons are accepted. Therefore, the main attention when developing a method for calculating of post-tensioned concrete structures with unbonded tendons was paid to determining the stresses in such reinforcement at the ultimate limit state capacity check. As a result, a method for determining the stresses and increase of the stress from the external load in the unbonded tendons was developed for calculating the ultimate moment resistance of structures. The proposed method presented in the article showed a close correspondence with the data obtained from other studies, in which the stresses in the unbonded tendons were determined by the results of experimental and theoretical studies.

About the election strength criteria in calculations for long-term strength for non-isothermal processes of loading

In the paper the research methods of axially symmetric elastic - plastic stress strain state of structures in the form of thin single and multiple layer shells of rotation with an account of material damage at creep is represented. The long-term strength criterion definition, on the basis of which the time to failure of the structure is calculated, is one of the important task. There are multiple long-term strength criteria, but very little detail recommendations on their usage and concretizing, which is what makes this problem so difficult to solve. The authors proposed a simple and easy-to-use method for concretizing the Pisarenko–Lebedev generalized long-term strength criterion. To verify the reliability of the proposed method of concretizing the long-term strength criterion, the calculations of time to failure a cylindrical shell under the action of internal pressure and a thin lamina with a round hole stretched by external radial forces are carried out. The calculation results obtained by the proposed method differ from the experimental ones by 1.8% and 3.1%. These results are the most reliable. Therefore, proposed method for calculating the long-term strength criterion enables more accurate damage and time-to-rupture predictions, compared with other calculation methods.

РАСЧЕТНЫЕ МОДЕЛИ ДЕФОРМИРОВАНИЯ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ В ЗДАНИЯХ И СООРУЖЕНИЯХ ПРИ КРУЧЕНИИ С ИЗГИБОМ

A computational model of the complex resistance of reinforced concrete structures in buildings and structures under torsion with bending is proposed, consisting of a support block (formed by a spatial crack and a compressed concrete zone closed on it, - spatial section k) and a second block formed by a vertical section I– I, passing perpendicular to the longitudinal axis of the reinforced concrete element along the edge of the compressed zone, closing the spatial spiral-shaped crack. Cases are considered when the torque effect has the greatest influence on the stress-strain state of structures. We have a design diagram A of the resistance of a reinforced concrete structure under the combined action of a bending moment, torque and shear force for a spiral-shaped spatial crack, as well as a design diagram B for a spatial X-shaped crack. In this case, as the design forces in the spatial section, the following are taken into account: normal and tangential forces in the concrete of the compressed zone; components of axial and thrust forces in the working reinforcement crossed by a spatial crack. Resolving equations are constructed that form a closed-loop system and the Lagrange function that unites them is written. Using the partial derivatives of the constructed function with respect to all the variables included in it and equating them to zero, an additional system of equations is compiled, from which, after the appropriate algebraic transformations, a dependence is obtained that allows one to find the projection of a dangerous spatial crack.

Monitoring System of a High-Rise Building during Operation

Monitoring of structures during operation is a direct requirement of the current legislation, especially relevant for technically complex structures, which include high-rise buildings. It is important not only for ensuring mechanical safety during construction operation, but also as a tool for reverse analysis of the actual stress-strain state of structures and foundations for compliance with the design calculation forecast, which should ultimately contribute to the development of construction theory and practice. The article is devoted to the organization of monitoring during the operation of the Lakhta Center skyscraper in St. Petersburg. The basis of the monitoring system is a design model of the building that interacts with the base making it possible to give the monitoring an interactive character. Particular attention is paid to the definition of «alarms» that make it possible to signal timely about the occurrence of negative trends helping to eliminate the occurrence of an emergency. It is shown that the calculations for justifying the criteria of monitoring systems differ significantly from the usual calculations when designing. The article defines the features of a workable monitoring system, to which the system implemented in practice fully corresponds. A comparison of the readings set in the design of measuring equipment and design expectations is given. The example of a high-rise building shows how to assign the «alarm» and «accident» criteria to ensure the operability of the monitoring system during operation.

Research of the Materials and Reinforcement Schemes Effects on a Mechanical Behavior Smart Structure with Embedded Piezo Actuators

The present work is devoted to the research of a helicopter blade segment stress-strain state. The segment was made of polymer composite materials with embedded piezoelectric actuators. The computational model of the blade segment takes into account the technological order of laying and the anisotropy of the reinforcing layers properties. The reinforcement schemes under consideration were [0°/90°], [45°/-45°], [0°/45°/-45°/90°]. The static strength margin was estimated using the criterion of maximum stresses. A layered analysis of the structure stress-strain state was carried out. It was shown that the most dangerous, determining the structure margin of safety, are normal interlayer stresses. It was found that the GFRP material and the structural reinforcement scheme [0°/90°], selected during the design, provide the greatest torsion angles.