Stress-strain Curve Of Concrete Research Articles

Determination of rotation capacity requirements for steel and composite beams

A method is presented for the calculation of the necessary joint rotations to permit the use of moment redistribution as the basis for the design of semi-continuous steel and composite frames. The method is based on the use of moment-curvature relationships obtained from consideration of the basic steel and concrete stress-strain curves. It simplifies the determination of the support rotations required for specific percentage redistributions of support moments to the mid-span cross-section as used in EC4 by considering these to be composed of an elastic and a plastic part. Several different load cases are considered, together with a wide range of beam properties. The resulting calculation method, which uses only formulae and graphs, is illustrated by an example.

Flexural Stiffness of Rectangular Reinforced Concrete Columns

The ACI Building Code permits a moment magnifier approach for design of slender reinforced concrete (RC) columns. This approach is strongly influenced by the effective flexural stiffness EI of the column which varies due to cracking, creep, and nonlinearity of the concrete stress-strain curve, among other factors. However, the EI expressions given in the ACI Building Code are quite approximate when compared with the values of EI derived from thrust-moment-curvature relationships. This study was undertaken to determine the influence of a full range of variables on EI of slender tied rectangular RC columns bent in symmetrical single curvature under short-time loads. Approximately 9500 columns, each with a different combination of variables, were used to generate the stiffness data. The EI expresions were then statistically developed for use in slender column designs. Two sets of equations are proposed in this paper; (a) Eq. 21 through 23 for initial sizing and preliminary design of structures; and (b) Eq. 18 through 20 for use in final more accurate structural designs.

Étude expérimentale sur les poutres mixtes

This paper presents a summary of the first part of a general research program on the nonlinear theory of composite beams and columns. The paper deals with the experimental study of simply supported composite beams, submitted to uniaxial bending about the major axis. Test results are compared with theoretical results obtained from an elaborate nonlinear analysis.A total of eight composite beams have been tested, four of them with special dowels welded to the wide-flange section web, and steel plates welded at both ends, in order to limit sliding between steel and concrete.By adequately adjusting the concrete stress–strain curve measured on control cylinders, to take into account the effects of strain rate, strain gradient, and steel reinforcement confinement, we obtain a theoretical ultimate bending moment identical to the experimental moment, and a deflection at rupture 10% smaller than the measured one. Key words: reinforced concrete, stress–strain curve, bending, ultimate moment, ultimate deflection, nonlinear theory, composite beams, composite sections.

An Experimental Technique for Obtaining Complete Stress-Strain Curves for High Strength Concrete

Abstract For a rational design of concrete structures, it is necessary to know both the ascending and the descending parts of the stress-strain curve of concrete subjected to uniaxial compression. It is difficult to determine the descending part experimentally because of the interaction between the testing system and the specimen, especially for concrete of high compressive strength. The influence of the testing machine depends on the stiffness of the machine, the frequency response of the system, the length and diameter of the specimen, the strength of concrete, the rate of loading, and the inherent brittleness of the material. For a closed-loop testing machine, the specimen-machine interaction also depends on the parameter chosen to control the loading. It is shown that the descending part of the curve can be obtained by controlling the circumferential strain even when the axial strain control produces an unstable failure. A method of testing specimens at a controlled rate of circumferential strain increase is described. Stress-strain curves of concrete subjected to uniaxial compression using both the axial and the lateral strain as a control were compared for compressive strengths ranging between 70 to 90 MPa (10 000 to 13 000 psi).

Stress-Strain Curves of Normal and Lightweight Concrete in Compression

A relatively simple experimental technique is used to obtain the stress-strain curves of concretes up to a strain of 0.006. The stress-strain curves of normal weight concretes of strenghts up to 11,000 psi and lightweight concrete of strengths up to 8000 psi are reported. An analytic expression for the stress-strain curve of concrete is developed to reflect experimental results. The analytic expression has four constants which depend on the properties of both the ascending and the descending portions of the stress-strain curve and can be evaluated from the knowledge of four key points of the curve. The coordinates of the four key points were expressed in function of the compressive strength of concrete so as to allow prediction of the entire curve solely from the knowledge of the compressive strength. /Author/

