Deformation Characteristics Of Concrete Research Articles

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.

EXPERIMENTAL AND THEORETICAL STUDIES OF REINFORCED CONCRETE BENDING ELEMENTS MADE OF HIGH-STRENGTH CONCRETE

The use of quality materials is necessary for the manufacture of load-bearing reinforced concrete structures that are subject to heavy loads. To meet such requirements, it is necessary to use high-strength concrete, which has high compressive strength, water and gas tightness, corrosion resistance due to its dense structure. The use of high-strength concrete makes it possible to reduce the cross-sectional dimensions of structures, thereby reducing the weight of structures compared to structures of traditional classes of concrete.The results of experimental and theoretical researches of work of reinforced concrete beams from high-strength and ordinary concrete at crossbending are resulted in work.A program of experimental research has been developed, which includes the manufacture and testing of concrete samples of prisms and cubes todetermine the strength and deformation characteristics of concrete of different composition, the manufacture and testing of experimental reinforcedconcrete beams for transverse loading. Three series of rays were tested, four in each. The composition of the concrete mixture for high-strength concreteusing metakaolin and hyperplasticizer is proposed.The proposed algorithm for calculating the bearing capacity of bending elements, based on the method of deformation, allows obtaining resultswith sufficient accuracy. The calculation is performed according to the developed algorithm, which is implemented in the Mathcad program.The analysis of experimental and theoretical values of bearing capacity of reinforced concrete beams from high-strength and usual concrete attransverse bend.

Experimental Study on the Strength and Deformation Characteristics of Concrete under True Triaxial Compression after Sulfate Attack

To explore the mechanical properties of concrete under true triaxial static compressive load after sulfate attack, uniaxial static compression test and true triaxial static compression test at four stress ratios were carried out on concrete specimens immersed in 15% sulfate solution for 0–120 days by the integrated true triaxial static and dynamic load testing system, and the variation of performance indicators such as the strength and deformation of concrete under the coupling action of sulfate attack and complex stress state was analyzed. The results show that the uniaxial compressive strength of concrete increases at the beginning and then decreases with the increase of sulfate attack time and reaches the peak on the 30th day, with an increase rate of 16.57%; the strength of concrete under triaxial compression increases significantly, and the maximum triaxial compressive strength is 3.18 times of uniaxial compressive strength under the combination of 0-day sulfate attack and 0.2 : 0.8 stress ratio; and the deterioration of concrete under sulfate attack is more prominent at high confining pressure, and as the sulfate attack worsens, the sensitivity of triaxial compressive strength of concrete to lateral compressive stress is reduced. In conclusion, triaxial compression can significantly enhance the ductility of concrete by playing a role in restraining the deformation and cracking of concrete after sulfate attack.

Зависимость коэффициентов прочностной и деформативной вариатропной эффективности центрифугированного бетона от зернового состава крупного заполнителя

At present, developing and improving low-material, energy- and resource-intense technologies to manufacture concrete and reinforced concrete products and structures have become a topical issue in the construction industry. Therefore, centrifugation technology is promising. In this article, the formu-lation of concrete with variatropic structure was improved, and the methods for its qualitative and quan-titative assessment were developed. Seven annular cross-section reference samples were manufac-tured and tested. Based on the test results of centrifuged concrete samples with different grain size compositions of the coarse aggregate, the empirical values of the integral and differential strength and deformation characteristics of concrete were determined. The structural and stress-strain variational efficiency coefficients were calculated and analysed. The optimal grain size composition of the coarse aggregate was determined and allows centrifuged concrete with an enhanced variatropy to be ob-tained, as well as the most effective coefficient of variatropic efficiency. The prospects for further en-hancing the variatropy of centrifuged and reinforced concrete products and structures by improving the formulation-technological factors were determined.

Research on the Mechanical Properties of Recycled Aggregate Concrete under Uniaxial Compression Based on the Statistical Damage Model.

