The article proposes a solution to the problem of more accurately taking into account the influence of scale factors on the qualitative and quantitative indicators of the stress-strain state obtained by testing both individual structures and structural systems made of reinforced concrete. Methodical approaches to modeling tests for static and dynamic loads are considered, with the aim of taking into account the scale effects that occur during the manufacture of prototypes of models of individual structures and structural systems made of reinforced concrete. Comparative analysis estimated effect of different geometric proportions for free opera statically determinate beams and for a fragment of a monolithic reinforced concrete frame multistory buildings, experimental studies which were performed by the authors earlier. Analytical patterns were established to assess the impact of large-scale factors on the particular static and dynamic deformation of structures and structural systems of reinforced concrete. The results can be taken into account when conducting experimental studies of model reinforced concrete structures for dynamic emergency loads
Indirect reinforcement is one of the effective ways to increase the strength and deformation characteristics, which is achieved by creating a volumetric stress state in concrete. For the design of reinforced concrete structures with indirect reinforcement, the calculation method based on a nonlinear deformation model is well suited. For such calculations, it is required to construct the stress-strain diagram, which will most accurately describe the relationship σ-ε. The article presents a numerical analysis of increasing the bearing capacity and deformations of concrete of various classes with indirect reinforcement in the form of welded meshes. Selected formulas to determine strength and ultimate compressibility. The problems arising in determining the compressibility limit of concrete with indirect reinforcement for engineering calculations are noted. Recommendations for calculating the parametric points of the stress-strain diagram are given.
Currently, the issue of increasing the efficiency of the use of traditional materials in building structures due to rational structural solutions and improving design methods and material models is relevant. The use of indirect reinforcement improves the strength and deformation characteristics of concrete. The article considers the influence of indirect reinforcement in the form of transverse welded meshes on the strength and ultimate compressibility of concrete. The main attention is paid to the determination of the strain values determining the stress-strain diagram for concrete with indirect reinforcement. It is known that with an increase in the strength of concrete, the value of its ultimate compressive strains decreases. Indirect reinforcement can significantly increase the ultimate compressibility of concrete and makes the difference in ultimate deformations even more significant for concrete of different strengths. In this context, when calculating structures in accordance with the limit state design and decreasing the strength values of concrete in order to obtain the necessary security, it is possible to overestimate the ultimate compressibility of concrete. This is unacceptable in calculations based on the deformation model, since the achievement of ultimate deformations of the material is the main criterion for structural failure. To confirm the hypothesis, the results of tests for central compression of concrete with indirect reinforcement in the form of transverse welded meshes were selected. The strain values at the peak of the diagram were calculated for the experimental samples. Calculations were also performed for the characteristic compressive strength values and the design values of strength. The results are compared with experimental data. A significant overestimation of the values of strain at the peak of the diagram was noted in the calculations based on the characteristic compressive strength values and the design values of strength.
1 ФГБОУ ВО «Национальный исследовательский Московский государственный строительный университет», г. Москва, Россия К РАСЧЕТУ КРИВИЗНЫ ЖЕЛЕЗОБЕТОННЫХ БАЛОК НА ОСНОВЕ ДЕФОРМАЦИОННОЙ МОДЕЛИ Аннотация. В статье рассмотрены основные предпосылки к расчету железобетонных конструкций на основании деформационной модели. Обозначены основные особенности и возможности расчета. Выбраны диаграммы состояния, позволяющие рассчитывать железобетонные балки, в том числе, с применением косвенного армирования сжатой зоны. Показана возможность учета работы бетона растянутой зоны после образования нормальных трещин путем перехода к диаграмме усредненного деформирования арматуры σ sm -ε sm посредством введения в расчеты коэффициента ψ s . Для трех серий железобетонных балок представлены результаты расчета кривизны в зоне чистого изгиба с учетом коэффициента ψ s и без. Произведено сравнение с результатами проведенных экспериментов. Ключевые слова: нелинейная деформационная модель, диаграмма состояния, изгибаемый элемент, косвенное армирование, трещины, кривизна.Abstract. The article considers the basic prerequisites for the calculation of reinforced concrete structures based on the deformation model. The main features and calculation options are indicated. Deformation diagrams have been selected to calculate reinforced concrete beams, including those using indirect reinforcement of the compressed zone. The work of concrete in the stretched area after the formation of normal cracks is taken into account by switching to the diagram of the average deformation of the reinforcement σ sm -ε sm by introducing the coefficient ψ s into the calculations. For three series of reinforced concrete beams the results of calculating the curvature in the zone of pure bending with the coefficient ψ s and without are presented. Comparison with the results of the experiments is shown. ВведениеСовременный уровень развития науки и широкое распространение компьютерных технологий позволяют реализовывать на практике методы расчета строительных конструкций, позволяющие описывать напряженно-деформированное состояние (НДС) более приближенно к реальному и учитывать особенности распределения напряжений и деформирования на различных этапах нагружения. При этом для железобетонных конструкций необходимо учитывать ярко выраженный нелинейный характер работы [1,2]. И хотя современные программные комплексы, реализующие метод конечных элементов, представляют различные модели железобетона [3][4][5][6], многие из них достаточно сложны и сходимость решения сильно зависит от введенных параметров материала, размеров сетки конечных элементов и других факторов. Сами нелинейные расчеты методом конечных элементов весьма трудоемки, требуют высокой квалификации пользователя и являются «напряженной борьбой за результат» Строительство и реконструкция 20 _________________________________________________________ №6 (86) 2019 (ноябрь-декабрь) Рисунок 1 -Схема испытания балок: П -прогибомер; М -мессура на основе индикатора часового типа; 1-14 -тензорезисторы Теория инженерных сооружений. Стро...
At accidental impacts caused by the sudden removal of a load-bearing element of the building frame, the stress-strain state of the sections of eccentrically compressed structural elements such as columns, pylons, braces and belts of trusses, etc. becomes more disadvantageous than their stress-strain state at the stage of normal operation. The factors that lead to such a situation are sharp increase in the eccentricities of loads attaching, slenderness of cross sections, corrosion, initial curvature and mechanical damages. In these cases, buckling scenario for the exhaustion of their bearing capacity is a possible scenario. The paper proposes an approach to the obtaining of deformation criteria for assessing the special limiting state of eccentrically compressed bar elements of reinforced concrete frames. Such an approach is based on the use of a combination of nonlinear deformation analysis and nonlinear stability analysis. Paper shows that the limiting values of deformations for the considered reinforced concrete element can be determined by the criteria of strength or buckling, depending on the ratio of the forces acting in the sections of the structural element.
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