鉄筋コンクリート断面の破壊時コンクリート圧縮縁ひずみに関する研究

The flexural failure of reinforced concrete section is generally caused by crushing of concrete at the compression zone. For the calculation of ultimate flexural capacity or corresponding deformation of a beam, the compressive fiber strain of concrete at failure should be assumed. In practice, the empirical values, for instance, εcu=0.25∼0.35%, are being used in the calculation. However, these values are not always clearly defined from the theoretical viewpoint.In this study, based on the stress-strain curve of concrete having the strain softening region, the theoretical estimation was made on the compressive fiber strain of concrete at the ultimate flexural capacity as well as that at the failure or the crushing of concrete in compression zone of the reinforced concrete rectangular beam section. The results obtained are as follows:(1) The extreme compressive fiber strain to be used for ultimate flexural strength calculation is defined as the value at which the compressive stress brock coefficient, k2/k1k3, obtained from the stress-strain curve of concrete becomes minimum, where k1k3 and k2 denote the ratio of the average stress of stress-strain curve up to an arbitrary strain to the compressive strength and the ratio of the location of center of gravity of the corresponding area to the arbitrary strain, respectively.(2) It is reasonable to assume that the compression failure of concrete in compression zone takes place primarily when the distance of neutral axis from compressive fiber becomes minimum. The corresponding compressive fiber strain can be defined from the stress-strain curve of concrete as the strain at the maximum value of stress brock coefficient, k1k3.(3) Practically, the compressive strain at the failure of concrete described in (2) can be used for the calculation of ultimate flexural strength or deformation of beams.(4) The increase of negative slope of the strain softening region in concrete stress-strain curve reduces the value of compressive fiber strains, especially that for the failure of concrete. On the contrary, the increase of strain at the peak stress (that is, at the compressive strength) in stress-strain curve results in much increase of the ultimate compressive fiber strains.

A Study on the Properties of the Compressive Stress-Strain Curves of Lightweight Aggregate Concrete

The remarkable differences are usually noticed between the stress-strain curves of lightweight aggregate concrete and the curves of river sand and gravel concrete in their gradient and the curvature of their curves.The shapes of stress-strain curves of various sorts of lightweight aggregate concrete were studied in detail by graphical analysis of curves showing their difference in stress-strain relations. And the characteristics of the finite difference curves obtained can be used commonly to classify the stress-strain curves for normal and lightweight aggregate concretes. The finite difference curves of stress-strain relations indicating cord modulus Δσ/Δδ on the ordinate and strain δ on the abscissa, were quite effective for distinguishing the characteristics of stress-strain curves, since they magnify the variation of the curvature of stress-strain curves.The graphical characteristics of finite difference curves may be summarized as follows.(1) The finite difference curves of stress-strain relations of concretes can be devided into three stages of comparatively linear parts, (1) early stage of slowly descending part, (2) steeply descending part and (3) last stage of slowly descending part.(2) Most finite difference curves consist of one or two stages. Typical patterns of finite difference curve are composed of (1)-(2) stages, (2) stage only or (2)-(3) stages of combination. These three typical patterns may also be corresponding to high strength type, medium strength type and low strength type of stress-strain relations, respectively.(3) The normal concrete and the lightweight aggregate concrete have similar combination patterns of three stages. The compressive strength of concrete corresponding to its above-mentioned patterns, however, varies with concrete composition (fine-coarse aggregate combinations).Since mechanical behaviors of concrete at a certain stress level are reflected in the characteristics of finite difference curve, the results of analysis of finite difference curves obtained in this report will offer a qualitative estimation of mechanical properties of concrete with various mix proportions and various aggregate properties.

Evaluation of the Stress-Strain Curve of Concrete in Flexure Using Method of Least Squares

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Effect of Strain Gradient on the Stress-Strain Curve of Motar and Concrete

Effect of Strain Gradient on the Stress-Strain Curve of Motar and Concrete

7004 コンクリートの高温加熱中における応力歪曲線について : 第1報

7004 コンクリートの高温加熱中における応力歪曲線について : 第1報

Equation for the Stress-Strain Curve of Concrete

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The behaviour of prestressed concrete sections near the maximum moment

Summary Tests are described in which prestressed concrete sections were tested in pure bending in such a way that the complete moment-curvature curves could be obtained. The special requirements of the testing equipment are discussed and it is shown that there are descending branches to the moment-curvature curves of both underand over-reinforced sections. A theoretical discussion is given of the conditions of maximum moment of underand over-reinforced sections, including the cases of combinations of bending moment and axia load. The analysis is based on the stress-strain curve of concrete and it is shown that the conventional curves are not the true stress-strain curves of concrete. Attempts to obtain the actual curves are described; the parameters thus obtained are used in the analysis and give close agreement with measurements of maximum bending moments and curvatures in actual tests.

112 コンクリートの降伏点に関する研究(1報) : 普通コンクリートの応力度-歪度曲線式及び降伏点決定のための準備(材料・施工)

112 コンクリートの降伏点に関する研究(1報) : 普通コンクリートの応力度-歪度曲線式及び降伏点決定のための準備(材料・施工)