In this paper, uniaxial compression tests were carried out for recycled aggregate concrete with water cement ratios of 0.38, 0.49, and 0.66 and replacement ratios of 0%, 25%, 50%, 75%, and 100%, respectively. The influence of the replacement ratio of recycled aggregate and water cement ratio on the strength, elastic modulus, and deformation characteristics of concrete was discussed. The results show that the replacement rate of recycled aggregate has a significant effect on the macro stress–strain behavior of concrete. In the case of a constant water cement ratio, the peak nominal stress first decreases and then increases with the increase of the replacement rate; while the water cement ratios equal 0.38, 0.49, and 0.66, the corresponding transition states are 25%, 50%, and 50% of the replacement rate, respectively. The deformation and failure is characterized by two stages: distributed damage and local failure. Combined with the statistical damage mechanics, the influence of the aggregate replacement rate on the damage evolution mechanism of recycled concrete on a mesoscopic scale was explored. Two mesoscopic damage modes, fracture and yield, are considered. Their cumulative evolutions are assumed to follow triangular probability distributions, which could be characterized by four parameters. The peak nominal stress state and the critical state are distinguished, and the latter is defined as a precursor to local failure. With the increase of the replacement rate of recycled aggregate, the inhomogeneous evolution of mesoscopic damage shows obvious regular change, which is consistent with the internal chemical and physical mechanism and macro nonlinear stress–strain behavior.

Calculation of deformations of concrete with indirect reinforcement according to limit state design

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.

Экспериментальное исследование диаграмм σ - ε бетона при одноосном сжатии и влияния на их форму циклов замораживания и оттаивания

As a result of the experimental study, there was estimated the variability of the form of complete diagrams σ-ε of concrete under uniaxial compression. It is shown that the coefficients of variation of concrete deformation characteristics are comparable with the coefficient of variation of strength within one concrete class in terms of compressive strength. It was found out that the effect of freezing and thawing cycles leads not only to a decrease in the compressive strength of concrete, but also to a decrease in the ultimate deformations and the initial modulus of elasticity. Thus, when using diagram methods for calculating reinforced concrete structures, it is necessary to take into account the influence of variability not only in the strength, but also in the deformation characteristics of concrete.

Effect Of Elevated Temperatures On Complete Concrete Deformation Diagrams

The analysis of the previous results of the study on concrete stress-strain behavior at elevated temperatures has been carried out. Based on the analysis, the main reasons for strength retrogression and elastic modulus reduction of concrete have been identified. Despite a significant amount of research in this area, there is a large spread in experimental data received, both as a result of compression and tension. In addition, the deformation characteristics of concrete are insufficiently studied: the coefficient of transverse deformation, the limiting relative compression deformation corresponding to the peak load and the almost complete absence of studies of complete deformation diagrams at elevated temperatures. The two testing chambers provided creating the necessary temperature conditions for conducting studies under bending compression and tension have been developed. On the basis of the obtained experimental data of physical and mechanical characteristics of concrete at different temperatures under conditions of axial compression and tensile bending, conclusions about the nature of changes in strength and deformation characteristics have been drawn. Compression tests conducted following the method of concrete deformation complete curves provided obtaining diagrams not only at normal temperature, but also at elevated temperature. Based on the experimental results, dependences of changes in prism strength and elastic modulus as well as an equation for determining the relative deformation and stresses at elevated temperatures at all stages of concrete deterioration have been suggested.

Evaluation Of The Effect Of Eccentricity Of Longitudinal Force On The Provision Of Bearing Capacity Of Compressed Concrete Elements

This work evaluates the influence of the eccentricity of longitudinal force on the provision of the bearing capacity of an eccentrically compressed reinforced concrete element in the normal section at different percentages of longitudinal reinforcement. The nonlinear deformation model was used for probabilistic calculations, which made it possible to take into account the influence of strength and deformation characteristics of concrete on the bearing capacity of the elements of reinforced concrete structures. The dependences of the relative average value of the maximum longitudinal force and the coefficient of variation for the given percent of reinforcement on the eccentricity of the longitudinal force are obtained. The significant influence of the value of the longitudinal force eccentricity on the coefficient of variation of the bearing capacity of the eccentrically compressed concrete element in the normal cross section is shown. It is noted that the revealed dependence of the bearing capacity of eccentrically compressed reinforced concrete elements on the eccentricity of the longitudinal force is not taken into account in the existing methods of calculation.

