Stress-strain Behavior Of Concrete Research Articles

A comparison of stress-strain behaviour of conventional and high strength concrete

Strength performance of concrete is characterized by its compressive strength, elastic modulus, stiffness and energy absorption capacity. Stress strain behaviour of concrete encompasses information on all these parameters, and is thus one of the most vital data to assess its overall performance. The present study utilizes the stress strain response, as a tool, to compare the relative variation in performance of conventional and high strength concrete. Two set of mix compositions (viz., M40 and M80 grade concrete) have been designed. The designed compositions are checked for their target strength by performing load controlled tests on 28 day cured cube specimens. M40 grade concrete comprises of cement and water as binding material, and fine and coarse aggregates as filler. High strength concrete (M80 grade) is designed with cement, mineral admixture and water as binding material; while the fine and coarse aggregates contribute to the filler material. For high strength concrete, super plasticizer has been added in required proportion to ensure adequate workability. Displacement control tests, with controlled strain rate, have been performed on 28 day cured cube specimens. Variability in pre-peak and post-peak stress strain response is analysed for both conventional and high strength concrete. An average of response over atleast four samples is computed for both the M40 and M80 grade concrete. In present study, the characteristic response is normalized with respect to peak strength to obtain a common reference basis and compared. The comparison is summarized in terms of change in pre-peak response and post-peak ductility. The observed results enable quantification of relative change in performance for M40 and M80 grade of concrete. The results are significant for benchmarking performance of high strength concrete structures with those of conventional concrete structures.

Investigation of the Effect of Confinement on the Stress-Strain Behavior of Concrete and Comparing the Existing Models

Investigation of the Effect of Confinement on the Stress-Strain Behavior of Concrete and Comparing the Existing Models

An investigation of concrete stress-strain behavior by the image analysis method

Concrete is a composite load-bearing building material. The deformation behavior of load-bearing materials under load is vital for the building system. Investigation of these brittle and quasi-brittle behavior patterns at various load levels provides an advantage in the evaluation of mechanical properties. In this study, the deformations occurring within the concrete samples in different stress-strain regions were investigated using an image analysis technique. The experimental samples experienced elastic-limit loading for two hours to clearly monitor the deformations at elastic, plastic, and breaking points. For the microstructure studies, the samples were prepared with epoxy for image analysis. Thin-sections were taken from each series of epoxy-impregnated concrete test samples, examined under a microscope, and photographed. Deformation studies on the digital photographs were carried out by the image analysis method. The results show that crack formation and crack types change because of increased stress and deformations. Crack formations within the concrete are parallel to the loading direction and occurred mainly in the aggregate–cement-paste interface. At 85% of the ultimate stress, crack length was measured as 0.665-29.505 mm and crack width 0.180-4.128 mm, while the crack length was 0.305-32.688 mm and crack width were 0.106-2.906 mm at fracture stress.

Influence of Metakaolin and steel fibers on stress strain behavior of concrete

This article describes the effects of different proportions of metakaolin and steel fiber on the stress-strain behavior of concrete. Concrete has become an important part of infrastructure development due to its wide and wide application. However, its brittleness can cause cracking, and cause some deterioration problems and infrastructure failures. Considering the problem of cracking performance, researchers around the world have conducted various studies to develop concrete with higher performance, longer life, and minimized destructive effects on nature. In order to obtain such characteristics, researchers only focus on the improvement of strength. It is observed that the higher compressive strength can make the substitution rate of metakaolin 16% and that of steel fiber 1.5%. Although the published literature provides some theoretical models and a large amount of experimental data on the compressive performance of fiber-reinforced concrete, there are still considerable reservations about the applicability of these models in design. Stress-strain curve is required for correct design and repair. This article introduces the results of compression tests of steel fiber reinforced concrete carried out in accordance with standard procedures, and rigorously evaluates the proposed model to define compressive stress-strain behavior. The reported test was performed on cylindrical specimens of plain and steel fiber reinforced metakaolin with fiber content of 0.5%, 1.0% and 1.5%. The concrete grade considered in this study is M40.