Deformation Characteristics of Concrete under Uniaxial Compression

Depth study of deformation characteristics of concrete can reveal failure mechanism of concrete materials based on strain. This paper studies the deformation characteristics of concrete under uniaxial compression, and draw conclusions that deformation can cause the expansion of internal micro cracks, in accordance with the expansion of micro cracks, the law of cracks development of concrete under uniaxial loads is divided into three stages, micro-cracks relatively stable, stable crack development period and unstable crack development period. The research results can provide valuable reference for future research work.

Deformation Characteristics of Concrete Containing High Volume Palm Oil Fuel Ash

With the increasing building activities in both developed and developing countries, the utilization of supplementary cementing materials will continue to increase in the years to come because of their technical, economical and ecological advantages. One of such pozzolanic materials is palm oil fuel ash (POFA) which has been identified to be a good cement substitute in mortar and concrete mixes. This paper highlights some laboratory test results on the deformation characteristics of concrete containing high volume palm oil fuel ash. Concrete specimens containing 50% POFA were made and tested for compressive strength, modulus of elasticity, shrinkage and creep. The results were compared with that of control specimen i.e. concrete made with 100% ordinary Portland cement (OPC). It has been observed that POFA concrete had lower compressive strength compared to OPC concrete. Along with lower strength development, the modulus of elasticity of concrete containing 50% ash was found to be lower. Although a relatively higher creep strain was been recorded in POFA concrete, there has been no significant difference of drying shrinkage in concrete with or without palm oil fuel ash.

OS01-4-2 Local Deformation Characteristics of Concrete Measured by Digital Image Correlation Method

OS01-4-2 Local Deformation Characteristics of Concrete Measured by Digital Image Correlation Method

OS01F084 Local Deformation Characteristics of Concrete Measured by Digital Image Correlation Method

OS01F084 Local Deformation Characteristics of Concrete Measured by Digital Image Correlation Method

Influence of initial static stress on the dynamic properties of concrete

Abstract Concrete structures prior to being subjected to dynamic loadings such as earthquake have already withstood initial stress. So the study of strain-rate sensitivity of concrete should be closely related to the initial loading history that concrete experiences. Yet majority of available documents concerning the dynamic properties of concrete do not take the initial static loading history into consideration. In this study, experiments were carried out to investigate the effect of initial static stress on the dynamic strength and deformation characteristics of concrete. A prescribed load was initially applied on the specimen at a very low strain-rate and then a dynamic load was applied at a high strain-rate up to failure of the specimen. The relationship between dynamic strength factor and the initial stress is obtained. The comparison between the results by the proposed formula and those by experiments in this study indicates a good agreement. The stress–deformation curves obtained in the tests show that the initial static loading history plays an important role in the total deformation behavior of concrete. An explanation to the physical mechanisms of high strain-rate strength enhancement with different initial static stress was proposed.

Strength and deformation characteristics of concrete of the vilyui III hydroelectric station

1. The concrete of the Vilyui III hydrostation is characterized by a strength exceeding the grade and a high modulus of elasticity, and for the structural members of the main structures by a long stay during construction at low temperatures —to minus 15–35°C. 2. The strength and deformation characteristics determined by tests of specimens and cores from mature concrete (up to 4.6 years) of grades M250 W8 F100, M300 W10 F100, and M400 W12 F400 were: cube Rcub and prism Rpr strengths, respectively, 40–57 and 20–45 MPa; initial modulus of elasticity Ec=(4–4.3)·104 MPa and Poisson's ratiov=0.127; for M250 and M300 Rpr/Rcub=0.65 and for M400, 0.8. 3. The initial modulus of elasticity of the on-site concrete M250 at an age of 400–500 days at positive temperatures was Ec=4.6·104 MPa. Freezing of concrete to minus 30°C leads to an increase of Ec by 1.6 times according to a linear dependence. An increase of Ec practically ceases in the minus 30–38°C temperature range. 4. The strength and deformation characteristics of the concrete obtained as a result of tests, which considerably exceed the standard values and those adopted in the design, can be used for analyzing the state of the main structures of the Vilyui III hydrostation during the construction and operation periods and when processing the results of observations by means of the installed monitoring and measuring instruments.