Properties of Concrete Containing Palm Oil Fuel Ash and Expanded Polystyrene Beads

This paper investigates the stress strain behaviour of concrete containing Palm Oil Fuel Ash and Expanded Polystyrene, axial compressive strength, tensile strength and modulus of elasticity. EPS-POFA concrete was prepared by substituting fine aggregates with EPS beads and cement replaced with POFA by 10%, 20% and 30%. Results of this study showed that EPS-POFA concrete exhibited low axial compressive strength, peak strain, tensile strength and elastic modulus when the EPS and POFA contents in concrete increased. However, the decrease in axial compressive strength of concretes with containing 10 to 20% EPS and POFA are suitable amount and acceptable to be applied on building structure as per stated in America Concrete Institute 318 with minimum specified compressive strength for structural concrete is 2500 psi (17 MPa). While, the failure of EPS-POFA concrete under axial compression gradually occurred and the concretes were able to retain the load after failure without full collapse. The slope of stress-strain curve of concretes with containing EPS and POFA was lower than that of normal concrete, demonstrating that the normal concrete more brittleness that EPS-POFA concretes.

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.

Experimental Study of Rubberized Concrete Stress-Strain Behavior for Improving Constitutive Models.

Inclusion of rubber into concrete changes its behavior and the established shape of its stress-strain curve. Existing constitutive stress-strain models for concrete are not valid in case of rubberized concrete, and currently available modified models require additional validation on a larger database of experimental results, with a wider set of influential parameters. By executing uniaxial compressive tests on concrete with rubber substituting 10%, 20%, 30%, and 40% of aggregate, it was possible to study and evaluate the influence of rubber content on its mechanical behavior. The stress-strain curve was investigated in its entirety, including compressive strength, elastic modulus, strains at significant levels of stress, and failure patterns. Experimental results indicated that increase of rubber content linearly decreases compressive strength and elastic modulus, but increases ductility. By comparing experimental stress-strain curves with those plotted using available constitutive stress-strain models it was concluded that they are inadequate for rubberized concrete with high rubber content. Based on determined deviations an improvement of an existing model was proposed, which provides better agreement with experimental curves. Obtained research results enabled important insights into correlations between rubber content and changes of the stress-strain curve required when utilizing nonlinear material properties.

Stress-strain behavior of concrete in circular concrete columns partially wrapped with FRP strips

Fiber-reinforced polymer (FRP) wrapping has become an attractive strengthening technique for concrete columns. Within this strengthening technique, FRP jackets are wrapped around the concrete column with the fibers in the jacket being oriented in the hoop direction. In practice, the FRP jackets can be either continuous or discontinuous along the column height and thus the resulting column is referred to as FRP fully or partially wrapped concrete columns. Existing research has demonstrated that the FRP partial wrapping strengthening technique by discrete FRP strips (rings) is a promising and economic alternative to the FRP full wrapping strengthening technique. Although a number of experimental investigations have been conducted on FRP partially wrapped concrete columns, the stress-strain behavior of FRP-confined concrete in partially wrapped concrete columns is not yet completely understood. This paper presents an experimental program to investigate the axial compressive behavior of circular concrete columns partially wrapped with FRP strips. The test results are presented and compared with five existing representative stress-strain models to examine the reliability and accuracy of each model. It has been demonstrated that the Teng et al.’s (2007) model is superior to the other four representative models and it provides reasonably accurate predictions of the ultimate axial stress of FRP partially wrapped concrete while it usually underestimates the ultimate axial strain.

Cross-Sectional Unification on the Stress-Strain Model of Concrete Subjected to High Passive Confinement by Fiber-Reinforced Polymer.

The stress-strain behavior of concrete can be improved by providing a lateral passive confining pressure, such as fiber-reinforced polymer (FRP) wrapping. Many axial stress-strain models have been proposed for FRP-confined concrete columns. However, few models can predict the stress-strain behavior of confined concrete columns with more than two specified cross-sections. A stress-strain model of FRP-confined concrete columns with cross-sectional unification was developed in this paper based on a database from the existing literature that includes circular, square, rectangular and elliptical concrete columns that are highly confined by FRP jackets. Using the database, the existing theoretical models were evaluated. In addition, the ultimate stress and strain models with cross-sectional unification were proposed using two parameters: the cross-sectional aspect ratio and corner radius ratio. The elliptical cross-section can be considered as a rectangular one with a special corner radius for the model calculations. A simple and accurate model of the equivalent corner radius ratio for elliptical columns was proposed. Compared to the other existing models and experimental data, the proposed models show good performance.

Mechanical Behavior of Concrete Modified by Replacement of Cement by Rice Husk Ash

ABSTRACT Construction industry is in need of lump sum quantities of materials which has increased both their demand and price. The use of large quantities of cement leads to increasing CO2 emission and as a consequence, the greenhouse effect. Consumption of wastes and byproducts from various sources in the manufacture of concrete has gained a great deal of importance in present days. Various researches are currently being conducted concerning the use of such products in concrete. RHA is a carbon neutral green product. Lots of ways are being thought of for disposing them by making commercial use of this. Rice husk ash is a good super-pozzolan which can be used to make special concrete mixes. The rice husk ash has been taken for this present study due to its easy availability and effective pozzolonic properties that are expected to improve the mechanical strength properties of concrete. Concrete specimens were made for evaluation of Compressive, Split Tensile, Flexural strength and Stress-Strain Behavior of concrete. The tests were conducted at the age of 7 and 28 days. Generally all mixes containing RHA achieved better properties than the conventional mix without RHA. By the experimental investigation the recommendation is given for using optimum percentage of RHA in concrete.

Effect of Testing Method and Strain Rate on Stress-Strain Behavior of Concrete

The flexural behavior of concrete is often different from its behavior under direct tension. This paper presents an experimental program aimed at the testing method and strain rate effects on the tensile behavior of concrete. Concrete specimens were tested with different testing methods (direct tension and four-point loading) and four strain rates (10(−6), 10(–5), 10(–4), and 10(−3) s(−1)). The results show that the peak stresses increase with an increase in the strain rate; the strain rate dependence of the peak stress is stronger for direct tensile specimens than for four-point loading specimens. The dynamic increase factor is expressed as a function of the strain rate and highly stressed volume method. The continuous damage model is also used to predict the strain rate effects on the ascending stress-strain behavior of concrete. Using the model parameters for the stress-strain curve of concrete at a static strain rate, the stress-strain curves of concrete for dynamic strain rates in four-point loading and direct tension are satisfactorily predicted.

Bond-Slip Analytical Formulation toward Optimal Embedment of Concrete-Filled Circular FRP Tubes into Concrete Footings

This paper presents a robust analytical model for a moment connection of concrete-filled fiber reinforced-polymer (FRP) tubes (CFFTs) to concrete footings. The CFFT connection is based on a simple approach of direct embedment into the footing, thereby eliminating the need for connection rebar or mechanical devices. The CFFT is externally subjected to lateral and axial loads, resembling practical applications such as piles affixed to pile caps, bridge columns, or utility poles. The model adopts the concepts of equilibrium, deformations compatibility, and nonlinear concrete stress-strain behavior. It also employs a “bond stress-slip” relation that can be obtained from simple push-through tests on some of the commercially used tubes. The model can predict the critical embedment length Xcr , which is the minimum length required to achieve material failure of the CFFT outside the footing, and bond failure inside the footing, simultaneously. If the actual embedment length is less than Xcr , bond failure occurs ...

Modeling Stress-Strain Behavior of Concrete Damaged by Alkali-Aggregate Reaction (AAR)

It has been shown by field observation and laboratory testing that the mechanical properties of concrete, such as stiffness, strength, and deformation capacity, are adversely affected by expansion in the material microstructure. Expansion is the overall effect of cracking within the aggregate, at the aggregate-paste interface, and in the matrix, and therefore signifies damage that may have been caused either by stress effects or aggressive chemical activity. This paper presents the development of a simple stress-strain model for concrete that has been damaged by alkali-aggregate reaction (AAR) prior to application of the mechanical load. The approach taken relates the residual stiffness of the material at any level of imposed deformation to the total amount of expansion damage resulting from AAR and from the subsequently applied mechanical load. In evaluating the influence of AAR damage on the initial stiffness and the shape (rate of softening) of the stress-strain response, the model considers the area-strain in the cross section of the principal compressive strut as the governing state variable. The model was validated using experimental data from mechanical tests conducted in the course of this study on a series of concrete specimens that had previously undergone various degrees of expansion because of AAR. The ability of the model to reproduce certain behavioral features of AAR-affected concrete, such as the restraining action of conditioning stress or reinforcement, is evaluated by correlation with published experiments.

Stress-Strain Behavior of Concrete under Cyclic Loading

A rational analysis of reinforced concrete (RC) structures requires satisfactory modeling of the behavior of concrete under general loading patterns. The behavioral characteristics of concrete dominantly depends upon its load history. For the study of concrete behavior, parametric study and experimental investigation into the behavior of concrete under load history of random cycles are performed. Through parametric study, the applicability of the previous concrete models is examined and a physically motivated modeling for the cyclic stress-strain relationships is proposed. The present modeling of concrete under general cyclic loading is initiated to provide substantial applicability, flexibility of mathematical expressions, and furthermore, to describe the behavior of random cycles. For the experimental study of concrete subjected to cyclic axial compressions, tests of 3 in (76 mm) by 6 in (152 mm) concrete cylinders are conducted under four different loading regimes to determine the major experimental parameters for the proposed analytical expressions. The model developed is based on the results of parametric study and experimental data obtained for the present study. The validity of the proposed general cyclic model is confirmed through a comparison of the experimental results and simulated behavior of the model.

Influence of damage orientation distribution on the multiaxial stress strain behaviour of concrete

The paper describes some geometrical features of the degradation process of concrete specimens subjected to uni- and triaxial compressive loadings. The development of weak zones under larger aggregate particles during hardening of the concrete, leads to anisotropic stress-strain behaviour. By means of surface crack-detection techniques, differences observed in macroscopic stress-strain behaviour were shown to be the result of different crack orientation distributions. The concept of crack orientation distributions can be extended to triaxial states of stress, including those situations where rotation of principal loading axes with regard to the principal material axes occurs. In the triaxial cubical machine which was used for the experiments, small angle rotations were performed by sawing cubes from pre-cracked blocks. Results of some preliminary rotation tests are discussed in relation to the crack orientation concept.

Inelastic behaviour of reinforced concrete members with cyclic loading

The results of an investigation into the behaviour of reinforced concrete members subjected to cyclic loading in the inelastic range are summarized. The investigation commences with studies of the Bauschinger effect for cyclically stressed mild steel reinforcement and the influence of rectangular steel hooping on the stress-strain behaviour of concrete. Using these derived stress-strain curves the moment-curvature relation ships for reinforced concrete members under cyclic loading are studied theoretically and compared with the results of a series of tests on reinforced concrete beams under cyclic loading.

Effects of Flexural Strain Gradients on Microcracking and Stress-Strain Behavior of Concrete

TO INVESTIGATE THE INFLUENCE OF FLEXURAL STRAIN GRADIENTS ON MICROCRACKING AND THE STRESS-STRAIN BEHAVIOR OF PLAIN CONCRETE, ECCENTRICALLY AND CONCENTRICALLY LOAD SPECIMENS WERE COMPARED. IT WAS FOUND THAT A FLEXURAL STRAIN GRADIENT RETARDS MICROCRACKING, ESPECIALLY MORTAR CRACKING AS COMPARE TO CRACKING AT THE SAME STRAIN IN AXIAL COMPRESSION. THE STRESS-STRAIN CURVE FOR ECCENTRIC COMPRESSION, WHICH WAS COMPUTED BY AN EXPERIMENTAL STATISTICAL APPROACH, WAS FOUND TO DIFFER MATERIALLY FROM THAT FOR CONCENTRIC COMPRESSION. THE PEAK OF THE FLEXURAL CURVE WAS LOCATED AT A STRAIN ABOUT 50 PERCENT HIGHER AND AT A STRESS ABOUT 20 PERCENT LARGER THAN THE PEAK OF THE CURVE FOR CONCENTRIC COMPRESSION. STRUCTURAL IMPLICATIONS OF THESE FINDINGS ARE DISCUSSED BRIEFLY. /RRL/A/